AbstractID: 8206 Title: An Automated Registration Procedure for IMRT Film Dosimetry
One difficulty in quantitative IMRT QA is the co-registration of measured data with the corresponding
computer generated isodose plan. For film dosimetry analysis, registration of plan and film is often accomplished
by locating high dose gradient areas that appear on both distributions. Unfortunately, this technique relies on a
correct reproduction of particular dosimetric area of the film (e.g., a high gradient region), which may not be
accurate. A simple method is introduced to register IMRT QA films to the corresponding isodose plans. This
technique involves the placement of multiple 6x6 mm2 fiducial markers placed outside the irradiated portion of the
film. The markers are placed at least 10 cm from the geometric center of the isodose plan to both minimize their
dosimetric effect on the planned distribution and decrease the registration error near the center of the field. For the
treatment plan, an automated script is used to add the fiducial beams either to an individual treatment field or to an
existing patient-specific composite isodose plan. These beams are then transferred to a standard in-house QA
phantom for evaluation. Isodose distributions in either the coronal or transverse plane are generated and transferred
to a commercially available film analysis system for comparison. For film irradiation, similar fiducial marks are
made either with a standard beam dataset (for coronal films), or using a pressure artifact tool (for transverse films).
A step by step protocol for the implementation of this method will be presented.