Program Information
Retrospective Study of Treatment Site Using IntraBeam System for Intraoperative Breast Irradiation
K Dou1*, M Jacobs2, (1) MedStar Health, Mercy Radiation Oncology, Baltimore, MD, (2) Mercy Medical Center Radiation Oncology, Baltimore, MD
Presentations
MO-RPM-GePD-TT-4 (Monday, July 31, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater
Purpose: To predict availability of tumor location for intraoperative breast irradiation by retrospective data analysis of our 128 patients treated with the intraoperative radiation therapy (IORT) for early-stage breast cancer.
Methods: The Zeiss IntraBeam intraoperative device was used for 50 kV x-ray generation and radiation delivery. Five sizes of solid applicators are available ranging from 3.0 cm to 5.0cm in diameter. Early-stage breast cancer patients of 50 years and older with a tumor size of ≤3cm were selected for IORT. Ultrasound was used to verify both skin distance to applicator surface (≥1cm) and conformality of the applicator to cavity after the applicator was placed. The coordinates relative to patient’s nipples were recorded and analyzed for 128 patients receiving IORT by January 1, 2017. OSL dosimeters were used for verification of skin radiation dose. Potential backscattering effect on skin from a lead shield during treatment was studied with Ionization chamber and film in a water phantom.
Results: Treatment site was classified as four groups: 12:00 for superior, 6:00 for inferior, 9:00 and 3:00 for left and right lateral while the origin is located at patient’s nipples. Tumor located at 6:00 was found an unfavorite site for IORT due to less breast tissue in the location and thus only 8% of our total patients were treated at the site with IORT. Ionization chamber and film measurement indicated that a maximum 5% of the prescribed radiation dose resulted from backscattering of the lead apron shield and that creating 7mm spacing between skin and the lead shield was able to eliminate backscattering.
Conclusion: Tumor site would be one of the important criteria for selection of IORT patients in terms of skin reaction to radiation because IORT is a high dose of radiation up to 20Gy given during surgery to the tumor bed.
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