Purpose: The purpose of this work was to quantify the difference in plan quality between intensity- modulated proton therapy (IMPT) and photon-based stereotactic radiosurgery (SRS) treatment planning for multiple brain metastases.
Methods: Twenty-two brain lesions from six patients, were planned using scanning beam proton and compared against photon-based SRS plans. Proton plans were optimized and evaluated using the Monte Carlo algorithm and photon plans were optimized using a collapsed cone convolution algorithm. Dose coverage to each lesion was set to 99% of the target volume receiving the prescription dose for all plans. Conformity index (CI), gradient index (GI), total V4.5Gy, mean brain dose and V12Gy for each lesion, were used to compare plan quality between the proton and photon plans using dose-volume histograms (DVHs) generated from each plan.
Results: Both average CI and GI across all lesions were generally lower than the proton plans than those from the photon plans, but both were comparable, with a mean CI of 2.29 ± 1.47 and 2.48 ± 2.48 for protons and photons, respectively, with p>0.05. Mean GI was 4.58 ± 3.13 and 5.18 ± 2.60 for protons and photons respectively, with p>0.05. Mean V4.5Gy was 59.3 ± 35.7 cm3 and 203.8 ± 121.9 cm3 for proton plans and photon plans, respectively, with p<0.05. Mean brain dose was 36.7 ± 25.8 cm3 and 135.2 ± 47.5 cm3 for protons and photons, respectively, with p<0.05.
Conclusion: We quantified the plan quality for both IMPT treatment plans and photon SRS plans for brain metastases. Proton therapy for brain lesions offers a good alternative to photon-based SRS treatment, with a lower average CI and GI, V4.5Gy and mean brain dose, and can significantly increase preservation of normal brain tissue.
Funding Support, Disclosures, and Conflict of Interest: Support for this project provided by Advanced Oncotherapy (AVO), plc (London, UK).
Not Applicable / None Entered.