Room: ePoster Forums
Purpose: To investigate the dosimetric differences between photon and proton therapy using simultaneous-integratedboost (SIB) and photon therapy alone using sequential-boost (SEB) for patients treated for glioblastoma (GBM) following dose-escalation trial NRG-BN001.
Methods: Ten patients were retrospectively identified. Three plans were generated for each patient following NRG-BN001 protocol: a SEB of 60Gy/46Gy using 6 MV photon with non-coplanar VMAT on a TrueBeam STx, a SIB of 75Gy/50Gy using 6 MV photon with non-coplanar VMAT on a TrueBeam STx, and a SIB of 75Gy/50Gy using passive-scattering proton technique on a Mevion S250. All the plans were optimized in Varian Eclipse TPS with planning objectives specified in the protocol. One-way ANOVA test were performed to compare the PTV conformity and OAR sparing among three cohorts. A p<0.05 was considered as statistically significant.
Results: The dosimetric parameters in both SIB cohorts were comparable to those in SEB photon cohort despite the escalated prescription doses in SIB cohorts. The OARs distant from PTVs, such as lenses and spinal cord, were better spared in SIB proton cohort with significantly lower Dmax. The integral dose in SIB proton plan was also significantly lower with the lowest V(2Gy) of brain. On the other hand, the Dmax to OARs in SIB photon cohort were lower than those in SEB photon cohort, however the differences were not significant. While all PTV coverage was met per protocol, both photon cohorts had significantly higher Paddick conformity indices than SIB proton cohorts, likely due to the complex anatomies of PTVs and OARs, limitation of the passive scattering proton technique, and the range uncertainties taken into account for proton beams.
Conclusion: Compared to SEB photon therapy, SIB photon and proton therapy allow one to intensify treatment dose while not compromising OAR sparing. Further studies are warranted to investigate clinical indications of the dosimetric benefits.