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Clinical Implementation Experiences of Low KV Intraoperative Radiation Therapy (IORT) Intrabeam System for Low Risk Breast Cancer Patients


D Pokhrel

D Pokhrel*, J David, W Small, J Hayes, J Strauss, K Bethke, V Sathiaseelan,

SU-E-T-325 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Clinical implementation of the IORT (Intrabeam X-ray) system for low risk breast cancer patients in terms of quality assurance, reproducibility, treatment time, and operating room ambient radiation exposures.
Methods and materials: We have clinically implemented a new treatment system (Intrabeam) for early stage low risk breast cancer patients using 50kV X-rays. Pretreatment QA is performed in four major steps: probe straightening, dynamic offsets check, photo-diode-array check, and X-ray output check. Treatment time is verified by dose-rate measurement. An intraoperative ultrasound is performed to determine distance of the applicator surface to the skin. Ambient radiation levels were measured at different locations in the OR during treatment.
Results: We have treated in excess of 35 patients in the past 11 months, using spherical applicators from 3 to 5 cm in diameter, with a boost dose of 20Gy in a single fraction. The mean probe straightening, dynamic offset, and photo-diode-array source checks were within tolerances of 0.1mm, 0.7mm and ±1.5%, respectively. Pretreatment daily X-ray output checks agreed within to ±2.0% of baseline values and calculated treatment times within ±1% of given values. Radiation surveys of the OR during IORT showed that when ~1mm of soft lead sheet covered the breast under treatment, exposures to the Physicist and Anesthesiologist were =2mR/hr.
Summary and Discussion: With the IORT Intrabeam system, it is feasible to deliver a single high dose fraction to the breast immediately following tumor resection in the OR, providing the patient a convenient, waiting time free treatment, with no geographic miss. The nearly 1/r3 dose fall off minimizes dose to the distal breast and healthy tissues, with relatively fewer side effects compared to EBRT. Daily QA showed very small output variations. Radiation exposure in the OR was reduced nearly 12 folds when using a thin lead shield on the patient.


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