Room: Exhibit Hall
Purpose: To develop an in-house software that allows an advanced gamma analysis for TomoTherapy patient-specific QA procedure and to demonstrate the ability of the software to detect positional uncertainty during the patient-specific QA delivery procedure.
Methods: An in-house software was developed to perform a thorough gamma analysis between three-dimensional calculated dose and two-dimensional measured dose using MATLAB. In the developed software, the dose measured using a film was compared to the calculated doses at multiple coronal planes while the vendor-provided software only compares the film dose to the calculated dose at a user-specified vertical location, which is corresponding to the film-inserting location in Virtual WaterTM phantom. For each of the coronal planes considered for the dose comparison, the calculated dose and film dose were registered using a rigid image registration. A scaling factor was determined to minimize the square sum of difference between the two dose distributions. The in-house gamma analysis software was tested on four patients, in which the vendor-supplied software (TomoTherapy, Inc.) resulted in failure in 3 %/3 mm gamma analysis (criteria for gamma analysis at our institution: 90 % of pixels passing).
Results: By using the in-house software, it was demonstrated that the gamma analysis results varied depending on how the two dimensional film dose is aligned to the three dimensional calculated dose. For the four patients considered, in which the initial gamma analysis by experienced medical physicists failed, the percentage of pixels passing increased by 10.9 % on overage by changing the vertical location to which the film dose was aligned. The maximum percentage of pixels passing was found at locations averagely 11.1 mm distant from the film-inserting location in the phantom.
Conclusion: The in-house software can be useful for further investigation on the patients, in which the gamma analysis fails by the vendor-supplied software.