Abstract
The aim of this work was to investigate correlations between 2D and quasi-3D gamma passing rates. A total of 20 patients (10 prostate cases and 10 head and neck cases, H&N) were retrospectively selected. For each patient, both intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were generated. For each plan, 2D gamma evaluation with radiochromic films and quasi-3D gamma evaluation with fluence measurements were performed with both 2%/2 mm and 3%/3 mm criteria. Gamma passing rates were grouped together according to delivery techniques and treatment sites. Statistical analyses were performed to examine the correlation between 2D and quasi-3D gamma evaluations. Statistically significant difference was observed between delivery techniques only in the quasi-3D gamma passing rates with 2%/2 mm. Statistically significant differences were observed between treatment sites in the 2D gamma passing rates (differences of less than 8%). No statistically significant correlations were observed between 2D and quasi-3D gamma passing rates except the VMAT group and the group including both IMRT and VMAT with 3%/3 mm (r = 0.564 with p = 0.012 for theVMAT group and r = 0.372 with p = 0.020 for the group including both IMRT and VMAT), however, those were not strong. No strong correlations were observed between 2D and quasi-3D gamma evaluations.
Highlights
Both intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques provide excellent dose conformity to the target volume while minimizing the dose to normal tissue [1]
In the case of VMAT, the largest monitor unit (MU) deviation was observed at the starting control point of each arc for VMAT delivery, which ranged from -0.06 MU to 0.08 MU
The prostate group with both 2%/2 mm and 3%/3 mm and the VMAT group with 2%/2 mm followed the normal distribution of the Shapiro-Wilk test (p > 0.05)
Summary
Both intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) techniques provide excellent dose conformity to the target volume while minimizing the dose to normal tissue [1]. The IMRT technique achieves optimal dose distributions by modulating multi-leaf collimator (MLC) positions while VMAT generates optimal dose distributions by modulating MLC positions, gantry rotation speeds and dose rates, simultaneously [2]. These modulated delivery techniques can involve large uncertainties in the treatment planning process as well as beam delivery [3,4,5]. Heilemann et al and Fredh et al recommended stricter 2D gamma criterion should be used for pre-treatment QA of VMAT plans than IMRT QA [15, 16]. The consensus on pre-treatment QA for VMAT and IMRT still seems to be ambiguous and disputable
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