Dose Escalation in Pediatric Pelvic Ewing's Sarcoma: Insights from a National Training Initiative

Objective

The Inter Ewing-1 trial investigates dose escalation in definitive radiotherapy (randomization 54Gy versus 64.8Gy). Before opening the trial, a national training initiative was conducted by the French Pediatric Radiotherapy Group (GFRP) to assess dosimetric discrepancies in definitive RT with dose escalation.

Methods and Materials

A large non-operated pelvic pediatric case of Ewing's sarcoma was selected. Delineated structures associated with CT-scan were distributed to participants, all of whom were accredited for pediatric radio- and/or proton-therapy. Treatment planning involved a simultaneous integrated boost: 54Gy in 30 fractions (1.80Gy/fraction) for the pre-chemotherapy tumor volume and 63.9Gy (2.13Gy/fraction) for the post-chemotherapy volume. Dose constraints for organs-at-risk and target coverage were provided. All treatment plans for photons and protons were collected, analyzed for minor and major deviations and compared using 21 dosimetric criteria.

Results

Eleven French centers participated, submitting 14 plans (10 photon/4 proton plans). One photon plan showed a minor deviation in CTV coverage (V60.7GyCTV=98.8%, expected value=100%), and another one exhibited two minor deviations in organ-at-risk constraints (V55GyBowel=32cc [limit:28 cc] and V50GyRectum=52.4% [limit:50%]). No significant difference was observed between photons and protons in target coverage for PTV63.9Gy(p=0.95) and CTV63.9Gy(p=0.66), as well as in sparing the most critical organs. However, significant differences were reported in favor of protons regarding the integral dose criterion (p<0.01), DmeanBowel(9.9±1.1Gy for photons vs 4.1±1.3 Gy for protons, p<0.01), and DmeanAnalCanal(3.9±0.7Gy for photons vs 2.2±0.9Gy for protons, p<0.01).

Conclusion

This national training initiative provided French centers conducting pediatric radio/proton-therapy with an initial insight into the Ewing-1 protocol. Analysis showed a good treatment planning homogeneity between the centers and a successful adhesion to the dose escalation arm constraints. Protons did not demonstrate considerable advantages for this particular clinical case except with respect to the limitation of integral dose.