Current Status and Perspectives of Irradiation-Based Conditioning Regimens for Patients with Acute Leukemia Undergoing Hematopoietic Stem Cell Transplantation.

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (allo-HCT) is the treatment of choice for many hematologic conditions. Acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) are the most common indications for allo-HCT [ 1 , 2 ]. Transplantation must be preceded by administration of a conditioning regimen given to prevent graft rejection and leukemia relapse through the elimination of host T cells and reduction of the tumor burden. Conditioning may be based on either an irradiation and chemotherapy combination or chemotherapy alone. The purpose of this review is to summarize the most frequently used irradiation-based conditioning regimens, to discuss potential advantages and disadvantages of irradiation—compared to chemotherapy-based protocols in acute leukemia, and to present perspectives in this field.

TOTAL BODY IRRADIATION

As defined by the Center for International Blood and Marrow Transplant Research (CIBMTR) during the Bone Marrow Transplantation Tandem Meeting in 2006, the regimens are classified by their intensity as myeloablative conditioning (MAC), reduced intensity conditioning (RIC), or nonmyeloablative conditioning (NMAC) [ 3 ]. MAC regimens contain high doses of alkylating agents with or without TBI, leading to complete ablation of bone marrow. NMAC regimens are those that do not require stem cell support and allow recovery of the patient's own marrow. Regimens that do not fit either criterion are called RIC. There is a wide spectrum of regimens that are used as RIC. Usually, it involves reduction of ≥30% in TBI or chemotherapy myeloablative doses.

TBI is an integral part of many MAC regimens. TBI alone was first used in 1957 for acute leukemia [ 4 ]. The first successful use of TBI with cyclophosphamide (Cy/TBI) took place in 1979 [ 5 ]. The standard dose of TBI in a MAC conditioning is 12 Gy. Currently, various other TBI regimens are used, including a single fraction of 5–10 Gy, fractionated TBI of 10–14 Gy, hyperfractionated TBI up to 14–15 Gy, and other less common schedules. In addition to cyclophosphamide, various agents, such as cytarabine (AraC) [ 6 ], etoposide [ 7 ], melphalan [ 8 ], and busulfan (Bu) [ 9 ], have been combined with high-dose TBI. Due to the lack of randomized trials, there is currently no evidence suggesting that any of these combinations are superior to Cy/TBI.

With the development of NMA conditioning, a single dose of 2 Gy of TBI was successfully used as the Seattle protocol [ 10 ]. This protocol was associated with 20% nonfatal graft rejection, which was reduced to 3% by the addition of fludarabine at 90 mg/m 2 [ 11 ]. RIC regimens encompass a variety of protocols, including TBI administered at a total dose of 4 to 8 Gy, which allows for dose-adjustment according to patients' age and biological status on the one hand, and the risk of disease recurrence on the other. Finally, TBI-based RIC may be administered sequentially after cytoreductive chemotherapy (e.g., FLAMSA protocol) in patients with relapsed/refractory disease undergoing allo-HCT [ 12 – 14 ].

The most frequently used irradiation-based conditioning regimens are listed in Table 1 .

ADVANTAGES AND DISADVANTAGES OF TBI

TBI-based regimens have specific advantages over conditioning based on chemotherapy alone. Ionizing radiation can be delivered to sanctuary sites like brain or testes with the same efficiency as in lymph nodes or bone marrow. This is a considerable advantage over chemotherapy-based conditioning. There is no issue of cross-resistance. Application of ionizing radiation does not alter the response to chemotherapeutic agents and moreover, it usually allows for effective elimination of neoplastic cells even in heavily pretreated patients. With the development of modern radiation planning, delivery techniques and the advantages of in vivo , on-line dose monitoring, the prescribed dose is homogeneously delivered to the whole body without creating cold- or hot spots. Finally, radiation treatment is not associated with the issues of medication metabolism and excretion, which can limit the utility of chemotherapeutic agents.

Unfortunately, TBI is associated with a significant risk of early and late side effects. The former may include nausea, vomiting, headache, mucositis, esophagitis, decreased appetite, indigestion, parotitis, mild erythema, and fatigue syndrome [ 15 , 16 ]. Late effects can be pulmonary toxicity, renal dysfunction, cataract, infertility, hypothyroidism, growth hormone deficiency (GHD) leading to growth retardation in children, and secondary malignancies. Long-term side effects may be irreversible and may affect the patient's lifespan and their quality of life [ 17 – 20 ].

The risk of late toxicities is particularly high in children. In a study of 129 pediatric patients who underwent TBI-based MAC for hematologic malignancies, 70.5% developed pulmonary toxicity [ 21 ]. Clinically, these patients present with the symptoms of fever, cough, hypoxia, and dyspnea. Chest radiographs often show bilateral diffuse shadowing, with pulmonary function tests showing a low diffusing capacity (DLCO) and a restrictive pattern. Pulmonary toxicities can be acute or late in onset, and encompass several syndromes broadly divided into infectious and noninfectious categories. The exact pathophysiology of these conditions is still unclear and likely multifactorial. The TBI dose rate is significantly associated with pulmonary toxicity. Other factors like TBI total dose, dose per fraction, disease type, transplantation chemotherapy, the age of the patient, sex, and donor type did not significantly impact pulmonary toxicity in a recent study [ 21 ]. Adult survivors of childhood allo-HCT using TBI for ALL demonstrated reduced β-cell reserve and smaller pancreatic volume associated with reduced insulin sensitivity, leading to increased risk of diabetes and an exaggerated form of the metabolic syndrome with hypertriglyceridemia [ 22 – 25 ]. One German study, which included 110 ALL patients, showed that 15% suffered from pulmonary symptoms and lung fibrosis, 11% developed osteoporosis, 4.5% developed hypothyroidism, and 2 patients developed diabetes mellitus following TBI [ 26 ]. TBI also affected gonadal function leading to erectile dysfunction, infertility and postmenopausal syndrome [ 26 ].

It must be emphasized that the risk of developing some of the above-listed complications may be effectively reduced by attempts to spare the organs at risk (OAR). This can be achieved by a reduction in total dose, reduction in organ dose, fractionation, limiting the dose rate, and avoiding concomitant use of chemotherapy with similar side effect profile. Reduction in organ dose may be effectively achieved by organ shielding. This includes placement of blocks to reduce the irradiation dose to critical normal structures. Lung blocks are designed to include the pulmonary volumes identified on AP-PA films and to reduce the dose delivered to the mid-plane of the lungs. This has been shown to protect lung tissue and to improve overall survival (OS) after TBI in patients with compromised pulmonary function before allo-HCT. Lung shielding using lead alloy to reduce the radiation dose to the majority of the lung tissue is recommended during myeloablative-dose TBI, but not during low-dose TBI. It results in a reduction of the risk of radiation pneumonitis, particularly in patients with lung dysfunction [ 27 ]. Similarly, eye shielding and kidney blocks are also used. Despite this, many vital organs cannot be feasibly blocked during delivery of TBI, as this would also block areas of marrow and lymph nodes requiring treatment [ 28 ]. Other radio protective agents like Amifostine and Diindolylmethane (DIM) are under consideration, more studies are required to prove their efficacy [ 29 , 30 ]. Some other complications, such as veno-occlusive disease, may be more frequent after the use of alkylating agents than after irradiation. A meta-analysis of four randomized trials comparing Cy/TBI with busulfan combined with cyclophosphamide (BuCy) revealed an increased risk of cataract after Cy/TBI and increased risk of irreversible alopecia after BuCy [ 31 ]. With the median follow-up of seven years, the incidence of other late complications was comparable. Considering the risk of severe side effects, radiation-free, chemotherapy-based regimens have been developed and are commonly used.

TBI-BASED VERSUS CHEMOTHERAPY-BASED MYELOABLATIVE REGIMENS FOR AML

Evaluation of the efficacy and safety of myeloablative Cy/TBI in comparison with BuCy for patients with AML treated with allo-HCT in first complete remission (CR1) was the goal of a prospective trial by a French group [ 32 ]. The outcome for Cy/TBI at 2 years was better for the probability of disease-free survival (DFS) (72% vs. 47%, p < 0.01), OS (75% vs. 51%, p < 0.02), relapse (14% vs. 34%, p < 0.04), and non-relapse mortality (8% vs. 27%, p < 0.06). A significant advantage of TBI-based compared to chemotherapy-based myeloablative regimens for patients with AML in CR1 was also demonstrated by a retrospective analysis performed on behalf of the Acute Leukemia Working Party (ALWP) of the European Society for Blood and Marrow Transplantation (EBMT) [ 33 ]. The use of TBI was associated with reduced risk of relapse (hazard ratio [HR] = 0.74, p = 0.003) and improved DFS (HR = 1.2, p = 0.02).

In recent years, an intravenous (IV) formulation of busulfan became available and is associated with more predictable pharmacokinetics compared with the oral counterpart. A retrospective analysis by the EBMT ALWP including patients with AML in CR1 or CR2 showed that the risk of relapse was reduced after the use of Cy/TBI compared to IV busulfan + cyclophosphamide (HR = 0.71, p = 0.004) but the effect on DFS and OS was not significantly different [ 34 ]. Another retrospective study by the CIBMTR compared IV busulfan-based conditioning with various TBI-based regimens in patients with myeloid malignancies undergoing matched sibling or unrelated allo-HCT [ 35 ]. Among patients with AML, the use of IV busulfan was associated with superior OS rate (57% vs. 46%, p = 0.003). However, the interpretation of the result is difficult due to lack of disease-oriented multivariate analyses and high heterogeneity of the AML stages, including patients in either CR or active disease.

In recent years, chemotherapy-based regimens incorporated thiotepa. According to a recent matched-pair analysis by the EBMT ALWP including patients with AML in CR1 treated with allo-HCT, the results after thiotepa-based and TBI-based conditioning were comparable in terms of OS, DFS, relapse rate, non-relapse mortality (NRM), as well as the incidence of chronic graft-versus-host disease (GVHD). There was a trend for reduced incidence of grade II-IV acute GVHD after thiotepa-based conditioning (25% vs. 35%, p = 0.06) [ 36 ]. In parallel to chemotherapy-based regimens, the TBI-based protocols are also evolving. The German study group performed a prospective, randomized trial comparing Cy/TBI 12 Gy with TBI 8 Gy combined with fludarabine. The authors revealed that the use of RIC was associated with comparable results in patients below 40 years of age while, among older adults (40–60 years), it was associated with reduced NRM and improved survival [ 37 ].

TBI-BASED VERSUS CHEMOTHERAPY-BASED MYELOABLATIVE REGIMENS FOR ALL

TBI is considered a standard basis for MAC in adults with ALL in CR1. Although it has never been prospectively evaluated, results of numerous retrospective analyses indicated its advantage over chemotherapy-based regimens mainly due to reduced risk of relapse. In a multivariate analysis by the EBMT ALWP restricted to patients treated in CR1 between the years 2008 and 2012, the use of TBI was associated with more than twice reduction of the risk of relapse (HR = 0.48, p = 0.004) and treatment failure (HR = 0.63, p = 0.02) compared to irradiation-free conditioning [ 38 ]. Also, in patients with primary refractory ALL who fail to achieve a CR after ≥2 courses of chemotherapy, the use of TBI-based conditioning was found to be associated with improved OS (HR = 0.53, p = 0.04) and leukemia-free survival (HR = 0.44, p = 0.01) [ 39 ]. Mitsuhashi et al . showed that IV busulfan in combination with cyclophosphamide in ALL patients may be associated with results comparable to TBI. However, the limitation of that study is that the number of patients treated was relatively small ( n = 40) and, therefore, further verification is needed [ 40 ]. Similar to AML, thiotepa-based conditioning regimens are being incorporated in the treatment of ALL. Promising results have been published based on a retrospective analysis, showing leukemia-free and OS at 2 years of 58.9% and 61.4%, respectively, for patients treated in CR1 [ 41 ].

For patients with ALL, TBI is most frequently combined with cyclophosphamide but, according to some retrospective analyses, the combination with etoposide may be at least equally effective. In a study by Marks et al . in patients treated with CR2, the use of TBI/etoposide was associated with reduced risk of relapse, treatment failure, and overall mortality compared to Cy/TBI 12 Gy [ 42 ].

HETEROGENEITY OF TBI TECHNIQUES

Conventional TBI treatment techniques can be classified into anteroposterior/poster-anterior (AP/PA) and parallel-opposed lateral (LAT) techniques. The AP/PA technique often provides a more homogeneous dose distribution than the LAT technique, because in this dimension (relative to the lateral dimension) the reference depth at which the dose is calculated is more uniform. However, due to the lower density of lung tissue (compared to the remainder of the body), the lungs can be overdosed. Hence, lung blocks are required with the AP/PA technique. Recent advances in radiotherapy allow performing TBI on the standard treatment table with dynamic techniques. Along with three-dimensional treatment planning, it allows for OAR sparing, without the need of casting individualized shields, and for controlling dose distribution in the body, without the risk of over- or under dosage. Consequently, the data concerning the frequency and severity of late adverse effects of TBI performed with older methods are becoming obsolete, and new evidence must be gathered in order to draw conclusions on the risk and effectiveness of radiation-based conditioning regimens as compared to chemotherapy-based regimens.

While administration of chemotherapy is relatively easy and uniform, TBI is associated with multiple technical issues. TBI is very heterogeneous in terms of the dosage, timing, other technical aspects and, therefore, insufficiently standardized at the international level. The EBMT performed a survey from February to July 2013 [ 43 ]. The questionnaires were sent to all 205 EBMT centers, out of which 57 responded. The survey showed that delivery of TBI varies significantly among centers, and the total dose of TBI used varied from 8 Gy to 14.4 Gy. The TBI fractions ranged from 1 to 8, and dose per fraction from 1.65 Gy to 8 Gy. The most commonly used fractionation was 6 fractions of 2 Gy each, delivered twice daily. Not only the dose but the dose rate also varied between 11 and 30 cGy/min. A total of 91.1% of the centers used linear accelerators, while 8.9% still used Cobalt-60 machines. Most of the treatment centers used “patient in one field” with 2 fields per fraction and 2 patient positions per fraction technique. Lung was the most commonly shielded organ, but some centers also used shields for lenses, thyroid gland, larynx, kidneys, and/or salivary glands. German and American radiation oncology groups have published guidelines on the use of TBI. But the guidelines provide only general requirements and do not deal with specific details [ 44 , 45 ]

PERSONALIZED IRRADIATION-BASED CONDITIONING

Considering potential side effects and technical problems associated with TBI, various novel techniques are emerging in the field of HCT-related radiotherapy. The principle of TBI is to deliver a homogenous dose of radiation to the whole body. However, the distribution of residual malignancy may not necessarily be homogenous. Novel wide-field techniques allow more distinctive distribution of the dose, adjustment to the type of disease or even to individual patient's needs. Such personalized approaches entail potential to escalate the dose and increase efficacy, while sparing organs not involved in the disease in order to reduce toxicity.

Intensity-modulated radiation therapy (IMRT) is a technology that allows for shaping of the isodoses, by changing positions of the leaves in the multileaf collimator (MLC) during irradiation. It results in the concentration of the high-dose regions within the target volume, while relatively sparing the surrounding normal tissues. It was first introduced in 1999, and has been shown to minimize acute treatment-related morbidity, making dose escalation feasible, which may ultimately improve local tumor control [ 46 ].

Total Marrow Irradiation

TMI focuses the dose to the entire skeleton, while sparing the rest of the body. This markedly reduces the toxicity of the treatment, while keeping the same or higher dose in the bone marrow as used in TBI. Introduction of TMI has allowed for dose escalation with acceptable toxicity, which cannot be achieved with traditional TBI techniques [ 47 – 53 ]. TMI can be delivered using either helical tomotherapy (HT), fixed-gantry angle linear accelerator-based IMRT, or volumetric modulated arc therapy (VMAT).

Clinically, there are multiple advantages of TMI as compared to TBI. For patients with advanced leukemia (relapsed, refractory, high risk), TMI offers a chance to escalate the dose of irradiation, therefore potentially increasing the efficacy compared to TBI, with yet acceptable toxicity. Hui et al . conducted a phase 1 trial in high-risk leukemia patients undergoing allo-HCT. The conditioning regimen included TMI + fludarabine + Cy. The TMI dose escalation to 15 Gy and 18 Gy resulted in 42% 1-year probability of OS and 22% DFS rate. This study demonstrated that TMI dose escalation is feasible with acceptable toxicity [ 48 ]. In another study by Wong et al . including relapsed/refractory AML, TMI was used in combination with etoposide 60 mg/kg and Cy 100 mg/kg. The TMI dose was escalated up to 13.5 Gy and 15 Gy resulting in acceptable toxicity [ 54 ]. Other study used 9 Gy TMI in combination with sequential fludarabine and busulfan to treat AML patients at high risk of relapse [ 55 ] (see Table 2 ).

For patients with early-stage acute leukemia (CR1) undergoing allo-HCT, TMI doses equivalent to those of TBI may be equally effective, while much less toxic [ 56 ]. This may be of particular importance for older patients and those with comorbidities considered ineligible for myeloablative TBI.

TMI Combined with Total Lymphoid Irradiation

Total lymphoid irradiation (TLI) has been used for a long time to produce long-lasting lymphoid depletion and immunosuppression for solid organ transplantation [ 57 ]. The first use of TLI combined with cyclophosphamide for allo-HCT in aplastic anemia patients took place in 1980 [ 58 ]. Lowsky et al . described a non-myeloablative, chemotherapy-free protocol containing TLI in combination with anti-thymocyte globulin, which was associated with very low risk of GVHD, and the results were enhancing especially for patients with lymphoma [ 59 ]. For treatment of acute leukemia, there are current attempts to combine TLI with TMI (TMLI). Such combinations are expected to reduce the risk of graft failure compared to TMI alone. In the case of ALL, it should also increase the efficacy of eliminating disease that may reside in lymphoid tissue. Stein et al . conducted a phase-1 trial of TMLI dose escalation to 20 Gy along with Cy and etoposide in patients with high-risk leukemia undergoing allo-HCT. The study showed a 3.9% incidence of NRM at day +100 and 8.1% at 1 year. The TMLI/Cy/etoposide conditioning regimen was well tolerated at TMLI doses up to 20 Gy with no increase in GVHD [ 60 ]. Two studies by Wong et al . and Rosenthal et al . have successfully used 12 Gy of TMI and TLI along with fludarabine and high-dose melphalan in patients over 50 years of age with multiple comorbidities, and compromised organ function [ 51 , 53 ].

ULTRA-PERSONALIZED IRRADIATION-BASED CONDITIONING

The whole skeleton is the target for TMI. However, the distribution of leukemic cells within bones is not homogenous. Therefore, more selective techniques focusing irradiation on particular bone marrow compartments are being considered. The bone marrow has 3 primary components: 1) trabeculae-rich osseous matrix, 2) hematopoietic active red marrow with increased affinity for cancer cells and vascular endothelium, 3) fat-reach yellow marrow with minimal hematopoiesis and scarce vasculature. The principal mechanism of action by which radiation works is by creating oxygen free radicals leading to damage to the DNA. As yellow marrow has a scarcity of vasculature, this part of the marrow is characterized by hypoxia and is more radio-resistant. Some studies have reported survival of leukemia cells in this part of the bone marrow, which was associated with leukemia resistance and/or relapse [ 61 – 64 ]. Modern imaging techniques like whole-body dual-energy CT (DE CT) lead to better differentiation of marrow composition [ 65 ]. This can help with more selective irradiation of bone marrow compartments. A recent study evaluating irradiation of functional bone marrow included delivering high dose to the red and yellow marrow, and lower doses to the remaining skeleton [ 66 ]. This study was conducted on 7 cadavers and 6 leukemia patients. Seven cadavers were scanned with DECT and the treatment planning was simulated to target irradiation. The dose of 18 Gy was planned for red and yellow marrow, while 12 Gy was planned to the entire skeleton. While treating functional marrow with higher doses, this method reduced the dose to OAR compared to standard TMI. Such strategy can further increase the efficacy of conditioning. However, the limitation of the study was that it was a preclinical study on cadavers and we need further clinical studies.

SUMMARY

Acute leukemias are highly radiosensitive. Allo-HCT offers a chance to deliver myeloablative doses of irradiation with high antileukemic activity and therefore TBI is still widely used as a part of conditioning for both AML and ALL. In the latter case, it remains a standard of care. Novel technologies allow for very precise dose delivery to organs affected by leukemia, in particular to the bone marrow. Such targeted irradiation may further be enhanced by modern imaging techniques accompanied by increasing knowledge of the disease biology. These new techniques may represent a new era of the use of irradiation as a part of conditioning regimens emerging for prospective, clinical trials.

Peer review is under the responsibility of IACH

CONFLICTS OF INTEREST

All authors declared no conflicts of interest.

REFERENCES

[1] Passweg JR Baldomero H Bader P Bonini C Cesaro S Dreger S Duarte RF Dufour C Kuball J Farge-Bancel D Gennery A Kroger N Lanza F Nagler A Sureda A Mohty M Hematopoietic stem cell transplantation in Europe 2014: more than 40 000 transplants annually Bone Marrow Transplant 2016 51 6 786 92 10.1038/bmt.2016.20 26901709 PMC4895175

[2] Potdar R Varadi G Fein J Labopin M Nagler A Shouval R Shouval, prognostic scoring systems in allogeneic hematopoietic stem cell transplantation: where do we stand? Biol Blood Marrow Transplant 2017 23 11 1839 46 10.1016/j.bbmt.2017.07.028 28797781

[3] Giralt S Ballen K Rizzo D Bacigalupo A Horowitz M Pasquini M Sandmaier B Reduced-intensity conditioning regimen workshop: defining the dose spectrum. Report of a workshop convened by the center for international blood and marrow transplant research Biol Blood Marrow Transplant 2009 15 3 367 69 10.1016/j.bbmt.2008.12.497 19203728 PMC3110087

[4] Atkinson JB Mahoney FJ Schwartz IR Hesch JA Therapy of acute leukemia by whole-body irradiation and bone marrow transplantation from an identical normal twin Blood 1959 14 3 228 34 13628820

[5] Thomas ED Buckner CD Clift RA Fefer A Johnson FL Neiman PE Sale GE Sanders JE Singer JW Shulman H Storb R Weiden PL Marrow transplantation for acute nonlymphoblastic leukemia in first remission N Engl J Med 1979 301 11 597 99 10.1056/nejm197909133011109 381925

[6] Riddell S Appelbaum FR Buckner CD Stewart P Clift R Sanders J Storb R Sullivan K Thomas ED High-dose cytarabine and total body irradiation with or without cyclophosphamide as a preparative regimen for marrow transplantation for acute leukemia J Clin Oncol 1988 6 4 576 82 10.1200/jco.1988.6.4.576 3282031

[7] Horning SJ Chao NJ Negrin RS Hoppe RT Kwak LW Long GD Stallbaum B O'Connor P Blume KG The Stanford experience with high-dose etoposide cytoreductive regimens and autologous bone marrow transplantation in Hodgkin's disease and non-Hodgkin's lymphoma: preliminary data Ann Oncol 1991 2 Suppl 1 47 50 10.1093/annonc/2.suppl_1.47 2043498

[8] Moreau P Facon T Attal M Hulin C Michallet M Maloisel F Sotto JJ Guilhot F Marit G Doyen C Jaubert J Fuzibet JG François S Benboubker L Monconduit M Voillat L Macro M Berthou C Dorvaux V Pignon B Rio B Matthes T Casassus P Caillot D Najman N Grosbois B Bataille R Harousseau JL Intergroupe Francophone du Myélome Comparison of 200 mg/m(2) melphalan and 8 Gy total body irradiation plus 140 mg/m(2) melphalan as conditioning regimens for peripheral blood stem cell transplantation in patients with newly diagnosed multiple myeloma: final analysis of the Intergroupe Francophone du Myelome 9502 randomized trial Blood 2002 99 3 731 35 10.1182/blood.v99.3.731 11806971

[9] Scott B Deeg HJ Storer B Chauncey T Petersdorf S Slattery J Appelbaum F Targeted busulfan and cyclophosphamide as compared to busulfan and TBI as preparative regimens for transplantation in patients with advanced MDS or transformation to AML Leuk Lymphoma 2004 45 12 2409 17 10.1080/10428190412331283206 15621753

[10] McSweeney PA Niederwieser D Shizuru JA Sandmaier BM Molina AJ Maloney DG Chauncey TR Gooley TA Hegenbart U Nash RA Radich J Wagner JL Minor S Appelbaum FR Bensinger WI Bryant E Flowers ME Georges GE Grumet FC Kiem HP Torok-Storb B Yu C Blume KG Storb RF Hematopoietic cell transplantation in older patients with hematologic malignancies: replacing high-dose cytotoxic therapy with graft-versus-tumor effects Blood 2001 97 11 3390 400 10.1182/blood.V97.11.3390 11369628

[11] Baron F Sandmaier BM Current status of hematopoietic stem cell transplantation after nonmyeloablative conditioning Curr Opin Hematol 2005 12 6 435 43 10.1097/01.moh.0000177830.63033.9d 16217159

[12] Schmid C Schleuning M Ledderose G Tischer J Kolb HJ A sequential regimen of chemotherapy, reduced-intensity conditioning for allogeneic stem-cell transplantation, and prophylactic donor lymphocyte transfusion in high-risk acute myeloid leukemia and myelodysplastic syndrome J Clin Oncol 2005 23 24 5675 87 10.1200/jco.2005.07.061 16110027

[13] Schmid C Schleuning M Hentrich M Markl GE Gerbitz A Tischer J Ledderose G Oruzio D Hiddemann W Kolb HJ High antileukemic efficacy of an intermediate intensity conditioning regimen for allogeneic stem cell transplantation in patients with high-risk acute myeloid leukemia in first complete remission Bone Marrow Transplant 2008 41 8 721 27 10.1038/sj.bmt.1705965 18176613

[14] Schmid C Schleuning M Schwerdtfeger R Hertenstein B Mischak-Weissinger E Bunjes D Harsdorf SV Scheid C Holtick U Greinix H Keil F Schneider B Sandherr M Bug G Tischer J Ledderose G Hallek M Hiddemann W Kolb HJ Long-term survival in refractory acute myeloid leukemia after sequential treatment with chemotherapy and reduced-intensity conditioning for allogeneic stem cell transplantation Blood 2006 108 3 1092 99 10.1182/blood-2005-10-4165 16551971

[15] Buchali A Feyer P Groll J Massenkeil G Arnold R Budach V Immediate toxicity during fractionated total body irradiation as conditioning for bone marrow transplantation Radiother Oncol 2000 54 2 157 62 10.1016/s0167-8140(99)00178-4 10699479

[16] Keklik M Kaynar L Yildirim A Sivgin S Eroglu C Cingoz S Pala C Eser B Cetin M Unal A An acute transverse myelitis attack after total body irradiation: a rare case Case Rep Hematol 2013 2013 523901 10.1155/2013/523901 23984124 PMC3741696

[17] Leiper AD Late effects of total body irradiation Arch Dis Child 1995 72 5 382 85 10.1136/adc.72.5.382 7618901 PMC1511084

[18] Bolling T Kreuziger DC Ernst I Elsayed H Willich N Retrospective, monocentric analysis of late effects after Total Body Irradiation (TBI) in adults Strahlenther Onkol 2011 187 5 311 15 10.1007/s00066-011-2190-1 21533759

[19] Omorim M Yamashita H Shinohara A Kurokawa M Takita J Hiwatari M Nakagawa K Eleven secondary cancers after hematopoietic stem cell transplantation using a total body irradiation-based regimen in 370 consecutive pediatric and adult patients Springerplus 2013 2 424 10.1186/2193-1801-2-424 24040584 PMC3769541

[20] Davis NL Stewart CE Moss AD Woltersdorf WW Hunt LP Elson RA Cornish JM Stevens MC Crowne EC Growth hormone deficiency after childhood bone marrow transplantation with total body irradiation: interaction with adiposity and age Clin Endocrinol (Oxf) 2015 83 4 508 17 10.1111/cen.12773 25807881

[21] Abugideiri M Nanda RH Butker C Zhang C Kim S Chiang KY Butker E Khan MK Haight AE Chen Z Esiashvili N Factors influencing pulmonary toxicity in children undergoing allogeneic hematopoietic stem cell transplantation in the setting of total body irradiation-based myeloablative conditioning Int J Radiat Oncol Biol Phys 2016 94 2 349 59 10.1016/j.ijrobp.2015.10.054 26853343

[22] Wei C Thyagiarajan M Hunt L Cox R Bradley K Elson R Hamilton-Shield J Stevens M Crowne E Reduced beta-cell reserve and pancreatic volume in survivors of childhood acute lymphoblastic leukaemia treated with bone marrow transplantation and total body irradiation Clin Endocrinol (Oxf) 2015 82 1 59 67 10.1111/cen.12575 25132503

[23] Wei C Thyagiarajan MS Hunt LP Shield JP Stevens MC Crowne EC Reduced insulin sensitivity in childhood survivors of haematopoietic stem cell transplantation is associated with lipodystropic and sarcopenic phenotypes Pediatr Blood Cancer 2015 62 11 1992 99 10.1002/pbc.25601 25989749

[24] Rajendran R Abu E Fadl A Byrne CD Late effects of childhood cancer treatment: severe hypertriglyceridaemia, central obesity, non alcoholic fatty liver disease and diabetes as complications of childhood total body irradiation Diabet Med 2013 30 8 e239 42 10.1111/dme.12234 23692373

[25] Mayson SE Parker VE Schutta MH Semple RK Rickels MR Severe insulin resistance and hypertriglyceridemia after childhood total body irradiation Endocr Pract 2013 19 1 51 58 10.4158/ep12115.or 23186952 PMC4569090

[26] Marnitz S Zich A Martus P Budach V Jahn U Neumann O Arnold R Long-term results of total body irradiation in adults with acute lymphoblastic leukemia Strahlenther Onkol 2014 190 5 453 58 10.1007/s00066-014-0607-3 24595415

[27] Shank B Simpson L The role of total body irradiation in bone marrow transplantation for leukemia Bull N Y Acad Med 1982 58 9 763 77 6762897 PMC1805382

[28] Hill-Kayser CE Plastaras JP Tochner Z Glatstein E TBI during BM and SCT: review of the past, discussion of the present and consideration of future directions Bone Marrow Transplant 2011 46 4 475 84 10.1038/bmt.2010.280 21113184

[29] Kouvaris JR Kouloulias VE Vlahos LJ Amifostine: the first selective-target and broad-spectrum radioprotector Oncologist 2007 12 6 738 47 10.1634/theoncologist.12-6-738 17602063

[30] Zhang C Lin J Cui J Li B Liu C Wang J Gao F Cai J Radioprotection of bone marrow hematopoiesis by CpG-oligodeoxynucleotides administered to mice after total-body irradiation J Radiat Res 2011 52 6 828 33 10.1269/jrr.10098 22104272

[31] Blaise D Maraninchi D Michallet M Reiffers J Jouet JP Milpied N Devergie A Attal M Sotto JJ Kuentz M Ifrah N Dauriac C Bordigoni P Gratecos N Guilhot F Guyotat D Gluckman E Vernant JP Long-term follow-up of a randomized trial comparing the combination of cyclophosphamide with total body irradiation or busulfan as conditioning regimen for patients receiving HLA-identical marrow grafts for acute myeloblastic leukemia in first complete remission Blood 2001 97 11 3669 71 10.1182/blood.v97.11.3669 11392326

[32] Blaise D Maraninchi D Archimbaud E Reiffers J Devergie A Jouet JP Milpied N Attal M Michallet M Ifrah N Allogeneic bone marrow transplantation for acute myeloid leukemia in first remission: a randomized trial of a busulfan-Cytoxan versus Cytoxan-total body irradiation as preparative regimen: a report from the group d'Etudes de la Greffe de Moelle Osseuse Blood 1992 79 10 2578 82 1586710

[33] Giebel S Labopin M Ehninger G Beelen D Blaise D Ganser A Bacigalupo A Czerw T Holowiecki J Fagundes EM Nowara E Frassoni F Rocha V Acute Leukemia Working Party of the European Group for Blood and Marrow Transplantation Association of Human Development Index with rates and outcomes of hematopoietic stem cell transplantation for patients with acute leukemia Blood 2010 116 1 122 28 10.1182/blood-2010-01-266478 20395416

[34] Nagler A Rocha V Labopin M Unal A Ben Othman T Campos A Volin L Poire X Aljurf M Masszi T Socie G Sengelov H Michallet M Passweg J Veelken H Yakoub-Agha I Shimoni A Mohty M Allogeneic hematopoietic stem-cell transplantation for acute myeloid leukemia in remission: comparison of intravenous busulfan plus cyclophosphamide (Cy) versus total-body irradiation plus Cy as conditioning regimen—a report from the acute leukemia working party of the European group for blood and marrow transplantation J Clin Oncol 2013 31 28 3549 56 10.1200/jco.2013.48.8114 23980086

[35] Bredeson C LeRademacher J Kato K Dipersio JF Agura E Devine SM Appelbaum FR Tomblyn MR Laport GG Zhu X McCarthy PL Ho VT Cooke KR Armstrong E Smith A Rizzo JD Burkart JM Pasquini MC Prospective cohort study comparing intravenous busulfan to total body irradiation in hematopoietic cell transplantation Blood 2013 122 24 3871 78 10.1182/blood-2013-08-519009 24081656 PMC3854109

[36] Eder S Labopin M Arcese W Or R Majolino I Bacigalupo A de Rosa G Volin L Beelen D Veelken H Schaap NP Kuball J Cornelissen J Nagler A Mohty M Acute Leukemia Working Party. Thiotepa-based versus total body irradiation-based myeloablative conditioning prior to allogeneic stem cell transplantation for acute myeloid leukaemia in first complete remission: a retrospective analysis from the Acute Leukemia Working Party of the European Group for Blood and Marrow Transplantation Eur J Haematol 2016 96 1 90 97 10.1111/ejh.12553 25807864

[37] Bornhauser M Kienast J Trenschel R Burchert A Hegenbart U Stadler M Baurmann H Schafer-Eckart K Holler E Kroger N Schmid C Einsele H Kiehl MG Hiddemann W Schwerdtfeger R Buchholz S Dreger P Neubauer A Berdel WE Ehninger G Beelen DW Schetelig J Stelljes M Reduced-intensity conditioning versus standard conditioning before allogeneic haemopoietic cell transplantation in patients with acute myeloid leukaemia in first complete remission: a prospective, open-label randomised phase 3 trial Lancet Oncol 2012 13 10 1035 44 10.1016/s1470-2045(12)70349-2 22959335

[38] Giebel S Labopin M Socie G Beelen D Browne P Volin L Kyrcz-Krzemien S Yakoub-Agha I Aljurf M Wu D Michallet M Arnold R Mohty M Nagler A Improving results of allogeneic hematopoietic cell transplantation for adults with acute lymphoblastic leukemia in first complete remission: an analysis from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation Haematologica 2017 102 1 139 49 10.3324/haematol.2016.145631 27686376 PMC5210244

[39] Pavlum J Labopin M Zoellner AK Sakellari I Stelljes M Finke J Fanin R Stuhler G Afanasyev BV Bloor AJ Anagnostopoulos A Mohty M Giebel S Nagler A Allogeneic hematopoietic cell transplantation for primary refractory acute lymphoblastic leukemia: a report from the Acute Leukemia Working Party of the EBMT Cancer 2017 123 11 1965 70 10.1002/cncr.30604 28211939

[40] Mitsuhashi K Kako S Shigematsu A Atsuta Y Doki N Fukuda T Kanamori H Onizuka M Takahashi S Ozawa Y Kurokawa M Inoue Y Nagamura-Inoue T Morishima Y Mizuta S Tanaka J Adult Acute Lymphoblastic Leukemia Working Group of the Japan Society for Hematopoietic Cell Transplantaion Comparison of Cyclophosphamide Combined with Total Body Irradiation, Oral Busulfan, or Intravenous Busulfan for Allogeneic Hematopoietic Cell Transplantation in Adults with Acute Lymphoblastic Leukemia Biol Blood Marrow Transplant 2016 22 12 2194 200 10.1016/j.bbmt.2016.09.007 27638362

[41] Eder S Beohou E Labopin M Sanz J Finke J Arcese W Or R Bonifazi F Aljurf M Socie G Passweg J Giebel S Mohty M Nagler A Thiotepa-based conditioning for allogeneic stem cell transplantation in acute lymphoblastic leukemia-A survey from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation Am J Hematol 2017 92 1 18 22 10.1002/ajh.24567 27673280

[42] Marks DI Forman SJ Blume KG Perez WS Weisdorf DJ Keating A Gale RP Cairo MS Copelan EA Horan JT Lazarus HM Litzow MR McCarthy PL Schultz KR Smith DD Trigg ME Zhang MJ Horowitz MM A comparison of cyclophosphamide and total body irradiation with etoposide and total body irradiation as conditioning regimens for patients undergoing sibling allografting for acute lymphoblastic leukemia in first or second complete remission Biol Blood Marrow Transplant 2006 12 4 438 53 10.1016/j.bbmt.2005.12.029 16545728

[43] Giebel S Miszczyk L Slosarek K Moukhtari L Ciceri F Esteve J Gorin NC Labopin M Nagler A Schmid C Mohty M Extreme heterogeneity of myeloablative total body irradiation techniques in clinical practice: a survey of the Acute Leukemia Working Party of the European Group for Blood and Marrow Transplantation Cancer 2014 120 17 2760 65 10.1002/cncr.28768 24804873

[44] Quast U Whole body radiotherapy: a TBI-guideline J Med Phys 2006 31 1 5 12 10.4103/0971-6203.25664 21206634 PMC3003894

[45] Wolden SL Rabinovitch RA Bittner NH Galvin JM Giap HB Schomberg PJ Rosenthal SA American College of Radiology, American Society for Radiation Oncology American College of Radiology (ACR) and American Society for Radiation Oncology (ASTRO) practice guideline for the performance of total body irradiation (TBI) Am J Clin Oncol 2013 36 1 97 101 10.1097/coc.0b013e31826e0528 23334484

[46] Teh BS Woo SY Butler EB Intensity modulated radiation therapy (IMRT): a new promising technology in radiation oncology Oncologist 1999 4 6 433 42 10631687

[47] Einsele H Bamberg M Budach W Schmidberger H Hess CF Wormann B Meisner C Straka C Hebart H Trumper L Kroger N Zander AR Hegewisch-Becker S Hossfeld DK Schmidt H Muller P Schlimok G Hertenstein B Peest D Metzner B Frickhofen N Kanz L Bensinger WI A new conditioning regimen involving total marrow irradiation, busulfan and cyclophosphamide followed by autologous PBSCT in patients with advanced multiple myeloma Bone Marrow Transplant 2003 32 6 593 99 10.1038/sj.bmt.1704192 12953132

[48] Hui S Brunstein C Takahashi Y DeFor T Holtan SG Bachanova V Wilke C Zuro D Ustun C Weisdorf D Dusenbery K Verneris MR Dose escalation of total marrow irradiation in high-risk patients undergoing allogeneic hematopoietic stem cell transplantation Biol Blood Marrow Transplant 2017 23 7 1110 16 10.1016/j.bbmt.2017.04.002 28396164 PMC5531195

[49] Hui SK Kapatoes J Fowler J Henderson D Olivera G Manon RR Gerbi B Mackie TR Welsh JS Feasibility study of helical tomotherapy for total body or total marrow irradiation Med Phys 2005 32 10 3214 24 10.1118/1.2044428 16279075

[50] Hui SK Verneris MR Froelich J Dusenbery K Welsh JS Multimodality image guided total marrow irradiation and verification of the dose delivered to the lung, PTV, and thoracic bone in a patient: a case study Technol Cancer Res Treat 2009 8 1 23 28 10.1177/153303460900800104 19166239

[51] Rosenthal J Wong J Stein A Qian D Hitt D Naeem H Dagis A Thomas SH Forman S Phase 1/2 trial of total marrow and lymph node irradiation to augment reduced-intensity transplantation for advanced hematologic malignancies Blood 2011 117 1 309 15 10.1182/blood-2010-06-288357 20876852 PMC3037752

[52] Schultheiss TE Wong J Liu A Olivera G Somlo G Image-guided total marrow and total lymphatic irradiation using helical tomotherapy Int J Radiat Oncol Biol Phys 2007 67 4 1259 67 10.1016/j.ijrobp.2006.10.047 17336225

[53] Wong JY Rosenthal J Liu A Schultheiss T Forman S Somlo G Image-guided total-marrow irradiation using helical tomotherapy in patients with multiple myeloma and acute leukemia undergoing hematopoietic cell transplantation Int J Radiat Oncol Biol Phys 2009 73 1 273 79 10.1016/j.ijrobp.2008.04.071 18786784 PMC3896447

[54] Wong JY Forman S Somlo G Rosenthal J Liu A Schultheiss T Radany E Palmer J Stein A Dose escalation of total marrow irradiation with concurrent chemotherapy in patients with advanced acute leukemia undergoing allogeneic hematopoietic cell transplantation Int J Radiat Oncol Biol Phys 2013 85 1 148 56 10.1016/j.ijrobp.2012.03.033 22592050 PMC4312108

[55] Patel P Aydogan B Koshy M Mahmud D Oh A Saraf SL Quigley JG Khan I Sweiss K Mahmud N Peace DJ DeMasi V Awan AM Weichselbaum RR Rondelli D Combination of linear accelerator-based intensity-modulated total marrow irradiation and myeloablative fludarabine/busulfan: a phase I study Biol Blood Marrow Transplant 2014 20 12 2034 41 10.1016/j.bbmt.2014.09.005 25234438

[56] Hui SK Verneris MR Higgins P Gerbi B Weigel B Baker SK Fraser C Tomblyn M Dusenbery K Helical tomotherapy targeting total bone marrow - first clinical experience at the University of Minnesota Acta Oncol 2007 46 2 250 55 10.1080/02841860601042449 17453378

[57] Sutherland DE Ferguson RM Simmons RL Kim TH Slavin S Najarian JS Total lymphoid irradiation Urol Clin North Am 1983 10 2 277 88 6344387

[58] Slavin S Strober S Mechanisms of transplantation tolerance to allogeneic bone marrow cells following total lymphoid irradiation (TLI) Haematol Blood Transfus 1980 25 323 31 10.1007/978-3-642-67319-1_27 7021350

[59] Lowsky R Takahashi T Liu YP Dejbakhsh-Jones S Grumet FC Shizuru JA Laport GG Stockerl-Goldstein KE Johnston LJ Hoppe RT Bloch DA Blume KG Negrin RS Strober S Protective conditioning for acute graft-versus-host disease N Engl J Med 2005 353 13 1321 31 10.1056/nejmoa050642 16192477

[60] Stein A Palmer J Tsai NC Al Malki MM Aldoss I Ali H Aribi A Farol L Karanes C Khaled S Liu A O'Donnell M Parker P Pawlowska A Pullarkat V Radany E Rosenthal J Sahebi F Salhotra A Sanchez JF Schultheiss T Spielberger R Thomas SH Snyder D Nakamura R Marcucci G Forman SJ Wong J Phase I trial of total marrow and lymphoid irradiation transplantation conditioning in patients with relapsed/refractory acute leukemia Biol Blood Marrow Transplant 2017 23 4 618 24 10.1016/j.bbmt.2017.01.067 28087456 PMC5382014

[61] Kode A Manavalan JS Mosialou I Bhagat G Rathinam CV Luo N Khiabanian H Lee A Murty VV Friedman R Brum A Park D Galili N Mukherjee S Teruya-Feldstein J Raza A Rabadan R Berman E Kousteni S Leukaemogenesis induced by an activating beta-catenin mutation in osteoblasts Nature 2014 506 7487 240 44 10.1038/nature12883 24429522 PMC4116754

[62] Konopleva MY Jordan CT Leukemia stem cells and microenvironment: biology and therapeutic targeting J Clin Oncol 2011 29 5 591 99 10.1200/jco.2010.31.0904 21220598 PMC4874213

[63] Scheller EL Doucette CR Learman BS Cawthorn WP Khandaker S Schell B Wu B Ding SY Bredella MA Fazeli PK Khoury B Jepsen KJ Pilch PF Klibanski A Rosen CJ MacDougald OA Region-specific variation in the properties of skeletal adipocytes reveals regulated and constitutive marrow adipose tissues Nat Commun 2015 6 7808 10.1038/ncomms8808 26245716 PMC4530473

[64] Schepers K Pietras EM Reynaud D Flach J Binnewies M Garg T Wagers AJ Hsiao EC Passegue E Myeloproliferative neoplasia remodels the endosteal bone marrow niche into a self-reinforcing leukemic niche Cell Stem Cell 2013 13 3 285 99 10.1016/j.stem.2013.06.009 23850243 PMC3769504

[65] Arentsen L Hansen KE Yagi M Takahashi Y Shanley R McArthur A Bolan P Magome T Yee D Froelich J Hui SK Use of dual-energy computed tomography to measure skeletal-wide marrow composition and cancellous bone mineral density J Bone Miner Metab 2017 35 4 428 36 10.1007/s00774-016-0796-1 27942979 PMC5689468

[66] Magome T Froelich J Takahashi Y Arentsen L Holtan S Verneris MR Brown K Haga A Nakagawa K Holter Chakrabarty JL Giebel S Wong J Dusenbery K Storme G Hui SK Evaluation of functional marrow irradiation based on skeletal marrow composition obtained using dual-energy computed tomography Int J Radiat Oncol Biol Phys 2016 96 3 679 87 10.1016/j.ijrobp.2016.06.2459 27681765 PMC5081224