Exhibit Hall | Forum 5
Purpose: In IMPT of Head and Neck (H&N) cancer, daily alignment and anatomic changes may introduce large dose variations due to the sharp dose gradients at the end of the proton range. The daily setup uncertainties and organ motion may demand frequent evaluation dose and plan adaptation of HN patients. This study provides an assessment for the feasibility and potential benefits of CBCT-based adaptive (ART) planning using automated planning for treatment of HN cancer.
Methods: Five patients with HN cancer treated with IMPT were included. First, initial IMPT plans were created using automated planning (RapidPlanPT, Varian Medical Systems) with ±3mm / 3% patient setup and range uncertainties on planning CT (pCT). The pCT was deformably registered to weekly CBCTs to create synthetic CTs (sCT) by transferring the electron densities from pCT to CBCTs. Doses were recalculated on weekly sCTs (non-Adapt). Adaptive IMPT plans were created on weekly sCTs using automated planning (RapidPlanPT) using the same beam setup and uncertainty scenarios from pCT (Adapt). CTVprimary was normalized such that 95% of the volume covered by the prescription dose. Both non-Adapt and Adapt weekly doses were accumulated back to the pCT and assessed using the dose volume constraints for CTVs and Organs at Risk (OARs).
Results: For non-Adapt, the coverage constraints for CTVs failed for all fractions and patients. Larynx Dmean was lower with Adapt as compared to non-Adapt (28.3 Gy vs. 30.7 Gy). For right parotid, V20 was also lower with Adapt compared to non-Adapt (38.2Gy vs.40Gy). For other OARs, differences between Adapt and non-Adapt were not statistically significant.
Conclusion: Online adaptive using automated planning of H&N cancer using weekly plan re-optimization resulted in better target conformality, coverage and better sparing for some OARs compared with non-adaptive IMPT. However, there is a variability in the amount of benefit achievable from ART.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA. (GR013242)
Intensity Modulation, Cone-beam CT, Protons
TH- External Beam- Particle/high LET therapy: Proton therapy – adaptive therapy