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. 2015 Jan 1;91(1):65-72.
doi: 10.1016/j.ijrobp.2014.09.008. Epub 2014 Oct 25.

Patient-specific quality assurance for the delivery of (60)Co intensity modulated radiation therapy subject to a 0.35-T lateral magnetic field

H Harold Li  1 , Vivian L Rodriguez  2 , Olga L Green  2 , Yanle Hu  2 , Rojano Kashani  2 , H Omar Wooten  2 , Deshan Yang  2 , Sasa Mutic  2
Affiliations

Patient-specific quality assurance for the delivery of (60)Co intensity modulated radiation therapy subject to a 0.35-T lateral magnetic field

H Harold Li et al. Int J Radiat Oncol Biol Phys. .

Abstract

Purpose: This work describes a patient-specific dosimetry quality assurance (QA) program for intensity modulated radiation therapy (IMRT) using ViewRay, the first commercial magnetic resonance imaging-guided RT device.

Methods and materials: The program consisted of: (1) a 1-dimensional multipoint ionization chamber measurement using a customized 15-cm(3) cube-shaped phantom; (2) 2-dimensional (2D) radiographic film measurement using a 30- × 30- × 20-cm(3) phantom with multiple inserted ionization chambers; (3) quasi-3D diode array (ArcCHECK) measurement with a centrally inserted ionization chamber; (4) 2D fluence verification using machine delivery log files; and (5) 3D Monte Carlo (MC) dose reconstruction with machine delivery files and phantom CT.

Results: Ionization chamber measurements agreed well with treatment planning system (TPS)-computed doses in all phantom geometries where the mean ± SD difference was 0.0% ± 1.3% (n=102; range, -3.0%-2.9%). Film measurements also showed excellent agreement with the TPS-computed 2D dose distributions where the mean passing rate using 3% relative/3 mm gamma criteria was 94.6% ± 3.4% (n=30; range, 87.4%-100%). For ArcCHECK measurements, the mean ± SD passing rate using 3% relative/3 mm gamma criteria was 98.9% ± 1.1% (n=34; range, 95.8%-100%). 2D fluence maps with a resolution of 1 × 1 mm(2) showed 100% passing rates for all plan deliveries (n=34). The MC reconstructed doses to the phantom agreed well with planned 3D doses where the mean passing rate using 3% absolute/3 mm gamma criteria was 99.0% ± 1.0% (n=18; range, 97.0%-100%), demonstrating the feasibility of evaluating the QA results in the patient geometry.

Conclusions: We developed a dosimetry program for ViewRay's patient-specific IMRT QA. The methodology will be useful for other ViewRay users. The QA results presented here can assist the RT community to establish appropriate tolerance and action limits for ViewRay's IMRT QA.

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Conflict of interest statement

Conflict of Interest: None.

Figures

Figure 1
Figure 1
Histogram of the difference between the ionization chamber measured and TPS calculated point doses. The mean difference was 0.0% ± 1.3% (1 standard deviation, n=102), ranging from −3.0% to 2.9%.
Figure 2
Figure 2
Typical results for 2D radiographic film measurement vs. TPS. (a) Film measurement; (b) TPS computed dose; (c) Gamma comparison. The points with gamma index greater than 1 are shown in red.
Figure 3
Figure 3
Typical results for 3D ArcCHECK measurement vs. TPS. (a) ArcCHECK measurement; (b) TPS computed dose; (c) Gamma comparison; (d) Dose profile along the green line shown in (c). The detectors with gamma index greater than 1 are shown in red or blue.
Figure 4
Figure 4
Typical results for machine delivery log file QA. The tolerance was set to 0.5 degrees for gantry, 2 mm for MLC leaf positioning, and 0.2 sec for beam-on time. The 2D fluence passing rate was defined as the percentage of the pixels with delivery errors less than 2% of the maximum fluence in the field.
Figure 5
Figure 5
Typical results for 3D reconstructed dose to an ArcCHECK phantom vs. TPS. (a) Plan dose; (b) Reconstructed 3D dose using machine delivery file; (c) Gamma comparison.
See this image and copyright information in PMC

References

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