G. Gambarini

Study of light transmittance from layers of Fricke-xylenol-orange-gel dosimeters

In-phantom absorbed dose is imaged by measuring the optical transmittance through ferrous-sulphate and xylenol-orange infused gel, in form of layers. Images are acquired with a CCD camera provided with a suitable optical filter. The dependence of dosimeter sensitivity and of linearity range on the amount of xylenol orange and on parameters of optical analysis has been inspected. In order to check the capability of the method, dose profiles in the central axis of a phantom irradiated with a collimated γ-beam have been compared with the results obtained with a ionisation chamber.

Dose-response curve slope improvement and result reproducibility of ferrous-sulphate-doped gels analysed by NMR imaging

Ferrous sulphate gel analysed by relaxation time measurements with NMR imaging is considered a useful dosimeter for 3D determinations of absorbed dose. A protocol for the gel preparation with agarose SeaPlaque that leads to a dosimeter with very high dose sensitivity is described. The dose-response curve slope is about 0.2 s(-1) Gy(-1) and the G factor turns out to be approximately 185 ions per 100 eV of absorbed energy. A method for making the measurements and analysing the results that brings about good result reproducibility is suggested. A thorough experimental study of the dependence of the dosimeter response on the elapsed time from preparation to irradiation and from irradiation to NMR measurement has revealed good reproducibility. The above characteristic of the gel system is very interesting, because it shows the possibility of utilizing the dosimeter for absolute dose determinations with satisfactory reliability.

Discrimination of various contributions to the absorbed dose in BNCT: Fricke-gel imaging and intercomparison with other experimental results

A method is described for the 3D measurements of absorbed dose in a ferrous sulphate gel phantom, exposed in the thermal column of a nuclear reactor. The method, studied for Boron Neutron Capture Therapy (BNCT) purposes, allows absorbed dose imaging and profiling, with the separation of different contributions coming from different secondary radiations, generated from thermal neutrons. In fact, the biological effectiveness of the different radiations is different. Tests with conventional dosimeters were performed too.

Imaging and profiling of absorbed dose in neutron capture therapy

Imaging and profiling of the absorbed dose in tissue-equivalent gel phantoms exposed to thermal neutrons were performed at the TAPIRO fast reactor (ENEA, Italy). The proposed method, aimed at supporting the planning of neutron capture therapy, allows measurement of three-dimensional distributions of the therapy dose not only in tumors but also in normal tissue. This feature is very important, because the value of the maximum fluence admitted for therapy is limited by the dose absorbed in the healthy tissue. Fricke-infused gel phantoms were designed that allow imaging of the absorbed dose by means of optical analysis, based on the detection of visible-light absorbance with a charge-coupled device camera. Moreover, the various components of the secondary radiation contributing to the dose can be separated through the differential analysis of images obtained with gels with different elemental compositions. Dose mapping in a phantom was also performed with thermoluminescent dosimeters (TLDs). A method for separating the different dose contributions was studied, based on the analysis of the glow-curve shapes of different kinds of TLDs. The agreement of the results obtained with the two techniques confirmed the validity of the methods. Fluence measurements performed with activation techniques and Monte Carlo simulations gave further support.

In vivo rectal wall measurements during HDR prostate brachytherapy with MOSkin dosimeters integrated on a trans-rectal US probe: Comparison with planned and reconstructed doses.

BACKGROUND AND PURPOSE To study if MOSkin detectors coupled to a trans-rectal ultrasound (TRUS) probe may be used for in vivo dosimetry on the rectal wall surface during US-based HDR prostate brachytherapy and to quantify possible discrepancies between planned and delivered doses. MATERIALS AND METHODS MOSkins are a specific type of MOSFET dosimeter optimized to measure dose in steep dose gradients on interfaces. Two MOSkins were assembled on a TRUS probe used for on-line treatment planning. Measurements of the dose to the rectal wall were performed over 18 treatment sessions and compared to the doses calculated on the pre-treatment plan (DPRE) and reconstructed on post-treatment images (DPOST). RESULTS Averages of the absolute differences between MOSkin readings and DPRE, MOSkin readings and DPOST and DPRE and DPOST were 6.7 ± 5.1%, 3.6 ± 1.9% and 6.3 ± 4.7%, respectively. Agreement between measurements and DPOST was significantly better than between measurements and DPRE (p=0.002) and DPRE and DPOST (p=0.004). Discrepancy between DPOST and DPRE correlated with the time required for treatment planning. CONCLUSION MOSkin dosimeters integrated to the TRUS probe proved to be an accurate instrument for measuring the dose delivered to the rectal wall in HDR prostate brachytherapy. The delivered doses may differ significantly from those calculated in the treatment plan.

Online in vivo dosimetry in high dose rate prostate brchytherapy with MOSkin detectors: in phantom feasibility study.

MOSkin detectors were studied to perform real-time in vivo dose measurements in high dose rate prostate brachytherapy. Measurements were performed inside an urethral catheter in a gel phantom simulating a real prostate implant. Measured and expected doses were compared and the discrepancy was found to be within 8.9% and 3.8% for single MOSkin and dual-MOSkin configurations, respectively. Results show that dual-MOSkin detectors can be profitably adopted in prostate brachytherapy treatments to perform real-time in vivo dosimetry inside the urethra.

Evaluation of all dose components in the LVR-15 reactor epithermal neutron beam using Fricke gel dosimeter layers

Fricke gel dosimeters in the form of layers are suitable to reconstruct bidimensional distributions of the absorbed dose; in accordance with their chemical composition and applying suitably developed algorithms, they can provide dose images of the different radiation components in a BNCT field. After the description of the applied method, this work presents the results obtained at the epithermal column of the BNCT facility at the NRI in Rez (CZ). The measured dose distributions are shown in comparison with data taken by means of other dosimeters thermoluminescence dosimeters (TLDs) and with calculations carried out with the Monte Carlo code MCNP5. The agreement with the results obtained by means of the different techniques is satisfying.

Proton nuclear activation in stable tracer technique for ruthenium metabolism studies

Abstract A methodology is presented, based on proton nuclear activation (PNA), for the contemporary determination of two stable isotopes of ruthenium in biological samples. This technique can be successfully applied in studying the biokinetics of oligoelements, avoiding radiation hazards. On the basis of the possible proton-induced nuclear reactions and the decay characteristics of radioactive products, (p, n) reactions on 99 Ru and 101 Ru resulted to be the most convenient. The minimum detectable quantities resulted to be 15 and 3 ng/ml of plasma respectively. Ru fractional intestinal absorption in an experimental animal was determined, as a feasibility test for applications to humans. Following double tracer technique, one male rabbit was orally given 1 mg of 99 Ru and was injected 78 μg of 101 Ru. Eleven blood samples were drawn within 300 min after administration. Concentrations in plasma samples of intravenously and orally given Ru tracers are reported, as a function of time after administration. Fractional intestinal absorption was determined from concentrations of both isotopes, using the convolution integral technique. A Ru intestinal absorption of (5.5 ± 0.8)% within 300 min from the oral administration was obtained. The results show the effectiveness of this methodology and its applicability for future investigations in humans.

A system for 3-D absorbed dose measurements with tissue-equivalence for thermal neutrons

Abstract A ferrous sulphate gel with a proper composition to thermalise epithermal neutrons with tissue equivalence with brain tissue gives the possibility of making phantoms which act as a continuous dosimeter for the gamma radiation, with the possibility of 3-D dose determination. If in the phantom a volume of gel containing 10 B (in the amount typical for BNCT) is set, information on the absorbed dose in the tumour site may also be drawn.

Solid state TL detectors for in vivo dosimetry in brachytherapy

In vivo dosimetry provides information about the actual dose delivered to the patient treated with radiotherapy and can be adopted within a routinary treatment quality assurance protocol. Aim of this study was to evaluate the feasibility of performing in vivo rectal dosimetry by placing thermoluminescence detectors directly on the transrectal ultrasound probe adopted for on-line treatment planning of high dose rate brachytherapy boosts of prostate cancer patients. A suitable protocol for TLD calibration has been set up. In vivo measurements resulted to be in good agreement with the calculated doses, showing that the proposed method is feasible and returns accurate results.