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Comparative study for Dose-Distribution and Reproducibility between semilateral Decubitus position and Supine position for left Breast Cancer Irradiation.

Omar Saeed Emam1, Mohamed Abouegylah1, Rasha Elsaka1, Amr Muni1r, Fady Aziz1, Horeya M. Ismail, MPH.2 Nermin A. Osman, M.D., Ph.D.3,4, Amr Abdelmoneim Mahmoud , MD, 5 Tamer Refaat M.D., Ph.D.1,6, MSCI, Abdelsalam Attia Ismail1 and Amr Abdelaziz Elsaid1.

1.Department of Clinical Oncology, Faculty of Medicine, Alexandria University, Alexandria, Egypt.

2. Department of Biostatistics, The High Institute of Public Health, Alexandria University, Alexandria, Egypt.3. Department of Biomedical Informatics and Medical Statistics, Medical Research Institute, Alexandria University, Alexandria, Egypt4. Cancer Surveillance Branch, International Agency for Research on Cancer, Lyon, France5. Department of Clinical Oncology, Kafr Elsheikh University, kafr Elsheikh ,Egypt6 .Department of Radiation Oncology, Loyola University Chicago, USA

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Introduction and Aim: This study aims to compare the reproducibility and dose distribution of Semi-lateral decubitus position (SLDP) utilizing Alexandria left breast board-16 (ALB-16) versus supine position (SP) in women undergoing left breast and/or chest wall irradiation.

Methods: This is a prospective IRB approved study. Fifty patients underwent CT Simulation in two different positions (SLDP and SP) utilizing free breathing scans. The mean radiation dose to the CW/ WB, axilla, thyroid, left lung, heart, LAD, Spinal cord and the contra-lateral right breast in SLDP and the SP for the same patient were compared. Subgroup analysis was conducted on 46 patients who were actually treated in SLDP by ALB-16 compared to 46 patients treated in SP to determine ALB-16 reproducibility.

Results: SLDP significantly decreased the mean dose to the heart when compared with SP (2.2Gy vs. 2.9Gy respectively), LAD (5.4Gy vs. 7.2Gy),  and the Spinal cord Dmax (7.5Gy vs. 12.6Gy) with a  (p<0.01), while maintaining a similar coverage to the axillary lymph nodes levels I, II and III and the SCV group (91.13%, 89.9%, 88.9% and 93.9% vs. 91.3%, 90.2%, 89.5% and 94.1% respectively)(p =0.73, 0.37, 0.29 and 0.67). SLDP improved coverage to the target PTV mean dose (95.2% vs. 94.2%, p<0.01). SLDP decreased the mean dose to the contralateral breast (2.27Gy vs. 2.52Gy, p= 0.08). For the subgroup analysis, the mean difference between vector lengths was only (0.08 cm) and this difference wasn’t statistically significant (p= 0.441) indicating the overall reproducibility of the ALB-16 breast board in comparison to standard supine breast board.

Conclusion This study demonstrated that ALB-16 Breast board is a reproducible method of setup for patients receiving left breast cancer adjuvant radiotherapy. SLDP spared the heart, LAD, and the spinal cord, with a better WB/CW PTV coverage compared to SP.