ESTRO 2023 - Abstract Book

S2047

Digital Posters

ESTRO 2023

Between October 2021 and September 2022, 8 breast cancer patients underwent 2 CTs (without (NB) and with bra (WB)) to evaluate the impact of radiation bras. According to the patient’s chest and cup , a suitable bra was selected. Using FIF 3D- CRT, 6 of them were planned with the FAST-forward (FFW) schedule and 2 with the 42.4 Gy/16 fractions hypo-fractionated scheme. Measured parameters included the nipple-to-pectoral muscle distance (NPD), the maximum mediolateral thickness (MLT) along tangential fields, target coverage, its conformity (CI), and homogeneity indexes (HI). The evaluated OARs were the ipsilateral lung and the heart. The setup reproducibility has been evaluated through a daily pre-treatment CBCT. Results The bra sizes ranged from 4 to 10 with optimal patient compliance. The bra provided a decrease in the median NPD (NB 8.0 cm; WB 7.3 cm) with a similar median MLT (NB 25.3 cm; WB 25 cm). While the target coverage was maintained (V95%: NB 98.9%; WB 99.4%), the median volume of the 105% and 107% isodoses NB and WB was 13.0 cm ³ and 0.2 cm ³ , and 0.5 cm ³ and 0.0 cm ³ , respectively. This led to a 0.6 median CI value for both NB and WB and a slight HI improvement (NB 0.09; WB 0.07). Although not clinically significant, a slight increase in lung doses was registered in WB plans. Heart doses did not registered any relevant variation. WB plans were successfully delivered with a daily pre-treatment CBCT correction. Only 1 patient registered a significant weight loss undermining the bra effectiveness. Having an acceptable NB plan, the delivery was terminated with it. A second CBCT was needed to verify the bra setup that was corrected in 23 out of 46 fractions. The final x, y, and z translational corrections registered a median value of -0.2, 0.5, and -0.2 cm, respectively. No acute toxicities have been registered. Conclusion The bra implementation was associated with improved geometric and dosimetric planning parameters: higher and properly positioned breasts guaranteed reduced hot spots. In particular, it could offer the FFW schedule to patients whose breast volume would not permit a sufficient dose homogeneity. A higher number of patients will allow the definition of the best cut-off parameters in the choice to use the bra and confirm its dosimetric impact. Nowadays, daily imaging is mandatory but higher expertise in repositioning could avoid the need of a second CBCT. The clinical follow-up will give a critical feedback on the opportunity to reduce toxicities thanks to a more homogeneous dose distribution. 1 University of Debrecen, Clinic of Oncoradiology, Debrecen, Hungary; 2 University of Pécs, Faculty of Health Sciences, Doctoral School of Health Sciences, Pécs, Hungary; 3 University of Pcs, Faculty of Health Sciences, Doctoral School of Health Sciences, Pécs, Hungary; 4 University of Debrecen, Faculty of Medicine, Doctoral School of Clinical Medicine, Debrecen, Hungary Purpose or Objective The internationally accepted care of advanced, inoperable cervical tumours (St. 1B2-4A) consists of definitive radio- chemotherapy (RKT), followed by intracavitary or interstitial brachytherapy (BT) additional (boost) irradiation. BT is a key part of the treatment, its completion improves both pelvic control and overall survival. The purpose of Image Guided Adaptive Brachytherapy (IGABT) is to treat the cervix and any other residual tumour while protecting the organs at risk. In our institute, we use a bladder and rectum protocol to keep the volume of the bladder and rectum at the same level before each planned CT scan and treatment fraction. During the daily image control, we receive information about the position, volume, and shape of the organs at risk located around the cervix. This way, the anatomical conditions existing on the given day can be taken into account during the treatment planning and the areas that not meant to be treated can be spared accordingly. Our aim is to present the role of CT-based 3D irradiation planning in brachytherapy of cervical tumour patients. Materials and Methods Between January 1, 2022 and September 30, 2022, 28 patients received 3D-planned CT-guided adaptive brachytherapy. 10 patients with advanced, inoperable cervical cancer treated with BT were randomly selected and included in our study model. During the CT-based radiation planning, the target volumes were determined and the organs at risk were contoured by processing the images of the 40 planning CT examinations. We examined the changes in the target volume and the volumes of the organs to be protected (rectum, urinary bladder) during the four treatment fractions. Results The average of bladder volumes were 68.46 cm3 [48.16-99-89], the average of daily standard deviations were 10.67 cm3 [2.35-22.39], the average of the rectum volumes were 62.47 cm3 [35.94-143.65] and the daily average standard deviations were 10.33 cm3-ig [2.9-24.14]. Conclusion Based on our results, applying a bladder and rectal protocol before treatment could prevent extreme changes in bladder or rectal filling. Taking into account the daily volume changes and the high dose of the organs at risk that are close to the target volume a daily planning CT is justified before brachytherapy. Based on our clinical experience, 3D CT-assisted brachytherapy applied to patients with locally advanced cervical carcinoma is a safe intervention with a well-tolerated side effect profile, few complications, adequate local control and significant morphometabolic regression. PO-2276 Importance of daily CT imaging in brachytherapy of cervical tumor patients J. Papp 1,2 , M. Simon 1,3 , E. Csiki 1,4 , Á. Kovács 1,4,2

PO-2277 Inter/intra-operator comparison study in daily CBCT for prostate IGRT with or without fiducials

L. De Cicco 1 , L. Marzoli 2 , R.M. Mancuso 1 , R. Lorusso 1 , E. Petazzi 1 , A.G. Lanceni 1 , E. Della Bosca 1 , S. Buttignol 1 , A. Starace 1 , B. Bortolato 1 , C. Verusio 3