USE OF CEA TVS FILM FOR MEASURING HIGH-ENERGY PHOTON-BEAM DOSE DISTRIBUTIONS

CEA TVS film is a therapy verification film that has been recently int roduced in the North American market. This film features linear charac teristic curves for photon energies from Cs-137 to 18 MV as reported b y Cheng and Das [Med. Phys. 23, 1225 (1996)]. In Saskatoon, TVS film w as investigated for its application in the measurement of dose distrib utions with 4 and 18 MV linacs and a Co-60 unit. The TVS film jacket h as a layer of conductive material that has a minimal effect on the fil m's response. Film sensitivity generally increases for exposures norma l to the incident beam as compared with parallel exposures, but was hi ghly dependent on beam energy and depth of measurement. Fractional dep th doses obtained in the parallel orientation agreed well with ion cha mber measurements for the linac beams at depths beyond D-max; ion cham ber measurements differed by a maximum of 1.6% and 2.6% for the 4 and 18 MV beams, respectively. In the buildup region, an increase in film response was found when compared to the ion chamber measurements for b oth linac beams. With the 60Co beam, the TVS film showed an increase i n sensitivity with depth as the proportion of scattered soft x rays in creases; the maximum difference between ion chamber and film fractiona l depth doses was 7.8%. The TVS film demonstrates a substantial improv ement over Kodak X-Omat V film for measuring depth doses in the parall el orientation, for all beams considered. Generally, the results confi rm TVS film as an accurate and practical dosimeter for the measurement of dose distributions in high energy photon beams. (C) 1998 American Association of Physicists in Medicine.