Sarcomes d'Ewing localisés du rachis chez l'enfant: Étude préliminaire d'escalade de dose comparant les techniques innovantes

Purpose: Although radiosensitive, spinal locations of Ewing's sarcomas are challenging for the radiation oncologist due to poor radiation tolerance of the spinal cord. However, some favorable anatomical compartments - that may represent more than 20% - were associated with a better outcome and could benefit from a radiation dose escalation using the most recent radiation therapy techniques. Materials and methods: We performed a dose escalation study on one patient, declined in two scenarios: (1) a tumour located within a single vertebral body and (2) a locally advanced disease involving the vertebral foramen and paraspinal soft tissues. Five dose-levels are proposed: 44.8Gy, 54.4Gy, 59.2Gy, 65.6Gy and 70.4Gy (1.6Gy per session, 8Gy per week). The 3D-conformational technique is compared with static intensity modulated radiation therapy (IMRT), helical tomotherapy, volumetric modulated arc therapy (VMAT), stereotactic body robotic radiation therapy (SBRT) and protontherapy (passive scattering). Two constraints had to be respected in order to skip to the next level: the planned target volume (PTV) coverage must exceed 95% and the D_2% on the spinal cord shall not exceed a given constraint set at 50Gy in case 1 and 44Gy in case 2 due to initial neurological sufferance. Results: Only protontherapy, SBRT, helical tomotherapy and VMAT appear able to reach the last dose level while respecting the constraints in case 1. On the other hand, only helical tomotherapy seems capable of reaching 59.2. Gy on the PTV in case 2. Conclusion: With the most recent radiation therapy techniques, it becomes possible to deliver up to 70.4. Gy in a favorable compartment in this sham patient. Unfavorable compartments can receive up to 59.2. Gy. Definitive radiation therapy may be an interesting local treatment option to be validated in an early phase trial.