title: Energy dependence of response of new high sensitivity radiochromic films for megavoltage and kilovoltage radiation energies.
abstract: The purpose of this paper is to evaluate the energy dependence of the response of two new high sensitivity models of radiochromic films EBT and XR-QA. We determined the dose response curves of these films for four different radiation sources, namely, 6 MV photon beams (6 MVX), Ir-192, I-125, and Pd-103. The first type (EBT) is designed for intensity modulated radiation therapy (IMRT) dosimetry, and the second type (XR-QA) is designed for kilovoltage dosimetry. All films were scanned using red (665 nm) and green (520 nm) light sources in a charge-coupled device-based densitometer. The dose response curves [net optical density (NOD) versus dose] were plotted and compared for different radiation energies and light sources. Contrary to the early GAFCHROMIC film types (such as models XR, HS, MD55-2, and HD810), the net optical densities of both EBT and XR-QA were higher with a green (520 nm) than those with a red (665 nm) light source due to the different absorption spectrum of the new radiochromic emulsion. Both film types yield measurable optical densities for doses below 2 Gy. EBT film response is nearly independent of radiation energy, within the uncertainty of measurement. The NOD values of EBT film at 1 and 2 Gy are 0.13 and 0.25 for green, and 0.1 and 0.17 for red, respectively. In contrast, the XR-QA film sensitivity varies with radiation energy. The doses required to produce NOD of 0.5 are 6.9, 5.4, 0.7, and 0.9 Gy with green light and 19, 13, 1.7, and 1.5 Gy with red light, for 6 MVX, Ir-192, I -125, and Pd-103, respectively. EBT film was found to have minimal photon energy dependence of response for the energies tested and is suitable for dosimetry of radiation with a wide energy spectrum, including primary and scattered radiation. XR-QA film is promising for kilovoltage sources with a narrow energy spectra. The new high sensitivity radiochromic films are promising tools in radiation dosimetry.
authors.affiliation: Radiation Oncology Department, Beth Israel Medical Center and St. Luke's-Roosevelt Hospital Center, New York, New York 10003, USA. schiutsa@chpnet.org
authors.forename: Sou-Tung
authors.initials: ST
authors.lastname: Chiu-Tsao
authors.forename: Yunsil
authors.initials: Y
authors.lastname: Ho
authors.forename: Ravi
authors.initials: R
authors.lastname: Shankar
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Louis B
authors.initials: LB
authors.lastname: Harrison
mesh_terms: D003720:Densitometry / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D005373:Film Dosimetry / Q000379:methods*; D007457:Iodine Radioisotopes; D007496:Iridium Radioisotopes; D010165:Palladium; D017785:Photons; D011827:Radiation; D011829:Radiation Dosage; D011868:Radioisotopes; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014962:X-Ray Film
chemical_list: D007457:Iodine Radioisotopes; D007496:Iridium Radioisotopes; D011868:Radioisotopes; D010165:Palladium