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Worth Attention rhabdomyosarcoma Protons Retrospective

Proton therapy timing was not independently associated with worse rhabdomyosarcoma outcomes

Four-year overall survival was 81.2%, and starting proton therapy at week 14 or later was not independently associated with worse outcomes.

RadOncToday · ·1 min read

KEY POINTS

  • This single-centre retrospective study included 84 patients with nonmetastatic rhabdomyosarcoma treated with definitive proton beam therapy at a national United Kingdom centre. Median age was 7.6 years, 51% had parameningeal primaries, and 75% had high- or very high-risk disease.
  • Patients were treated according to RMS 2005 or FaR-RMS protocols. Median proton dose was 50.4 Gy relative biological effectiveness (range, 41.4–58.1), and median time from chemotherapy initiation to radiotherapy was 13 weeks; 44 patients started by week 13 and 40 at week 14 or later.
  • After a median follow-up of 48 months, four-year overall survival, disease-free survival, local control, and distant metastasis-free survival were 81.2%, 70.8%, 75.4%, and 89.7%, respectively. All 15 local failures occurred in-field within the high-dose region.
  • Parameningeal location was associated with inferior overall survival (hazard ratio 34.3, 95% confidence interval 4.58–4380; p<0.001) and disease-free survival (hazard ratio 3.30, 95% confidence interval 1.38–8.89; p=0.007). T3–4 disease was also associated with worse overall and disease-free survival.
  • After adjustment for parameningeal site, radiotherapy initiation at week 14 or later was not associated with worse overall survival (hazard ratio 0.30, 95% confidence interval 0.10–1.00; p=0.052). The apparent disease-free survival advantage in the delayed group was considered likely confounded by baseline imbalance; acute and late toxicity outcomes were not reported.

CLINICAL TAKEAWAY

Definitive proton therapy produced encouraging four-year outcomes in this predominantly paediatric, high-risk cohort, with prognosis driven mainly by parameningeal location, intracranial extension, and advanced T stage. The results do not establish that delaying radiotherapy is safe because timing groups were unbalanced, event numbers were limited, residual confounding remained likely, and no photon-treated comparator was included.

SOURCE

International Journal of Radiation Oncology, Biology, Physics