Adaptive Radiation Therapy in Lymphomas: Indications, Early Experiences, and Future Directions.

Purpose: Adaptive radiation therapy (RT) allows for smaller treatment volumes and adaptation to shrinking tumors, which is particularly intriguing in lymphomas that are radiosensitive and sometimes in difficult to target locations. We hypothesize that adaptive RT may be beneficial in a variety of lymphoma cases and describe our early experience to outline indications for adaptive RT in lymphomas.

Methods and materials: An institutional review board-approved prospective registry was reviewed to identify patients with lymphoma who were treated with cone-beam computed tomography-based online adaptive RT (oART) at our institution from 2021 to 2024. Patients were categorized by lymphoma type, rationale for adaptation was elicited, and adaptive data were collected and analyzed.

Results: Seventy-two radiation treatment courses from 67 unique patients were identified, with 26 low-grade (14 gastric mucosal associated lymphoid tissue, 8 follicular, and 4 other) and 46 high-grade (33 diffuse large B-cell, 5 mantle cell, and 8 other) lymphomas. Seventy-one percent of patients were treated with daily oART, whereas the remaining had adapt-on-demand. The main indications for oART were better targeting (69%) in locations with high interfraction motion (eg, stomach, mesentery) and/or abutting critical structures, gross disease (69%) that may change during treatment, desire for hypofractionation (38%) and planned target volume (PTV) margin reduction, and complicated treatment plans with multitargets and/or simultaneous integrated boosts (14%). On average, adaptation led to improved PTV coverage from 72.2% ± 22.7% ("scheduled plan") to 95.2% ± 1.2% ("adapted plan") (P < .001). For cases with gross disease, PTV size reduced on average 24.6% ± 21.6% from first to last fraction.

Conclusions: We demonstrated that oART can be successfully implemented in a variety of lymphoma cases to reduce treatment volume while maintaining PTV coverage, allowing RT to be used more safely, with shorter treatment courses, and in scenarios where it previously may have been avoided. Future studies are needed to further elicit the clinical benefit of oART in lymphomas.