Verification of a commercial 3-D treatment planning system algorithm under conditions simulating tangential breast treatment

The accuracy of the photon dose algorithm employed by a commercial radiation treatment planning system (ADAC Pinnacle³, ADAC Laboratories, Milpitas, CA) was verified for conditions simulating a tangential breast treatment, a breast phantom was fabricated out of machineable wax and placed on an anthropomorphic phantom. Radiographic film was used to measure the dose distribution at the midplane of the breast and thermoluminescent dosimeters (TLD) were used to measure the dose in four regions within the midplane. Film measurements were compared to calculations performed by the treatment planning system (TPS) for 4 situations: 6 MV optimal wedge, 18 MV optimal wedge, 6 MV compensating filter, and 18 MV compensating filter. Measured and calculated doses agreed to within ±3% for both the film and TLD measurements in most areas, Two exceptions to the ±3% agreement were one small area each in the 18 MV optimal wedge and 6 MV compensating filter film measurements and measured dose to isocenter for the 6 MV compensating filter using TLD. Agreement was not expected in the buildup region for any of the measurements due to the limitations of the convolution/superposition algorithm in areas of charged particle disequilibrium, or at the TLD measurements at isocenter, which was located at the interface between the breast and anthropomorphic phantoms. The results obtained indicate that the TPS accurately calculates dose in conditions simulating a tangential breast treatment