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Patient-Specific Bulk Electron Density Overridden Planning for Prostate and Brain Cancer

D Du

D Du*, H Wooten, Y Feng, J Olsen, S Mutic, Y Hu, Washington University School of Medicine, St Louis, MO

SU-E-J-178 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the use of patient-specific bulk electron density overridden plans for prostate and brain IMRT dose calculations.

Methods: CT images and IMRT treatment plans for 10 prostate cancer patients and 10 brain cancer patients were retrospectively reviewed and analyzed. For each patient, a region of interest(ROI) was selected to cover all radiation beam paths plus 1cm margins in both superior and inferior directions. Patient anatomy within the ROI was segmented into fat, non-fat soft tissue, bone and air based on CT number ranges of [-150,-50], [-49,200], [201,4000], [-1200,-800], respectively. Average electron densities for each tissue type were obtained from CT values for each patient, and all plans were recalculated on patient-specific density overridden datasets to generate patient-specific bulk density overridden plans. These overridden plans were compared to the clinically approved CT-based plan using dose-volume metrics for PTV coverage and OAR sparing.

Results: Dose deviations between the patient-specific density overridden plan and the clinically approved plan were minimal. Most parameters used to describe planning target volume coverage and OAR sparing were within 0.3% of approved CT based plans and all parameters were within 1% of the approved CT based plans.

Conclusion: This study demonstrates that by assigning patient-specific bulk electron densities to different tissue types, the dosimetric error of the patient-specific bulk density overridden plans is within 1% of the approved CT based plan. This, patient-specific bulk density override technique may potentially be used to map the CT values from CT images to MR images.

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