Proton Radiotherapy Bests Standard Radiotherapy

Researchers at Massachusetts General Hospital (MGH; Boston, MA, USA) and Brigham and Women's Hospital (Boston, AM, USA) conducted a non-randomized, open-label, phase 2 trial involving 59 patients (aged 3–21 years) with medulloblastoma to assess late complications, acute side-effects, and survival associated with PBT. All patients underwent craniospinal irradiation of 18–36 Gy radiobiological equivalents (GyRBE), followed by a boost dose. The primary outcome was cumulative incidence of ototoxicity at three years; secondary outcomes were neuroendocrine toxic effects and neurocognitive toxic effects, as assessed by intention-to-treat.

The results showed that three years after treatment, progression-free survival was at 83%, and at five years, progression-free survival was 80%; 12% of patients had serious hearing loss, which rose to 16% at five years. Processing speed and verbal comprehension were also affected, but perceptual reasoning and working memory were not. At five years, 55% had problems with the neuroendocrine system, with growth hormone being the most commonly affected. On the other hand, the researchers found no cardiac, pulmonary, or gastrointestinal toxic effects, which are common in patients treated with photon radiotherapy. The study was published on January 29, 2016, in the Lancet Oncology.

“Proton radiotherapy resulted in acceptable toxicity and had similar survival outcomes to those noted with conventional radiotherapy, suggesting that the use of the treatment may be an alternative to photon-based treatments,” concluded lead author Torunn Yock, MD, and colleagues of the MGH Proton Center. “Although there remain some effects of treatment on hearing, endocrine, and neurocognitive outcomes, particularly in younger patients, other late effects common in photon-treated patients were absent.”

PBT is a precise form of radiotherapy that uses charged particles instead of X-rays to deliver a dose of radiotherapy more precisely and with minimal damage to surrounding tissue. Evidence is growing that protons can be effective in treating a number of cancers, in particular children and young people with brain tumors, for whom PBT appears to produce fewer side effects such as secondary cancers, growth deformity, hearing loss, and learning difficulties.

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