Document Type : Original Article
Authors
1
M.Sc. in Biophysics, Radiotherapy Department, El-galaa Hospital
2
Medical Radiation Biophysics, Faculty of Medicine, Al-Azhar University
3
Physics Department,Women Faculty for Arts, Science, and Education, Ain -Shams University
4
National Center for Radiation Research and Technology, Atomic Energy Authority
Abstract
Radiotherapy has a vital part in the treatment of prostate tumor. Three-dimensional conformal radiotherapy (3D-CRT), intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques are currently used. In this concern, the present study is a trial to shed further light on the mean differences and to note the similarity or dissimilarity between the proposed three techniques of radiotherapy for head & neck (H & N) cancer. Measurements were carried out based on two dimensional (2D) array PTW and portal dosimetry in patient with head and neck canceras tool for evaluation. Specifically, the aim of the first part was to demonstrate that quality assurance (QA) tool for IMRT and its passing rate criteria might not expect dose errors in patient. This study examines the effect of systematic positional multi-leaf collimator (MLC) bank errorson gamma (Γ) examination results used for QA of treatment technique and to assess the result of dose changes presented in dynamic multi-leaf collimator (DMLC) modeling and delivery methods on metrics for IMRT.
Twenty head and neck IMRT plans were selected for current study using the same group of dose–volume constraints. Treatment plans were created using 3D-CRT, VMAT and IMRT techniques. Homogeneity index (HI), Conformity index (CI), max. spinal cord dose, max. brainstem dose, mean parotid dose, larynx dose, oral cavity dose, and monitor units (MUs) were compared. For every patient, a group of data analysis was done for each technique and then imported to the DVH (PTW 2D array) for processing. A measured dose volume histogram metrics (DVH) was created in QA system and note the similarity to the calculated DVH from the treatment plan. Their variations due to errors related to the treatment planning system (TPS) (its algorithm for dose calculation) in addition to beam delivery.
It is clearly shown that VMAT has a little better CI whereas the volume of small doses was higher.VMAT had lesser MUs than IMRT. 3D-CRT had the lowest common MU, CI and HI. IMRT would be preferred to VMAT in head and neck radiotherapy. Also, the current study showed even if the whole of IMRT QA had high Gamma passing rates 98.3 ± 1.3% (96.7-99.7%) for “3%/3 mm” criteria, there were located significant errors in some of the calculated clinical dose metrics. This study approves that conventional IMRT QA are not a prescient warning of errors in PTV dose and OAR dose (organs at risk). The dose QA has to allow us to expect and evaluate the relation of results of gamma test and DVH for treatment technique plan.
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