Conversion of an infrared densitometer for radiochromic film analysis

By the simple incorporation of a high intensity red LED into a typical infrared film densitometer, radiochromic film can be analysed using existing detectors and scanning software. Results show an accurate dose measurement using radiochromic film and this system compared to conventional detectors for percentage depth dose and penumbral measurements in high and low energy x-ray beams. A small circuit including a red Light Emitting Diode (LED) was positioned inside the film densitometer which does not obscure the infrared source. The red and infrared diodes work independently. For 6 MV x-rays, the 80%/20% penumbral width at 15 mm depth for a 10 x 10 cm field at 100 cm SSD was measured to be 3.5 mm with radiochromic film as compared to 3.3 with corrected diode measurements. Percentage depth doses were measured to within +/- 3% of ionisation chamber data at 6MV and within +/- 2% for 250 kVp x-ray with the film placed parallel to the beam direction in both cases.