SU-D-BRCD-05: Evaluation of New Exit Detector Based Transit Dosimetry Software for TomoTherapy Treatments

The prospect of 3D transit dosimetry to verify treatment delivery is a novel and emerging technology in TomoTherapy. Math Resolutions, LLC, has expanded their Dosimetry Check (DC) quality control software to include transit dosimetry calculations for TomoTherapy treatments. The data recorded by the MVCT detectors during patient treatment is used in conjunction with the planning CT to calculate the delivered dose to the patient from each fraction. This study presents a summation of our experiences at the University of Virginia in collaboration with Math Resolutions in verifying and implementing the transit-dose calculation aspects of this new TomoTherapy specific product.

Low and high modulation cheese phantom plans and clinical plans (prostate, GYN, pituitary, and thoracic vertebra) were used to evaluate the DC transit dosimetry software. The TomoTherapy planning CT, structure set, plan, and dose for each plan were imported into the DC software. The fluence maps were reconstructed from the exit detector data by correcting for patient attenuation and used to compute the delivered dose. The resulting dose distribution is compared with the TPS planned dose using isodose line comparison and gamma index.

The percent difference between the planned and DC calculated doses ranged between 0.63% for a low modulation cheese phantom plan to 5.94% for a prostate plan. Using criteria of 3%, 3mm, the gamma index passing rate for the tested plans ranged from 94.7% to 99.1% <1 for the overall patient area and from 88% to 96.4% for the treatment area receiving at least 80% of the prescribed dose.

The results from our evaluation of Math Resolutions' DC look promising and generally within an acceptable range for portal dosimetry programs. Further investigations will include developments to improve the DC algorithm and determine how it can best be implemented in a typical TomoTherapy clinical workflow. Research Grant from Math Resolutions LLC 01/12/2012-01/11/2013 Math Resolutions™ Dosimetry Checksoftware was given to UVa to assist with evaluating the precision of the product in reconstructing dose from the TomoTherapy exit detector data.