Systematic assessment of clinical outcomes and toxicities of proton radiotherapy for reirradiation

Reirradiation (reRT) for locoregional recurrences poses unique challenges and risks; re-treatment using proton beam radiotherapy (PBT) could prove advantageous. Assessing clinical outcomes and toxicity profiles, this systematic review comprehensively evaluated available evidence regarding PBT reRT. Fourteen original investigations across central nervous system (CNS) (n = 6), head/neck (H&N) (n = 4), lung (n = 2), and gastrointestinal (n = 2) malignancies were analyzed. PBT for recurrent uveal melanoma achieved 5-year eye retention of 55%; for chordomas, reRT afforded a 2-year local control and overall survival (OS) of 85% and 80%, respectively. Multiple PBT reRT studies for adult gliomas illustrate no grade ≥3 toxicities. Two pediatric CNS tumor studies demonstrated the safety and efficacy of reRT, with one total grade 3 toxicity and achievement of longer-term OS. PBT for H&N malignancies shows appropriate local/locoregional control and favorable toxicity profiles versus historical photon-based methods, including low (9-10%) rates of feeding tube placement. PBT for recurrent lung cancer can achieve favorable survival with expected toxicities/complications of reRT, especially with concurrent chemotherapy and centrally located recurrences. Lastly, PBT reRT in gastrointestinal malignancies induced very few high-grade complications. Hence, based on the limited existing data, PBT is a notably safe reRT modality for effective salvage of recurrent disease. Institutional experiences must continue to be reported: dosimetric correlations, late toxicities, and advanced PBT techniques.