D. Alonso

A comprehensive study of the Gafchromic EBT2 radiochromic film. A comparison with EBT

PURPOSE Radiochromic film has become an important tool to assess complex dose distributions. In particular, EBT was accepted by the scientific community as a reference two-dimensional detector. Recently, Gafchromic EBT2 has replaced old film, providing new improvements in both accuracy and handling. METHODS This work presents a dosimetric study of the new Gafchromic EBT2 using an Epson 10000XL flatbed scanner, also comparing the results with EBT film as reference when necessary. The most important film characteristics have been studied, such as ambient light sensitivity, different possibilities of the three RGB color channels, postirradiation development, high dose behavior, exposition at temperatures similar to the human body, and dependence on orientation during the scanning process. RESULTS The results obtained confirm a considerably lower sensitivity to ambient light of EBT2, as well as a fast stabilization of the film within 2 h. It has also been found that the green channel has a better behavior at high dose levels up to 35 Gy, in addition to good behavior of the red channel at doses below 10 Gy. Other features, such as temperature independence and scanning orientation dependence, have also been shown. CONCLUSIONS Gafchromic EBT2 can be used for clinical practice in the same way as the old EBT film. However, a much easier handling as the result of all new enhancements improves film behavior, expanding in this way the potential applications of radiochromic film dosimetry.

Patient doses and occupational exposure in a hybrid operating room

PURPOSE This study aimed to characterize the radiation exposure to patients and workers in a new vascular hybrid operating room during X-ray-guided procedures. METHODS During one year, data from 260 interventions performed in a hybrid operating room equipped with a Siemens Artis Zeego angiography system were monitored. The patient doses were analysed using the following parameters: radiation time, kerma-area product, patient entrance reference point dose and peak skin dose. Staff radiation exposure and ambient dose equivalent were also measured using direct reading dosimeters and thermoluminescent dosimeters. RESULTS The radiation time, kerma-area product, patient entrance reference point dose and peak skin dose were, on average, 19:15min, 67Gy·cm2, 0.41Gy and 0.23Gy, respectively. Although the contribution of the acquisition mode was smaller than 5% in terms of the radiation time, this mode accounted for more than 60% of the effective dose per patient. All of the worker dose measurements remained below the limits established by law. CONCLUSIONS The working conditions in the hybrid operating room HOR are safe in terms of patient and staff radiation protection. Nevertheless, doses are highly dependent on the workload; thus, further research is necessary to evaluate any possible radiological deviation of the daily working conditions in the HOR.

131I activity in urine to the sewer system due to thyroidal treatments.

In nuclear medicine, estimating the radioactivity contained in the urine of patients treated with 131I and discharged to the environment could prevent the exposure of a population to radioactive effluents and the pollution of the aquatic environment with ionizing radiation. This can be a regulatory requirement (as in Spain) or requested by the sewer authority. Seventy-nine differentiated thyroid cancer cases (undergone as inpatients) and 187 hyperthyroidism cases (undergone as outpatients) were treated in our hospital with 131I throughout the year 2009. In hyperthyroidism treatments, the effective elimination constant was used to calculate the corresponding discharged activity in the urine, giving an activity level always bellow 0.7 GBq. In differentiated thyroid cancer treatments, patients urine was collected in storage tanks during the hospitalization. Measurements of external exposure at 1 m made every day were used to calculate the activity contained in the urine. The tank activity was always below 15 GBq, but always higher than 2 GBq. Obtained results show that effective doses to sewage workers, received from liquid discharges, can only be reduced to less than 10 &mgr;Sv if storage tanks are installed. Without tanks, 157 &mgr;Sv can be reached, above the constrain dose used in nuclear installations (100 &mgr;Sv). Our calculations may be helpful to the regulatory authority to review the clinical radiation waste normative, especially in countries where the discharges are released directly into public sewage plants.

Virtual instrument to obtain an optimal linear model for piezoelectric elements involved in road traffic energy harvesting

A new Virtual Instrument (VI) system is presented in this paper. The VI is designed to obtain the linear electrical models of the piezoelectric elements involved in energy harvesting applications in road traffic environments. The system, the modelling and the verification methodology are described in this paper, comparing the obtained results. The piezoelectric devices under test (PDUT) are mechanically driven by a test bench, which simulates the effect of heavy or light vehicles passing over a lane in a real road. Parameters such as the traffic flow rate and vehicle speed are configurable. In addition, the VI system controls the specific hardware designed to store the energy with different harvesting topologies. The VI system described in this paper is able to parameterize the test and to control both the test bench and the harvesting hardware. It also conditions and measures electrical signals from the PDUT, and obtains the electrical model of the piezoelectric element. Using this model it is possible to scale both the number of elements and find the optimal topology needed to harvest the required energy by an electronic load. The Virtual Instrument controls an automatized measurement system and a power system even with a low expertise of the user.The VI controls with a friendly user interface our designed Harvesting Electronic Hardware and our patented test bench.The methodology presented is able to characterize several harvesting topologies and connections.The designed procedure obtains the previously unknown piezoelectric elements key parameters in road traffic environments.The VI developed calculates the Fourier model limiting the relative error between original and reconstructed signals.

An approach to vmat on radiation therapy treatments of pelvic and paraaortic lymph nodes

Abstract Introduction When large volumes need to be irradiated multiple organs at risk are involved. There is no doubt about the preeminence for conformal index and sparing of critical structures for VMAT, but an alternative regarding the use of single or multiple isocenter shows a subject for detailed analysis. Purpose To compare VMAT in treatment of pelvic and paraaortic lymph nodes using single or double isocenter. Materials and Methods A set of five patients are selected. For every patient an expert radiation oncologist contoured on CT images volumes and organs according to the RTOG guidelines. Plans were done in Eclipse 11 using Accuros XB algorithm for 6MV X-rays from a Clinac 2100-120MLC, using VMAT double full rotation arc with collimator rotation 30°-330°. For isocenter placement the Arc Geometric tool are used, for double isocenter only we allowed only longitudinal couch movement between isocenters. The same plan objectives are used for every single isocentre plan, but for organs at risk adjustments are made during optimization in order to get the best result for each case. When using double isocentre the VMAT paraoortic plan is used as dose base for VMAT pelvic optimization. Results Single isocenter shows higher irradiated volumes V5 are 1–2% and V20 up to 14%, sparing for liver and kidneys are improve for the double isocenter but with an average increase of 10% in monitor units each plan. Conclusion Double isocenter plan improves organ sparing but worse PTV dose homogeneity. Disclosure No conflicts of interest to declare.