Caudally directed posterior high-dose-rate brachytherapy for reirradiation of para-aortic lymph node recurrence: A technical innovation enabled by interventional radiology.

PURPOSE: Reirradiation for para-aortic lymph node (PALN) recurrence is technically challenging due to prior radiation exposure and the anatomical proximity of critical organs such as the small intestine and kidneys, making external beam radiation therapy (EBRT) difficult or unfeasible. High-dose-rate interstitial brachytherapy (HDR-IBT) offers a highly localized treatment alternative; however, it requires precise applicator placement to ensure safety and efficacy.

METHODS AND MATERIALS: We report a case of PALN recurrence located between the aorta and inferior vena cava (IVC) in a patient previously treated with multiple courses of EBRT. Due to the lesion's high-risk location and prior irradiation, further EBRT was not a viable option. In collaboration with interventional radiologists, a novel posterior paravertebral approach was adopted. Under fluoroscopic and computed tomography (CT) guidance, a 17 G percutaneous transhepatic cholangiography (PTC) needle was inserted from the patient's back. The guidewire was advanced through the psoas muscle and intentionally redirected caudally at an angle of nearly 90 degrees to avoid major vascular structures. Following tract dilation using a ureteral balloon and dilator system, a flexible brachytherapy applicator was inserted and fixed in place. The patient received six fractions of 5 Gy (total dose: 30 Gy), with the applicator maintained in situ throughout the treatment period.

RESULTS: The treatment was completed without any adverse events. CT imaging at 4 months post-treatment showed tumor shrinkage and reduced contrast enhancement. No radiation-related toxicities were observed during or after treatment. Local control has been maintained for over 4 years.

CONCLUSIONS: This case demonstrates the feasibility and safety of fractionated HDR-IBT for reirradiation of deeply located PALN recurrence in a previously irradiated field. While single-fraction HDR-IBT can be performed via a direct posterior approach, fractionated treatment requires stable applicator placement over several days. To mitigate the risk of vascular injury due to applicator displacement, precise angulation of the insertion trajectory was critical. This report highlights how interdisciplinary collaboration enabled accurate, vessel-sparing needle placement, providing a minimally invasive and effective treatment option for patients with PALN recurrence who are not candidates for further EBRT.