Document Type : Original Paper
Authors
1
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.
2
Medical Physics Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
3
Mashhad University Of Medical sciences
4
Department of medical physics, Faulty of medicine, Mashhad University of Medical Sciences, Mashhad, Iran
5
Medical physics Department, Reza Radiation Oncology Center, Mashhad, Iran
6
Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
7
Statistics research center, Mashhad university of Mathematical of sciences, Mashhad, Iran
Abstract
Introduction:
Interfractional set-up variations can lead to deviations of the actual delivered dose from the prescribed dose distribution. The aim of the current study was to quantify systematic and random set-up errors by means of electronic portal imaging device (EPID) to determine the optimal planning target volume (PTV) margins in head and neck cancer patients treated with three-dimensional conformal (3DCRT) and intensity-modulated radiotherapy (IMRT).
Material and Methods:
A total of fifty patients who had underwent 3DCRT with one weekly electronic portal image (EPI) and fifty patients underwent IMRT with daily imaging included in this study. Digitally Reconstructed Radiographs (DRRs) were compared to EPIs to determine the systematic, random, and 3D vector length of set-up errors in three translational directions(X, Y, Z). PTV-margins were calculated according to International Commission on Radiation Units and Measurements (ICRU) report 62, Stroom’s and van Herk’s formulae.
Results:
The overall mean 3D vector length of displacement was 3.9 and 2.7 mm for 3DCRT and IMRT technique. The largest magnitude of systematic and random errors was 2 and 2.9 mm for 3DCRT and 1.3 and 1.9 mm for IMRT technique, respectively. PTV margins were comprised between 2 and 7.2 mm in the three acquisition directions.
Conclusion: Based on the results, approximately 7 mm extension of clinical target volume (CTV) to PTV margin can ensure that 95% of the prescribed dose will received by the 90% of the head and neck cancer patients.
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