Comparison of 50 kV facilities for contact radiotherapy

The radiation characteristics of a short source to surface distance (SSD) contact therapy tube in clinical use at the Centre Antoine-Lacassagne, Nice and a long SSD unit at the Clatterbridge Centre for Oncology were compared. The output from the tube at Nice had a dose rate of approximately double that of the tube at Clatterbridge, whereas the tube at Clatterbridge had a slightly higher value of the half value layer. Depth dose measurements were made with GafChromic MD55 film and SSD corrected depth dose curves showed good agreement between centres. Profiles at 2 mm depth also showed comparable levels of flatness and uniformity.