ESTRO 2022 - Abstract Book

S266

Abstract book

ESTRO 2022

images. Automatic segmentation also achieved a good result for HR-CTV (median DSC 79% and median JSC 66%) and IR-CTV (median DSC 88% and median JSC 79%) clinical target volumes. The most inferior segmentation accuracies were observed on the segmentations of rectum and small bowel (DSC = 64%, JI = 48% and DSC = 52%, JI = 35%, respectively). Conclusion We presented a deep learning-based method using MIM v.7.1.5 architecture to automatically segment the target volumes and OARs in the planning CT images for cervical cancer IRT. Quantitative evaluation results showed that the proposed method could segment the HR/IR-CTV and bladder with relatively good accuracy.

MO-0304 Dosimetric comparison of ACE algorithm and TG-43 formalism in HDR brachytherapy of carcinoma cervix

S. Srivastava 1 , A. K V 1 , M. Jabir A 1 , N. Moirangthem Singh 2

1 King George's Medical University, Radiotherapy, Lucknow, India; 2 Dr. B. Borooah Cancer Institute, Radiotherapy, Lucknow, India Purpose or Objective TG-43 formalism has been widely used in brachytherapy for dose calculation. However, this method does not consider the tissue and applicator heterogeneities. In the present study, we have compared the effect of model-based dose calculation algorithms like Advanced Collapsed cone Engine (ACE) on dose calculation with the TG-43 dose calculation formalism in patients with cervical carcinoma. Materials and Methods 8 patients with 24 CT data sets of HDR intracavitary brachytherapy plans in cervical cancer were retrospectively studied. HR-CTV and organs at risk (OAR) were contoured in the Oncentra treatment planning system using GYN GEC-ESTRO guidelines. Patients were planned for 7 Gy per fraction for 3 fractions. Plans were initially calculated using TG 43 formalism and then recalculated using the ACE (Elekta, Stockholm, Sweden) algorithm with applicator models selected from the applicator library. The dosimetric parameters of TG-43 and ACE-based plans were compared in terms of target coverage (V100, D90, D100), OAR doses (D2cc, D1cc, and D0.1cc), homogeneity index (HI), and conformity index (CI). Results The mean percentage difference between right point A values of TG-43 and ACE was -0.08±0.27%. For HR-CTV, the average D90 values for TG-43 and ACE calculated plans were 5.27±1.17 Gy and 5.27±1.16 Gy respectively. The mean percentage difference for doses D90 and D100 was found to be -0.02±0.59 % and 0.60±1.18% respectively. The average V100 values for TG-43 and ACE calculated plans were 74.80±13.90% and 74.83±13.31% respectively. For bladder, the mean percentage differences for D2cc, D1cc, and D0.1cc values between TG-43 and ACE were -0.39±0.61%, -0.40±0.59%, and -0.28±0.54 % respectively. In the case of the rectum, the mean percentage differences for D2cc, D1cc, and D0.1cc values between TG- 43 and ACE were -0.21±0.59%, -0.20±0.55%, and -0.15±0.47% respectively. Similarly, for sigmoid these values were 0.27±1.19%, 0.20±0.98% and 0.14±0.67% respectively. Conclusion The ACE improved the dose accuracy compared to the TG-43 formalism. However, we did not find any significant difference between the dose-volume parameters of TG-43 and ACE calculated plans. 1 UCLH, Radiotherapy, London, United Kingdom; 2 UCLH, Dept Of Medical Physics and Biomedical Engineering, London, United Kingdom Purpose or Objective Earplugs used for hearing protection in diagnostic MRI can be too large for paediatric patients who are exposed to noise when undergoing MRI for radiotherapy (RT). Thermoplastic shells do not allow for the use of alternative devices The acoustic noise levels with 3 types of hearing protection were measured, to minimise clinically significant noise levels, maximise patient compliance and optimise RT paediatric MRI workflow. Materials and Methods Acoustic noise measurements were performed in a 1.5T Philips Ingenia Ambition using an OptiSLM 100 sound meter with Optimic 1150 microphone, Figure 1. 3 different hearing protection types were tested: silicone earplugs (SEP; Boots Soft Silicone®), otological putty (OP; Oto-soft®) and foam earplugs (SFEP; Acro Essentials®). Sound Pressure Levels (SPL) were recorded during scanning and a Single Number Rating (SNR) was calculated as a difference between the mean Sound Pressure Level (A-weighted) without and with protection. Acoustic noise at ear was calculated using HSE noise calculator, manufacturer-quoted SNR values where available and highest SPL value (C-weighted) recorded at the scanner centre without the funnel. The results were compared to the Medicines and Healthcare products Regulatory Agency (MHRA) guidelines that hearing protection must reduce noise at the eardrum to below 85dB. Mini-Oral: 08: Patient care, preparation, immobilisation and IGRT verification protocols MO-0305 Novel method of investigating hearing protection for paediatric patients undergoing RT planning MRI A. Crawley 1 , A. Kruezi 2 , C. Thould 1 , A. Bainbridge 2 , M. Sokolska 2