en Radiotherapy Radiotherapy پژوهشي orginal article <span style="font-size:12pt"><span style="line-height:16.0pt"><span new="" roman="" style="font-family:" times=""><b><i><span style="font-size:9.0pt">Background & Aims</span></i></b><b><span style="font-size:9.0pt">: </span></b>&nbsp;<span style="font-size:9.0pt">The collimator angle significantly impacts radiation leakage between the multi-leaf collimator (MLCs) leaves. This study aims to examine dose-volume evaluation in planning target volume (PTV) and organs at risk (OARs) for Head & Neck patients undergoing volumetric-modulated arc therapy (VMAT) with 2.5 arcs and varying collimator angles.</span></span></span></span><br> <span style="font-size:12pt"><span style="line-height:16.0pt"><span new="" roman="" style="font-family:" times=""><b><i><span style="font-size:9.0pt">Materials & Methods:</span></i></b><span style="font-size:9.0pt"> &nbsp;In this experimental study, five patients with nasopharyngeal cancer were selected for treatment with the VMAT method. CT images were prepared using a CT simulator and transferred to the treatment planning system. For optimizing VMAT plans, volume and dose constraints were applied to OARs and PTVs by the algorithm. Then, the doses were calculated using the AAA algorithm.</span></span></span></span><br> <span style="font-size:12pt"><span style="line-height:16.0pt"><span new="" roman="" style="font-family:" times=""><b><i><span style="font-size:9.0pt">Results</span></i></b><b><span style="font-size:9.0pt">:</span></b><span style="font-size:9.0pt"> &nbsp;Although no significant differences were observed in DVH curves across different collimator angles, other parameters exhibited variations. Notably, in Head & Neck cancer patients, optimal values for dose conformity, homogeneity, MUs, and gradient index were found at collimator angles of 20&deg; and 30&deg;. Additionally, OAR sparing was favorable at these angles. Based on target coverage, homogeneity, and MUs, the collimator angles were optimized for VMAT planning.</span><b><span style="font-size:9.0pt"></span></b></span></span></span><br> <span style="font-size:12pt"><span style="line-height:16.0pt"><span new="" roman="" style="font-family:" times=""><b><i><span style="font-size:9.0pt">Conclusion</span></i></b><b><span style="font-size:9.0pt">: </span></b>&nbsp;<span style="font-size:9.0pt">Our findings offer valuable guidance to clinical medical physicists in making informed decisions regarding collimator angles. The dosimetric analysis underscores the importance of selecting the optimal collimator angle for accurate PTV coverage.</span></span></span></span><br> &nbsp; Dose-Volume Histogram, Collimator Angle, Head and Neck Carcinoma, Planning Target Volume, Volumetric-Modulated Arc Therapy 94 102 http://ijrabms.umsu.ac.ir/browse.php?a_code=A-10-268-1&slc_lang=en&sid=1 Sadiq Ullah taukeerameer@gmail.com 10031947532846002831 0009-0000-4783-7594 No Medical Physics Division, Atomic Energy Cancer Hospital CENAR, Quetta, Baluchistan, Pakistan Touqir Ahmad Afridi taukeerameer@gmail.com, 10031947532846002832 10031947532846002832 Yes Medical Physics Division, Atomic Energy Cancer Hospital NORIN, Nawabshah, Sindh, Pakistan Muhammad Zia-Ul-Islam Arsalan ziamedicalphysicist@gmail.com 10031947532846002833 10031947532846002833 No Medical Physics Division, Atomic Energy Medical Centre (AEMC), Karachi, Sindh, Pakistan Umar Hussain Haider umarstg88@gmail.com 10031947532846002834 10031947532846002834 No Medical Physics Division, Atomic Energy Medical Centre (AEMC), Karachi, Sindh, Pakistan Muhammad Umar Farooq umarmedicalphysicist@gmail.com 10031947532846002835 10031947532846002835 No Medical Physics Division, Cancer Care Hospital, Lahore, Punjab, Pakistan Hashir Saeed dastaan7777@gmail.com 10031947532846002836 0009-0006-2246-8589 No Department of Medical Physics, Center for Nuclear Medicine and Radiotherapy, Quetta, Baluchistan, Pakistan