ESTRO 38 Abstract book

S1070 ESTRO 38

DIBH is effective tool for cardiac sparing showing significant dose reduction to heart, and LAD. Changes in anatomical parameters in FB and DIBH scan, like MHD, Sternal angle and heart/ left ventricle contact with chest wall can be helpful in predicting the dose reduction. EP-1962 A simple and low-cost method of deep inspiration breath-hold irradiation for breast cancer Y. Koide 1 , T. Kitagawa 1 , T. Aoyama 1 , H. Shimizu 1 , H. Tanaka 1 , H. Tachibana 1 , T. Kodaira 1 1 Aichi Cancer Center, Radiation oncology, Nagoya, Japan Purpose or Objective Voluntary deep inspiration breath-hold (DIBH) was useful technique for cardiac dose reduction in left-sided breast cancer radiotherapy. It usually needs some devices to trace patients’ respiratory cycle. However, there is a problem of expense and technical challenges of its implementation. Our institution started DIBH with the combination of video-monitoring thoracic motion and the setup using cine-images on an electronic portal imaging detector (EPID) and digitally reconstructed radiograph (DRR). The purpose of this study is to evaluate the accuracy and the reproductivity of this DIBH technique and to compare dose metrics of DIBH and free-breathing (FB) plans. Material and Methods Ten patients with left-sided breast cancer were included in this study. They were coached and must voluntarily hold their breath during the treatment. Each patient was performed DIBH and FB computed tomography (CT) and created both treatment plans. Patients’ thoracic motion was traced with video-monitoring, and the treatment beam was delivered manually when their surface marker was within the acceptable position. Treatment setup was verified comparing DRR and an EPID image. The inter- fractional variation was measured using DRR and the first frame of cine-EPID images acquired during each irradiation. The intra-fractional variation was measured from comparing cine-EPID images from the first frame to the last one at each irradiation. The dose metrics of breast planning target volume (PTV), heart, left ascending artery (LAD), and lung contours were compared between the DIBH plan and the FB plan. Reported results are mean ± SD (DIBH plan vs. FB plan). Results Eligible patients were all completed planned treatment. The average median inter-fractional movement in the left- right direction (X axis in our study) and in the cranio- caudal direction (Y axis in our study) was -0.05 ± 1.61 mm and 1.2 ± 1.58 mm, and median intra-fractional movement was 0.01 ± 0.49 mm and -0.2 ± 0.27 mm. The mean volume of PTV, heart, LAD, and lung between DIBH and FB plan were 500 ± 232 mL vs. 475 ± 224 mL (p = 0.42), 587 ± 153 mL vs. 584 ± 130 mL (p = 0.48), 2.5 ± 0.58 mL vs. 2.3 ± 0.62 mL (p = 0.26), and 3591 ± 574 mL vs. 2246 ± 418 mL (p = 0.0003), respectively. The mean PTV dose was 42.3 ± 0.40 Gy vs. 42.1 ± 0.64 Gy (p = 0.25) and conformity index of PTV was 0.3 ± 0.094 vs. 0.29 ± 0.079 (p = 0.42). The mean heart dose was 0.76 ± 0.11 Gy vs. 1.33 ± 0.52 Gy (p = 0.02), the mean LAD dose was 2.6 ± 0.85 Gy vs. 7.8 ± 5.6 Gy (p = 0.03), and the mean lung dose was 1.7 ± 0.42 Gy vs. 1.8 ± 0.45 Gy (p = 0.29). Conclusion As only minor inter-fractional and intra-fractional movements were observed, this simple low-cost DIBH technique could ensure a feasible method of voluntary DIBH irradiation. It could reduce the mean heart dose and mean LAD dose with maintaining PTV coverage compared to FB plans. EP-1963 IGRT to improve accuracy in lung SBRT C. Anson Marcos 1 , D. Hernández 1 , P. Castro Tejero 1 , M. Roch González 1 , A. Valiente González 2 , P. García Castañón 1 , A. Viñals Muñoz 1 , R. Fayos-Sola Capilla 1 , L.

been proposed to reduce cardiac morbidity. We evaluated dosimetric and anatomic characteristics of patient undergoing Deep Inspiratory Breath Hold Technique (DIBH). Material and Methods A total of 35 patients were analyzed retrospectively undergoing DIBH for adjuvant radiotherapy for left breast/ chest wall (CW) [BCS (n = 24) or CW (n= 11)] with or without regional nodes irradiation. 20/35 patients were treated with 40Gy/15 fractions and 15/35 patients were treated with 50Gy in 25 fractions +/- 12.5-15 Gy tumor bed boost. All patients trained for DIBH on Real-Time Position Management (RPM) system (Varian Medical Systems). All patients underwent Free Breathing (FB) and Breath-hold scans and were planned on both with tangential field in field technique. Doses to heart, left anterior descending artery (LAD), contralateral breast and lung were documented. Anatomical parameters like sternal angle, Haler’s index, maximal heart distance (MHD) and heart and left ventricle to chest wall contact were calculated. Results Average Breath-hold amplitude was 1.96 cm (Breast), 1.75cm (CW) and average Breath hold duration was 20.8 sec (Breast), 21sec (CW). Average mean heart dose in DIBH patients receiving 50Gy/25fr is 2.24Gy vs 2.96 Gy in patients receiving 40Gy/15fr. Average reduction in mean heart dose in BCS was 56.5% vs 40.9% in CW patients. Average V30% of heart reduced from 6.58 to 1.36 % in 50Gy/25 fr subgroup (p= <0.001) and 7% to 3.03% in 40Gy/15fr subgroup (<0.001) from FB to DIBH respectively. Average MHD reduced from 1.35cm to 0.52cm in 50Gy/25fr subgroup (<0.001) and 1.89 to 1 cm in 40Gy/15fr subgroup (<0.001) from FB to DIBH respectively. Average reduction in irradiated volume of heart (50% isodose line) from 36.8 cc to 7.2cc in 50 Gy/25fr subgroup (<0.001) and 40.5cc to 18.2cc in 40Gy/15fr subgroup (<0.001) from FB to DIBH respectively. Average mean LAD dose reduced from 21.76Gy to 12.16 Gy in 50 Gy/25fr subgroup (<0.001) and 18.5 Gy to 13.4Gy in 40Gy/15fr subgroup (<0.001) from FB to DIBH respectively. Average maximum LAD dose reduced from 40.9 Gy to 32.4 Gy in 50 Gy/25fr subgroup (p=0.04) and 37.6 Gy to 31.9Gy in 40Gy/15fr subgroup (p=0.03), from FB to DIBH respectively. Average reduction in Mean LAD was 42.25 % in BCS patients compared to 25.96% in CW patients. There was statistically significant difference between sternal angle (p= 0.003), MHD (p=<0.001) and heart and left ventricle to chest wall contact (p=<0.001) in FB vs DIBH which correlated with decrease in cardiac and LAD doses. No significant difference in lung V20, mean lung dose & dose to the contralateral breast between FB and DIBH.

Conclusion