ESTRO 2023 - Abstract Book

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ESTRO 2023

IGBT. We followed institutional bladder and rectal protocols. A Planning CT scan was performed after the implant followed by a planning MRI scan in all fractions. Images were registered using the applicator on both CT and MRI. OARs were contoured on both CT and MRI images by two experienced radiation oncologists independently which was peer-reviewed as well. Patient’s demographic, applicator type and time between CT and MRI were recorded. Volumes, contour shifts and doses (D0.1cc and D2cc) of rectum, bladder and sigmoid were assessed. Statistical analysis was performed using SPSS version 21 to calculate the frequency and central tendencies of the recorded values. Results The median age was 64 years (range 33 to 74 years). The total number of implants was 31, of which 17 (54%) were multichannel cylinders and 14 (46%) implants were tandem and ovoids. The recorded mean time between CT and MRI images was 28 minutes (range 18 to 50 minutes). The bladder volume increased by an average of 38% in 88% of patients between images. There was an average increase of 5.6% in sigmoid volume in 58% of the patients. The rectum volumes were reduced by an average of 14% in 91% of patients. During analysis, we found that the center of the bladder and rectum contours were shifted on average by 0.4 and 0.1 cm away from the target respectively. However, sigmoid was shifted on average 0.1 cm toward the target. These recorded volumes and shifts resulted in changes of D0.1cc and D2cc of OARs parameters. For bladder, there was an average increase of 2% for D0.1cc and 2.3% for D2cc. In the rectum, there was an average increase of 0.09% in D0.1cc and an average decrease of 1.3% in D2cc. For Sigmoid, there was an average increase of 4.9% D0.1cc and an average decrease of 2.8% in D2cc. Conclusion Time-dependent analysis of pretreatment CT and MRI scans for IGBT in our institute identified that there is variation in OARs in between the acquired images. These changes resulted in deviations of OARs volumes and doses of D0.1cc and D2cc. These variation in OAR doses in IGBT during the interval between implant and treatment delivery is a cautionary alert that needs further investigation and correlation with the changes and their clinical impacts on OARs. 1 irccs Istituto Nazionale Dei Tumori, S.C. Radioterapia, Milano, Italy; 2 irccs Istituto Nazionale Dei Tumori, S.S. Fisica Medica, Milano, Italy; 3 university Of Milan, Oncology And Haematology, Milano, Italy; 4 irccs Istituto Nazionale Dei Tumori, S.C. Radioterapia , Milano, Italy Purpose or Objective The standard of care for women diagnosed with Federation of Gynecology and Obstetrics stage IB2 to IVA cervical cancer (locally advanced uterine cervical cancer- LAUCC) is concurrent chemoradiation followed by intracavitary brachytherapy (BT). Supplemental interstitial catheters may be added in order to cover the maximum extent of gross residual disease (interstitial brachytherapy, HBT). The incorporation of magnetic resonance imaging in BT (Image Guided Adaptive Brachytherapy, IGABT) has increased the use of HBT in order to create a comprehensive treatment plan that covers the visualized tumor. Materials and Methods Between January 2018 and December 2021, 199 patients with LAUCC were treated with primary radiation therapy including HBT. At the time of IGABT, the majority of women had a decrease in gross tumor from 50.4 cc to 35.7 cc. Interstitial needles, with the use of an intracavitary tandem, has been selected for patients with large cervical lesions and/or lower vaginal involvement. A preliminary plan helped determine where to insert needles to increase the delivered dose. Results Median follow-up was 19.2 months (range 6 – 41.4). Progression free survival and local control rate were 54.4, and 80.2%, respectively. Fifteen patients experienced local recurrence (7%). Of those, nine were confined to the uterus and six at the parametria. Acute adverse event ≥ grade 2 were seen in patients; late adverse events ≥ grade 2 were seen in 3 patients. Conclusion The precision availed by MR-guided brachytherapy results in substantial improvements in needle positioning, and resulting treatment plans. Hybrid brachytherapy can be performed safely and with a high quality of radiation dose distribution. Education and clinical trial are very important to establish hybrid brachytherapy in the management of cervical cancer. PO-2155 Image Guided Brachytherapy And Implementation Of The Interstitial Technique In Cervical Cancer C.T. Delle Curti 1 , G. Tommaso 2 , T. Chiara 2 , S. Meroni 2 , F. Lezzi 3 , A. Rejas Mateo 3 , P. Brigida 4

PO-2156 Optimization of catheter placement for transperineal interstitial gynaecological brachytherapy

J. Bennett 1 , C. Bélanger 2,3 , P. Chatigny 2 , L. Beaulieu 2,3 , A. Rink 4,1,5

1 University of Toronto, Department of Medical Biophysics, Toronto, Canada; 2 l’Université Laval, Département de physique, de génie physique et d’optique et Centre de recherche sur le cancer, Québec City, Canada; 3 CHU de Québec - Université Laval, Département de radio-oncologie et Centre de recherche du CHU de Québec, Québec City, Canada; 4 University Health Network, TECHNA Institute, Toronto, Canada; 5 University of Toronto, Department of Radiation Oncology, Toronto, Canada Purpose or Objective Brachytherapy (BT) is an essential pillar in the treatment of cervical cancer. However, there are currently no established guidelines regarding the optimal number and placement of interstitial (IS) gynaecological (GYN) BT catheters. One method