Long-Term Outcomes of Consolidative Proton Therapy for Pediatric Classical Hodgkin Lymphoma

Classical Hodgkin lymphoma (cHL) is associated with favorable prognosis and high overall survival (OS). Consolidative proton therapy (cPT) represents a modality recommended for young patients due to its reduction in exit dose, with a goal to minimize late effects. We present outcomes of pediatric patients with cHL receiving cPT at initial diagnosis or relapse/refractory (R/R) disease.

From 10/2007 to 12/2022, 74 patients between the ages of 6 and 22 with cHL treated with cPT after systemic therapy (ST) were included. Risk groups were classified by ST into low, intermediate, and high risk. Involved-site radiotherapy was used for most patients (90%). OS and relapse-free survival (RFS) were estimated using the Kaplan-Meier method; crude cumulative incidence estimates were used to describe recurrence patterns.

Median follow-up was 5.5 years (30% > 8 years). Sixty-one (82.4%) patients were treated at initial diagnosis, and 13 (17.6%) received cPT for R/R disease. Median age at diagnosis was 16 years (range, 6.3-21.7), with most being female (58.1%), nodular sclerosing subtype (82.4%), and bulky disease (78.4%). 10-year OS was 96% overall (97% initial, 92% R/R); 10-year RFS was 84% overall (82% initial, 92% R/R). 10-year RFS was 100%, 82%, and 72% for low, intermediate, and high-risk groups. Of the 61 patients treated for initial diagnosis, 8 experienced relapse, with 4 (6.6%) out-of-field & in-field, 3 (4.9%) out-of-field, and 1 (1.6%) in-field. Of the 13 patients treated for R/R disease, 1 experienced an out-of-field recurrence. One patient developed papillary thyroid carcinoma 11.9 years post-cPT (in-field); no other grade 3+ radiation-related late toxicities were observed.

cPT is an effective and well-tolerated treatment for young patients with cHL, demonstrating excellent 10-year OS and RFS, even for those treated at relapse. These findings support cPT as a treatment modality, warranting further studies to assess long-term outcomes.