ESTRO 2025 - Abstract Book

S771

Clinical - Gynaecology

ESTRO 2025

48

Digital Poster Assessing 4 optimization strategies for altered brachytherapy applications in carcinoma cervix Vrushab Rao, Soumya Singh, Neeraj Dhingra, Bhooshan Zade CyberKnife Radiosurgery and Radiation Oncology, Ruby Hall Clinic, Pune, India Purpose/Objective: Ultrasound-guided brachytherapy application for carcinoma cervix is still not prevalent in many institutions across the globe. Blind applications in cases with altered anatomy may result in suboptimal geometry of the applicators. A lack of feasibility for reapplication requires most of such procedures to be treated with the same application. Optimization and normalization in such cases require modification to cover the target. We compare 4 different optimization and normalization techniques for applications with altered geometry. Material/Methods: 21 applications over 12 months were eligible for the study. Only cases that used the modified Fletcher-suit applicator were included. Eligible cases included tip perforations, anteverted applications in a retroverted uterus, ovoid slippage from the tandem, and single ovoid applications. The contoured volumes included the CTV high risk (CTV-HR), intermediate risk (CTV-IR), and low risk (CTV-LR), bladder, and rectum. All patients were optimised without inverse planning simulated annealing (IPSA) using the following techniques - 1. Normalized to CTV-HR using graphical optimization (ON1), 2. Normalized to point A and local graphical optimization (ON2), 3. Normalized to CTV HR using global optimization (ON3), 4. Normalized to point A with global graphical optimization (ON4). Coverage of the CTV-HR, the volume of CTV-IR receiving prescribed dose, bladder, and rectum dose received by 2cc (D2cc), and point A and B doses were noted. The results were evaluated to identify the most suitable technique.

Results: The results of the studied parameters are stated in the table below.

Technique

CTV-HR coverage

Volume (%) of CTV-IR receiving 7Gy

Bladder D2cc (in Gy)

Rectum D2cc (in Gy)

Point A dose (% of prescribed dose)

Point B dose (% of prescribed dose)

ON1

97.3% (97.1 100%)

89.4% (86.6%- 90.8%)

9.97 (7.1 11Gy)

7.56 (7.02 8.88Gy) 6.08 (5.09 7.23Gy) 7.98 (6.89 9.08Gy) 6.07 (5.23 7.2Gy)

160.62 (160%- 162.6%)

36.89 (28.39%- 38.2%)

ON2

100%

90.7% (88.4%-91%)

5.12 (5.02 6.81Gy) 11.07 (9.82 12.8Gy) 6.78 (5.78 7.53Gy)

100

27.33 (25.6%- 28.6%)

ON3

100%

88.8% (87.2%- 89.9%) 88.2% (86.2%- 89.8%)

164.92 (162.2%- 166.92%)

37.57 (34.58%- 39.22%) 28.69 (26.33%- 29.36%)

ON4

94.9% (93.8 97.6%)

100

ON2 provided the best coverage with controlled bladder and rectal doses. ON1 and ON3 provided good coverage as well, but at the cost of higher bladder and rectal doses. ON4 had inferior results compared to the other 3 techniques.