Dean Cutajar Copyright (c) 2012 All rights reserved. http://works.bepress.com/dcutajar Recent documents in Dean Cutajar en-us Fri, 23 Nov 2012 18:28:07 PST 3600 Dosimetry verification in eye brachytherapy using silicon pixelated detectors http://works.bepress.com/dcutajar/22 http://works.bepress.com/dcutajar/22 Tue, 13 Nov 2012 20:55:43 PST This study presents a high spatial resolution dosimetry system for quality assurance of I-125 eye plaques. The system is based on a silicon pixelated detector and is capable of deriving 3D dose distributions. A simple design was implemented, incorporating a movable eye plaque in a small water phantom above the silicon Medipix2 detector. It is designed for obtaining 2D dose distributions at different depths in water, for subsequent 3D dose mapping. The effect of backscattering in a medium placed behind the Medipix2 to simulate surrounding tissue has been studied in terms of dose distribution. Additionally, two modes of acquisition, event counting mode and the more complex time-over-threshold mode, were compared to the TG-43 protocol for the determination of their suitability for dosimetry.

]]> Michael Weaver et al. The teaching/research nexus and internationalisation: an action research project in radiation physics http://works.bepress.com/dcutajar/21 http://works.bepress.com/dcutajar/21 Tue, 13 Nov 2012 20:55:42 PST Susanna Guatelli et al. Introduction to the geant4 simulation toolkit http://works.bepress.com/dcutajar/20 http://works.bepress.com/dcutajar/20 Tue, 13 Nov 2012 20:55:39 PST Geant4 is a Monte Carlo simulation Toolkit, describing the interactions of particles with matter. Geant4 is widely used in radiation physics research, from High Energy Physics, to medical physics and space science, thanks to its sophisticated physics component, coupled with advanced functionality in geometry description. Geant4 is widely used at the Centre for Medical Radiation Physics (CMRP), at the University of Wollongong, to characterise and optimise novel detector concepts, radiotherapy treatments, and imaging solutions. This lecture consists of an introduction to Monte Carlo method, and to Geant4. Particular attention will be devoted to the Geant4 physics component, and to the physics models describing electromagnetic and hadronic physics interactions. The second part of the lecture will be focused on the methodology to adopt to develop a Geant4 simulation application.

]]> Susanna Guatelli et al. Megavoltage cone beam CT near surface dose measurements: potential implications for breast radiotherapy http://works.bepress.com/dcutajar/19 http://works.bepress.com/dcutajar/19 Tue, 13 Nov 2012 20:55:38 PST Purpose: Cone beam computed tomography (CBCT) is fast becoming standard on modern linear accelerators. CBCT increases the dose to regions within and outside the treatment field, potentially increasing secondary cancer induction and toxicity. This study quantified megavoltage (MV) CBCT skin dose and compared it to skin dose delivered during standard tangential breast radiotherapy.

Method: Dosimetry was performed both in- and out-of-field using thermoluminescent dosimeters (TLDs) and a metal-oxide-semiconductor-field-effect-transistor (MOSFET) detector specifically designed for skin dosimetry; these were placed superficially on a female anthropomorphic phantom.

Results: The skin dose from a single treatment fraction ranged from 0.5 to 1.4 Gy on the ipsilateral breast, 0.031–0.18 Gy on the contralateral breast, and 0–0.02 Gy in the head and pelvic region. An 8 MU MV CBCT delivered a skin dose that ranged from 0.02 to 0.05 Gy in the chest region and was less than 0.01 Gy in the head and pelvis regions. One MV CBCT per fraction was found to increase the outof- field skin dose from both the CBCT and the treatment fields by approximately 20%. The imaging dose as a percentage of treatment doses in the ipsilateral breast region was 3% for both dosimeters.

Conclusion: Imaging increases the skin dose to regions outside the treatment field particularly regions immediately adjacent the target volume. This small extra dose to the breasts should be considered when developing clinical protocols and assessing dose for clinical trials.

]]> Alexandra Quinn et al. Three-dimensional dosimetry imaging of I-125 plaque for eye cancer treatment http://works.bepress.com/dcutajar/18 http://works.bepress.com/dcutajar/18 Tue, 13 Nov 2012 20:55:35 PST Treatment of ocular cancers using eye plaque brachytherapy is now an established medical procedure. However, current QA for these eye plaques is quite rudimentary, limiting the opportunities for precise pre-tumour plaque customisation. This paper proposes and experimentally validates a new technique for imaging of eye plaque dose distributions using a high-resolution pixelated silicon detector. Results are presented demonstrating the 2D and 3D isodose surfaces produced using experimental data collected using this method.

]]> Michael Weaver et al. Verification of the plan dosimetry for high dose rate brachytherapy using metal-oxide-semiconductor field effect transistor detectors http://works.bepress.com/dcutajar/17 http://works.bepress.com/dcutajar/17 Tue, 13 Nov 2012 20:55:33 PST Zhen-Yu Qi et al. Dosimetric image reconstruction in eye brachytherapy using silicon pixelated detectors http://works.bepress.com/dcutajar/16 http://works.bepress.com/dcutajar/16 Tue, 13 Nov 2012 20:55:31 PST This study presents a high spatial resolution dosimetry system for quality assurance of I-125 eye plaques. The system is based on a silicon pixelated detector and is capable of deriving 3D dose distributions. A simple design was implemented, incorporating a movable eye plaque in a small water phantom above the silicon Medipix2 detector. It is designed for obtaining 2D dose distributions at different depths in water, for subsequent 3D dose mapping. The effect of backscattering in a medium placed behind the Medipix2 to simulate surrounding tissue has been studied in terms of dose distribution. Additionally, two modes of acquisition, event counting mode and the more complex time-over-threshold mode, were compared to the TG-43 protocol for the determination of their suitability for dosimetry.

]]> M Weaver et al. In vivo verification of superficial dose for head and neck treatments using intensity-modulated techniques http://works.bepress.com/dcutajar/15 http://works.bepress.com/dcutajar/15 Tue, 13 Nov 2012 20:55:26 PST Zhen-Yu Qi et al. Monte Carlo study of the energy response and depth dose water equivalence of the MOSkin radiation dosimeter at clinical kilovoltage photon energies http://works.bepress.com/dcutajar/14 http://works.bepress.com/dcutajar/14 Tue, 13 Nov 2012 20:55:25 PST Skin dose is often the quantity of interest for radiological protection, as the skin is the organ that receives maximum dose during kilovoltage X-ray irradiations. The purpose of this study was to simulate the energy response and the depth dose water equivalence of the MOSkin radiation detector (Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia), a MOSFET-based radiation sensor with a novel packaging design, at clinical kilovoltage photon energies typically used for superficial/orthovoltage therapy and X-ray CT imaging. Monte Carlo simulations by means of the Geant4 toolkit were employed to investigate the energy response of the CMRP MOSkin dosimeter on the surface of the phantom, and at various depths ranging from 0 to 6 cm in a 30 9 30 9 20 cm water phantom. By varying the thickness of the tissue-equivalent packaging, and by adding thin metallic foils to the existing design, the dose enhancement effect of the MOSkin dosimeter at low photon energies was successfully quantified. For a 5 mm diameter photon source, it was found that the MOSkin was water equivalent to within 3% at shallow depths less than 15 mm. It is recommended that for depths larger than 15 mm, the appropriate depth dose water equivalent correction factors be applied to the MOSkin at the relevant depths if this detector is to be used for depth dose assessments. This study has shown that the Geant4 Monte Carlo toolkit is useful for characterising the surface energy response and depth dose behaviour of the MOSkin.

]]> C P. L Lian et al. From HEP to medical radiation dosimetry - The silicon strip detector dose magnifying glass http://works.bepress.com/dcutajar/13 http://works.bepress.com/dcutajar/13 Tue, 13 Nov 2012 20:55:23 PST Michael L. Lerch et al. From imaging to dosimetry: GEANT4-based study on the application of Medipix to neutron dosimetry http://works.bepress.com/dcutajar/12 http://works.bepress.com/dcutajar/12 Thu, 12 Jan 2012 14:19:28 PST An application of Medipix2 using a newly developed segmented multiple thickness polyethylene (PE) converter for fast neutron detection is presented. The system has the ability to provide an energy independent response for the dose equivalent for fast neutrons. The application of weighting factors to each defined thickness of PE allows for a flattening of the response of the detector system for dosimetry applications. Six PE converter segments were applied, and their thicknesses and weighting factors were optimised to obtain the required energy independent detector response. The study performed by means of GEANT4. Its suitability for neutron dosimetry was studied with respect to a previously published work.

]]> M A. Othman et al. In vivo real-time rectal wall dosimetry for prostate radiotherapy http://works.bepress.com/dcutajar/11 http://works.bepress.com/dcutajar/11 Thu, 12 Jan 2012 14:19:25 PST Rectal balloons are used in external beam prostate radiotherapy to provide reproducible anatomy and rectal dose reductions. This is an investigation into the combination of a MOSFET radiation detector with a rectal balloon for realtime in vivo rectal wall dosimetry. The MOSFET used in the study is a radiation detector that provides a water equivalent depth of measurement of 70 μm. Two MOSFETs were combined in a face-to-face orientation. The reproducibility, sensitivity and angular dependence were measured for the dual MOSFET in a 6 MV photon beam. The dual MOSFET was combined with a rectal balloon and irradiated with hypothetical prostate treatments in a phantom. The anterior rectal wall dose was measured in real time and compared with the planning system calculated dose. The dual MOSFET showed angular dependence within ±2.5% in the azimuth and +2.5%/−4% in the polar axes. When compared with an ion chamber measurement in a phantom, the dual MOSFET agreed within 2.5% for a range of radiation path lengths and incident angles. The dual MOSFET had reproducible sensitivity for fraction sizes of 2–10 Gy. For the hypothetical prostate treatments the measured anterior rectal wall dose was 2.6 and 3.2% lower than the calculated dose for 3DCRT and IMRT plans. This was expected due to limitations of the dose calculation method used at the balloon cavity interface. A dual MOSFET combined with a commercial rectal balloon was shown to provide reproducible measurements of the anterior rectal wall dose in real time. The measured anterior rectal wall dose agreed with the expected dose from the treatment plan for 3DCRT and IMRT plans. The dual MOSFET could be read out in real time during the irradiation, providing the capability for real-time dose monitoring of the rectal wall dose during treatment.

]]> Nicholas Hardcastle et al. Monte Carlo study of mosfet packaging, optimised for improved energy response: single mosfet filtration http://works.bepress.com/dcutajar/10 http://works.bepress.com/dcutajar/10 Thu, 12 Jan 2012 14:19:23 PST Monte Carlo simulations of the energy response of a conventionally packaged single metal-oxide field effect transistors (MOSFET) detector were performed with the goal of improving MOSFET energy dependence for personal accident or military dosimetry. The MOSFET detector packaging was optimised. Two different ‘drop-in’ design packages for a single MOSFET detector were modelled and optimised using the GEANT4 Monte Carlo toolkit. Absorbed photon dose simulations of the MOSFET dosemeter placed in free-air response, corresponding to the absorbed doses at depths of 0.07 mm (Dw(0.07)) and 10 mm (Dw(10)) in a water equivalent phantom of size 30 x 30 x30 cm3 for photon energies of 0.015–2 MeV were performed. Energy dependence was reduced to within +60 % for photon energies 0.06–2 MeV for both Dw(0.07) and Dw(10). Variations in the response for photon energies of 15–60 keV were 200 and 330 % for Dw(0.07) and Dw(10), respectively. The obtained energy dependence was reduced compared with that for conventionally packaged MOSFET detectors, which usually exhibit a 500–700 % over-response when used in free-air geometry.

]]> M A. R Othman et al. Transferring advanced physics research tools to education: how to teach simulation tools used in radiation physics research to university students http://works.bepress.com/dcutajar/9 http://works.bepress.com/dcutajar/9 Thu, 12 Jan 2012 14:19:20 PST At the Centre of Medical Radiation Physics (CMRP), School of Engineering Physics, Faculty of Engineering, at the University of Wollongong (UOW), we are implementing a hands-on computing laboratory, commencing in autumn 2010, to teach scientific computing methods and modern, advanced research tools for radiation physics to postgraduate and undergraduate students. Engaging undergraduates and postgraduates together in work with a tool widely used in research laboratories is a unique development, and represents the articulation of the University’s commitment to the enhancement of the teaching/research nexus, and to the development of learning communities. The object of the laboratory is to teach students how to use Geant4 in the study of radiation physics related problems. Geant4 (www.cern.ch/geant4) is a Monte Carlo Simulation Toolkit, describing the interactions of particles with matter. It is widely used in research laboratories all over the world, from High Energy Physics to medical physics and space science. While the Geant4 Collaboration organizes courses all around the world to familiarise researchers and postgraduates with the Toolkit, insufficient attention is paid to undergraduates. The objectives of our program are that, upon completion of the practical laboratory, the students will be familiar with radiation physics and its applications, software development methods, computing instruments for research, the Monte Carlo approach, and the C++ language. They will also have had a unique opportunity to improve their problem solving skills and research methodologies. The design of the Geant4 hands-on lab faces two important issues: the heterogeneous computing skills and differing knowledge of radiation physics amongst students. Independent of their education grade, students have different expertise with programming, and computing matters in general. This problem can easily be overcome as Geant4 is developed for use by those with minimal computing expertise. However, the correct use of Geant4 requires a deep knowledge of radiation physics; this poses the second issue faced. The higher levels of motivation of postgraduate students will be one factor supporting undergraduates, in that working with Geant4 should foster a learning community, with peer learning and teaching occurring, and also provide undergraduates with a sense of future. Furthermore, we think we can overcome the problem of lower levels of knowledge through designing a guided hands-on course, providing Geant4 simulation exercises for students, based on their level of preparation. This course has high potential to increase the commitment of students towards radiation physics.

]]> Susanna Guatelli et al. Surface dosimetry for breast radiotherapy in the presence of immobilization cast material http://works.bepress.com/dcutajar/8 http://works.bepress.com/dcutajar/8 Thu, 12 Jan 2012 14:19:18 PST Curative breast radiotherapy typically leaves patients with varying degrees of cosmetic damage. One problem interfering with cosmetically acceptable breast radiotherapy is the external contour for large pendulous breasts which often results in high doses to skin folds. Thermoplastic casts are often employed to secure the breasts to maintain setup reproducibility and limit the presence of skin folds. This paper aims to determine changes in surface dose that can be attributed to the use of thermoplastic immobilization casts. Skin dose for a clinical hybrid conformal/IMRT breast plan was measured using radiochromic film and MOSFET detectors at a range ofwater equivalent depths representative of the different skin layers. The radiochromic film was used as an integrating dosimeter, while the MOSFETs were used for real-time dosimetry to isolate the contribution of skin dose from individual IMRT segments. Strips of film were placed at various locations on the breast and the MOSFETs were used to measure skin dose at 16 positions spaced along the film strips for comparison of data. The results showed an increase in skin dose in the presence of the immobilization cast of up to 45.7% and 62.3% of the skin dose without the immobilization cast present as measured with Gafchromic EBT film and MOSFETs, respectively. The increase in skin dose due to the immobilization cast varied with the angle of beam incidence and was greatest when the beam was normally incident on the phantom. The increase in surface dose with the immobilization cast was greater under entrance dose conditions compared to exit dose conditions.

]]> Andrew Kelly et al. Skin dosimetry with new MOSFET detectors http://works.bepress.com/dcutajar/7 http://works.bepress.com/dcutajar/7 Thu, 12 Jan 2012 14:19:15 PST The MOSkin, a new MOSFET-based detector designed by the Centre for Radiation Physics, was engineered to provide accurate measurements of skin doses in radiotherapy and personal monitoring. The International Commission on Radiological Protection (ICRP) estimates the radiosensitive basal layer to be at an average depth of 0.070 mm. Current commercially available MOSFETs utilize an epoxy bubble encapsulation, making measurements at equivalent depths of 0.070mm difficult. The MOSkin utilizes a novel packaging design that allows the measurement of doses at this equivalent depth. The MOSkin has shown excellent agreement with the Attix chamber for surface measurements in a 6MV photon beam of various field sizes and has minimal angular dependence due to the encapsulation. The new design will diversify the use of MOSFETs for dosimetry in radiotherapy and radiation protection.

]]> Ian S. Kwan et al. Urethral spectroscopic alarm (USA) probe for prostate implants http://works.bepress.com/dcutajar/6 http://works.bepress.com/dcutajar/6 Thu, 12 Jan 2012 14:19:12 PST Urethral Spectroscopic Alarm (USA) Probe for Prostate Implants 1A.B. Rosenfeld, 1D.L. Cutajar, 1M.L.F. Lerch, 1G.J. Takacs, 2J.A. Bucci, 2L.J. Duggan, 3M. Zaider, 4M. Zelefsky and 3G.N. Cohen 1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia, 2Institute for Prostate Cancer, St. George Cancer Care Centre, Kogarah, Australia, 3Department of Medical Physics and 4Department of Radiation Oncology, MSKCC, New York, NY Purpose: Prostate implants are associated with excellent biochemical outcome; however, their benefit in terms of overall survival remains unknown. For many patients with early, localized prostate cancer the decision to undergo a treatment of questionable benefit yet because of potentially significant morbidity - tangibly impacting upon their quality of life is understandably difficult. Thus, diminishing the risk of complications, whilst at the same time maintaining good dosimetric coverage of the tumor, remains the overriding concern in prostate brachytherapy. We describe a probe which reports in real time the dose delivered at selected locations in the urethra and alerts the physician if the planned dose was exceeded. Methods and Materials: In vivo dosimetry is commonly performed with miniature counters such as mosfets or diodes (1). The main disadvantages of such systems are their energy dependence and low sensitivity. The USA probe circumvents these problems by measuring the actual energy spectrum of the radiation field; the dose is evaluated in relation to the magnitude of the photopeak and this makes for an essentially noise-free system. The probe is silicon mini-detector connected to a shaping amplifier and discriminator and placed in a cable that can be inserted in a urethral catheter Results: In a previous study (2) we have shown that urethral NTCP (meaning: grade 2 urinary symptoms that remain unresolved at 12 months post implant) correlate with DU20 [meaning that 20% of the urethral volume is treated to a dose of at least DU20]. Specifically: where g= -2.60±0.50 and d=0.0066±0.0016 Gy-1. After each seed insertion the planned DU20 is calculated and compared to the probes signals. The workings of this system are illustrated with data obtained in a training phantom. Conclusions: The USA probe offers the physician-implanter the opportunity to monitor on the fly the urethral dose and modify the implantation plan should the dose surpass the pre-set DU20 value. As well, the fact that the probe operates in spectroscopic mode eliminates the need for a tissue-equivalent dosimeter. Reference List 1. A.B. Rosenfeld, D.L. Cutajar, M.L.F. Lerch, G.J. Takacs, J. Brady, T.Braddock, V.L. Perevertaylo, J. Bucci, J. Kearsley, Zaider M, Zelefsky, In vivo dosimetry and seed localization in prostate brachytherapy with permanent implants. IEEE Trans. Nucl. Science, 51: 3013-3018 (2004). 2. Zaider M, Zelefsky M, Cohen AM, Chui C, Yorke ED, Ben-Porat L et al. Methodology for biologically-based treatment planning for combined low dose-rate (permanent implant) and high dose-rate (fractionated) treatment of prostate cancer. International Journal of Radiation Oncology Biology Physics (in press, 2005).

]]> Anatoly Rozenfeld et al. Modelling the use of solid state detectors to determine seed locations in low dose rate brachytherapy http://works.bepress.com/dcutajar/5 http://works.bepress.com/dcutajar/5 Thu, 12 Jan 2012 14:19:10 PST Dean Cutajar Spectroscopic dosimetry: the development of the urethral mini-dosimetry system http://works.bepress.com/dcutajar/4 http://works.bepress.com/dcutajar/4 Thu, 12 Jan 2012 14:19:08 PST Dean Cutajar Miniature semiconductor detectors for in vivo dosimetry http://works.bepress.com/dcutajar/3 http://works.bepress.com/dcutajar/3 Thu, 12 Jan 2012 14:19:05 PST Silicon mini-semiconductor detectors are found in wide applications for in vivo personal dosimetry and dosimetry and microdosimetry of different radiation oncology modalities. These applications are based on integral and spectroscopy modes of metal oxide semiconductor field effect transistor and silicon p–n junction detectors. The advantages and limitations of each are discussed.

]]> Anatoly Rozenfeld et al.