Maximization of Peak-to-Valley Dose Ratio and Normal-Tissue Survival Fraction for Proton Minibeam Radiation Therapy

Abstract

<h3>Purpose/Objective(s)</h3> Proton minibeam radiation therapy (pMBRT) is a novel proton modality of spatially fractionated RT (SFRT). pMBRT can reduce the radiation damage to normal tissues via biological dose sparing of high peak-to-valley dose ratio (PVDR). This work will develop a new pMBRT treatment planning method that jointly optimizes the plan quality and maximizes the PVDR. <h3>Materials/Methods</h3> The new optimization method simultaneously maximizes the normal-tissue PVDR and optimizes the dose distribution at tumor targets and organs-at-risk (OAR). The PVDR maximization is through the joint total variation (TV) and L1 regularization with respect to the normal-tissue dose. That is, at beam-eye-view projected dose slices of several depths for each beam angle, the TV of dose is maximized, corresponding to the PVDR maximization, while the L1 of dose is minimized, corresponding to the minimization of the OAR dose and maximization of survival fraction (SF). <h3>Results</h3> The new IMPT method with TV and L1 regularization (TVL1) was validated in comparison with the conventional IMPT method (CONV) for pMBRT on several clinical cases. The results show that TVL1 provided larger PVDR and SF than CONV for biological sparing of normal tissues, with preserved plan quality in terms of physical dose distribution. <h3>Conclusion</h3> A new pMBRT treatment planning method is developed that can optimize and improve normal-tissue PVDR and SF, by incorporating TV and L1 dose regularization into IMPT.