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Purpose: Combined modality therapy with multiagent chemotherapy and radiation therapy is a standard treatment option for aggressive mediastinal non-Hodgkin lymphomas (AMNHLs); however, concerns regarding acute and late radiation toxicities have fueled an effort to use systemic therapy alone. The use of proton therapy (PT) is a promising treatment option, but there are still limited data regarding clinical outcomes with this treatment modality. In this Particle Therapy Cooperative Group lymphoma subcommittee collaboration, we report outcomes of patients with AMNHL treated with pencil-beam scanning PT or double-scatter PT after chemotherapy. Methods and Materials: This was a multi-institutional retrospective observational cohort study of patients with AMNHL treated with PT following chemotherapy between 2011 and 2021. Progression-free survival (PFS), local recurrence–free survival (LRFS), and overall survival (OS) rates were estimated with the Kaplan-Meier method. PT toxicity was graded by the Common Terminology Criteria for Adverse Events version 5.0. A 2-tailed paired t test was used for dosimetric comparisons. Results: Twenty-nine patients were identified. With a median follow-up time of 4.2 years (range, 0.2-8.9 years), the estimated 5-year PFS for all patients was 93%, 5-year LRFS was 96%, and estimated 5-year OS was 87%. Maximum acute grade 1 (G1) toxicities occurred in 18 patients, and 7 patients had maximum G2 toxicities. No G3+ radiation-related toxicities were observed. Average mean lung dose and lung V20 Gy were lower for patients treated with pencil-beam scanning PT compared with double-scatter PT (P = .016 and .006, respectively), while patients with lower mediastinal disease had higher doses for all evaluated dosimetric heart parameters. Conclusions: PT after chemotherapy for patients with AMNHL resulted in excellent outcomes with respect to 5-year PFS, LRFS, and OS without high-grade toxicities. Future work with larger sample sizes is warranted to further elucidate the role of PT in the treatment of AMNHL.

Purpose: To report objective response rates (ORR), time to local failure (TTLF), and overall survival (OS) among patients with relapsed or refractory diffuse large B-cell lymphoma after salvage- or palliative-intent radiation therapy (RT) and to investigate whether outcomes differed with conventional versus hypofractionated (≥2.5 Gy/fraction) RT. Methods and Materials: A single-institution observational cohort study was performed for patients who completed a course of RT for relapsed or refractory diffuse large B-cell lymphoma between January 1, 2008, and April 1, 2020. Predictors of ORR, TTLF, and OS were calculated using univariable and multivariable regression models. The Kaplan-Meier method was used to estimate TTLF and OS, and log-rank analysis was used to compare outcomes. Equivalent dose in 2 Gy fractions (EQD2) was calculated using an α/β of 10. Results: One-hundred and sixty-nine patients were treated with 205 RT courses (73 [36%] salvage, 132 [64%] palliative), and hypofractionated RT was used in 100 RT courses (49%). Median RT dose was 30 Gy (range, 8-60 Gy). ORR was 60% for the total cohort (53% and 69% for palliative and salvage cohorts, respectively). Over a median follow-up time of 4 months, median OS in all patients was 5 months (3 and 22 months for palliative and salvage cohorts, respectively). No statistically significant differences in ORR, TTLF, and OS were observed with hypofractionation compared with conventional fractionation. EQD2 ≥35 Gy was associated with improved ORR (odds ratio, 3.79 [1.19-12.03]; P = .024) and prolonged TTLF (0.39 [0.18-0.87]; P = .022), while double-hit receptor status (8.18 [1.08-62.05]; P = .042), cell of origin (3.87 [1.17-8.74]; P = .0012), and bulky disease (≥7.5 cm; 2.12 [1.18-3.81]; P = .012) were associated with inferior TTLF. In the palliative-only cohort, a low-dose regimen of 8 Gy in 2 fractions was associated with similar ORR compared with other fractionation schema but trended towards inferior TTLF (P = .36). Conclusions: Hypofractionation is not associated with differences in disease outcomes for patients with relapsed or refractory diffuse large B-cell lymphoma, while higher RT dose (EQD2 ≥35 Gy) may improve ORR and TTLF. Future work is warranted to elucidate the ideal dose and fractionation schema for such patients who will likely also undergo novel systemic agents and cellular therapies.

Purpose: Concurrent chemoradiation therapy is a curative treatment for squamous cell carcinoma of the anus, but patients can suffer from significant treatment-related toxicities. This study was undertaken to determine whether intensity modulated proton therapy (IMPT) is associated with less acute toxicity than intensity modulated radiation therapy (IMRT) using photons. Materials and Methods: We performed a multi-institutional retrospective study comparing toxicity and oncologic outcomes of IMRT versus IMPT. Patients with stage I-IV (for positive infrarenal para-aortic or common iliac nodes only) squamous cell carcinoma of the anus, as defined by the American Joint Committee on Cancer's AJCC Staging Manual, eighth edition, were included. Patients with nonsquamous histology or mixed IMPT and IMRT treatment courses were excluded. Acute nonhematologic toxicities, per the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE), version 4, were recorded prospectively at all sites. Acute and late toxicities, dose metrics, and oncologic outcomes were compared between IMRT and IMPT using univariable and multivariable statistical methods. To improve the robustness of our analysis, we also analyzed the data using propensity score weighting methods. Results: A total of 208 patients were treated with either IMPT (58 patients) or IMRT (150 patients). Of the 208 total patients, 13% had stage I disease, 36% stage II, 50% stage III, and 1% stage IV. IMPT reduced the volume of normal tissue receiving low-dose radiation but not high-dose radiation to bladder and bowel. There was no significant difference between treatment groups in overall grade 3 or greater acute toxicity (IMRT, 68%; IMPT, 67%; P = .96) or 2-year overall grade 3 or greater late toxicity (IMRT, 3.5%; IMPT, 1.8%; P = .88). There was no significant difference in 2-year progression-free survival (hazard ratio, 0.8; 95% CI, 0.3-2.0). Conclusions: Despite reducing the volume of normal tissue receiving low-dose radiation, IMPT was not associated with decreased grade 3 or greater acute toxicity as measured by CTCAE. Additional follow-up is needed to assess whether important differences arise in late toxicities and if further prospective evaluation is warranted.

Purpose: Myeloma lesions of the head can present with central nervous system (CNS) involvement (leptomeningeal disease or brain metastasis), cranial neuropathy (CN), or impending neurologic involvement (INI). We analyzed response and survival after palliative radiation therapy (RT) to the brain and/or skull for myeloma lesions to determine whether CNS involvement fared worse than other RT indications. Methods and Materials: We retrospectively analyzed 54 palliative RT courses administered at our institution from 2008 to 2019. Eleven courses were administered for CNS disease, 28 for CN, and 15 for INI. Demographic, disease, and RT variables were recorded as well as clinical response, radiographic response, and survival. Univariate analyses were performed for differences between groups, effects of clinical and RT treatment factors on response, as well as dose response. Survival was analyzed with the Kaplan-Meier method and compared by the log-rank test. Results: This heavily pretreated cohort received a median of 20 to 24 Gy, most often to the base of skull, orbit(s), calvarium, or whole brain. Any clinical response (partial or complete vs no response or progressive disease) was significantly more likely for patients with CN and INI when collectively compared with patients with CNS disease (P < .001). Dose response was significant for doses ≥15 and 20 Gy for the whole cohort (P = .026 and .005, respectively) and patients with CN/INI (P = .023 and .002, respectively). Additionally, patients with high-risk cytogenetics were less likely to clinically respond (P = .009). Patients with CNS disease had worse survival (P = .005). Conclusions: Patients with leptomeningeal disease/brain metastasis have poor clinical response and survival after RT and their responses do not demonstrate a dose response. Given these poor outcomes, the potential benefit of RT may be limited for some patients who may be alternatively managed by supportive care or short RT courses. Patients with CN/INI have longer survival and better response rates and may benefit from RT courses ≥15 to 20 Gy.