Abstract. A software program, SpekCalc, is presented, for the calculation of x-ray 15

By comparing the resultant change in net absorbance between the latest EBT-2 and previous EBT GAFCHROMIC film models, the authors conclude that the addition of the yellow marker dye to the sensitive layer does not affect dosimetric properties of the latest film model. The authors also describe a procedure by which one can establish an acceptable time window around chosen postirradiation scanning time protocol that would provide an acceptable dose error for practical purposes.

The energy response of films in the energy range <100 keV can be improved by adjusting the active layer chemical composition. Removing bromine eliminated the over response at about 40 keV. The under response at energies ≤ 30 keV is improved by adding 7% Al to the active layer in the latest commercial EBT3 film models.

Radiochromic film dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one-sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on film exposure calibration in terms of "air kerma in air," which simplifies both the calibration procedure and reference dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR-QA film dose at the surface into dose to water (or water kerma) at the surface of the phantom indicate that, for typical beam qualities used in CBCT, this conversion can be approximated by simple mass-energy absorption coefficient ratios water-to-air.

In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic film based reference dosimetry system. In this way, relative dosimetry can be conveniently performed using radiochromic film dosimetry system without the need of establishing calibration curve.

Kilovolt x-rays are clearly suboptimal compared to MV photon beams for radiotherapy of deep-seated tumours because of the increased attenuation in tissue, causing a rapid dose fall-off. This picture could change drastically when tumours can be labelled with contrast medium, containing high atomic number elements. This causes a significant dose enhancement to the tumour by exploiting the high cross sections for the photo-electric effect for kV x-rays. In this work, we have investigated the dosimetric and microdosimetric characteristics of kV contrast-enhanced radiation therapy (CERT) for different photon energies, contrast-medium concentrations and types (I and Gd). Two idealized patient treatment plans (head and lung) for irradiation with CT-arc beams were calculated. It is shown that the dose enhancement in tumours can be highly significant (up to about sixfold for realistic 80-120 kVp x-ray spectra and an iodine concentration of 50 mg ml-1) but that dose homogeneity in the tumour depends on photon energy, contrast-medium concentration and type, and irradiation scheme. An attempt to optimize the irradiation scheme is discussed. The microdosimetric study of the dose mean lineal energy shows that radiation quality changes in the contrast-medium-labelled region compared to homogeneous tissue are fairly small and limited to 10%. It is concluded that kV-CERT is a promising radiotherapy technique, provided contrast medium can be delivered reliably to tumours.

Recent work has shown that there is significant uncertainty in measuring build-up doses in mega-voltage photon beams especially at high energies. In this present investigation we used a phantom-embedded extrapolation chamber (PEEC) made of Solid Water to validate Monte Carlo (MC)-calculated doses in the dose build-up region for 6 and 18 MV x-ray beams. The study showed that the percentage depth ionizations (PDIs) obtained from measurements are higher than the percentage depth doses (PDDs) obtained with Monte Carlo techniques. To validate the MC-calculated PDDs, the design of the PEEC was incorporated into the simulations. While the MC-calculated and measured PDIs in the dose build-up region agree with one another for the 6 MV beam, a non-negligible difference is observed for the 18 MV x-ray beam. A number of experiments and theoretical studies of various possible effects that could be the source of this discrepancy were performed. The contribution of contaminating neutrons and protons to the build-up dose region in the 18 MV x-ray beam is negligible. Moreover, the MC calculations using the XCOM photon cross-section database and the NIST bremsstrahlung differential cross section do not explain the discrepancy between the MC calculations and measurement in the dose build-up region for the 18 MV. A simple incorporation of triplet production events into the MC dose calculation increases the calculated doses in the build-up region but does not fully account for the discrepancy between measurement and calculations for the 18 MV x-ray beam.

A radiochromic film based dosimetry system using only the green color channel of a flatbed document scanner showed superior precision if used alone in a dose range that extends up to 50 Gy, which greatly decreases the complexity of work. In addition, Solid Water™ material was shown to be a viable alternative to water in performing radiochromic film based dosimetry with HDR (192)Ir brachytherapy sources.