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3D dose distributions are calculated for a 32 P impregnated stent and a 198 Au stent for intravascular brachytherapy with the EGS4 Monte Carlo simulation code. The stents were modeled as a combination of eight helicoidal struts. This allowed investigation of the effect of the stent geometry and the electron absorption in the strut material on the dose distributions. Absorbed dose to water was calculated at radial distances ranging from 50 μm to 5 mm from the stent surface. The dose distributions around the stents are compared to the dose distribution around an intravascular brachytherapy 192 Ir source, also calculated with the EGS4 Monte Carlo code. The dose profiles near the struts show hot spots. At 50 μm distance a peak to valley ratio of 3 for 32 P and 6 for 198 Au in the dose distribution is obtained. For both the isotopes the inhomogeneities decrease with distance and at a radial depth of 350 μm the effect becomes negligible. The calculations showed the importance of the effect of the absorption in the stent material as this leads to a dose decrease to 67% for the 198 Au stent and to 77% for 32 P near the stent at a distance of 2 mm from the stent axis. It is concluded that from the dosimetric point of view, the 198 Au stent is inferior to the 32 P stent and the 192 Ir source. Application of the 198 Au stent in clinical practice requires further investigation of the importance of the adventitia in the restenosis process, and the tolerance dose of the intima.

Low energy photons are more and more in use in clinical practice, for treatment in radiotherapy as well as for imaging purposes. Their relative biological effectiveness is however still debated. In this paper, some microdosimetric parameters have been calculated for different sources: (125)I, (103)Pd, (131)Cs, an electronic brachytherapy source and various clinical mammography X-ray qualities. These parameters have been used to deduce the quality factors as defined in ICRU 40.

The micronucleus assay in human lymphocytes is, at present, frequently used to assess chromosomal damage caused by ionizing radiation or mutagens. Manual scoring of micronuclei (MN) by trained personnel is very time-consuming, tiring work, and the results depend on subjective interpretation of scoring criteria. More objective scoring can be accomplished only if the test can be automated. Furthermore, an automated system allows scoring of large numbers of cells, thereby increasing the statistical significance of the results. This is of special importance for screening programs for low doses of chromosome-damaging agents. In this paper, the first results of our effort to automate the micronucleus assay with an image-analysis system are represented. The method we used is described in detail, and the results are compared to those of other groups. Our system is able to detect 88% of the binucleated lymphocytes on the slides. The procedure consists of a fully automated localization of binucleated cells and counting of the MN within these cells, followed by a simple and fast manual operation in which the false positives are removed. Preliminary measurements for blood samples irradiated with a dose of 1 Gy X-rays indicate that the automated system can find 89% {plus_minus} 12% ofmore » the micronuclei within the binucleated cells compared to a manual screening. 18 refs., 8 figs., 1 tab.« less

At the occasion of the EUROMET Workshop on Ionising Radiation and Radioactivity at the NPL, it was decided to carry out a second intercomparison on air kerma rate (AKR) and activity measurements on 192 Ir brachytherapy sources in the frame of EUROMET project no. 219. The intercomparison has shown that both air kerma rate measurements and activity measurements of 192 Ir brachytherapy wires are not trivial. One of the drawbacks is the appreciable inhomogeneity of the wires. Disregarding some outliers, the spread of the AKR measurements was below 1.5%, while the variation in the activity measurements was very large, due to reasons which are not completely understood.

Purpose: To describe a new infrastructure and process that will enable end-users to commission model-based dose calculation (MBDC) software for brachytherapy planning, and to invite end-users to participate in the beta testing phase of this process. Methods: The AAPM working groups on model-based dose calculation algorithms in brachytherapy (WGDCAB) and brachytherapy source registry (WGBSR) collaboratively implemented the basic MBDC software commissioning workflow described in the AAPM+ESTRO TG-186 report. For a small number of initial test cases virtual CT image, anatomical structure set, treatment plan, and associated 3D dose data for a single dwell position occupied by a WGDCAB generic high-dose-rate Ir-192 virtual source, with or without a generic shielded applicator, were generated. Dose distributions were calculated using Monte Carlo (MC) code MCNP6, Elekta’s Advanced Collapsed cone Algorithm (ACE™), and Varian’s Acuros™ BV module. All data were saved in DICOM RT format and uploaded to a provisional, web-accessible repository in the joint AAPM—IROC Houston brachytherapy source registry. It is envisioned that end-users will download data for a test case from the repository, verify its correctness, calculate 3D dose locally, and then compare with MCNP6 and MBDC doses obtained from the repository using TPS-based comparison tools. User guides in preparation for each TPS will facilitate the process. Results: Initial evaluations of DICOM data download, TPS import, MBDC dose calculation, and reference dose comparison indicate that the infrastructure and process described above are both viable and practicable. Ancillary data including generic source and shielded applicator specifications, CAD drawings, and MC code definitions are also available in the repository. Conclusion: With further refinement and beta-test input from end-users, a practical MBDC software commissioning process for brachytherapy can be established. A procedure for adding new test cases submitted by end-users to the repository will be put in place by WGDCAB.

Purpose: Previously, generic HDR 192 Ir source and shielded applicator were designed by WG- MBDCA, the AAPM-ESTRO-ABG Working Group on model-based dose calculation algorithms. TPS vendors have incorporated both into their TPS. A charge of WG-MBDCA is to develop a limited number of well-defined test cases and perform MBDCA dose calculations and comparisons. Here, we describe the test cases proposed, the 3D dosimetric data generation process and the 3D gamma analysis performed. Methods: A voxelized phantom of 512×512×512 voxels (HU=-1024,Air), with each voxel being 1×1×1 mm3, containing a concentric cubic contour structure (HU=0,Water) of dimension 201×201×201 voxels, was created in the DICOM- RT format. Three configurations were tested: i) source located at the center with surrounding structure assigned to water to mimic TG-43 conditions, ii) source displaced +7 cm along the x axis, iii) source located at the center with the shielded applicator in place. Advanced Collapsed-cone Engine (ACE, Elekta) and AcurosBV (Varian) were benchmarked. Reference datasets were independently produced by different groups using BrachyDose (1010 photons), GEANT4(4×1010), Penelope (2×1010), MCNP5(2 x1010), MCNP6(1011), and ALGEBRA(4×1010) Monte Carlo (MC) dose calculation platforms. Results: For the three configurations, MC agreed within 1% for the volume bounded by the 1% isodose surface; MCNP6 data sets were designated as reference (statistical error < 0.2% across the phantom). A 2%/1mm 3D γ- index criteria was used, within the volume bounded by 5% isodose surface, to account for both dose difference and source placement errors in TPS. Voxel pass rates were 95.2%, 99.5% and 90% for ACE and 98%, 98.4% and 95.9% for AcurosBV, respectively. Conclusion: The evaluated test cases are suitable for MBDCA QA. DICOM-RT files are being integrated into the joint AAPM/IROC Houston registry to support end-user TPS software commissioning.

Summary The importance of water calorimetry in clinieal proton beam dosimetry has increased for various reasons: there has been an increasing interest in proton therapy from the radiotherapy world; existing dosimetry protocols for clinical proton beams recommend calorimetry as the primary dosimetry method (ie, AAPM and ECHED); water has recently become the reference material for dose specification. For the water calorimetric dose evaluation, the water calorimeter developed in Ghent was used. Ionometry was performed following the ECHED protocol. The study resulted in a calorimetric to ionometric dose ratio of 0.974 ± 0.009. The discrepancy should in our opinion be attributed to the ( W/e ) p,air value of 35.2 J/C implemented in the protocol, possibly next to ion chamber dependent effects for which indications are found in the ionometry measurements.

Fluence perturbation of secondary electrons from clinical proton beams (50-250 MeV) by thin high-Z planar interfaces was studied with Monte Carlo simulations. Starting from monoenergetic proton pencil beams, proton depth doses and proton fluence spectra were calculated, both in homogeneous water and near thin high-Z interfaces by using the proton transport Monte Carlo code PTRAN. This code was modified extensively to enable modelling of proton transport in non-homogeneous geometries. From the proton fluence spectra in water and in the interface materials, electron generation spectra were calculated analytically and were then used as input for an electron transport calculation with the Monte Carlo code EGS4/PRESTAII to obtain electron doses and electron fluence spectra. The interface materials used in the study were graphite, Al, Ti, Cu, Sn and Au. We found significant electron fluence perturbations on both sides of the planar interfaces, resulting in an electron dose increase upstream and a decrease downstream from the interfaces, with the magnitude of the effect depending strongly on the atomic number of the interface. For the most extreme case studied, 250 MeV protons and a gold interface, we obtained an electron dose increase of 41% upstream of the interface and a decrease of 15% downstream with both perturbations having a spatial extent of about 700 microm. The total dose perturbation due to this effect amounts to a 5% increase upstream and a 2% decrease downstream. A detailed analysis of dose and fluence perturbation is presented for a wide range of materials and proton energies.

This thesis retrospectively analyzes prostate's daily motion provided by three-dimensional US localization and investigates its dosimetric impacts based on XVMC calculation which takes into account patient geometry, heterogeneity and prostate motion correction. The retrospective analysis on 32 prostate patients shows that the mean  SD displacements of prostate in the AP, SI, and RL directions are -3.3  7.9 mm, -1.1  6.4 mm, -0.2 5.6 mm, respectively. The largest rotation occurs about lateral axis with mean  SD of -0.9  4.6, ranging between -6.7 and 8.0 from a preliminary study including three patients. To assess the dosimetric impacts of prostate motion, five motion scenarios including with and without prostate translation and correction, with translation and rotation but no correction or only having translation correction are simulated. Analysis based on dose-volume histograms and isodose curves shows that prostate motion (translation and rotation) will deteriorate the dose delivered to patient target and OARs. With translation correction method, the degraded patient dose could be recovered nearly completely. For the scenarios with both translation and rotation, translation correction method could dramatically improve the degraded patient dose, but could not completely eliminate the dosimetric impact of prostate motion. Besides, the dosimetric impact of metal prosthesis in three patients has been analysed as well. Up to 5% discrepancies in their D90%, D95%, V90%, and D95% for PTV have been observed., Le mouvement de la prostate est un problème critique dans le traitement conforme du cancer de la prostate, le plus commun cancer parmi les hommes au Canada. La radiothérapie guidée par l'image (IGRT) utilisant les images ultrasons (US) quotidiennes est une technique largement utilisée pour régler ce problème. Une nouvelle technique de localisation ultrasons en trois dimensions, basée sur une méthode de vérification intra modalités, a été testée à l'Hôpital General de Montreal en 2005. L'objectif principal de cette thèse a été de mieux quantifier l'amplitude du mouvement de la prostate à travers une analyse rétrospective de 32 patients et d'évaluer son impacte dans la dosimétrie des traitements de la prostate avec et sans localisation US. L'analyse rétrospective a montré que la moyenne  écart-type des mouvements de la prostate dans les directions AP, SI et DG est de -3.3  7.9 mm, -1.1  6.4 mm et -0.2  5.6 mm, respectivement. La plus grande rotation survient autour de l'axe latérale, avec une moyenne  écart-type de -0.9  4.6, s'échelonnant entre -6.7 et 8.0. Pour estimer l'impacte dosimétrique du mouvement rigide de la prostate, la dose a été calculée en utilisant la méthode XVMC, qui prend en considération la géométrie du patient, les hétérogénéités et les corrections pour le mouvement. Une déviation moyenne de la D95% de jusqu'à -11.9% a été observe pour le PTV, -5.1% pour le CTV et -4.2% pour le GTV. Le V95% du PTV a été réduit par un facteur de -22.2% lorsque la translation quotidienne de la prostate était présente mais aucune correction n'a été appliquée. La dégradation de la dose à la cible a pu être corrige presque complètement en appliquant une correction du mouvement de translation, cependant lorsque la rotation a été prise en compte, le recouvrement de la dose a été moins adéquat. L'effet des prothèses m

Small-field and stereotactic radiosurgery (SRS) dosimetry with radiation detectors, used for clinical practice, have often been questioned due to the lack of lateral electron equilibrium and uncertainty in beam energy. A dosimetry study was performed for a dedicated 6 MV SRS unit, capable of generating circular radiation fields with diameters of 1.25-5 cm at isocentre using the BEAM/EGS4 Monte Carlo code. With this code the accelerator was modelled for radiation fields with a diameter as small as 0.5 cm. The radiation fields and dosimetric characteristics (photon spectra, depth doses, lateral dose profiles and cone factors) in a water phantom were evaluated. The cone factor (St) for a specific cone c at depth d is defined as St(d, c) = D(d, c)/D(d, c(ref)), where c(ref) is the reference cone. To verify the Monte Carlo calculations, measurements were performed with detectors commonly used in SRS such as small-volume ion chambers, a diamond detector, TLDs and films. Results show that beam energies vary with cone diameter. For a 6 MV beam, the mean energies in water at the point of maximum dose for a 0.5 cm cone and a 5 cm cone are 2.05 MeV and 1.65 MeV respectively. The values of St obtained by the simulations are in good agreement with the results of the measurements for most detectors. When the lateral resolution of the detectors is taken into account, the results agree within a few per cent for most fields and detectors. The calculations showed a variation of St with depth in the water. Based on calculated electron spectra in water, the validity of the assumption that measured dose ratios are equal to measured detector readings was verified.

An ionometric calibration procedure for 192Ir PDR brachytherapy sources in terms of dose rate to water is presented. The calibration of the source is performed directly in a water phantom at short distances (1.0, 2.5 and 5.0 cm) using an NE2571 Farmer type ion chamber. To convert the measured air-kerma rate in water to dose rate to water a conversion factor (CF) was calculated by adapting the medium-energy x-ray dosimetry protocol for a point source geometry (diverging beam). The obtained CF was verified using two different methods. Firstly, the CF was calculated by Monte Carlo simulations, where the source-ionization chamber geometry was modelled accurately. In a second method, a combination of Monte Carlo simulations and measurements of the air-kerma rate in water (at 1.0, 2.5 and 5.0 cm distance) and in air (1 m distance) was used to determine the CF. The obtained CFs were also compared with conversion factors calculated with the adapted dosimetry protocol for high-energy photons introduced by Tölli. All calculations were done for a Gammamed PDR 192Ir source-NE2571 chamber geometry. The conversion factors obtained with the four different methods agree to within 1% at the three distances of interest. We obtained the following values (medium-energy x-ray protocol): CF(1 cm) = 1.458; CF(2.5 cm) = 1.162; CF(5.0 cm) = 1.112 (1 sigma = 0.7% for the three distances of interest). The obtained results were checked with TLD measurements. The values of the specific dose rate constant and the radial dose function calculated in this work are in accordance with the literature data.

Purpose: The purpose of this work is to investigate the importance of heterogeneity corrections for dosimetry in brachytherapy. In particular, we are interested to see how the estimations of the a/b parameter for prostate cancer may change if accurate dose calculations are implemented in brachytherapy.Methods: A Monte Carlodose engine called ALGEBRA (Based on GEANT4) is used to accurately calculate dose distributions for 30 prostate cancer patients treated with brachytherapy at our institution. The equivalent uniform BED (EUBED) is used to take the high spatial dose heterogeneity of BT into account for estimating the biological efficiency of treatments. For the same level of clinical outcome, the EUBED of BT can be assumed is‐effective with BED of external beam radiotherapy to extract the a/b value for prostate cancer.Results: When the heterogeneities are neglected, a/b value equals 3.1 Gy as reported in the literature. When heterogeneities are considered in BT, an a/b value of 5.4 Gy is predicted for prostate cancer.Conclusions: The importance of a precise dosimetry method in plan evaluation has been recognized but its importance on the radiobiological evaluations is usually neglected. This study shows that by using an accurate dosimetry method in BT, the estimation of a/b can change considerably with regard to the reported value of 3.1 Gy in the literature.

An improved slide preparation technique is described for the automated detection of micronuclei in binucleate cytokinesis-blocked human lymphocytes. This automated system (Discovery Image Analyser, Becton-Dickinson Image Cytometry Systems, Leiden, The Netherlands) searches for the pattern of two touching nuclei in binucleate cells instead of the edges of the cytoplasm. For this purpose several ratios of the fixative mixture, methanol/acetic acid, were checked. After fixation with a ratio of 25:1, touching nuclei were obtained in almost 100% of the binucleate cells. A hydrolysis treatment with 5 N HCl before staining with Romanowsky-Giemsa resulted in binucleate cells with dark-stained nuclei and micronuclei and a vaguely stained cytoplasm. The high visual contrast between cytoplasm and nuclear material obtained by this staining procedure makes an accurate automated detection of micronuclei feasible. Additionally, a 64 h culture time resulted in an optimal yield of binucleate cells. The results of manual micronucleus scoring on slides prepared with the 'manual protocol' and with the 'automation protocol' indicate no significant differences between both sets of data supporting the validity of the automation protocol.