Radiochromic film dosimetry for clinical proton beams

Depth doses and lateral profiles for proton beams with energies of 100-250 MeV were measured with a high-sensitivity GafChromic MD-55 film, which requires no post-irradiation development. The exposed MD-55 films were evaluated with the RIT 113 film dosimetry system. Depth doses measured with MD-55 film were compared with those obtained with a plane-parallel ionization chamber. The GafChromic film was found to be less sensitive at the distal edge for both modulated and unmodulated beams compared with an ionization chamber, however, the difference in penetration of the beam at the depth of 80-50% distal fall-off measured with this film and the ionization chamber is within 0.1-0.2 mm for studied beams. The lateral beam profiles measured with MD-55 film were in a good agreement with profiles obtained from Kodak XV-2 radiographic film, scanned with the Wellhofer densitometer. It is concluded that MD-55 film, with some limitations, is a useful detector for dosimetry measurements in a single proton beam and can be employed for verification dosimetry in multiple-beam radiation therapy.