Investigating the use of ionization chamber and solid-state detectors to evaluate kerma-area product meter accuracy under TG-125 geometry across variable field of views.

BACKGROUND

A kerma-area product (KAP) meter has been installed in a fluoroscopic system, and its accuracy has been evaluated in task group (TG)-190 geometry using an external detector. However, it is unclear that external detectors could evaluate the KAP meter accuracy under the TG-125 geometry.

PURPOSE: This study investigated whether the reference air kerma rate ( K ̇ a , r ${\dot{K} _{a,r}}$ ) values of the KAP meter increase with increasing field of view (FOV) and whether an external ionization chamber and solid-state detector (SSD) could be used to evaluate KAP meter accuracy in TG-125 geometry.

METHODS

An ionization chamber and three different SSDs (Radcal AGMS-DM+, Raysafe X2 R/F sensor, and RTI Dose Probe) were placed at the patient entrance reference point in a C-arm fluoroscopic system, and measurements were taken at FOV settings of 18, 25, 34, and 42 cm using both the TG-190 and TG-125 geometries. The K ̇ a , r $\dot{K} _{a,r}$ , incident air kerma rate ( K ̇ a , i ) $\dot{K} _{a,i})$ , and entrance surface air kerma rate ( K ̇ a , e ) $\dot{K} _{a,e})$ values were recorded simultaneously and compared. The measurement data were used to calculate the backscatter factor.

RESULTS

The K ̇ a , r ${\dot{K} _{a,r}}$ increased linearly with the relative X-ray output, and their slopes significantly increased with the FOV. The K ̇ a , e ${\dot{K} _{a,e}}$ values of the ionization chamber increased with the FOV; however, the K ̇ a , i $\dot{K} _{a,i}$ values of the ionization chamber, K ̇ a , i $\dot{K} _{a,i}$ and K ̇ a , e $\dot{K} _{a,e}$ values of the SSDs were not dependent on the FOV and were nearly identical to each other. Although the backscatter factor for the KAP meter and ionization chamber increased with the FOV, the backscatter for the SSDs were close to unity in all FOVs and no significant difference was observed.

CONCLUSIONS

The results indicated that the K ̇ a , r ${\dot{K} _{a,r}}$ values of KAP meter were increased with the FOV. Furthermore, the SSDs could be utilized to evaluate the KAP meter accuracy in TG-125 geometry.