Search results for "DOSIMETRY"

SU-F-T-63: Dosimetric Relevance of the Valencia and Leipzig HDR Applicators Plastic Cap

2016

Purpose: Utilization of HDR brachytherapy treatment of skin lesions using collimated applicators, such as the Valencia or Leipzig is increasing. These applicators are made of cup-shaped tungsten material in order to focalize the radiation into the lesion and to protect nearby tissues. These applicators have an attachable plastic cap that removes secondary electrons generated in the applicator and flattens the treatment surface. The purpose of this study is to examine the dosimetric impact of this cap, and the effect if the cap is not placed during the HDR fraction delivery. Methods: Monte Carlo simulations have been done using the code Geant4 for the Valencia and Leipzig applicators. Dose r…

SU-E-T-516: Limitations and Clinical Implications of the TG-43 Formalism for High-Dose-Rate Skin Brachytherapy

2013

Purpose: In high‐dose‐rate (HDR) skin brachytherapy, sources are located outside, in contact with, or implanted at some depth below the skin surface. Nowadays, most TPS use the TG‐43 formalism that is based on sources within an infinite water medium, without accounting for the scatter defect due to surrounding air. The purpose of the present study is to evaluate the limitations of the TG‐43 formalism in HDR skin brachytherapy. Methods: This study examined two HDR sources (Ir‐192 and Co‐60) together with a hypothetical Yb‐169 source. Dose distributions were obtained using Monte Carlo methods (i.e., GEANT4). The following configurations were investigated: 1)A typical clinical case consisting …

Design and characterization of a new high-dose-rate brachytherapy Valencia applicator for larger skin lesions

2016

Purpose: The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a 192Ir source; (ii) to calculate by means of the Monte Carlo(MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water. Methods: The penelope2008MC code was used to optimize dwell positions and dwell times. Next, the dose distribution in a water phantom and the leakage dose distribution arou…

Calibration of a thermoluminescent dosimeter worn over lead aprons in fluoroscopy guided procedures

2018

Fluoroscopy guided interventional procedures provide remarkable benefits to patients. However, medical staff working near the scattered radiation field may be exposed to high cumulative equivalent doses, thus requiring shielding devices such as lead aprons and thyroid collars. In this situation, it remains an acceptable practice to derive equivalent doses to the eye lenses or other unprotected soft tissues with a dosimeter placed above these protective devices. Nevertheless, the radiation backscattered by the lead shield differs from that generated during dosimeter calibration with a water phantom. In this study, a passive personal thermoluminescent dosimeter (TLD) was modelled by means of …

Phenol compounds as new materials for electron spin resonance dosimetry in radiotherapy

2016

Physics Contributions Evaluation of interpolation methods for TG-43 dosimetric parameters based on comparison with Monte Carlo data for high-energy b…

2010

Purpose: The aim of this work was to determine dose distributions for high-energy brachytherapy sources at spa- tial locations not included in the radial dose function gL(r) and 2D anisotropy function F(r,θ) table entries for radial dis- tance r and polar angle θ. The objectives of this study are as follows: 1) to evaluate interpolation methods in order to accurately derive gL(r) and F(r,θ) from the reported data; 2) to determine the minimum number of entries in gL(r) and F(r,θ) that allow reproduction of dose distributions with sufficient accuracy. Material and methods: Four high-energy photon-emitting brachytherapy sources were studied: 60Co model Co0.A86, 137Cs model CSM-3, 192Ir model I…

SU-E-T-530: Comparison of Analytical and Monte Carlo Calculations for Heterogeneity Corrections in LDR Prostate Brachytherapy

2013

Purpose: It is well‐known that tissue heterogeneities and calcifications have significant influence on low energy brachytherapy. The aim of this work is to study the application of a simplified analytic algorithm that could be compatible with commercial Treatment Planning System (TPS) based on TG‐43. The algorithm, based on the classic equivalent path length method, has been compared with Monte Carlo (MC) computations using Penelope2009. Methods: The analytical model scales the distance from the seed to the calculation point according to the electronic density of the medium relative to water. Then, the dose is calculated from TG‐43 consensus data (stored on a TPS) by scaling the radial dose…

Characterization of phenolic pellets for ESR dosimetry in photon beam radiotherapy

2017

This work deals with the dosimetric features of a particular phenolic compound (IRGANOX 1076 ® ) for dosimetry of clinical photon beams by using electron spin resonance (ESR) spectroscopy. After the optimization of the ESR readout parameters (namely modulation amplitude and microwave power) to maximise the signal without excessive spectrum distortions, basic dosimetric properties of laboratory-made phenolic dosimeters in pellet form, such as reproducibility, dose–response, sensitivity, linearity and dose rate dependence were investigated. The dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam. A satisfactory intra-batch reproducibility of the ESR signal of the …

Dose determination using alanine detectors in a mixed neutron and gamma field for boron neutron capture therapy of liver malignancies

2011

IntroductionBoron Neutron Capture Therapy for liver malignancies is being investigated at the University of Mainz. One important aim is the set-up of a reliable dosimetry system. Alanine dosimeters have previously been applied for dosimetry of mixed radiation fields in antiproton therapy, and may be suitable for measurements in mixed neutron and gamma fields.Materials and MethodsTwo experiments have been carried out in the thermal column of the TRIGA Mark II reactor at the University of Mainz. Alanine dosimeters have been irradiated in a phantom and in liver tissue.ResultsFor the interpretation and prediction of the dose for each pellet, beside the results of the measurements, calculations …

MONTE CARLO SIMULATIONS OF THE RESPONSE OF ESR DOSIMETERS TO NEUTRON BEAMS

2009

Electron Spin Resonance (ESR) spectroscopy is extensively used in gamma photon dosimetry. It relies on the detection of the signal from free radicals (paramagnetic species) produced after sample irradiation. Organic materials, such as alanine and ammonium tartrate, are widely used for dosimeter preparation, thanks to the good photon sensitivity and tissue equivalence of such compounds. However, the low neutron cross section of their nuclei does not make them suitable for neutron dosimetry. Thanks to its very high neutron capture cross section and to the high Linear Energy Transfer of released particles, even small additions of gadolinium will yield large sensitivity enhancements of the dosi…