Lucio P. Neves

Evaluation and Simulation of a New Ionization Chamber Design for use in Computed Tomography Beams

A newly-designed pencil ionization chamber with a sensitive volume of 3.4 cm3 was evaluated at the Calibration Laboratory of IPEN (São Paulo, Brazil) for use in the dosimetry of computed tomography (CT) medical equipment. The main differences between this CT ionization chamber and the commercial ones are related to the respective design and constituent materials. In the ionization chamber characterized in this work an alternative wall material was tested and a different BNC connector position was evaluated. This novel dosimeter was also designed to have an assembling process as simple and cheap as possible. To estimate the chamber performance, several pre-operational tests were undertaken. The energy dependence test was also evaluated using Monte Carlo simulation with the PENELOPE code system. In addition, Monte Carlo simulations were done to study the influence of various components on the energy deposition in its sensitive volume. The results obtained in the tests showed that the analyzed configuration of the CT ionization chamber is a good alternative for use in CT dosimetry, because it is easy to construct, and it presents a relatively low cost.

Characterization of an extrapolation chamber for low-energy X-rays: Experimental and Monte Carlo preliminary results

The extrapolation chamber is a parallel-plate ionization chamber that allows variation of its air-cavity volume. In this work, an experimental study and MCNP-4C Monte Carlo code simulations of an ionization chamber designed and constructed at the Calibration Laboratory at IPEN to be used as a secondary dosimetry standard for low-energy X-rays are reported. The results obtained were within the international recommendations, and the simulations showed that the components of the extrapolation chamber may influence its response up to 11.0%.

Characterization of a CT ionization chamber for radiation field mapping

A pencil-type ionization chamber, developed at Instituto de Pesquisas Energéticas e Nucleares (IPEN), was characterized with the objective to verify the possibility of its application in radiation field mapping procedures. The characterization tests were evaluated, and the results were satisfactory. The results obtained for the X radiation field mapping with the homemade chamber were compared with those of a PTW Farmer-type chamber (TN 30011-1). The maximum difference observed in this comparison was only 1.25%, showing good agreement.

Characterization of a homemade ionization chamber for radiotherapy beams

A homemade cylindrical ionization chamber was studied for routine use in therapy beams of (60)Co and X-rays. Several characterization tests were performed: leakage current, saturation, ion collection efficiency, polarity effect, stability, stabilization time, chamber orientation and energy dependence. All results obtained were within international recommendations. Therefore the homemade ionization chamber presents usefulness for routine dosimetric procedures in radiotherapy beams.

Application of a Pencil Ionization Chamber (0.34 cm

Ionization chambers are the most utilized dosimeters for precise measurements of absorbed dose, as required e.g., in radiotherapy. The most common type, for this application, is the Farmer type with a wall made of PMMA and/or graphite. With the aim to test new materials and configurations of ionization chambers, using low-cost and easily-available components, this work presents the study of a device developed at the Calibration Laboratory of IPEN (São Paulo). This dosimeter is a pencil-type cylindrical ionization chamber, with a wall of PVC coated with graphite, for routine use in 60Co beams. Following international recommendations, several characterization tests were conducted, and all achieved results were found to fulfill those recommendations. The influence of the chamber components on its response was also studied using the PENELOPE Monte Carlo code. According to the obtained results, this prototype presents potential usefulness for routine dosimetric procedures in radiotherapy.

^{3}

In this study we evaluated the occupational exposures during an abdominal fluoroscopically guided interventional radiology procedure. We investigated the relation between the Body Mass Index (BMI), of the patient, and the conversion coefficient values (CC) for a set of dosimetric quantities, used to assess the exposure risks of medical radiation workers. The study was performed using a set of male and female virtual anthropomorphic phantoms, of different body weights and sizes. In addition to these phantoms, a female and a male phantom, named FASH3 and MASH3 (reference virtual anthropomorphic phantoms), were also used to represent the medical radiation workers. The CC values, obtained as a function of the dose area product, were calculated for 87 exposure scenarios. In each exposure scenario, three phantoms, implemented in the MCNPX 2.7.0 code, were simultaneously used. These phantoms were utilized to represent a patient and medical radiation workers. The results showed that increasing the BMI of the patient, adjusted for each patient protocol, the CC values for medical radiation workers decrease. It is important to note that these results were obtained with fixed exposure parameters.

Volume) for

A cavity ionization chamber, made of PVC coated with graphite, was developed and tested to verify its applicability as a reference dosimeter for 60Co beams. In order to characterize this new ionization chamber, several tests were made, following international recommendations, as saturation, ion collection efficiency, polarity effect, short- and medium-term stabilities, linearity of response, angular dependence and leakage current. All results obtained were within those recommended internationally, showing that this prototype may be used as a dosimetric standard system at the Calibration Laboratory of IPEN.

^{60}

In this work the peak kilovoltage (kVp), practical peak voltage (PPV) and air kerma rate were measured with the noninvasive meters Radcal Accu-kV® Diagnostic Sensor™ model 40×12-W, and PTW Diavolt. The results were compared in order to ensure the quality control, compare the meters and establish the new quantity PPV, at the Calibration Laboratory of IPEN. These tests were performed using the standard diagnostic radiology quality beam RQR5, and the results are in good agreement.

Co Beams: Experimental and Monte Carlo Results

In the event of an environmental contamination with radioactive materials, one of the most dangerous materials is 137Cs. In order to evaluate the radiation doses involved in an environmental contamination of soil, with 137Cs, we carried out a computational dosimetric study. We determined the radiation conversion coefficients (CC) for effective (E) and equivalent (H T) doses, using a male and a female anthropomorphic phantoms. These phantoms were coupled with the MCNPX (2.7.0) Monte Carlo simulation software, for three different types of soil. The highest CC[H T] values were for the gonads and skin (male) and bone marrow and skin (female). We found no difference for the different types of soil.

Occupational exposures during abdominal fluoroscopically guided interventional procedures for different patient sizes — A Monte Carlo approach

New glass matrices were evaluated for high dose dosimetry by the thermoluminescence technique. Their nominal composition are 20Li 2 CO 3 .10Al 2 O 3 .15CdO.55B 2 O 3 and 20Li 2 CO 3 .10Al 2 O 3 .20CdO.50B 2 O 3 (mol%). The glass matrices were irradiated with different doses: 50, 100, 200, 500, 700 and 900 Gy, and the thermoluminescence emission curves were obtained for each of these values. The results show a great potential of using these matrices in high dose dosimetry.