ESTRO 2023 - Abstract Book

S2105

Digital Posters

ESTRO 2023

We proposed a novel method for analysing the quality of synthetic CTs using AI contouring that evaluates whether a synthetic CT captures the distribution of CT scans and if anatomical constraints are respected when translating across modalities.

PO-2338 Does gastric volume impact lung’s exposure in loco-regional left-sided breast cancer radiotherapy?

Z. Naimi 1 , M. El Bessi 1 , M. Bohli 1 , R. Ben Amor 1 , A. Hamdoun 1 , R. Haddad 1 , L. Kochbati 1

1 Abderrahmen Mami Hospital, Radiation Oncology Department, Ariana, Tunisia

Purpose or Objective The aim of this study was to assess the impact of gastric volume on doses delivered to the homolateral lung in left-sided loco-regional breast cancer irradiation. Materials and Methods We prospectively evaluated fifty women referred for adjuvant left-sided breast cancer loco-regional radiotherapy. All patients underwent 3D-conformal hypofractionated radiotherapy (40 Gy/15 fractions ± boost of 13.35 Gy), by two breast tangential fields plus a supraclavicular field, using a mono-isocentric technique. For each patient, the stomach was contoured and the gastric volume was assessed. Dose-volume histograms were generated. Statistical associations between gastric volume and left lung’s dosimetric parameters (mean dose, V20Gy, V30Gy) were analysed. Results Mean age was 47.5 years. Thirty-eight patients (77,6%) had T1-2 tumors. Breast conservative surgery was performed in 38% of cases. All patients received chemotherapy, neoadjuvant in 18% of the cases. Forty-three patients (86%) underwent adjuvant endocrine therapy and 32% received trastuzumab. All patients were planned for loco-regional radiotherapy. An additional boost was delivered in 42% of cases. Mean gastric volume was 194,38 (78-573) cc. No statistically significant correlation was found between gastric volume and V20 Gy, V30 Gy and the mean lung dose with Pearson correlation coefficient of - 0,6 (p=0,66), - 0,7 (p=0,6) and -0,6 (p=0,67), respectively. The contribution of supraclavicular field to lung’s doses et exposed volumes was on average of 37%, 32% and 39% respectively for the mean lung dose, V20 Gy and V30 Gy. Although not statistically significant, gastric volume tended to correlate with V30 Gy to the lung, when considering only the supraclavicular field dose contribution (p=0.02). Neither the primary (CTVp) nor nodal clinical target volumes (CTVn) volumes were correlated to lung’s doses. Conclusion This study showed that gastric volume did not impact doses delivered to the left lung, suggesting that pre- planning/treatment fast protocols are not needed in left-sided breast cancer radiotherapy. A. Huynh 1 , A. Sabharwal 2 , B. George 3 , E. Chinherende 4 , D. Yucel 5 , D. Murray 6 , P. Camilleri 2 , H. Harford-Wright 7 , J. Drabble 7 , P. Maungewe 7 1 GenesisCare , MR- Linac Senior Radiation Therapist, Oxfordshire, United Kingdom; 2 GenesisCare, MR-Linac Radiation Oncologist, Oxfordshire, United Kingdom; 3 GenesisCare, MR-Linac Lead Physicist, Oxfordshire, United Kingdom; 4 GenesisCare, MR-Linac Senior Dosimetrist, Maidstone, United Kingdom; 5 GenesisCare, MR-Linac Lead Physicist, London, United Kingdom; 6 GenesisCare, MR-Linac Senior Dosimetrist, London, United Kingdom; 7 GenesisCare, MR-Linac Senior Dosimetrist, Oxfordshire, United Kingdom Purpose or Objective In the presence of metal hip prosthesis, CT-based planning images and CT-guided treatment images contain considerable image artefacts. This can limit the ability to delineate the treatment target and perform on-line imaging matching, making planning and delivery of ultra- hypo-fractionated prostate radiotherapy infeasible for these patients. In contrast, MR images acquired for planning as part of the daily adaptive workflow in MR-guided radiotherapy (MRgRT) provides significantly improved characteristics, allowing for confident target visualization, image matching and real-time imaging during treatment. Through this improved anatomical visualisation and delineation, ultra hypo-fractionated treatment is considered feasible in these patients. In this retrospective study we review the accuracy, quality, safety, and outcomes of daily adaptive MR-guided ultra- hypofractionated prostate radiotherapy in patients with uni- or bilateral hip prosthesis. Materials and Methods Patients treated with daily adaptive MRgRT to their prostate ± seminal vesicles with doses of 36.25 in 5# with an optional 40 Gy boost to the prostate and proximal 1 cm of seminal vesicles for high-risk patients were eligible for inclusion. Treatment accuracy was confirmed by reviewing the impact of metal hip prosthesis on image spatial integrity measured with a 2D distortion phantom. Dosimetric play quality was compared between patients with and without hip prosthesis. Key metric included: volume of the PTV receiving the 100% and 95% of the prescription dose (PTV: V(100%), V(95%)), prescription dose spillage (PDS) and modified gradient index (MGI). PO-2339 Analysing the feasibility of adapted MR-guided SABR for prostate cancer patients with hip prosthesis