Dosimetric verification by using the ArcCHECK system and 3DVH software for various target sizes

Abstract

Objective: To investigate the usefulness of the 3DVH software with an ArcCHECK 3D diode array detector in newly designed plans with various target sizes.

Methods: The isocenter dose was measured with an ion-chamber and was compared with the planned and 3DVH predicted doses. The 2D gamma passing rates were evaluated at the diode level by using the ArcCHECK detector. The 3D gamma passing rates for specific regions of interest (ROIs) were also evaluated by using the 3DVH software. Several dose-volume histograms (DVH)-based predicted metrics for all structures were also obtained by using the 3DVH software.

Results: The isocenter dose deviation was <1% in all plans except in the case of a 1 cm target. Besides the gamma passing rate at the diode level, the 3D gamma passing rate for specific ROIs tended to decrease with increasing target size; this was more noticeable when a more stringent gamma criterion was applied. No correlation was found with the gamma passing rates and the DVH-based metrics especially in the ROI with high-dose gradients.

Conclusions: Delivery quality assurance by using 3DVH and ArcCHECK can provide substantial information through a simple and easy approach, although the accuracy of this system should be judged cautiously.

Fig 1

Axial slices of the ArcCHECK CT phantom with the target, adjacent organ at risk (OAR), and peripheral OAR (a). Five portals were used for the planning to cover 95% of the target volume with the prescribed dose. The beam angles were 0°, 72°, 144°, 216° and 288° (b).

Fig 2. The dose deviation of the isocenter between the 3DVH-predicted dose and the treatment planning system (TPS)-planned dose is plotted as a solid line.

The dashed line represents the dose deviation between the ion-chamber measured isocenter dose and planned dose. The dose deviations decreased with increasing target size.

Fig 3. Variations of gamma passing rates at the diode level with various target sizes.

The gamma passing rates were calculated with both the 3%/3 mm criterion (lower graph) and the 2%/2 mm criterion (upper graph) in absolute doses with a threshold of 5%. The gamma passing rate decreased as the target size increased.

Fig 4. Variation of 3D gamma passing rates for (a) target, (b) adjacent organ at risk (OAR), and (c) peripheral OAR with various target sizes.

The gamma passing rates were calculated with both the 3%/3 mm criterion (upper graph) and the 2%/2 mm criterion (lower graph) in absolute doses with a threshold of 5%. The 3D gamma passing rate decreased as the target size increased in all specific regions of interest.

Fig 5. An example of a dose-volume histogram representing the dose distribution for the (a) target, (b) adjacent organ at risk (OAR), and peripheral OAR.

The treatment planning system (TPS)-planned doses are plotted as solid lines. The dashed lines represent the 3DVH software- predicted dose, which was calculated on the basis of the ArcCHECK data.