GafChromic HD-810 Research Articles

Gafchromic® film dosimetry for low energy X radiation

Recent developments have produced low energy X ray systems capable of providing a radiation dose to adequate volumes suitable for sterile inset programmes. To support the adoption of these new systems, the performance of the Gafchromic® HD-810 dosimetry system previously used for gamma irradiation needed to be better understood at the lower photon energies. For low energy photons, the optical density of the irradiated Gafchromic HD-810 film dosimeters significantly depends on the material surrounding them. For example, if paper, Mylar® or PVC is used to house the dosimeter during irradiation, the optical density can vary by as much as a factor of three or more for the same dose. This paper is an attempt to elucidate the performance of the Gafchromic HD-810 film dosimeters for such low energy X radiation (∼150 keV). Our data show that this behaviour can be explained by the fact that these materials have significantly different photon mass attenuation coefficient. This conclusion was reinforced with mathematical simulation using Monte Carlo modelling. We also show that with the different structure of another Gafchromic film dosimeter (MD-V2-55) this effect is virtually non-existent. An understanding of the behaviour of thin film dosimeters like Gafchromic HD-810 under radiation is crucial for reliable dosimetry. We hope that this work can also provide guidance in the use of other thin film dosimeters at similar low photon energies.

Study on ion irradiation response of Gafchromic films for the intensity distribution measurement of a large-area beam

It is required to precisely evaluate the large-area transverse intensity distribution of various ion beams applied to materials and biological research at an azimuthally-varying-field cyclotron in Japan Atomic Energy Agency. The response of radiochromic films, Gafchromic HD-810 and EBT2, was, therefore, investigated using proton and several heavy-ion beams for developing a measurement technique of the transverse beam intensity distribution. The optical density of the films increased linearly with the particle fluence of the beam in a low-fluence region. The linear-response range of the fluence was strongly dependent on ion species. By analyzing the film response to absorbed dose, it was found that the sensitivity of the film decreased for heavy-ion beams. The practical fluence range of the Gafchromic film HD-810 for an arbitrary ion beam was determined from the measurement result. The present technique with the use of the two types of Gafchromic films enables us to measure the intensity distribution of a large-area ion beam easily in a wide fluence range. Using the technique, we measured the relative intensity distribution of a large-area ion beam focused by multipole magnets and evaluated its size and uniformity.

Radiochromic film spectroscopy of laser-accelerated proton beams using the FLUKA code and dosimetry traceable to primary standards

AbstractA new approach to spectroscopy of laser induced proton beams using radiochromic film (RCF) is presented. This approach allows primary standards of absorbed dose-to-water as used in radiotherapy to be transferred to the calibration of GafChromic HD-810 and EBT in a 29 MeV proton beam from the Birmingham cyclotron. These films were then irradiated in a common stack configuration using the TARANIS Nd:Glass multi-terawatt laser at Queens University Belfast, which can accelerate protons to 10–12 MeV, and a depth-dose curve was measured from a collimated beam. Previous work characterizing the relative effectiveness (RE) of GafChromic film as a function of energy was implemented into Monte Carlo depth-dose curves using FLUKA. A Bragg peak (BP) “library” for proton energies 0–15 MeV was generated, both with and without the RE function. These depth-response curves were iteratively summed in a FORTRAN routine to solve for the measured RCF depth-dose using a simple direct search algorithm. By comparing resultant spectra with both BP libraries, it was found that the effect of including the RE function accounted for an increase in the total number of protons by about 50%. To account for the energy loss due to a 20 µm aluminum filter in front of the film stack, FLUKA was used to create a matrix containing the energy loss transformations for each individual energy bin. Multiplication by the pseudo-inverse of this matrix resulted in “up-shifting” protons to higher energies. Applying this correction to two laser shots gave further increases in the total number of protons, N of 31% and 56%. Failure to consider the relative response of RCF to lower proton energies and neglecting energy losses in a stack filter foil can potentially lead to significant underestimates of the total number of protons in RCF spectroscopy of the low energy protons produced by laser ablation of thin targets.

A new method of creating minibeam patterns for synchrotron radiation therapy: a feasibility study

Several synchrotrons around the world are currently developing innovative radiotherapy techniques with the aim of palliating and possibly curing human brain tumors. Amongst them, microbeam radiation therapy (MRT) and, more recently, minibeam radiation therapy (MBRT) have shown promising results. In MBRT the beam thickness ranges from 500 to 700 microm with a separation between two adjacent minibeams of the same value, whilst in MRT the thickness is of the order of 25-50 microm with a distance between adjacent microbeams of the order of 200 microm. An original method has been developed and tested at the ESRF ID17 biomedical beamline to produce the minibeam patterns. It utilizes a specially developed high-energy white-beam chopper whose action is synchronized with the vertical motion of the target moving at constant speed. Each opening of the chopper generates a horizontal beam print. The method described here has the advantage of being simple and reliable, and it allows for an easy control of the patient safety in future clinical trials. To study the feasibility of the method, dosimetric measurements have been performed using Gafchromic HD-810 films and compared with Monte Carlo simulations. The results of this comparison are discussed.

Dosimetry during mango irradiation using Gafchromic HD-810 film

The dosimetric characteristics of Gafchromic HD-810 film were evaluated for its possible use as a high-dose dosimeter for routine dosimetry during mango irradiation. The film dosimeter sample of size 2 x 2 cm(2) was used throughout the course of this work. The irradiation of the film dosimeter for characterisation and calibration purposes was carried out in a gamma irradiator. The dose-response of the Gafchromic HD-810 film dosimeter at 550 nm was found to be linear in the dose range 50-1000 Gy, which indicates the feasibility of using this film for dosimetry up to 1000 Gy. The mean inter-dosimeter variation was within 2%, which gives better dose-response consistency of the HD-810 film. The radiation absorbed dose measured by the Gafchromic HD-810 film dosimeter during mango irradiation was compared with that measured by a standard Ceric-cerous dosimeter. This study establishes the Gafchromic HD-810 film as a convenient and technically suitable dosimeter for high-dose dosimetry up to 1.0 kGy during mango irradiation.

Response of radiochromic dye films to low energy heavy charged particles

We have studied the possible use of radiochromic dye films (RCF) as heavy charged particle dosemeters. We present the results of irradiating two commercial RCF (GafChromic HD-810 and MD-55-1) with 1.5, 2.9 and 4.4 MeV protons, 1.4, 2.8, 4.7, 5.9, 6.8 MeV 4He ions and 8.5 and 12.4 MeV 12C ions, at proton doses from about 1 Gy up to 3 kGy, helium ions doses from 3 Gy to 5 kGy and carbon ion doses from 30 Gy to 20 kGy. The films were scanned and digitized using commercial equipment. For a given particle, the response per unit dose at different energies indicates an energy dependence of the sensitivity, which is discussed. Comparison was made for the use of a standard spectrophotometer to obtain optical density readings versus a white light scanner.