Film dosimetry of megavoltage photon beams: A practical method of isodensity‐to‐isodose curve conversion

Abstract

The central problems of photon beam film dosimetry are the dependence of film response upon photon energy, processing conditions, and film plane orientation. We have overcome these problems by accurately fitting the depth-dependent sensitometric curve of Kodak XV-2 film (exposed parallel to beam axis) to the equation OD(D,d) = ODs(1 - exp [- alpha 0[1 + beta(d-dm)]D]) where OD(D,d) is the optical density for dose D at depth d. ODs, alpha 0, and beta are constants characteristic of the film and beam energy but are independent of field size. Only central axis depth dose data for a single field are required to determine their values. A computer program based upon this equation has been written which successfully generates single field isodose curves from film data for a variety of field sizes (including wedged fields) with an accuracy of +/- 3%. Data are presented for 60Co, and 4 and 10 MV x rays.

Comparison of two-dimensional transmitted dose maps: evaluation of existing algorithms

“…Due to the much smaller grain size, used in the EDR2 film structure, it is a very slow speed film and nearly energy independent for dose values of less than 5 Gy 13, [16][17][18][19][20][21] . Dose values obtained from EDR2 film measurements have been reported to agree with ion chamber measurements within 1-2% [11][12][13] .…”

Intensity modulated radiation therapy: Film verification of planar dose maps

“…The calibration films for each film type and measurement depth were always exposed perpendicular to the central axis to avoid parallel film response uncertainty 16,17 . Each film envelope was cut to square of (a) (b) approximate 11x11 cm 2 and sealed with black insulation tape.…”

Comparison of Kodak EDR2 and Gafchromic EBT film for intensity-modulated radiation therapy dose distribution verification

“…In contrast, for XV films, the variation in sensitometric response goes up to 16%. [3][4][5][6] Moreover, XV films saturate at the dose of 200 cGy, whereas the saturation dose for EDR2 films goes up to 700 cGy. These dosimetric properties make EDR2 films best suited for IMRT dose distribution measurements.…”