Seminars
| 2012 |
Medical Physics seminars are usually held on Tuesdays 4.10 to 5.00pm in the Department of Physics & Astronomy seminar room 701. For information contact the seminar organiser Syen Nik.
2011
Mohamad Jaafar
Assoc. Prof. and Chairman of Medical Physics Programme,
School of Physics, Universiti Sains Malaysia
Low Level Laser Research in USM
1. Light Propagation in Human Skin Tissue and Influence of Skin Types and Hair Parameters on the Light Dose Delivery [
MS Jaafar, Farhad H. Mustafa and M. N. Salihin Yusoff]
The Graphics Processing Units (GPU) based Monte Carlo for Multi-Layered media (MCML) program was used to simulate the propagation of light in human skin tissue. The program is capable of running bulk data. This study shows that the program provides an appropriate result compared to previous studies with the advantage of graphic image and extremely practical computation time. The optical simulation program ASAP (Advanced Systems Analysis Program) which permits the simulation of photon propagation and the power density recording of laser in the skin layers was used to create realistic tissue phantoms for the investigation of the optical properties of skin. The present study shows that the present hair parameters on the scalp in PDT induce slight changes in the light dose delivery into the depth of the skin, and has a weakly role in reducing photodynamic dose activation. Thus, the hair parameter was not a main responsible factor for the reduction of light dose delivery into the depth of skin in PDT. it was shown that the PDT is sensitive with the human skin colour in laser-tissue interaction. The result proves that skin colour is an essential factor in PDT.
2. Study on Hemolysis and Effects of Laser Irradiation on Human Blood [
MS Jaafar, Hend A. A. Houssein, ZA Timimi, M Y Bermakai, AL Ahmad and NE Ismail]
Visible light were used to investigate hemolysis in the whole-blood due to time storage. The presence of free hemoglobin plasma (FHP) in samples increased the light absorbance. Highest absorption by human blood was at 415.0 nm which corresponds to the violet-blue region. The hematocrit, FHP and hemolysis were found to increase significantly for the first 3 days.
A 632.8 nm HeNe and 10,600 nm CO2 lasers were each employed to irradiate human blood samples and 2D contour and 3D profile images were acquired before and after irradiation. The statistical analysis shows consistencies with previous research. This can become a significant indicator for blood analysis, thus leading the way as a vibrant diagnosis tool to clarify diseases associated with blood cells.
A 532 nm 100 mW diode laser was used to study the effects on rheological properties of human blood in vitro. The counts of RBC, WBC, HGB, HCT, MCV, MCHC, PLT and neutrophils were obtained. The findings of this research showed that LLLT affects various rheological properties of different blood cells for example red cell deformability, aggregation of cells, critical stress on the cells during preservation time, leucocytarory, erytherocytatory indices, ESR etc. The study proved that LLLT with diode laser 532 nm and low power of 100 mw is advantageous for revitalizing the functional capability of preserved blood.
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4 - 5pm Tuesday 4th Oct - Room 701, Rutherford Building
Syen Nik, Medical Physics, PhD Student, Physics and Astronomy Department
Volume-of-interest reconstruction from truncated data and Optimal material discrimination using spectral x-ray imaging
This is a talk of two halves - the first part will be a review of my recent trip to the Dalhousie University in Halifax, Canada, where I took on an internship on x-ray computed tomography (CT) image reconstruction from truncated projection data. When, for example, only the volume-of-interest(VOI) is irradiated for the reduction of radiation dose delivered to the subject, the conventional Feldkamp-Davis-Kress (FDK) algorithm yields reconstructed images with artifacts. An algorithm known as the backprojection-filtration (BPF) algorithm has recently been developed for exact image reconstruction from helical and circular cone-beam CT (CBCT) data. The focus of this talk will be on the implementation of the BPF algorithm on volume-of-interest (VOI) megavoltage CBCT. The concept of Pi-lines for backprojection and the BPF algorithm will be introduced. Qualitative and quantitative comparisons with the FDK reconstructed images will be discussed.
In the second part of the talk, I will provide a brief overview of the optimisation of material discrimination using spectral x-ray imaging. Results from the optimisation metric as well as a Monte Carlo simulation model developed for verification purposes will be presented.
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Tuesday, 27 September
4 - 5pm
Alicia Cavan
Alicia is a registrar at the CDHB and also a part time PhD student at the Department of Physics and Astronomy.
Investigation of digital holographic interferometry for radiation dosimetry
This talk will present research for my PhD towards developing a new dosimetry system based on an optical technique called holographic interferometry. The work is proof-of principle, with the fundamental idea being to infer the absorbed dose deposited by a radiation beam to a water phantom by measuring the change in refractive index of the absorbed media as a result of the induced small increase in temperature.
The initial approach is to use a lensless Fourier Digital Holography set-up, with a HeNe laser and a CCD camera to measure small refractive index variations in simplified phantoms. The holographic interferograms are reconstructed to measure and visualise this variation. One of the challenges with this method is the thermal diffusion in the phantom.
Initial results show successful reconstructions of objects from the experimental interferograms, and work is ongoing to acquire phase information from these in order to be able to measure the small variations in path length difference that will be required. Further implementation of this method has potential for use to measure the distinctive dose profile of synchrotron produced microbeams.
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20 September
Juergen Meyer
An adaptive tumour tracking system
One of the most challenging parts of the treatment of lung tumours is to account for breathing induced tumour motion. In this talk I will describe the development of an adaptive tumour tracking system (ATTS), which has evolved out of an established clinical stereotactic body radiotherapy (SBRT) program. The ATTS consists of several independent components, which have been integrated into a prototype system. I will discuss the main components, system tests with a robotic phantom and latest tests with volunteers, modeling of the relationship between breathing and tumour motion and potential applications for gated radiotherapy.
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13 September
4:00-4:15
Nate Tang
The Physics of IMRT
A talk on the fundamental aspects of IMRT and a summary of a 10 year clinical trial of IMRT on prostate cancer patients.
4:15-4:30
David Wood
Boron Neutron Capture Therapy of Cancer: Current Status and Future Prospects
Talk purporting to introduce boron neutron capture therapy (BNCT). Here, the focus will be on the physics underpinning this novel therapeutic modality, the conditions upon which the clinical efficacy of BNCT depend, and the clinical application and future prospects of this binary treatment.
4:30-4:45
Stephen Bell
Technical Aspects of Image-Guided Respiration-Gated Radiation Therapy
In radiation therapy the movement of tumors due to respiratory function may be as much as 2-3 cm. In conventional radiation therapy this motion is accounted for by an addition margin included when defining the extent of the planning target volume (PTV). This additional margin results in an increase in the volume of normal tissue surrounding the tumor that is irradiated with the treatment field, which may limit treatment options and have a detrimental effect on treatment outcome. The respiratory gated approach aims to reduce the additional margin included in the PTV. This is achieved by real-time monitoring of tumor position either directly or by proxy to derive an on/off gating signal that activates the radiation field when the tumor is within a limited region. Technical challenges arise in the real-time determination of tumor position that affect both the derivation of the gating signal and verification of the treatment dose delivered. This paper reviews two respiratory gated IMRT systems to illustrate the technical challenges that arise and the different ways that these challenges are addressed in each system.
4:45-5:00
Christine Reed
Dose and Volume Parameters for MRI-Based Treatment Planning in Intrcavitary Brachytherapy for Cervical Cancer
The systematic development of 3D image guided treatment planning for brachytherapy treatment of cervical cancer is retrospectively reported by a clinical research group in Vienna. They conclude a standard loading pattern should be used as the starting point. Followed by an iterative process of tumour volume (and organs at risk) delineation and dose volume analysis to optimise target dose and dose distribution.
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The schedule is as follows:
4:00-4:15 pm
Jenny Lim
CyberKnife Stereotactic Ablative Radiotherapy for Lung Tumors
A talk on qualities of Stereotactic ablative radiotherapy using CyberKnife to treat lung cancer,
and summary of clinical data using this system.
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4:15-4:30 pm
Rowen De Vries
Feasibility of cranio-spinal axis radiation with the Hi-Art tomotherapy system
Background and purpose: Helical tomotherapy can eliminate the need for junction lines. The goal of this study is to evaluate tomotherapy in the delivery of CSA radiation and measurement of plan quality using physical parameters in comparing conventional (CSA-RT) and helical tomotherapy (CSA-TOMO) plans.
Patients and methods: CSA-TOMO and CSA-RT plans were created for dosimetric comparison. Integral dose values were calculated. The ratios D50% (dose received by 50% of the organ at risk’s volume) and D10% (dose received by 10% of the organ at risk’s volume) were calculated representing large volumes and small volumes of organs at risk receiving significant dose.
Results: When considering D50% and D10%, CSA-TOMO has a dosimetric advantage over CSA-RT for most organs at risk. The body integral dose was higher for the CSA-TOMO plan by approximately 6.5%.
Conclusions: Tomotherapy is a feasible alternative for treatment of CSA. Analysis shows that tomotherapy improves dose ratios over conventional radiation for most organs at risk. The impact of a small increase in whole body integral dose is unknown. Long-term follow-up will be needed to answer this question as others have argued of the possibility of increased risk of secondary malignancies due to delivery of radiotherapy with IMRT.
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4:30-4:45 pm
Ivy Au
Microsurgery plus whole brain irradiation versus Gamma Knife surgery alone for treatment of single metastases to the brain: a randomized controlled multicentre phase III trial
Abstract:TBA
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4:45-5:00 pm
Daniel Kim
Comparing Radiation Treatments Using Intensity-Modulated Beams, Multiple Arcs and Single Arc
A dosimetric comparison between multiple static-field intensity-modulated radiation therapy (IMRT), multi-arc intensity-modulated arc therapy (IMAT) and single-arc arc-modulated radiation therapy (AMRT) was performed by the authors to evaluate the clinical advantages and shortcomings. Twelve clinical cases that was already treated with IMRT was used as templates for comparison. Cases involved patients with complex tumour such as head and neck, brain, prostate and lung cancer. All the planning procedures for the techniques were performed in their in-house planning system called Pinnacle. In general IMAT provided the most conformal planning outcome with AMRT also showing similar target coverage with the IMRT. IMAT also seemed to show more effective tissue sparing compared to IMRT while achieving better coverage of the target that are more complex. The paper provides evidence to support the use of IMAT over the IMRT in more complex clinical cases. However these results still remain controversial as no clinical outcome as yet been reported officially and still requires further research. But due to the reduced treatment time and high potential dosimetric outcome, rotational arc therapy possesses all the positive attributes wanted by clinical departments.
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Note also the following upcoming departmental seminars on Fridays, 11am-12pm also in Room 701:
23rd September
Prof Anatoly Rozenfeld Professor and Director of the Centre of Radiation Physics (University of Wollongong)
30th September
Tony Cottrill (National Radiation Lab) on his recent trip to Japan post the nuclear situation.
14th October
Frederique Vanholsbeeck, Physics Department, University of Auckland, Optical coherence tomography