Rossi, Carl J.

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.

Purpose: As patients with mediastinal lymphoma are typically young with curable disease, advanced radiation techniques such as proton therapy are often considered to minimize subacute and late toxicity. However, it is unclear which mediastinal lymphoma patients are treated with proton therapy. Within a prospective, multi-institutional proton registry, we characterized mediastinal lymphoma patients treated with proton therapy and assessed concordance with consensus recommendations published in 2018 by the International Lymphoma Radiation Oncology Group (ILROG). Methods: Eligible patients included those with lymphoma of the mediastinum treated exclusively with proton therapy for whom digital imaging and communications in medicine (DICOM) treatment data were available for review. Given the challenge with reliably visualizing the left mainstem coronary artery, the inferior-most aspect of the left pulmonary artery (PA) was used as a surrogate. Extent of disease was characterized as upper mediastinum (above level of left PA), middle mediastinum (below left PA but at or above level of T8), or low mediastinum (below T8). Results: Between November 2012 and April 2019, 56 patients were treated and met inclusion criteria. Patients treated with proton therapy were young (median, 24 y; range: 12 to 88), with over half being female (55%). Patients were most commonly treated at initial diagnosis (86%) and had Hodgkin lymphoma (79%). Most patients (96%) had mediastinal disease that extended down to the level of the heart: 48% had middle and 48% had low mediastinal involvement. Nearly all patients (96%) met the ILROG consensus recommendations: 95% had lower mediastinal disease, 46% were young females, and 9% were heavily pretreated. Heart (mean) and lung dose (mean, V5, V20) were significantly associated with lowest extent of mediastinal disease. Conclusions: Mediastinal lymphoma patients treated with proton therapy are typically young with lower mediastinal involvement. Within a prospective, multi-institutional proton registry, nearly all treated patients fit the ILROG consensus recommendations regarding which mediastinal lymphoma patients may most benefit from proton therapy.

389 Background: The liver is one of the most radiosensitive organs, making radiation therapy (RT) for liver tumors extremely challenging. RT is appropriate only for a minority of liver patients with limited tumor burden; a reduction in the prescribed radiation dose may be needed to lower the probability of radiation-induced liver disease especially in the presence of cirrhosis. Proton beam therapy (PBT) delivers less dose to the liver than photon therapy and is expected to reduce toxicity while also permitting safe dose escalation for some patients with liver tumors. Methods: The Proton Collaborative Group REG001-09 trial (NCT01255748) prospectively collects data for PBT patients with a variety of cancer types. To better understand treatment details and outcomes associated with liver PBT, patients enrolled on the PCG registry trial from 5 institutions who received liver PBT for any cancer between 2012 and 2016 were analyzed. Results: A total of 43 liver cancer patients were included, most with hepatocellular carcinoma (48.8%) or cholangiocarcinoma (25.6%). The vast majority did not have surgery at any time (86%). Most were treatment naive prior to PBT; 2 previously had RT and 8 had prior chemotherapy (mostly cholangiocarcinoma patients). The median total prescribed PBT dose was 58.05 Gy(RBE) (range 21.7-67.5). The median number of prescribed fractions was 15 (range 12-37). PBT was delivered to only the liver in 90.7% of patients; inclusion of lymph nodes was rare. Uniform scanning was used in 26 (72.1%) and pencil beam scanning in 2 patients (4.7%); the delivery technique used for the remaining patients was unknown (23.2%). With median follow up of 4.4 months (range 1.3-17.9), 3 patients (7%) had an intrahepatic recurrence, 2 patients (4.6%) developed distant metastasis, and 10 patients (23.3%) died. No grade 3 or higher toxicity was reported although 17 patients (39.5%) had grade 2 toxicity predominantly fatigue, anorexia, nausea, or vomiting. Conclusions: Although longer follow up is needed to assess late toxicities as well as disease control, early outcomes from the PCG registry trial for liver cancer patients shows that predominantly hypofractionated PBT has a very favorable acute toxicity profile.