Room: AAPM ePoster Library
Purpose: Standard-of-care boluses for radiation therapy(RT) may not adequately conform to patients’ unique topographies, resulting in air-gap between the target surface and bolus. This is particularly problematic with superficial pelvic tumors. As a result of air-gap, dose received by the target site can be inconsistent with the prescribed dose. To increase predictability and homogeneity of dose in these cases, we created a custom bolus and evaluated it against the clinical standard.
Methods: Custom boluses were created for groins of an anthropomorphic phantom and an on-treatment patient. The CT-simulation scan was used to create a mold for each device. The molds were 3D-printed and cast with silicone rubber to create the bolus. Air-gap measurements were performed on both boluses by analyzing total volume between the bolus and target surface, as measured from CT scans. Therapeutic doses of radiation were delivered to the phantom using standard-of-care and custom boluses. Radiation dose at 9 points on the phantom was measured using OSLDs, and compared to expected dose as calculated by treatment planning software. The fitting of the patient-specific bolus and CT scan derived measurements was approved by the Institutional Review Board.
Results: The mean air-gap volume between the standard bolus and phantom was 197cm³, reduced to 9.30cm³ using the custom device. In the patient trial, the air-gap volume was 179cm³ with the standard bolus and 10.2cm³ with the custom. The dosimetry test showed that the mean difference between expected and received doses was 5.69%±4.56% (15.1% max) for the standard bolus and 1.91%±1.31% (3.51% max) for the custom device. Areas of larger dose difference corresponded to areas with larger air-gap.
Conclusion: The custom bolus reduced air-gap and increased predictability of radiation dose delivered as compared to the standard bolus. The custom bolus could increase the certainty of prescribed dose-delivery of RT for superficial tumors.
Funding Support, Disclosures, and Conflict of Interest: Dr. Tward reports grants and personal fees from Bayer, grants and personal fees from Myriad Genetics, and personal fees from Blue Earth Diagnostics, Merck, Janssen, DecipherBio, and Astellas, outside the submitted work
Not Applicable / None Entered.