Intensity modulated radiation therapy: film verification of planar dose maps

A new slow response radiographic film (Kodak EDR) is compared with a more traditional faster responding dosimetry film (Kodak XV) in an intensity modulated radiation therapy x-ray field. Dose profiles derived from the two films are compared with doses obtained using a radiotherapy dose planning system (Philips-Pinnacle) which calculates planar dose using a collapsed cone convolution algorithm. Comparisons of the dose maps delivered from film with the Pinnacle dose maps are useful to ensure accurate dose delivery. The Pinnacle dose maps agreed with measurement using both film types to within +/- 3% (in the umbral region) at depths ranging from d(max) to 15 cm. Both XV and EDR films can be used to verify IMRT. EDR film is better suited for dosimetry for combined field dose maps due to its useful dose range of 1-5 Gy. We found XV to be more suitable for individual field dose maps (dose range 0-1 Gy) as no scaling of monitor units were required to achieve acceptable optical density response.