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Session: Brachytherapy - I [Return to Session]

Predicting Benefit for Hybrid Tandem and Needle Applications in the Treatment of Cervical Cancer with Brachytherapy

WT Watkins1*, YJ Chen1, S Glaser1, (1) City Of Hope National Medical Center, Duarte CA 91010


SU-H300-IePD-F7-2 (Sunday, 7/10/2022) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 7

Purpose: To introduce a predictive metric for treatment planning guidance in hybrid tandem and ring and needle (T&R+N) applicators for high dose rate (HDR) brachytherapy treatment of cervical cancer.

Methods: Brachytherapy dose can be estimated by cylindrical volumes about a central tandem, but uterine cervix tumors are often asymmetric or ellipsoidal in shape. Estimating the tumor asymmetry by major and minor axis (a and b) of an ellipse may guide T&R+N utilization. We measured the asymmetry of the high-risk clinical target volume (HRCTV) at the point-A level, 2cm superior to the cervical os in 30 sequential cervical cancer patients treated at our institution. The volume ratio of a circular vs. ellipsoidal cylinder with major/minor axis = a/b is Vratio=¼(2+a/b+b/a). We test predictive power of Vratio and a/b in utilization and benefits of T&R+N.

Results: In 30-patients we evaluated the 3rd fraction of T&R treatment. The range and mean±standard-deviation in HRCTV volumes was 13.6-100.9cc(34.2cc±16.6cc), in D90 was 100.2-114.9%(106.3±4.1%), and in V100 was 90.1-98.5%(93.7±2.3%). The range of Vratio was 1.00-1.14 with corresponding a/b ratios of 0.93-2.10. Clinically, 9/30 patients were treated with T&R+N. Comparing these 9 patients with the 21 treated with T&R alone, average Vratio was 1.06+0.05 vs. 1.01+0.02; average a/b was 1.57+0.35 vs. 1.21+0.19, both significant predictors of T&R+N selection (p<0.001). In some patients an anatomic position 2-cm from the os missed some asymmetric HR-CTV components, and it may be feasible to use distances between 1.5-2.0cm for the a/b measurement. The dosimetric benefits in D90, V100, and normal tissue doses were not trivially correlated to Vratio or a/b due to tradeoffs.

Conclusion: In a sequential series of 30 clinical T&R patients, we show excellent and consistent HRCTV dosimetry in D90 and V100. We validated a measure of asymmetry to predict the utility of hybrid T&R with needle application.




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