Program Information
An Improved Distance-To-Dose Correlation for Predicting Bladder and Rectum Dose-Volumes in Knowledge-Based VMAT Planning for Prostate Cancer
P Wall1*, J Fontenot1,2 , R Carver1,2 , (1) Louisiana State University, Baton Rouge, LA, (2) Mary Bird Perkins Cancer Center, Baton Rouge, LA
Presentations
SA-B-BRA|B-7 (Saturday, March 18, 2017) 10:30 AM - 12:30 PM Room: Ballroom A|B
Purpose: The overlap volume histogram (OVH) is an anatomical metric commonly used to quantify the geometric relationship between an OAR and target volume when predicting expected dose-volumes in knowledge-based treatment planning. This work investigated the influence of additional variables contributing to variations in the assumed linear DVH-OVH correlation for the bladder and rectum in VMAT plans of prostate patients, with the goal of increasing prediction accuracy and achievability of knowledge-based planning methods.
Methods: VMAT plans were retrospectively generated for 124 prostate patients using multi-criteria optimization. DVHs quantified patient dosimetric data while OVHs quantified patient anatomical information. The DVH-OVH correlations were calculated for fractional bladder and rectum volumes of 30, 50, 65, and 80%. Correlation between potential influencing factors and dose were quantified using the Pearson product-moment correlation coefficient (R). Factors analyzed included the derivative of the OVH, prescribed dose, PTV volume, bladder volume, rectum volume, and in-field OAR volume.
Results: Out of the selected factors, only the in-field bladder volume (mean R = 0.86) showed a strong correlation with bladder doses. Similarly, only the in-field rectal volume (mean R = 0.76) showed a strong correlation with rectal doses. Therefore, an OVH formalism accounting for in-field OAR volumes was computed to measure the improvement in DVH-OVH correlation. Including this in-field factor strengthened the DVH-OVH correlation, with the mean R over the four fractional volume points increasing from -0.79 to -0.85 and -0.82 to -0.86 for the bladder and rectum respectively.
Conclusion: This work shows that use of the OVH can be improved by an additional factor accounting for in-field OAR volume. This can lead to more precise and achievable DVH predictions using a knowledge-based planning model. Other treatment and patient parameters, such as the prescribed dose and bladder/rectal fill volumes, were not observed to correlate with OAR dose.
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