Abstract
Purpose: To evaluate the agreement between measured and calculated doses for head and neck tumors using different gamma criteria and to establish quality assurance protocol for the delivery of IMRT in The National Cancer Institute in Cairo. Methods : The dose is calculated for 30 patients using CMS Treatment Planning System. The ionization chamber (0.6 cm 3 Farmer type) is used for point dose measurements. The 2D-array (PTW 729) and GafChromic films (EBT2) are used for 2D graphical dose distribution. Four different gamma criteria of dose difference (DD) and distance to agreement (DTA) (3%/3 mm, 3%/5 mm, 4%/4 mm and 5%/5 mm DD / DTA) are selected. These criteria are evaluated while suppressing the dose of 10%, 20% or 30% from dose distribution. Results: Point dose evaluations using the ion chamber ranged from -2.6% to 3.7% (mean and standard deviation of 0.46 ± 1.7) . Significant differences are observed between the films and 2D-array for all criteria except the 3%/5 mm criteria (96.89 ± 2.2% vs. 94.81 ± 4.2% (p < 0.01)). Conclusion : Differences may exceed about 3% when the ionization chamber is present in steep dose gradient regions. The present results suggest the gamma criteria of 3%/5 mm as the most suitable criteria for IMRT quality assurance. This gamma criterion of 3%/5 mm favorably exceeds 95% in case of maximum dose while suppressing the dose of 20%.The use of 2D-array can reduce the IMRT QA workload. ------------------------------ Cite this article as: Elawady RA, Attalla EM, Elshemey WM, Shouman T, Alsayed AA. Dose verification of intensity modulated radiotherapy in head and neck tumors. Int J Cancer Ther Oncol 2014; 2 (3):02037. DOI : 10.14319/ijcto.0203.7
Highlights
The standard quality assurance (QA) for IMRT before the patient treatment is to use an ionization chamber for absolute dose measurements and 2-dimensional (2D)-array or films for relative dose evaluation.[1, 2] During the introduction of intensity-modulated beams applied for IMRT, the physics community started to perform more extensive verification in 2D and even in 3D
Point dose measurements: The differences between the measured doses by ion chamber and that calculated for 30 patients (210 fields) using XIO treatment planning system (TPS) are expected to range from -2.6 % to 3.7 % for whole plan for head and neck tumors
From the above mentioned results, it is clear that the maximum dose data always show better results compared to local dose for all gamma values. This large reported difference between the gamma values obtained for maximum dose compared to local dose necessitates that different authors clarify whether their published results are calculated for maximum dose or local dose
Summary
The standard quality assurance (QA) for IMRT before the patient treatment is to use an ionization chamber for absolute dose measurements and 2-dimensional (2D)-array or films for relative dose evaluation.[1, 2] During the introduction of intensity-modulated beams applied for IMRT, the physics community started to perform more extensive verification in 2D (planes) and even in 3D (volumes). Kron et al 4 performed a check of absolute dose calibration in a slab phantom. This study found that the dose delivered to the ICRU reference point was correct in all centers. They found that the absolute dose calibration and the mean dose in the Corresponding author: Rasha A Elawady; National Cancer Institute, Cairo University, Cairo, Egypt
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