Energy dependence of radiochromic dosimetry films for use in radiotherapy verification

Aim

The purpose of the study was to examine the energy dependence of Gafchromic EBT radiochromic dosimetry films, in order to assess their potential use in intensity-modulated radiotherapy (IMRT) verifications.

Materials and methods

The film samples were irradiated with doses from 0.1 to 12 Gy using photon beams from the energy range 1.25 MeV to 25 MV and the film response was measured using a flat-bed scanner. The samples were scanned and the film responses for different beam energies were compared.

Results

A high uncertainty in readout of the film response was observed for samples irradiated with doses lower than 1 Gy. The relative difference exceeds 20% for doses lower than 1 Gy while for doses over 1 Gy the measured film response differs by less than 5% for the whole examined energy range. The achieved uncertainty of the experimental procedure does not reveal any energy dependence of Gafchromic EBT film response in the investigated energy range.

Conclusions

Gafchromic EBT film does not show any energy dependence in the conditions typical for IMRT but the doses measured for pre-treatment plan verifications should exceed 1 Gy.     

Calculation and measurement of doses in the surface layers of a phantom when using Tomotherapy

BackgroundThe calculation and measurement on the surface of the skin presents a significant dosimetric problem because of numerous factors which have an influence on the dose distribution in this region.AimThe overall aim of this study was to check the agreement between doses measured with thermoluminescent detectors (TLD) during tomotherapy photon beam irradiation of the skin area of a solid water cylindrical phantom with doses calculated with Hi-Art treatment planning system (TPS).Material and MethodThe measurements of the dose were made with the use of a solid water cylindrical phantom - Cheese Phantom. Two bolus phantoms were used: 5 mm and 10 mm Six different planning treatments were generated. The doses were measured using TL detectors.ResultsIn the case of a tumor located near the surface of the skin, the mean dose for 0.5 cm bolus was - 1.94 Gy, and for 1 cm bolus - 2.03 Gy. For the tumor located inside the phantom and organ at risk on the same side that TL detectors, for a 0.5 cm bolus, mean dose was 0.658 Gy, and for a 1 cm bolus, 0.62 Gy.ConclusionThe analysis of results showed that the relative percentage difference between measured and planned dose in the field of irradiation was less than 10%, while the largest differences were on the board of the field of radiation and outside of the field of irradiation, where the dose was 0.08 Gy to 1 Gy.     

A comparative assessment of the changes in absorbed neutron doses and in the frequency of chromosome aberrations in samples of human blood lymphocytes by the depth of the water phantom during irradiation by the biomedical BR-10 reactor beam

Distribution of the chromosome aberration frequency in human blood lymphocyte samples and absorbed doses have been compared by the water phantom depth during irradiation with 1.5 Gy neutrons (mean energy of 0.85 MeV). There is a good concordance of their depth distribution. The half-fall layer of the absorbed dose within the tissue-equivalent medium is similar (approximately 5 cm) with both measurements done. The aberration frequency in the biological samples placed outside the radiation field in the phantom increases which indicates that the neutron been bounds are indistinct upon passing the tissue-equivalent medium.