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A Comparison of Three Quality Assurance Tools Used for IMRT QA

Robert Hoffman

R Hoffman*, T Ivanova, G Cardarelli, K Norton, T Steger, K Dwyer, M Rossi, G Qian, A Jones, Hartford Hospital, HARTFORD, CT

PO-BPC-Exhibit Hall-14 Saturday  Room: Exhibit Hall

To evaluate IMRT QA plans using 3 different measurement methods.

Three IMRT QA techniques were compared: 1) 2D dose distributions acquired by 2D diode array (Mapcheck2, Sun Nuclear) processed with Mapcheck software; 2) EPID acquired fluences processed in Dosimetry Check (Standard Imaging) and 3) film dose measurements processed by RIT (Radiological Imaging Technology). The IMRT/VMAT plans used in this study included head and neck, prostate, chest, pelvis. The acceptance criteria for the gamma analysis used to evaluate the QA results are 3% dose difference and 3mm distance to agreement for 90% for all points in the plane or volume being compared. The cases that were chosen for the analysis initially provided less than the desired gamma analysis results using Dosimetry Check (DC).
Additionally each software analysis tool was used to evaluate the three different detectors, 2D diode array, EPID, and film for the same plan.

For the cases studied, MAPCHECK QA analyses passed with at least 95% of points analyzed having gamma less than 1. In all but one case, RIT QA analyses passed with 90% of points analyzed having gamma less than 1.

IMRT QA analysis based on the planar dose comparison, i.e.; MAPCHECK and RIT, provide higher passing rates than DC, which uses volumetric dose comparison (e.g. in the PTV) computed from fluence reconstructed from an EPID projected onto the patient 3D dataset. Results to date demonstrate the following:
1. Of the 3 detector types there was a higher passing rate for film for small field plans. For lower gradient plans, EPID ranked second and 2D Diode array ranked last.
2. For routine plans, Mapcheck is the tool of choice.
3. For complex plans, Dosimetry Check with EPID or Film is the desired IMRT QA tool.

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