On the sensitivity of TG-119 and IROC credentialing to TPS commissioning errors

Abstract

We investigate the sensitivity of IMRT commissioning using the TG-119 C-shape phantom and credentialing with the IROC head and neck phantom to treatment planning system commissioning errors. We introduced errors into the various aspects of the commissioning process for a 6X photon energy modeled using the analytical anisotropic algorithm within a commercial treatment planning system. Errors were implemented into the various components of the dose calculation algorithm including primary photons, secondary photons, electron contamination, and MLC parameters. For each error we evaluated the probability that it could be committed unknowingly during the dose algorithm commissioning stage, and the probability of it being identified during the verification stage. The clinical impact of each commissioning error was evaluated using representative IMRT plans including low and intermediate risk prostate, head and neck, mesothelioma, and scalp; the sensitivity of the TG-119 and IROC phantoms was evaluated by comparing dosimetric changes to the dose planes where film measurements occur and change in point doses where dosimeter measurements occur. No commissioning errors were found to have both a low probability of detection and high clinical severity. When errors do occur, the IROC credentialing and TG 119 commissioning criteria are generally effective at detecting them; however, for the IROC phantom, OAR point-dose measurements are the most sensitive despite being currently excluded from IROC analysis. Point-dose measurements with an absolute dose constraint were the most effective at detecting errors, while film analysis using a gamma comparison and the IROC film distance to agreement criteria were less effective at detecting the specific commissioning errors implemented here.

Figure 1

Workflow to determine the clinical severity of commissioning errors along with the sensitivity of IROC credentialing and IMRT commissioning from TG‐119.

Figure 2

3D rendering, axial, coronal, and sagittal dose distribution and DVH of head and neck IMRT plan.

Figure 3

3D rendering, axial, coronal, and sagittal dose distribution and DVH of mesothelioma IMRT plan.

Figure 4

3D rendering, axial, and sagittal dose distribution and DVH of scalp IMRT plan.

Figure 5

Axial view C‐shape structures (a) from TG‐119 suite, superimposed on a rectangular phantom. IROC phantom geometry (b) for targets, critical structure, film plane, and TLD locations.

Figure 6

Summary of clinical severity and probability of detection for errors implemented in Eclipse AAA.

Figure 7

Display of change in dose from original head and neck plan due to changes in the MLC DLG.

Figure 8

Percent of pixels in dose planes with gamma index $<1$ using $3\%/3$ mm and $2\%/2$ mm criteria as functions of magnitude of DLG commissioning error. Vertical lines represent the magnitude of DLG error that caused a 2% and 5% dosimetric error in select clinical treatment plans.

Figure 9

Percent change in TLD point dose in IROC phantom due to various commissioning errors.

Figure 10

Sensitivity of TLD point does measurements to DLG errors in IROC IMRT phantom.

Figure 11

Dose profile from TPS across IROC film plane with various commissioning errors introduced. The IROC sagittal film analysis passed the 4 mm distance criteria for all commissioning errors implemented.