A study to establish reasonable action limits for patient-specific quality assurance in intensity-modulated radiation therapy

Abstract

An effective patient quality assurance (QA) program for intensity-modulated radiation therapy (IMRT) requires accurate and realistic plan acceptance criteria--that is, action limits. Based on dose measurements performed with a commercially available two-dimensional (2D) diode array, we analyzed 747 fluence maps resulting from a routine patient QA program for IMRT plans. The fluence maps were calculated by three different commercially available (ADAC, CMS, Eclipse) treatment planning systems (TPSs) and were delivered using 6-MV X-ray beams produced by linear accelerators. To establish reasonably achievable and clinically acceptable limits for the dose deviations, the agreement between the measured and calculated fluence maps was evaluated in terms of percent dose error (PDE) for a few points and percent of passing points (PPP) for the isodose distribution. The analysis was conducted for each TPS used in the study (365 ADAC, 162 CMS,220 Eclipse), for multiple treatment sites (prostate, pelvis, head and neck, spine, rectum, anus, lung, brain), at the normalization point for 3% percentage difference (%Diff) and 3-mm distance to agreement (DTA) criteria. We investigated the treatment-site dependency of PPP and PDE. The results show that, at 3% and 3-mm criteria, a 95% PPP and 3% PDE can be achieved for prostate treatments and a 90% PPP and 5% PDE are attainable for any treatment site.

Figure 1

Overall results as a frequency distribution (total $\text{fields}=747$—that is, fluence maps for all localizations) of the percent of passing points measurements.

Figure 2

Histogram showing overall results as a frequency distribution (total $\text{fields}=747$—that is, fluence maps for all localizations) of the percent dose error measurements.

Figure 3

Selected results as a frequency distribution (total $\text{fields}=389$—that is, fluence maps for prostate and other localizations) of the percent of passing points measurements.

Figure 4

Histogram showing selected results as a frequency distribution (total $\text{fields}=389$—that is, fluence maps for prostate and other localizations) of the percent dose error measurements.

Figure 5

Selected results as a frequency distribution (total $\text{fields}=358$—that is, fluence maps for head and neck) of the percent of passing points measurements.

Figure 6

Histogram showing selected results as a frequency distribution (total $\text{fields}=358$—that is, fluence maps for head and neck) of the percent dose error measurements.