Program Information
Dose-Mass- and Dose-Volume-Optimization Sensitivity to Anatomical Changes During RT
M De Ornelas-Couto*, E Bossart , I Mihaylov , Univ Miami, Miami, FL
Presentations
SU-I-GPD-T-316 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To compare the sensitivity of dose-mass-histogram- (DMH) and dose-volume-histogram-based optimization (DVH) to anatomical changes during radiotherapy (RT).
Methods: Six lung and six head-and-neck (HN) patients were CT scanned before RT (CT1), mid-treatment (CT2), and at the end of treatment (CT3). All targets (PTVs) and organs at risk (OARs) were deformably propagated from CT1 to the subsequent CTs. For each case DMH- and DVH-based plans were generated on the planning CT1. All plans were normalized to 95% of the prescription dose to the PTV:70 Gy in 35 fractions for the lung cases and 70 Gy in 35 fractions to the primary PTV for the HN cases. The plans were then transferred to the subsequent CTs. Dose indices (DIs) were obtained for plan stability evaluation. DIs used for the lung cases were: PTV D95%, cord D2%, bilungs (both lungs without PTVs) D20% and D30%, and heart D33%. For the HN cases DIs included: PTV1 D95%, cord D2%, brainstem D2%, left_ and right_parotid D2% and D50%.
Results: Percent change between CT1 and CT3 were on average larger with DMH than DVH for all DIs, except PTV D95% for lung (DMH: 4.98cGy and DVH: 6.87cGy) and left_parotid D50% for HN (DMH: 8.19cGy and DVH: 7.95cGy).
Conclusion: Overall DMH showed larger changes in OARs by the end of RT compared to DVH. Some DI changes mid-way through RT were more pronounced for DVH and others for DMH, therefore no conclusion can be drawn regarding which optimization scheme is more stable. PTV coverage had larger changes with DVH, although DMH plans delivered slightly more dose to the PTVs by the end of the RT. The differences between the observed changes for DVH and DMH optimization was relatively small. Therefore larger cohorts are needed to determine whether the differences are statistically significant.
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