Reducing Number of Treatment Fractions for Patients With Abdominal Lymph Node Oligometastases: The Need for Online Adaptive Radiation Therapy to Provide Personalized Adaptive Fractionation.

PURPOSE: The aim of this in silico trial was to explore using online adaptive radiation therapy (OART) for isotoxic personalized fractionation and in-treatment dose adaptation for patients with abdominal-pelvic lymph node oligometastases. We hypothesized that this method could significantly reduce treatment fractions, increase treatment capacity, and improve patient comfort.

METHODS AND MATERIALS: Twenty patients with abdominal-pelvic lymph node metastases from a phase 2 study (STEAL, NL58442.078.17) were included. On the basis of the planning computed tomography (CT) scan, patients received a simulation plan of 5 × 9 Gy. If planning target volume coverage was ≥95% and the dose to the organs at risk (OAR) within constraints, fractions were minimized isotoxically. Daily fraction doses were simulated with and without OART on all fraction CTs (fCT). For patients with favorable anatomy on an fCT, an increase of fraction dose was attempted to conclude treatment.

RESULTS

On the basis of the planning CT, the total number of fractions was reduced by 37% (P < .01). Seven patients could be treated in 1 fraction and 3 patients in 2 fractions. For 10 patients, reduction was not possible. The plans were deliverable on the fCTs with OART in 97.1% of single fraction cases and 53.3% of 2-fraction cases, compared with 34.4% and 20.0% without OART. For 4 patients (40%) with 5 fractions, in-treatment dose adaptation reduced fractions by 16%, increasing total reduction from 37% to 45%. OART significantly increased the planning target volume Dmean, D98%, and coverage, whereas it decreased the OAR Dmax, D0.5cc, D1.0cc, and V50Gy. In non-OART simulations, OAR constraint violations occurred in the 5- and 2-fraction groups, with an exceeded D0.5cc in 60% and 66.7% of cases, respectively. These violations were completely resolved using OART.

CONCLUSIONS

Personalized fractionation with in-treatment dose adaptation reduced treatment fractions significantly by 45% when OART was used. This method provides significant dosimetric benefits and could increase treatment capacity and improve patient comfort. The outcomes of this study will be verified in an upcoming phase 2 trial.