The quality assurance of volumetric modulated arc therapy (VMAT) plans for early stage prostate cancer: a technical note.

As radiation therapy transitions from intensity modulated radiation therapy (IMRT) to volumetric modulated arc therapy (VMAT) it is important to consider the quality assurance (QA) of VMAT plans in light of what has previously been learned and developed in IMRT QA. This technical note assesses if IMRT based plan QA software, which has reduced the need in IMRT for phantom dose measurements on the linear accelerator, can be incorporated into VMAT QA processes. Twenty prostate cases were retrospectively planned using VMAT with one arc to deliver a prescription of 74 Gy in 37 fractions. A plan QA was performed using both (version 3.3), a software-based IMRT QA program, and (version 6.2.3.5713), a phantom-based VMAT QA tool. Outcomes assessed included the time needed to perform the QA of both the and QA methods, and agreement between planned dose and QA measured dose. On average per case, the technique needed 31.5 min to perform the VMAT plan QA, while required 3.5 min to perform the same QA. All 20 cases passed dosimetric QA using . However, using , three cases failed dosimetric QA using the departments existing IMRT QA criteria. This research has demonstrated that the IMRT QA software may be incorporated into the QA of VMAT plans, however the criteria to assess the dosimetry of the VMAT plans may need to be different to that for IMRT cases. The implication of this research for radiation therapists is to be critically aware of the differences between the plan QA requirements and methods for IMRT and those required for VMAT.