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A Logistic Function-Based Model to Predict Organ-At-Risk (OAR) DVH in IMRT Treatment Planning

S Chen

S Chen*, H Zhang , B Zhang , W D'Souza , University of Maryland School of Medicine, Baltimore, MD


SU-E-T-39 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the feasibility of a logistic function-based model to predict organ-at-risk (OAR) DVH for IMRT planning. The predicted DVHs are compared to achieved DVHs by expert treatment planners.

Methods: A logistic function is used to model the OAR dose-gradient function. This function describes the percentage of the prescription dose as a function of the normal distance to PTV surface. The slope of dose-gradient function is function of relative spatial orientation of the PTV and OARs. The OAR DVH is calculated using the OAR dose-gradient function assuming that the dose is same for voxels with same normal distance to PTV. Ten previously planned prostate IMRT plans were selected to build the model, and the following plan parameters were calculated as possible features to the model: the PTV maximum/minimum dose, PTV volume, bladder/rectum volume in the radiation field, percentage of bladder/rectum overlapping with PTV, and the distance between the bladder/rectum centroid and PTV. The bladder/rectum dose-gradient function was modeled and applied on 10 additional test cases, and the predicted and achieved clinical bladder/rectum DVHs were compared: V70 (percentage of volume receiving 70Gy and above), V65, V60, V55, V50, V45, V40.

Results: The following parameters were selected as model features: PTV volume, and distance of centroid of rectum/bladder to PTV. The model was tested with 10 additional patients. For bladder, the absolute difference (mean±standard deviation) between predicted and clinical DVHs is ΔV70=-0.3±3.2, ΔV65=-0.8±3.9, ΔV60=1.5±4.3, ΔV55=1.7±5.3, ΔV50=-0.6±6.4, ΔV45=0.6±6.5, and ΔV40=0.9±5.7, the correlation coefficient is 0.96; for rectum, the difference is ΔV70=1.5±3.8, ΔV65=1.2±4.2, ΔV60=-0.1±5.3, ΔV55=1.0±6.6, ΔV50=1.6±8.7, ΔV45=1.9±9.8, and ΔV40=1.5±10.1, and the correlation coefficient is 0.87.

Conclusion: The OAR DVH can be accurately predicted using the OAR dose-gradient function in IMRT plans. This approach may be used as a quality control tool and aid less experienced planners determine benchmarks for plan quality.

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