PO41

Purpose Cervical cancer is the second most common cancer among Indian women. Radical chemo-radiotherapy is the standard of care for the majority of patients in India since most patients get diagnosed late and have locally advanced disease. Traditional Manchester system based brachytherapy planning and dose delivery continues to be widely practiced. Cervical cancer with disease extension beyond upper vagina presents a unique problem for brachytherapy dose delivery. Ovoid in tandem in the vagina is considered ‘Non-standard application’ in the traditional Manchester system where a lower dose to ‘Point A’ is accepted respecting the tolerances. Even in the era of image based brachytherapy, the number and position of the source channels limit the extent of dose optimization possible within the various normal tissue tolerances. The Rotterdam applicator, with both Ovoids and vaginal cylinder, offers the possibility of improved dose delivery in this group of patients. The potential dosimetric advantage was tested in this study. Methods Consecutive cervical cancer patients with vaginal disease beyond mid vagina at presentation were selected for Rotterdam Application. All patients had MR imaging in addition to standard CT planning. High Risk target volume (HRCTV) and organs at risk (OAR) were contoured on MR images as per the GEC-ESTRO guidelines and dose optimized plans were generated on Oncentra planning system V4.6. Residual disease in the vagina was part of the HRCTV and the length of vagina to be treated (tandem vaginal loading) was decided by the extent of initial disease involvement. The prescription dose was 8 Gy and dose constraints to OARs were (≤6 Gy/fx) to rectal D2cc and (≤7.5 Gy/fx) to the bladder D2cc (Subir Nag HDR BT dosimetry data). Two sets of treatment plans were generated for each application 1) with central tandem loading only (IUT PLAN) and 2) Rotterdam plan where ovoids were loaded in addition to central tandem. The HRCTV D90, D2cc Bladder, D2cc Rectum were documented and compared between the two plans. Data was analyzed statistically using paired t-test (normally distributed) or Wilcoxon signed rank test (Non-normal). A p-value < 0.05 is considered to be statistically significant. Results Between 1st January 2021 and 30th June 2022, 24 patients were eligible for Rotterdam application. However, applicator placement was not feasible in 6 patients (25%) with severe upper vaginal narrowing. MR image based plans were generated for 31 applications. The mean age of the patients included in the study was 59 years. Stage wise distribution was as follows IIB-3, IIIB-4, IIIC1-4, IIIC2-2, & IVA-5. At the time of brachytherapy, 10 patients had minimal residual disease involving cervix and upper vagina. None of the patients had residual disease involving lower vagina. The mean HRCTV volume was 30cc (range- 14.29 cc- 51.92cc). The prescription goal of 8Gy or greater was achieved in 18 Rotterdam applications while with standard loading, 12 applications met the goal. The HRCTV D90 was >7Gy in 7 Rotterdam & 8 standard applications, >6Gy in 6 Rotterdam & 8 standard applications. With the standard plan, the dose was <6Gy for 3 applications. The minimum HRCTV D90 with Rotterdam plan was 6.3 Gy for HRCTV of 30cc. The difference in mean D90 HRCTV between the two plans (7.1Gy vs. 7.7Gy) was statistically significant (p <.001). The mean D2cc Bladder was found to be significantly better with the Rotterdam applicator, however, there was no statistically significant difference in mean D2cc Rectum between the two plans. Conclusion Rotterdam applicator offers greater optimization possibilities, thus improving HRCTV dose compared to standard Intrauterine and tandem application in cervical cancer patients with vaginal involvement. However, Rotterdam applicator placement was not feasible in a subset of patients (∼ 25%) due to anatomical limitations. Cervical cancer is the second most common cancer among Indian women. Radical chemo-radiotherapy is the standard of care for the majority of patients in India since most patients get diagnosed late and have locally advanced disease. Traditional Manchester system based brachytherapy planning and dose delivery continues to be widely practiced. Cervical cancer with disease extension beyond upper vagina presents a unique problem for brachytherapy dose delivery. Ovoid in tandem in the vagina is considered ‘Non-standard application’ in the traditional Manchester system where a lower dose to ‘Point A’ is accepted respecting the tolerances. Even in the era of image based brachytherapy, the number and position of the source channels limit the extent of dose optimization possible within the various normal tissue tolerances. The Rotterdam applicator, with both Ovoids and vaginal cylinder, offers the possibility of improved dose delivery in this group of patients. The potential dosimetric advantage was tested in this study. Consecutive cervical cancer patients with vaginal disease beyond mid vagina at presentation were selected for Rotterdam Application. All patients had MR imaging in addition to standard CT planning. High Risk target volume (HRCTV) and organs at risk (OAR) were contoured on MR images as per the GEC-ESTRO guidelines and dose optimized plans were generated on Oncentra planning system V4.6. Residual disease in the vagina was part of the HRCTV and the length of vagina to be treated (tandem vaginal loading) was decided by the extent of initial disease involvement. The prescription dose was 8 Gy and dose constraints to OARs were (≤6 Gy/fx) to rectal D2cc and (≤7.5 Gy/fx) to the bladder D2cc (Subir Nag HDR BT dosimetry data). Two sets of treatment plans were generated for each application 1) with central tandem loading only (IUT PLAN) and 2) Rotterdam plan where ovoids were loaded in addition to central tandem. The HRCTV D90, D2cc Bladder, D2cc Rectum were documented and compared between the two plans. Data was analyzed statistically using paired t-test (normally distributed) or Wilcoxon signed rank test (Non-normal). A p-value < 0.05 is considered to be statistically significant. Between 1st January 2021 and 30th June 2022, 24 patients were eligible for Rotterdam application. However, applicator placement was not feasible in 6 patients (25%) with severe upper vaginal narrowing. MR image based plans were generated for 31 applications. The mean age of the patients included in the study was 59 years. Stage wise distribution was as follows IIB-3, IIIB-4, IIIC1-4, IIIC2-2, & IVA-5. At the time of brachytherapy, 10 patients had minimal residual disease involving cervix and upper vagina. None of the patients had residual disease involving lower vagina. The mean HRCTV volume was 30cc (range- 14.29 cc- 51.92cc). The prescription goal of 8Gy or greater was achieved in 18 Rotterdam applications while with standard loading, 12 applications met the goal. The HRCTV D90 was >7Gy in 7 Rotterdam & 8 standard applications, >6Gy in 6 Rotterdam & 8 standard applications. With the standard plan, the dose was <6Gy for 3 applications. The minimum HRCTV D90 with Rotterdam plan was 6.3 Gy for HRCTV of 30cc. The difference in mean D90 HRCTV between the two plans (7.1Gy vs. 7.7Gy) was statistically significant (p <.001). The mean D2cc Bladder was found to be significantly better with the Rotterdam applicator, however, there was no statistically significant difference in mean D2cc Rectum between the two plans. Rotterdam applicator offers greater optimization possibilities, thus improving HRCTV dose compared to standard Intrauterine and tandem application in cervical cancer patients with vaginal involvement. However, Rotterdam applicator placement was not feasible in a subset of patients (∼ 25%) due to anatomical limitations.