West Asia Organization for Cancer Prevention (WAOCP), APOCP's West Asia Chapter. Asian Pacific Journal of Cancer Prevention 1513-7368 24 12 2023 12 01 A Study to Analyze Impact of Treatment Couch and Immobilization Devices on Surface Dose for Megavoltage Photon Beams 4133 4138 90946 10.31557/APJCP.2023.24.12.4133 EN Palanivelu D Department of Physical Sciences, School of Sciences, Arts and Media, Karunya Institute of Technology and Sciences, Coimbatore, Tamilnadu, India. Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. 0000-0001-7758-150X Khanna D Department of Physical Sciences, School of Sciences, Arts and Media, Karunya Institute of Technology and Sciences, Coimbatore, Tamilnadu, India. 0000-0015-2557-212X Mohandass P Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. 0000-0002-3832-9616 Narandra Kumar Bhalla Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. Prabhu R Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. Chandru M Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. Abhishek Puri Department of Radiation Oncology, Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, India. Journal Article 2023 06 23 Purpose/Objective: The purpose of this study is to investigate the effect of treatment couch and immobilization devices on surface dose for megavoltage photon beams. Material/Methods: Percentage surface dose (PSD) measurement was carried out in Elekta Synergy™ Linear accelerator using PTW Markus® Parallel plate ionization chamber of volume 0.05cm3 with water equivalent RW3 Slab phantom (PTW, Germany). The measurement depth was considered at 0.07mm. The reference PSD was measured at 0° gantry angle with 10×10cm2, 20×20cm2 and 30×30cm2 field sizes and 100cm SSD for 4MV, 6MV and 15MV photon beams. For comparison, PSD measurement was carried out at 180° gantry angle inclusion of treatment couch (TC), All in One positioning system (AIO – PS) and Vac lok Cushions (VLC). Results: Beam angle at 0°, for field sizes 10×10cm2, 20×20cm2 and 30×30cm2, the PSD was observed as 30.9%, 40.5%, 48.7% for 4MV; 23.7%, 33.8%, 42.2% for 6MV; and 17.0%, 29.6%, 38.6% for 15MV respectively. Beam angle at 180° with TC, an increase in PSD by maximum of 65.0% for 4MV, 64.9% for 6MV and 55.9% for 15MV as compared to 0° angle. The PSD increased when beam angle was 180° with TC and AIO – PS were 65.0% for 4MV, 67.4% for 6MV, and 60.9% for 15MV than 0° angle. Similarly, increased PSD for beam angle at 180° with TC and VLC were 66.8% for 4MV, 66.8% for 6MV and 61.3% for 15MV as compared to 0° angle. Conclusion: For all three-photon energies, at 180° gantry angle, the PSD increased significantly in case of TC, VLC, and AIO – PS for all the field sizes as compared to gantry angle at 0°. It is necessary to consider TC, AIO – PS and VLC during dose calculation to ensure accuracy of patient treatment delivery.  https://journal.waocp.org/article_90946_344d818750132c894e2bbe7870a58e0d.pdf