Verification of tangential breast treatment dose during 2D treatment planning

This study presents a water phantom study of verification of tangential breast treatment dose calculations in a two-dimensional treatment planning system (TPS) at the Department of Radiotherapy, in a National hospital in Sri Lanka. Measurements were made using a 0.6 cc Farmer-type cylindrical ionization chamber with an electrometer in a breast phantom made of water field Perspex structure. The measured doses in the breast were compared with calculations made on a two-dimensional radiotherapy treatment planning software THERAPLAN®PLUS version 3.55 using the digitized breast phantom contour. Overall, the measurements obtained from the TPS had an accuracy of ±5% compared to the direct measurements while most of the measurements lie within ±3%. And dose in the chest wall was below the tolerance level of the lung and heart. Thus, it was concluded that TPS calculations and dose distributions are within the clinically acceptable accuracy level of international standards (ICRU report 50).