Synergistic integration of ripple filter and penumbra reduction for enhanced dose conformity and beam delivery efficiency in proton therapy.

PURPOSE: This study evaluates the synergistic integration of Ripple Filter (RiFi) and Extended Penumbra Reduction (EPR) techniques, which reposition the patient closer to the nozzle, to enhance dose distribution and beam delivery efficiency in head and neck cancer patients.

METHODS

A retrospective analysis was performed on 30 patients with head and neck and intracranial tumors treated at SPHIC from 2023 to 2024. Three treatment planning strategies were compared: No-RiFi, EPR20+RiFi (20 cm forward shift), and EPR40+RiFi. Dosimetric parameters, including target coverage, homogeneity index (HI), conformity index (CI), and organ-at-risk (OAR) doses, were evaluated. In addition, energy layer counts and beam delivery time were compared.

RESULTS

The EPR+RiFi plans demonstrated non-inferior target coverage compared with the No-RiFi plans. With the exception of the maximum spinal cord dose, the EPR20+RiFi plans resulted in higher OAR doses compared with the No-RiFi plan, with mean differences within 0.5 Gy(RBE). In contrast, the EPR40+RiFi plans showed small dose reductions in most OARs (mean decrease 0.1-1.1 Gy(RBE)). Notably, the integration of RiFi with EPR significantly reduced the number of energy layers and shortened beam delivery time by an average of 54% (ranging from 46% to 60%).

CONCLUSIONS

The combined use of RiFi and EPR with a 40 cm forward shift significantly enhances beam delivery efficiency while maintaining or reducing OAR doses. These findings support the clinical feasibility of this approach and its potential to improve treatment capacity in high-volume proton therapy centers.