Po‐Poster ‐ 22: Patient specific quality assurance for helical tomotherapy

Abstract

Helical tomotherapy is a highly integrated platform for delivering image guided and inverse planned IMRT. The TomoTherapy system combines highly conformal external beam IMRT with on board megavoltage CT, as well as integrated image fusion, moveable lasers, and a highly accurate couch. Patient specific QA, using film and ion chamber, helps ensure that the dose distributions that are delivered as planned. The patient specific QA employs several software tools, some provided by TomoTherapy Inc., and some developed in house. The QA process hinges on the integrated system ability to export patient delivery sinograms for calculation in a phantom. Analysis tools for comparing calculation and measured results are also present. Results from the film dosimetry system, ion chamber point measurements, as well as the use of the gamma function to assess the resulting measured vs. calculated distribution are presented. An in house computer code is employed which allows the gamma analysis to be constrained to region of interest. Results for ten recent of patients on in house research protocols are presented, showing that average point dose measurement are within 1.06% of the planning system. The gamma value from film is better for more recent patients; differences found in earlier patients are shown to result from the inherent difficulties in using film as a dosimeter (processing, need for care and refinement in calibration technique).