Patterns of Failure in Pediatric Rhabdomyosarcoma Following Proton Therapy

Publication date: Available online 30 August 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Tamara Z. Vern-Gross, Daniel J. Indelicato, Julie A. Bradley, Ronny L. Rotondo
PurposeWe report on the patterns of failure in children with rhabdomyosarcoma treated with proton therapy.Patients and MethodsBetween February 2007 and November 2013, 66 children with a median age of 4.1years (range, 0.6-15.3 years) diagnosed with non-metastatic rhabdomyosarcoma were treated with proton therapy. Clinical target volume 1 (CTV1) was defined as the prechemotherapy tumor plus a 1-cm anatomically-constrained margin. CTV2 was defined as the postchemotherapy tumor (or tumor bed) plus a 0.5 cm anatomically-constrained margin, further expanded to encompass potential pathways of spread, including soft tissue infiltrated with tumor at diagnosis.ResultsOf the 66 children, 11 developed locally progressive disease at a median of 16 months (range, 14-32 months) for an actuarial 2-year local control rate of 88%. Among the children who progressed, median age and tumor size at diagnosis were 6.7 years (range 0.6-16 years) and 6 cm (range, 2-8 cm), respectively. Of the recurrences, 64% and 36% were embryonal and alveolar, respectively. Disease progression was observed in 7 (64%) parameningeal, 2 (18%) head and neck (other), and 2 (18%) bladder/prostate subsites. At diagnosis, 8 of 11 patients who developed a recurrence were Intergroup Rhabdomyosarcoma Study stage 3 and all 11 were group III. Of the relapses, 100% (11/11) were confirmed as in-field within the composite 95% isodose line. One of the 11 patients (9%) developed a new simultaneous regional nodal recurrence outside of the previously treated radiation field.ConclusionEarly data suggest that the sharp dosimetric gradient associated with proton therapy is not associated with an increased risk of marginal failure. Routine use of a 0.5- to 1-cm CTV1/2 margin with highly conformal proton therapy does not compromise local control in children diagnosed with rhabdomyosarcoma with unfavorable risk features.

Teaser

This study examines patterns of failure in children who received proton therapy for rhabdomyosarcoma. Routine use of a small CTV margin in the setting of highly conformal proton therapy does not compromise local control in children diagnosed with rhabdomyosarcoma with unfavorable risk features. The patterns of failure suggest improvements in local control will come through dose escalation of select high-risk tumors rather than larger CTV margins.


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