Document Type : Original Paper
1. Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran 2. Medical Radiation Science Research Team, Tabriz University of Medical Sciences 3. Department of Medical Physics, Faculty of Medicine, Tabriz 4.
Medical Physics Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
Mashhad University Of Medical sciences
Department of medical physics, Faulty of medicine, Mashhad University of Medical Sciences, Mashhad, Iran
Medical physics Department, Reza Radiation Oncology Center, Mashhad, Iran
Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
Statistics research center, Mashhad university of Mathematical of sciences, Mashhad, Iran
Introduction: Interfractional set-up variations may cause deviation of the delivered dose from the planned dose distribution. This study aimed at calculating random and systematic set-up errors using an electronic portal imaging device (EPID) to set the optimum planning target volume (PTV) margins in patients with head and neck cancer who were under treatment with three-dimensional conformal (3DCRT) and intensity-modulated radiotherapy (IMRT).
Material and Methods: In this study, 50 patients underwent 3DCRT along with weekly electronic portal image (EPI), and daily IMRT imaging was performed on 50 others. The EPIs were compared with Digitally Reconstructed Radiographs (DRRs) to quantify the systematic, random, and 3D vector length of set-up errors in three translational directions (X, Y, Z). The PTV margins were measured utilizing International Commission on Radiation Units and Measurements report 62, Stroom’s and van Herk’s models.
Results: For 3DCRT and IMRT techniques, the overall mean 3D vector length of displacement was obtained at 3.9 and 2.7 mm, respectively. The maximum systematic and random errors were 1.3 and 1.9 mm for the IMRT technique and 2 and 2.9 mm for 3DCRT, respectively. PTV margins in the three acquisition directions were 2-7.2 mm.
Conclusion: It was found that a 7 mm extension of the clinical target volume (CTV) to PTV margin ensures that 90% of head and neck cancer patients have received 95% of the planned dose.