A hybrid radiation detector for simultaneous spatial and temporal dosimetry

In this feasibility study an organic plastic scintillator is calibrated against ionisation chamber measurements and then embedded in a polymer gel dosimeter to obtain a quasi-4D experimental measurement of a radiation field. This hybrid dosimeter was irradiated with a linear accelerator, with temporal measurements of the dose rate being acquired by the scintillator and spatial measurements acquired with the gel dosimeter. The detectors employed in this work are radiologically equivalent; and we show that neither detector perturbs the intensity of the radiation field of the other. By employing these detectors in concert, spatial and temporal variations in the radiation intensity can now be detected and gel dosimeters can be calibrated for absolute dose from a single irradiation

Nanoscience and nanotechnology research publications : a comparison between Australia and the rest of the world

Nanoscience and nanotechnology are research areas of a multidisciplinary nature. Having a good knowledge of the rapidly evolving nature of these research areas is important to understand the research paths, as well as national and global developments in these areas. Accordingly, in this reported study nanoscience and nanotechnology research undertaken globally was compared with that of Australia by way of analyzing research publications. Initially, four different bibliometric Boolean-based search methodologies were used to analyze publications in the Web of Science database (Thomson Reuters ISI Web of Knowledge). These methodologies were (a) lexical query, (b) search in nanoscience and nanotechnology journals, (c) combination of lexical query and journal search and (d) search in the ten nano-journals with the highest impact factors. Based on results obtained, the third methodology was found to be the most comprehensive approach. Consequently, this search methodology was used to compare global and Australian nanoscience and nanotechnology publications for the period 1988-2000. Results demonstrated that depending on the search technique used, Australia ranks fourteenth to seventeenth internationally with a higher than world average number of nanoscience and nanotechnology publications. Over the last decade, Australia showed a relative growth rate in nanoscience and nanotechnology publications of 16 % compared to 12 % for the rest of the world. Researchers from China, the USA and the UK are from the main countries that collaborate with Australian researchers in nanoscience and nanotechnology publications.28 page(s

Monte Carlo water-equivalence study of two PRESAGE® formulations for proton beam dosimetry

Monte Carlo water-equivalence study of two PRESAGE® formulations for proton beam dosimetry5 page(s

Evaluation of Temperature Rise and Thermal Lesion Dimensions in Liver Laser Interstitial Thermotherapy

Introduction:  Laser  interstitial  thermotherapy  (LITT)  is  an  internal  ablation  therapy  method  consisting of a percutaneous or intraoperative insertion of laser fibers directly into the liver tumor with  maximum diameter of 5 cm. In this treatment method, there isn’t any general information about the  relationship  between  increasing  the  exposure  power,  coagulation  and  carbonization  areas  with  the  changes  in  temperature.  In  this  study,  according  to  the  power  range  of  LITT  the  changes  in  the  temperature of liver tissue and the diameter of the necrotic area were measured.   Materials and Methods: In vitro LITT was performed on fleshly sheep liver tissue using a bare-tip  optical  fiber  from  a  Nd:Yag  laser.  A  power  setting  of  2,  2.4,  3,  3.4,  and  4  watt  were  used  for  an  exposure time of 300 sec. The temperature monitoring was performed during the heating and cooling  down by fixing micro thermocouples at 2.5 mm from the fiber tip. The thermal lesions which include  necrosis and carbonization areas were compared for each power.   Results: The result of the temperature monitoring was expressed as the mean value for each power.  The temperature charts show that at 2.5 mm from the fiber tip the max. tissue temperature is increased  from 276.20 ºC (for a power setting of 2 watt and a 308 sec of exposure time) to 728.2 ºC (for a power  setting of 3.4 watt and a 365 sec exposure time). At 6 mm from the fiber tip the max. temperature was  measured to be 86.4 ºC for  a power setting of 4 watt and 325 sec exposure time. For each power a non  linear  regression  analysis  was  performed  during  the  heating  and  cooling  down  for  the  dependent  (temperature) and independent (time) parameters. The max. value for the cubic equation is shown to be  R = 0.99 during the heating and for the exponential equation to be R = 0.89 during the cooling down.  A p value of 0.01 is considered significant. The diameter of the necrotic liver tissue increases from  12.95  mm  at  600  joules  to  16.15  mm  at  1200  joules  of  energy.  When  the  total  applied  energy  is  increased  from  600  to  1200  joules,  the  thermal  ablation  increased  by  25%  while  there  was  a  56%  increase  in  the  carbonization  area.    Increasing  the  carbonization  area  caused  a  decreases  in  the  penetrability of the laser beam.   Discussion and Conclusion: A useful treatment planning based on a non-linear regression analysis  could  be  prepared  for  the  treatment  of  hepatocellular  carcinoma.  In  this  analysis,  the  temperature  changes in the necrotic area are monitored as a function of power setting in the range of 2-4 watts in  LITT

Water equivalence of micelle gels for x-ray beams

Micelle gel is a radiochromic hydrogel with the potential to be used as a three dimensional (3D) radiation dosimeter. Since an ideal dosimeter should present water equivalent properties, in this study the water equivalence of two formulations of micelle gel has been investigated by calculating electron density, effective atomic number, fractional interaction probabilities, mass attenuation coefficient. The depth doses for kilovoltage and megavoltage x-ray beams have also modelled using Monte Carlo code. Based on the results of this work, micelle gels can be considered as water equivalent dosimeters.5 page(s

Preliminary characterization of PRESAGE® for 3D dosimetry of 62 MeV proton beam

PRESAGE® has previously shown potential for 3D dosimetry of heavy particles. A new formulation has specifically developed for dosimetry of protons/heavy ions. This work provides a preliminary characterization the new formulation of PRESAGE® by measuring optical absorbance and dose response after irradiating by a 62 MeV proton beam for a dose range of 0.5 - 20 Gy. Results show linear dose response and the evolution over time of the optical density of the 3D dosimeter.4 page(s

Issues involved in the quantitative 3D imaging of proton doses using optical CT and chemical dosimeters.

Dosimetry of proton beams using 3D imaging of chemical dosimeters is complicated by a variation with proton linear energy transfer (LET) of the dose-response (the so-called 'quenching effect'). Simple theoretical arguments lead to the conclusion that the total absorbed dose from multiple irradiations with different LETs cannot be uniquely determined from post-irradiation imaging measurements on the dosimeter. Thus, a direct inversion of the imaging data is not possible and the proposition is made to use a forward model based on appropriate output from a planning system to predict the 3D response of the dosimeter. In addition to the quenching effect, it is well known that chemical dosimeters have a non-linear response at high doses. To the best of our knowledge it has not yet been determined how this phenomenon is affected by LET. The implications for dosimetry of a number of potential scenarios are examined.Dosimeter response as a function of depth (and hence LET) was measured for four samples of the radiochromic plastic PRESAGE(®), using an optical computed tomography readout and entrance doses of 2.0 Gy, 4.0 Gy, 7.8 Gy and 14.7 Gy, respectively. The dosimeter response was separated into two components, a single-exponential low-LET response and a LET-dependent quenching. For the particular formulation of PRESAGE(®) used, deviations from linearity of the dosimeter response became significant for doses above approximately 16 Gy. In a second experiment, three samples were each irradiated with two separate beams of 4 Gy in various different configurations. On the basis of the previous characterizations, two different models were tested for the calculation of the combined quenching effect from two contributions with different LETs. It was concluded that a linear superposition model with separate calculation of the quenching for each irradiation did not match the measured result where two beams overlapped. A second model, which used the concept of an 'effective dose' matched the experimental results more closely. An attempt was made to measure directly the quench function for two proton beams as a function of all four variables of interest (two physical doses and two LET values). However, this approach was not successful because of limitations in the response of the scanner