ESTRO 2023 - Abstract Book

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ESTRO 2023

The median follow-up was 60 months (52.5-67.4) in Group-1 and 42.4 months (10.1-69.1) in Group-2. In the present study vaginal-cuff relapse and late toxicities in bladder and rectum were not found. 40 (39%) patients showed late vaginal toxicity: 21/44 (47.7%) patients in Group-1 (G1: 16 (36.4%), G2: 4 (10%), G3: 1 (2%)) and 19/66 (27.3%) patients in Group-2 (G1: 13 (18.2%) G2: 6 (9.1%)) (P=0.069). The mean EQD2(a/b=3) received by 2cm3 of the most exposed part of vagina was 63.7 Gy (SD±10.02) in Group-1 and 60.6 Gy (SD±3.90) in Group-2 (p= 0.066). Use of dilators > 9 months: 32 (72.7%) and 45 (68.2%) patients in Group 1 and 2, respectively (p=0.766). 12/44 (27.3%) patients in Group-1 and 21/66 (31.8%) in Group-2 used vaginal dilators (P= 0.766). Conclusion Despite the different fractionation schedules in PEC treatment, this is the first comparison of the present schedules. Considering the lack of vaginal relapses and the same vaginal toxicity rate in both groups, 2 fractions of 7.5 Gy seems more efficient in comparison to 3 fractions of 6 Gy in terms of patient comfort, work load and cost. However, further studies including more patients with a longer follow-up are required to confirm the present hypothesis. S. Oultram 1,2 , G. Kaur 3 , B. Beeksma 1 , G. Govindarajulu 1,4 , S. Sridharan 1,4 , J. Waugh 1 , S. Wrightson 1 , P. Simpson 1 , C. Dempsey 1,5,6 1 Calvary Mater Newcastle, Radiation Oncology, Newcastle, Australia; 2 University of Newcastle, School of Health Sciences, Newcastle , Australia; 3 GenesisCare, Radiation Oncology Crows Nest, Sydney, Australia; 4 University of Newcastle, School of Medicine and Public Health, Newcastle, Australia; 5 University of Newcastle, School of Health Sciences, Newcastle, Australia; 6 University of Washington, Radiation Oncology, Seattle, USA Purpose or Objective There is no consensus regarding optimal bladder volume (50cc to full) for brachytherapy planning and treatment. Most bladder filling protocols use an in-dwelling catheter (IDC) to produce a consistent volume in the bladder for treatment planning imaging and treatment. It is speculated that filling the bladder with fluid will extend the bladder wall away from the cervix, reducing bladder wall dose. The aim of this study was to investigate the impact of bladder filling on bladder volume and dose to the bladder and bladder wall. Materials and Methods All patients in this study had T2-MRI scans acquired per fraction. Straight sagittal and para-axial scans were taken with the bladder IDC open to allow a free-draining bladder and with the IDC tube clamped and ≤ 60 ml sterile water injected in the bladder to achieve a consistent 100ml bladder volume. Images were imported to the Oncentra brachytherapy treatment planning system and bladder, rectum, sigmoid and high- risk clinical target volumes (HR-CTV) were contoured on para-axial scans for free-draining and filled bladder datasets. Optimised plans were created on both datasets, focusing on HR-CTV coverage and limiting OAR dose. Dose-volume histogram data for each plan was analysed. Results This study analysed 25 paired scans. There were deviations in free-draining and filled bladder volumes both inter-fraction and inter-patient. For a single patient, free-draining and filled bladder volumes varied by up to 210% and 171% inter-fraction respectively. The average filled bladder volume across all patients and fractions was 128.8 (±27.6) mL. Optimised plans for free-draining and filled bladder datasets had average HR-CTV D90 dose differences of 2.8%. Two thirds (66%) of cases had < 5% D2cc bladder dose difference between filled and free-draining bladder dataset. For cases with > 5% dose difference, 91% had a higher filled bladder than free-draining bladder D2cc dose. Bladder wall D0.1cc doses correlated loosely with bladder D2cc doses, with 52% of cases having < 5% D0.1cc bladder wall dose differences. For those cases with > 5% dose differences, 62% had higher filled bladder than free-draining bladder wall D0.1cc dose. Average D2cc rectum and sigmoid differences for rectum and sigmoid were –1.0% and 0.0% respectively between free- draining and filled bladder cases. Conclusion There is variation in bladder volumes from patient-to-patient and fraction-to-fraction despite using a bladder filling protocol. This may have major implications for patient dosimetry if patients do not have individual plans created for each treatment fraction. There appears to be no dosimetric benefit to the bladder or bladder wall to fill the bladder against leaving the bladder free draining, nor does bladder filling appear to impact on rectal or sigmoid dose. The increased risk of infection and patient preparation time would suggest that there is also no systematic benefit to using a bladder filling protocol. PO-2141 Cervix brachytherapy: determining the optimal bladder volume using empty and full bladder MRI scans

PO-2142 Dosimetric uncertainties due to inter-fraction organ at risk movement in HDR cervical brachytherapy.

O. Houlihan 1,2 , M. Byrne 3 , O. McLaughlin 3,2 , G. Workman 3 , S. Esteve 3 , C. McGarry 3 , U. McGivern 1 , A. Drake 1 , E. Baird 1 , K. Prise 2 , A. Hounsell 3 , S. Jain 1,1 1 Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Clinical Oncology, Belfast, United Kingdom; 2 Queen's University Belfast, Patrick G. Johnston Centre for Cancer Research, Belfast, United Kingdom; 3 Northern Ireland Cancer Centre, Belfast Health and Social Care Trust, Radiotherapy Medical Physics, Belfast, United Kingdom

Purpose or Objective