Abstract
BackgroundThe conventional dose rate of radiation therapy is 0.01–0.05 Gy per second. According to preclinical studies, an increased dose rate may offer similar anti-tumoral effect while dramatically improving normal tissue protection. This study aims at evaluating the early toxicities for patients irradiated with high dose rate pulsed proton therapy (PT).Materials and MethodsA single institution retrospective chart review was performed for patients treated with high dose rate (10 Gy per second) pulsed proton therapy, from September 2016 to April 2020. This included both benign and malignant tumors with ≥3 months follow-up, evaluated for acute (≤2 months) and subacute (>2 months) toxicity after the completion of PT.ResultsThere were 127 patients identified, with a median follow up of 14.8 months (3–42.9 months). The median age was 55 years (1.6–89). The cohort most commonly consisted of benign disease (55.1%), cranial targets (95.1%), and were treated with surgery prior to PT (56.7%). There was a median total PT dose of 56 Gy (30–74 Gy), dose per fraction of 2 Gy (1–3 Gy), and CTV size of 47.6 ml (5.6–2,106.1 ml). Maximum acute grade ≥2 toxicity were observed in 49 (38.6%) patients, of which 8 (6.3%) experienced grade 3 toxicity. No acute grade 4 or 5 toxicity was observed. Maximum subacute grade 2, 3, and 4 toxicity were discovered in 25 (19.7%), 12 (9.4%), and 1 (0.8%) patient(s), respectively.ConclusionIn this cohort, utilizing high dose rate proton therapy (10 Gy per second) did not result in a major decrease in acute and subacute toxicity. Longer follow-up and comparative studies with conventional dose rate are required to evaluate whether this approach offers a toxicity benefit.
Highlights
Proton Therapy (PT) is a particle therapy that utilizes a Bragg Peak to reduce the radiation dose received by healthy tissue, as demonstrated by previous in silico studies [1]
There is a scarcity of clinical data utilizing FLASH radiotherapy, with only 1 case report to date, which showed that electron FLASH reirradiation may mitigate toxicity and allow radiation delivery even if the theoretical cumulative doses to healthy tissue would be exceeded [14]
The purpose of the current study is to analyze the early toxicities for tumors treated pencil-beam scanning with pulsed high dose rate protons
Summary
Proton Therapy (PT) is a particle therapy that utilizes a Bragg Peak to reduce the radiation dose received by healthy tissue, as demonstrated by previous in silico studies [1]. To further improve the therapeutic ratio, several preclinical studies identified a considerable biological advantage to delivering radiation dose rate higher than the conventional 0.01 to 0.05 Gy/second. “FLASH” radiotherapy, or dose rates exceeding 10 Gy per 100 ms, significantly reduced the radiation damage to healthy cells/tissue without a decline in anti-tumoral effect [7,8,9]. This was initially demonstrated with electrons [7,8,9], but subsequently with photons [10] and protons [11,12,13]. This study aims at evaluating the early toxicities for patients irradiated with high dose rate pulsed proton therapy (PT)
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