Dose verification of intensity modulated radiotherapy in head and neck tumors

Rasha A Elawady, Ehab M Attalla, Wael M Elshemey, Tarek Shouman, Anwar A Alsayed


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 cm3 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


Quality Assurance; Intensity Modulation; Ionization Chamber; 2D-Array; GafChromic Films

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