ESTRO 2023 - Abstract Book

S96

Saturday 13 May

ESTRO 2023

There is a significant positive association between total ICRU-RV point dose and FSDS-R, MRS, and physician assessed VT. Those with ICRU-RV >65 Gy had a significantly higher FSDS-R and MRS scores compared to those with ICRU-RV <65 Gy (p=0.02). Furthermore, there is a significant positive association between MaxVagPoint and MaxVagPoint EQD2 and FSDS-R, and MRS. MaxVagTRAK and TotalVagTRAK have a significant positive association with FSDS-R score and MRS. MaxVagPoint doses typically greatly exceed values of ICRU-RV (Figure 1).

Conclusion This analysis indicates that there is a significant relationship between dosimetric markers and physician-reported VT and patient-reported sexual health outcomes. Opportunities exist for accurate identification of an appropriate vaginal D2cc, point-dose and TRAK constraints, de-escalating vaginal dose and reducing sexual morbidity. OC-0134 EviGUIDE - A tool for evidence-based decision making in image-guided adaptive brachytherapy S. Ecker 1 , C. Kirisits 1 , M. Schmid 1 , J. Knoth 1 , G. Heilemann 1 , A.A.C. De Leeuw 2 , A.E. Sturdza 1 , K. Kirchheiner 1 , S. Spampinato 3 , K. Tanderup 3 , R. Pötter 1 , N. Eder-Nesvacil 1 1 Medical University of Vienna, Department of Radiation Oncology, Comprehensive Cancer Center, Vienna, Austria; 2 University Medical Centre Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands; 3 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective The software tool EviGUIDE should enhance the traditional treatment planning workflow in radiation oncology (RO). It combines dosimetric information from the treatment planning system (TPS), patient and treatment characteristics and established tumor control probability (TCP), and normal tissue complication probability (NTCP) models, to extend the assessment of treatment plan quality beyond adherence to rigid dose objectives. Materials and Methods The concept is demonstrated for the treatment of cervical cancer using combined external beam radiotherapy and magnetic resonance image-guided adaptive brachytherapy (MR-IGABT). The tool was developed using R and Python. A software link to a TPS enables usage alongside routine treatment planning. It provides users with outputs for dose documentation based on equieffective dose in 2 Gy per fraction (EQD2), advanced visualizations, and statistical summaries of a treatment plan. Using uniform dose scaling for the entire or fractionated BT dose distribution, users are able to dynamically create alternative versions of the treatment plan and compare them via EQD2 parameters and in the TCP-NTCP space. In total, six Cox Proportional Hazards models based on outcome data from the multi-national EMBRACE-I study have been integrated. One TCP model for local tumor control, and five NTCP models for CTCAE Grade ≥ 2 morbidity endpoints. To quantify the optimization potential among patients treated with state-of-the-art MR-IGABT, a mono-institutional retrospective cohort of 45 patients was analyzed. Plans were optimized by scaling the dose distribution until the maximum attainable TCP within existing dose limits was achieved. Results A prototype was developed that can be run locally or on a webserver. It allows automatic import of dose-volume histograms (DVH) from a commercial TPS and the selection of patient specific clinical and treatment characteristics. EviGUIDE outputs include standard EQD2 dose documentation, attainable TCP/NTCP (Fig. 1) and boxplots of DVH parameters based on patient cohorts according to the specific treatment situation. Optimization of treatment plans revealed that for a sub-cohort of patients with increased risk factors (20%, 9/45), an average gain in TCP of 2% would have been possible, while increasing the risk for Grade ≥ 2 side-effects by up to 2% (Tab.