Program Information
Spatiotemporal Dose Shaping to Achieve Uniform Fractionation in Healthy Tissues Along with Hypo-Fractionation in Targets
J Unkelbach*, M Bussiere , H Shih , P Chapman , J Loeffler , Massachusetts General Hospital, Boston, MA
Presentations
TH-EF-BRD-10 (Thursday, July 16, 2015) 1:00 PM - 2:50 PM Room: Ballroom D
Purpose: Fractionation decisions in radiotherapy face the tradeoff between increasing the number of fractions to spare normal tissues, and increasing the total dose to achieve the same effect in the target volume. In that regard, the ideal treatment would fractionate in normal tissues while simultaneously hypo-fractionating in the target. Interestingly, this is possible to a limited degree by delivering distinct dose distributions in different fractions. The dose distributions have to be designed such that similar doses are delivered to normal tissues while delivering high single fraction doses to parts of the target. We demonstrate that this concept may lead to an improved therapeutic ratio for rotation therapy treatments using conventional photon beams.
Methods: Fractionation effects are modeled via the biologically equivalent dose (BED) model. Treatment plan optimization is performed using objective functions evaluated for the cumulative BED delivered at the end of treatment. This allows for simultaneously optimizing multiple distinct treatment plans for different fractions.
Results: The concept is demonstrated for large cerebral arteriovenous malformations (AVM) treated in two fractions. It is shown that the optimal treatment delivers a large dose to the center of the AVM in the first fraction. The second fraction delivers the missing dose to the rim of the target volume. The target is divided into center and rim in such a way that the dose received by normal brain adjacent to the AVM is approximately equal in both fractions.
Conclusion: The BED in the target can be increased by hypo-fractionating the central core. Since the fractionation effect is exploited in the normal tissue, this leads to an improved therapeutic ratio overall. The approach may potentially be beneficial for large AVMs or tumors embedded in a dose-limiting normal tissue treated with stereotactic regimens.
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