Single-Center Study Evaluates Proton Radiotherapy for Pediatric Medulloblastoma
In a phase II study reported in The Lancet Oncology by Yock et al, use of proton radiotherapy for pediatric medulloblastoma was associated with acceptable long-term toxic effects and good survival outcomes.
Study Details
In the study, 59 patients aged 3 to 21 years were treated at Massachusetts General Hospital between May 2003 and December 2009. Of them, 39 had standard-risk, 6 had intermediate-risk, and 14 had high-risk disease; all 59 received chemotherapy. Patients received craniospinal irradiation at 18 to 36 Gy radiobiologic at 1.8 Gy radiobiologic equivalents per fraction followed by a boost dose. The primary outcome was cumulative incidence of ototoxicity at 3 years on the Pediatric Oncology Group ototoxicity scale (0–4).
Toxic Effects
Survivors had a median follow-up of 7.0 years. All patients received the planned proton radiotherapy dose; the median dose was 23.4 Gy radiobiologic equivalents, and the median boost dose was 54.0 Gy radiobiologic equivalents.
Grade 3 or 4 ototoxicity occurred in both ears in 4 (9%) of 45 evaluable patients and in one ear in 3 patients (7%), with toxicity later reverting to grade 2 in one of the latter patients. The cumulative incidence of grade 3 to 4 hearing loss was 12% at 3 years and 16% at 5 years.
The Pediatric Oncology Group hearing ototoxicity score at median follow-up of 5.0 years was equal to baseline or improved by 1 point in 34 (35%) of 98 ears and worsened by 1 point in 21 (21%), by 2 points in 35 (36%), by 3 points in 6 (6%), and by 4 points in 2 (2%).
The Full Scale Intelligence Quotient decreased by 1.5 points per year after a median follow-up of 5.2 years, reflecting decreases in processing speed and verbal comprehension. No significant changes in perceptual reasoning or working memory were observed.
At 5 years, the cumulative incidence of hormone deficit was 55%, with growth hormone deficit in 46%. No late cardiac, pulmonary, or gastrointestinal toxic effects were observed.
Progression-Free Survival
Progression-free survival at 3 years was 83%. In a post-hoc analysis, 5-year progression-free survival was 80%, and 5-year overall survival was 83%.
The investigators concluded: “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.”
The study was funded by the National Cancer Institute and Massachusetts General Hospital.
Torunn I. Yock, MD, of Massachusetts General Hospital, Boston, is the corresponding author of The Lancet Oncology article.
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