Proton Pencil Beam Scanning Facilitates the Safe Treatment of Extended Radiation Targets for Hodgkin Lymphoma: A Report from the Proton Collaborative Group Registry.

Simple Summary: Using the Proton Therapy Collaborative group registry, we describe the impact of pencil beam scanning (PBS) proton beam therapy (PBT) for Hodgkin lymphoma patients who require radiation to both mediastinal and axillary targets. We performed dosimetric comparisons between delivered PBS plans and photons with butterfly volumetric arc therapy (BVMAT). Compared to BVMAT, PBS had greater target coverage, better conformity, and lower dose heterogeneity while achieving a lower dose to the lungs and heart. Nearly half of the BVMAT plans exceeded the lung V5 constraint (>55%). PBS was well tolerated without any pneumonitis or grade 3+ acute toxicity. We show here that patients requiring both mediastinal and axillary treatment may be another subgroup of lymphoma patients who may benefit from PBT. Because proton beam therapy (PBT) can lower the dose of radiation to the heart, lungs, and breast, it is an established radiation modality for patients with Hodgkin lymphoma (HL). Pencil beam scanning (PBS) PBT facilitates the treatment of more extensive targets. This may be especially of value for lymphoma patients who require RT to both mediastinal and axillary targets, defined here as extended target RT (ETRT), given the target distribution and need to minimize the lung, heart, and breast dose. Using the Proton Collaborative Group registry, we identified patients with HL treated with PBT to both their mediastinum and axilla, for which DICOM-RT was available. All patients were treated with PBS. To evaluate the dosimetric impact of PBS, we compared delivered PBS plans with VMAT butterfly photon plans optimized to have the same target volume coverage, when feasible. Between 2016 and 2021, twelve patients (median 26 years) received PBS ETRT (median 30.6 Gy (RBE)). Despite the large superior/inferior (SI, median 22.2 cm) and left/right (LR, median 22.8 cm) extent of the ETRT targets, all patients were treated with one isocenter except for two patients (both with SI and LR > 30 cm). Most commonly, anterior beams, with or without posterior beams, were used. Compared to photons, PBS had greater target coverage, better conformity, and lower dose heterogeneity while achieving lower doses to the lungs and heart, but not to the breast. No acute grade 3+ toxicities were reported, including pneumonitis. Proton ETRT in this small cohort was safely delivered with PBS and was associated with an improved sparing of the heart and lungs compared to VMAT. [ABSTRACT FROM AUTHOR]