Room: AAPM ePoster Library
Purpose: Applicator volumes are not subtracted from target volume while treating GYN patients, although those non-tissue volumes can be relatively large. In this study, we have evaluated the dosimetric effect of applicator volume removal for cervical cancer patients who were treated with the Venezia applicators.
Methods: A total of 14 patients (34 plans) with stage IIA to IIIC cervical cancer treated using Venezia applicator were reviewed. Patients were treated with 7Gy for 4 fractions(12 cases), 8.5Gy for 4 fractions (1 case), and 5.5Gy for 4 fractions (1 case). Five patients were treated with the applicator with multi-channel cylinder caps and needles. The applicator (central tandem and rings), caps, and needles were individually contoured on the planning CTs with pre-defined HU window (150-300) in MIM (version-6.8,USA). These contours were subtracted from the GTV, HR-CTV, and IR-CTV to generate new target contours (GTVsub, HR-CTVsub, IR-CTVsub). Dosimetric parameters including D90, D50, D30, V150, and V200 were evaluated for new contours and compared with those for the original contours.
Results: The average volumes of contoured applicators (including needles) with and without caps were 51.2±3.8cm3 and 25±9.6cm3, respectively. After applicator removal, the changes in D90 of GTV, HR-CTV, and IR-CTV were 1.6%±1.0%, 5.2%±3.7%, 6.7%±5.9%, respectively. The average changes of all the DVH parameters ranged from 2.3% (GTV D90) to 18.6% (IR-CTV D30). One case with cylinder caps and IR-CTV limited around the caps demonstrated the maximal change of 57.1% in IR-CTV D30, 42.6% in IR-CTV D50, 42.3% in V150, and 29.7% in V200.
Conclusion: This study reveals that small volume DVH parameters, such as D30, are more affected by the volume of the Venezia applicator. The cylinder caps have significant impact on of IR-CTV when it is limited around the caps and should be specified whether it is included in DVH parameter evaluation.