Program Information
Robust Intensity-Modulated Proton Therapy to Spare High Linear Energy Transfer in Organs at Risk
Y An1*, J Shan2 , S Steven3 , M Bues4 , W Liu5 , (1) Mayo Clinic Arizona, Phoenix, AZ, (2) Arizona State University, Phoenix, AZ, (3) Mayo Clinic Arizona, Phoenix, AZ, (4) Mayo Clinic Arizona, Phoenix, AZ, (5) Mayo Clinic Arizona, Phoenix, AZ
Presentations
TH-AB-605-9 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 605
Purpose: We propose a robust treatment planning model that simultaneously considers proton range and patient setup uncertainties and spares high linear energy transfer (LET) in the organs at risk (OARs) to minimize the possible high relative biological effectiveness (RBE) dose in OARs.
Methods: We retrospectively generated plans for 5 patients with prostate, head and neck, and lung cancer. The “worst-case robust optimization” model was applied. One additional term related to the “biological dose (BD)” of OARs was added into the objective function. The BD was defined as the sum of physical dose and the extra biological dose relating to high LET. The definition was adopted to avoid the controversy of calculating RBE from LET. Corresponding to each uncertainty scenario, LET distributions in patients’ CT geometry were calculated by a fast in-house developed method based on the LET data in simple mediums generated from Monte Carlo simulations. In each optimization iteration, the model used the worst-case BD among all scenarios and then penalized overly high BD to organs. The dose-volume histograms (DVHs) of the physical dose and BD for tumor and organs under nominal and uncertainty scenarios were assessed to evaluate the plan quality. Our new model was compared with the conventional robust planning model without considering the influence of LET.
Results: For the 5 cases included in this study, our model outperformed the conventional robust model in terms of avoiding high BD in OARs. At the same time, our method achieved physical dose distributions and plan robustness of tumors almost as good as those from the conventional robust model.
Conclusion: Explicitly considering LET in IMPT robust treatment planning can reduce the BD and minimize the possible toxicity of high RBE dose due to high LET to OARs without compromising the plan quality and robustness of tumors.
Funding Support, Disclosures, and Conflict of Interest: Supported by the National Cancer Institute (NCI) Career Developmental Award K25-CA168984, by the Fraternal Order of Eagles Cancer Research Fund Career Development Award, by The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, by Mayo Arizona State University Seed Grant, and by The Kemper Marley Foundation.
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