An Inverse Planning Technique for High Dose Rate Tandem and Ovoid
A Harnage1*, C Ramsey1,2, J Bowling1,2, I Pfeiffer2, G Clark2, (1) University of Tennessee Knoxville, Knoxville, TN, (2) Thompson Cancer Survival Center, Knoxville, TN
Presentations
(Saturday, 3/26/2022) [Central Time (GMT-5)]
Purpose: The purpose of this study was to develop a technique for inverse planning of tandem and ovoid (T&O) cases using the an IPSA optimization tool in the Oncentra HDR planning system. The goal was to develop a technique that would (1) Create the traditional “pear-shaped” dose in (2) a time that is comparable to forward planning while (3) meeting all clinical dose constraints.
Methods: The right ovoid, left ovoid, and tandem were individually contoured. The tandem was contoured from the level of the Cervical Os to 2-cm from the tip of the tandem. The tandem was then expanded 2-cm into a structure called “100Percent.” The RtOvoid, LtOvoid, 100Percent, and the CTV were defined as target structures in Oncentra. The the bladder, rectum, sigmoid, and small bowel were set as normal tissues.
Results: A total of 24 T&O plans were created using an IPSA technique and compared against the original forward plans. The additional contouring time was 4:49±1:03 minutes, while the added optimization time was 0:30±0:31. The mean 2-cc bladder dose was 539±144 cGy for forward plans and 522±66 cGy for IPSA plans. The mean 2-cc rectum dose was 371±91 cGy for forward plans and 358±54 cGy for IPSA plans. The mean 2-cc sigmoid dose was 340±104 cGy for forward plans and 347±73 cGy for IPSA plans. The mean 2 cc bowel dose was 256±89 cGy for forward plans and 276C for IPSA plans. The mean CTV100 dose was 94.3±5.4% for forward plans and 97.8±2.6% for IPSA plans. Based on these results, the dose constraints between the two techniques were equivalent.
Conclusion: A technique was developed that can quickly generate inverse treatment plans for tandem and ovoid cases. The treatment plans have dose distributions with the traditional pear-shape and have dose constraints that are equivalent to forward planning.
Keywords
HDR, Inverse Planning, Intracavitary Brachytherapy
Taxonomy
TH- Brachytherapy: Dose optimization and planning
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