SU‐C‐500‐02: Comparison of a Commercial Electronic Brachytherapy Source and Ir‐192/Co‐60 HDR Source for Endometrial and Cervical Cancers

Abstract

Purpose: To evaluate the dosimetric differences between Iridium‐192, Co‐60 based HDR plans and plans generated by electronic brachytherapy source (EBS) for cervical and endometrial cancers. Material/Methods: Our institution uses volume based planning for each tandem and ovoid (T&O) or vaginal cylinder insertion and treatment. We attempt to characterize the differences between the three sources (Ir‐192, Co‐60 and EBS). For vaginal cylinder cases, patients receive 6 Gy x3 prescribed to a depth 5 mm. For T&O cases, the prescription is 8Gy x3 to point A. Organs at risk (OARs) contoured were rectum, bladder, sigmoid & small bowel. Our planning protocol requires adjustment of source dwell times and positions to keep doses to the OARs below 70% of the prescription dose. For vaginal cylinder, dose coverage is optimized to a line drawn 5mm from the vaginal cylinder surface. This is a retrospective study of previously planned Ir‐192 treated patients. Results: There is no difference between the Co‐60 and Ir‐192 plans but plans generated using the EBS offer better sparing of OARs as evaluated using the dose to highest 2cc of the organ at risk but the differences are not statistically significant. However, there are significant differences in the DVH between EBS and the other two sources. There was a reduction of up to 50% between EBS and other two sources using v15%, v25%, v50% v75% (% of volume getting 15, 50, 75 percent of the prescription dose). Conclusion: All three sources are suitable for HDR Brachytherapy but the use of EBS can reduce the organ at risk dose while achieving similar dose coverage. Even though D2cc is the recommended dose volume point for HDR plans evaluation, V15%, V25%, V50% and V75% are also useful indicator of the plan quality as they characterize the lower dose region of the DVH curves more adequately