Patterns of Failure in Pediatric Rhabdomyosarcoma After Proton Therapy

Int J Radiat Oncol Biol Phys. 2016 Dec 1;96(5):1070-1077. doi: 10.1016/j.ijrobp.2016.08.028. Epub 2016 Aug 30.


Purpose: To report on the patterns of failure in children with rhabdomyosarcoma treated with proton therapy.

Patients and methods: Between February 2007 and November 2013, 66 children with a median age of 4.1 years (range, 0.6-15.3 years) diagnosed with nonmetastatic rhabdomyosarcoma were treated with proton therapy. Clinical target volume 1 was defined as the prechemotherapy tumor plus a 1-cm anatomically constrained margin. Clinical target volume 2 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.

Results: Of 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 of 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.

Conclusion: Early 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 clinical target volume 1/2 margin with highly conformal proton therapy does not compromise local control in children diagnosed with rhabdomyosarcoma with unfavorable risk features.

MeSH terms

  • Adolescent
  • Age Factors
  • Child
  • Child, Preschool
  • Disease Progression
  • Female
  • Humans
  • Infant
  • Male
  • Neoplasm Recurrence, Local* / diagnostic imaging
  • Neoplasm Recurrence, Local* / mortality
  • Neoplasm Recurrence, Local* / pathology
  • Proton Therapy / methods*
  • Retrospective Studies
  • Rhabdomyosarcoma, Alveolar / mortality
  • Rhabdomyosarcoma, Alveolar / pathology
  • Rhabdomyosarcoma, Alveolar / radiotherapy*
  • Rhabdomyosarcoma, Embryonal / diagnostic imaging
  • Rhabdomyosarcoma, Embryonal / mortality
  • Rhabdomyosarcoma, Embryonal / pathology
  • Rhabdomyosarcoma, Embryonal / radiotherapy*
  • Survival Rate
  • Treatment Failure
  • Tumor Burden