Comparing Organs at Risk Sparing Between Intensity-Modulated Radiotherapy and Pencil-Beam Scanning Plans Based on Disease Location for Hodgkin and Non-Hodgkin Lymphoma

Purpose: Radiotherapy (RT) is often used as a combined modality therapy for patients with Hodgkin (HL) and aggressive Non-Hodgkin Lymphoma (aNHL). RT options include photon intensity-modulated radiotherapy (IMRT) or proton therapy (PT). As PT is a limited and costly resource, it is important to identify cases in which PT may best benefit in order to offer providers and patients the best possible information for decision-making. Accordingly, the purpose of this study was to assess the difference in OAR sparing between photon IMRT and pencil-beam scanning (PBS) based on disease location using the Ann Arbor (AA) staging system. Materials and Methods: = 156) treated with RT at a single institution from 2007 to 2020. Two plans (IMRT and PBS) were developed for each patient using consistent planning techniques with a prescribed dose of 30 Gy. Disease anatomic classification was classified using AA, and OAR differences were assessed based on disease location. Mediastinal involvement was divided between upper, middle, and lower (UML). OAR doses were comparatively assessed by the AA site looking at absolute (AS) and relative sparing (RS) using patient plan pairs using the Wilcoxon signed-rank test. Results: PBS reduced the mean heart dose with the largest AS (6.4 Gy) for patients with UML mediastinal involvement. Greatest AS and RS for lung V20 was seen for patients with bilateral axillary involvement (20.9% AS, 53.5% RS), and for mean breast dose greatest sparing was seen for those with bilateral hilar disease (5.1 Gy AS, 58.6% RS). Conclusion: The use of PBS resulted in a substantial decrease in the mean dose to OARs, the magnitude of which depended on the location in which disease was present. This work advances that the anatomic location of involvement is an important influence on the relative benefit of PT.