Session Item

To assess the gamma index for the total treatment volume and various organs at risk (OARs) as well as the mean dose difference by using a secondary system, PTW VERIQA, that performs an independent Monte Carlo 3D dose calculation. At this time, gamma indices are evaluated for an overall delivery of a patient plan or in some cases for PTV volumes. However, VERIQA provides an expanded review of one’s gamma analyses by having the ability to evaluate specific OARs.

Twenty pelvic treatment plans were exported from the Pinnacle Treatment Planning System to VERIQA. The gamma analysis was performed for each patient plan at 3%/2mm with a low-dose threshold of 10% of the maximum compared dose. The gamma index for the total volume encompassed within the external contour was recorded along with the gamma index for the bladder, bowel, rectum, sigmoid, femoral heads, and kidney when applicable. The mean dose difference for the previously stated OARs were also noted for comparison purposes.

The total volume of each pelvic treatment plan had at least 90% of all voxels passing at a gamma rate of less than one at 3%/2mm. The bladder had a range of gamma indices from 90.74% to 100.00% with an average gamma index of 98.23%. The mean dose difference between Pinnacle and VERIQA was recorded for the bladder and demonstrated an absolute average difference of 0.421 Gy, whereas the bowel showed an absolute average difference of 0.504 Gy. The bowel had one failing gamma index at 84.08%, while the other 19 pelvic plans had an average passing gamma index of 98.19% for the bowel. A correlation was observed between the failing gamma index for the bowel and a nearly failing total volume gamma index of 90.29% for that specific plan. The sigmoid and left kidney were the only other OARs with a single failing gamma index of 86.32% and 88.69% out of the twenty pelvic treatment plans. The femoral heads exhibited high passing gamma indices compared to the other OARs with a range of 98.02% to 100.00% and an average of 99.74%.

VERIQA can be used as another assessment tool to help understand total volume gamma passing or failing rates by considering OAR gamma indices and their potential impact. VERIQA provides a more thorough evaluation of the delivery of the treatment plan and allows you to better evaluate dose to critical structures, which can be beneficial in cases where a structure is near a PTV or has previously received radiation.