Program Information
An Algorithm to Calculate Biologically Effective Dose Distributions for Low Dose Rate Prostate Brachytherapy
D Guest*, A Riegel , Northwell Health, Lake Success, NY
Presentations
SU-I-GPD-T-35 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To convert physical dose from prostate seed implant (PSI) brachytherapy to biological effective dose (BED) for summation with external beam dose distributions. The intention is to determine if accurate voxel-by-voxel dosimetry can yield better correlation between dosimetry, toxicity, and treatment outcomes, to therefore determine better dosimetric tolerances for organs at risk during combination therapy.
Methods: Patients (n = 269) with intermediate- to high-risk prostate cancer received permanent PSI brachytherapy in combination with external beam therapy from 2010 through to 2015. Palladium 103 (¹⁰³Pd) seeds, with a nominal air kerma strenth of 2.0 U/seed were used in all cases to deliver a prescribed dose of 100 Gy to the target volume using the dynamic intraoperative technique with Mick applicator and transrectal ultrasound guidance. Post-implant dosimetry was performed approximately one month after seed implantation. Contour information, seed location, physical dose, and pixel data were extracted from DICOM. The BED was calculated for every voxel encompassed within the prostate contours, taking into consideration the distance of the voxel from the center of each source.
Results: At the time of submission, validation of the BED conversion algorithm is underway and patient results are expected by the time of presentation.
Conclusion: The current work is the first step towards more accurate dosimetry for combination external beam and low dose rate brachytherapy treatments for intermediate to high risk prostate cancer patients. After converting brachytherapy and external beam to the same BED, the next step will be investigating accurate registration of BED distributions.
Funding Support, Disclosures, and Conflict of Interest: Dr. Guest has received funding from Varian Medical Systems for this research.
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