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Australasian Physical & Engineering Sciences in Medicine: The Official Journal of the Australasian College of Physical Scientists and Engineers in Medicine (v.35, #4)


AFOMP Policy Statement No. 4: recommendations for continuing professional development systems for medical physicists in AFOMP countries by W. H. Round; K. H. Ng; B. Healy; L. Rodriguez; K. Thayalan; F. Tang; S. Fukuda; R. Srivastava; A. Krisanachinda; A. C. Shiau; X. Deng; Y. Han (pp. 393-397).
This policy statement, which is the fourth of a series of documents being prepared by the Asia-Oceania Federation of Organizations for Medical Physics Committees Professional Development Committee, gives guidance on how member countries could develop a continuing professional development system for ensuring that its clinical medical physicists are up-to-date in their knowledge and practice. It is not intended to be prescriptive as there are already several CPD systems successfully operated by AFOMP member countries and elsewhere that vary considerably in scope and structure according to local culture, practice and legislation but all of which are capable of ensuring that physicists are up-to-date. It is intended to be advisory and set out options for member countries to develop their individual CPD systems.

Keywords: Continuing professional development; Continuing professional education; Medical physicists; Policy


Four dimensional radiotherapy: a review of current technologies and modalities by J. Moorrees; E. Bezak (pp. 399-406).
Organ motion is a substantial concern in the treatment of thoracic tumours using radiotherapy. A number of technologies have evolved in order to address this concern in both the fields of CT imaging and radiation delivery. This review paper investigates the technologies which have been developed for the delivery of radiotherapy as well as the accuracy and workload implications of their use. Treatment techniques investigated include: breath hold, breath gating, robotic compensation and MLC manipulation. Each technique has its own advantages and drawbacks in regards to accuracy, treatment time, linac alterations and workload. Further, some treatment techniques have specific requirements for what kind of CT scans needs to be used in the planning process. This, along with the aforementioned considerations, could influence the decision as to implement some of these treatment techniques in the clinic.

Keywords: 4DRT; Four dimensional; Radiotherapy; Review

The Australian Clinical Dosimetry Service: a commentary on the first 18 months by Ivan Williams; John Kenny; Jessica Lye; Joerg Lehmann; Leon Dunn; Tomas Kron (pp. 407-411).

Comparison of blood flow velocity through the internal carotid artery based on Doppler ultrasound and numerical simulation by Hajar Hassani-Ardekani; Farzan Ghalichi; Hanieh Niroomand-Oscuii; Mehdi Farhoudi; Mohammad Kazem Tarzmani (pp. 413-422).
Doppler ultrasound is a usual non-invasive method to estimate the stenosis percentage in large arteries such as carotid by measuring maximum velocity of blood flow. Based on clinical investigations, because of vessel wall motions, Doppler positioning and angle correction, some errors can arise in Doppler results which lead to incorrect diagnosis. The aim of this study was to compare the results of Doppler test and the numerical simulation of blood flow in the same case. For this evaluation, two patients including an 87-year-old man and a 72-year-old woman suffering from stenosis in the internal carotid artery were selected. First, clinical information of each patient such as CT-Angio scan images and Doppler ultrasound results on different locations of the stenosed artery were obtained. Then, the geometries were reconstructed and numerical simulations were carried out using ANSYS software. Results showed that the velocity profile of Doppler test and numerical simulation were in good agreement at the regions of pre-and post-stenosis. However, the value of maximum velocity at the stenotic region had significant differences.

Keywords: Blood velocimetry; Doppler ultrasound; Non-Newtonian fluid; Fluid–solid interaction; Turbulence model


Performance of independent dose calculation in helical tomotherapy: implementation of the MCSIM code by Eric Dzintars; Sotirios Stathakis; Panayiotis Mavroidis; Amir Sadeghi; Nikos Papanikolaou (pp. 423-438).
Currently, a software-based second check dose calculation for helical tomotherapy (HT) is not available. The goal of this study is to evaluate the dose calculation accuracy of the in-house software using EGS4/MCSIM Monte Carlo environment against the treatment planning system calculations. In-house software was used to convert HT treatment plan information into a non-helical format. The MCSIM dose calculation code was evaluated by comparing point dose calculations and dose profiles against those from the HT treatment plan. Fifteen patients, representing five treatment sites, were used in this comparison. Point dose calculations between the HT treatment planning system and the EGS4/MCSIM Monte Carlo environment had percent difference values below 5 % for the majority of this study. Vertical and horizontal planar profiles also had percent difference values below 5 % for the majority of this study. Down sampling was seen to improve speed without much loss of accuracy. EGS4/MCSIM Monte Carlo environment showed good agreement with point dose measurements, compared to the HT treatment plans. Vertical and horizontal profiles also showed good agreement. Significant time saving may be obtained by down-sampling beam projections. The dose calculation accuracy of the in-house software using the MCSIM code against the treatment planning system calculations was evaluated. By comparing point doses and dose profiles, the EGS4/MCSIM Monte Carlo environment was seen to provide an accurate independent dose calculation.

Keywords: Independent dose calculation; Helical tomotherapy; Implementation; MCSIM code


Performance evaluation of diverse T-wave alternans estimators under variety of noise characterizations and alternans distributions by Asim Dilawer Bakhshi; Sajid Bashir; Imran Shafi; Mohammad Ali Maud (pp. 439-454).
Prognostic significance of microvolt T-wave alternans (TWA) has been established since their inclusion among important risk stratifiers for sudden cardiac death. Signal processing schemes employed for TWA estimation have their peculiar theoretical assumptions and reported statistics. An unbiased comparison of all these techniques is still a challenge. Choosing three classical schemes, this study aims to achieve holistic performance evaluation of diverse TWA estimators from a three dimensional standpoint, i.e., estimation statistics, alternan distribution and ECG signal quality. Three performance indices called average deviation (ϑ L ), moment of deviation (ϑ m ) and coefficient of deviation ( $$varphi$$ ) are devised to quantify estimator performance and consistency. Both synthetic and real physiological noises, as well as variety of temporal distributions of alternan waveforms are simulated to evaluate estimators’ responses. Results show that modification of original estimation statistics, consideration of relevant noise models and a priori knowledge of alternan distribution is necessary for an unbiased performance comparison. Spectral method proves to be the most accurate for stationary TWA, even at SNRs as low as 5 dB. Correlation method’s strength lies in accurately detecting temporal origins of multiple alternan episodes within a single analysis window. Modified moving average method gives best estimation at lower noise levels (SNR >25 dB) for non-stationary TWA. Estimation of both MMAM and CM is adversely effected by even small baseline drifts due to respiration, although CM gives considerably higher deviation levels than MMAM. Performance of SM is only effected when fundamental frequency of baseline drift due to respiration falls within the estimation band around 0.5 cpb.

Keywords: Electrocardiography; Estimation; T-wave alternans; Ventricular repolarization


Water equivalence evaluation of PRESAGE® formulations for megavoltage electron beams: a Monte Carlo study by Tina Gorjiara; Zdenka Kuncic; Robin Hill; John Adamovics; Clive Baldock (pp. 455-463).
To investigate the radiological water equivalency of three different formulations of the radiochromic, polyurethane based dosimeter PRESAGE® for three dimensional (3D) dosimetry of electron beams. The EGSnrc/BEAMnrc Monte Carlo package was used to model 6–20 MeV electron beams and calculate the corresponding doses delivered in the three different PRESAGE® formulations and water. The depth of 50 % dose and practical range of electron beams were determined from the depth dose calculations and scaling factors were calculated for these electron beams. In the buildup region, a 1.0 % difference in dose was found for all PRESAGE® formulations relative to water for 6 and 9 MeV electron beams while the difference was negligible for the higher energy electron beams. Beyond the buildup region (at a depth range of 22–26 mm for the 6 MeV beam and 38 mm for the 9 MeV beam), the discrepancy from water was found to be 5.0 % for the PRESAGE® formulations with lower halogen content than the original formulation, which was found to have a discrepancy of up to 14 % relative to water. For a 16 MeV electron beam, the dose discrepancy from water increases and reaches about 7.0 % at 70 mm depth for the lower halogen content PRESAGE® formulations and 20 % at 66 mm depth for the original formulation. For the 20 MeV electron beam, the discrepancy drops to 6.0 % at 90 mm depth for the lower halogen content formulations and 18 % at 85 mm depth for the original formulation. For the lower halogen content PRESAGE®, the depth of 50 % dose and practical range of electrons differ from water by up to 3.0 %, while the range of differences from water is between 6.5 and 8.0 % for the original PRESAGE® formulation. The water equivalent depth scaling factor required for the original formulation of PRESAGE® was determined to be 1.07–1.08, which is larger than that determined for the lower halogen content formulations (1.03) over the entire beam energy range of electrons. All three of the PRESAGE® formulations studied require a depth scaling factor to convert depth in PRESAGE® to water equivalent depth for megavoltage electron beam dosimetry. Compared to the original PRESAGE® formulation, the lower halogen content formulations require a significantly smaller scaling factor and are thus recommended over the original PRESAGE® formulation for electron beam dosimetry.

Keywords: PRESAGE® ; Electron beam dosimetry; Monte Carlo; EGSnrc/BEAMnrc


Investigating the changes in heart rate asymmetry (HRA) with perturbation of parasympathetic nervous system by Chandan Karmakar; Ahsan Khandoker; Marimuthu Palaniswami (pp. 465-474).
The heart rate asymmetry (HRA) is a disproportionate distribution of heart rate signal. The current study was designed to assess the changes in HRA in experimental conditions using Poincaré plot during parasympathetic blockade (atropine infusion) and parasympathetic enhancement (scopolamine administration). After atropine infusion, the heart rate variability in 5 out of 8 subjects was found asymmetric. In contrast, all 8 subjects were found to be asymmetric during scopolamine administration. The physiological relevance of HRA was demonstrated by showing correlation with standard frequency domain parameters during all phases of the experiment. The deviation of asymmetry index (GI p ) from symmetric range was further analyzed, which was maximum during scopolamine administration and minimum during atropine infusion. These findings suggest that parasympathetic block reduces the prevalence of HRA, and has significant correlation of GI p with frequency domain features of HRV analysis.

Keywords: Heart rate asymmetry (HRA); Heart rate variability (HRV); Poincaré plot; Parasympathetic activity


A new evaluation method for image noise reduction and usefulness of the spatially adaptive wavelet thresholding method for CT images by Mitsuru Ikeda; Reiko Makino; Kuniharu Imai (pp. 475-483).
We have proposed a direct evaluation method concerning preservation of noise-free components for image noise reduction. This evaluation method is to graphically estimate how well a noise-reduction method will preserve noise-free image components by using the normal probability plot of the image pixel value difference between an original image and its noise-reduced image; this difference is equivalent to the “method noise” which was defined by Buades et al. Further, by comparing the linearity of a normal probability plot for two different noise reduction methods, one can graphically assess which method will be more able to preserve the noise-free component than the other. As an illustrative example of this evaluation method, we have evaluated the effectiveness of the spatially-adaptive BayesShrink noise-reduced method devised by Chang et al., when applied to chest phantom CT images. The evaluation results of our proposed method were consistent with the visual impressions for the CT images processed in this study. The results of this study also indicate that the spatially-adaptive BayesShrink algorithm devised by Chang et al. will work well on the chest phantom CT images, although the assumption for this method is often violated in CT images, and the assumption postulated for the spatially-adaptive BayesShrink method is expected to have sufficient robustness for CT images.

Keywords: Medical image analysis; Image evaluation; Image noise reduction; Wavelet transform


Variations in daily quality assurance dosimetry from device levelling, feet position and backscatter material by Abdurrahman Ceylan; Martin Butson; Ashley Cullen; Peter K. N. Yu; Hani Alnawaf (pp. 485-489).
Daily quality assurance procedures are an essential part of radiotherapy medical physics. Devices such as the Sun Nuclear, DQA3 are effective tools for analysis of daily dosimetry including flatness, symmetry, energy, field size and central axis radiation dose measurement. The DQA3 can be used on the treatment couch of the linear accelerator or on a dedicated table/bed for superficial and orthovoltage x-ray machines. This device is levelled using its dedicated feet. This work has shown that depending on the quantity of backscatter material behind the DQA3 device, the position of the levelling feet can affect the measured central axis dose by up to 1.8 % (250 kVp and 6 MV) and that the introduction of more backscatter material behind the DQA3 can lead to up to 7.2 % (6 MV) variations in measured central axis dose. In conditions where no backscatter material is present, dose measurements can vary up to 1 %. As such this work has highlighted the need to keep the material behind the DQA3 device constant as well as maintaining the accuracy of the feet position on the device to effectively measure the most accurate daily constancy achievable. Results have also shown that variations in symmetry and energy calculations of up to 1 % can occur if the device is not levelled appropriately. As such, we recommend the position of the levelling feet on the device be as close as possible to the device so that a constant distance is kept between the DQA3 and the treatment couch and thus minimal levelling variations also occur. We would also recommend having no extra backscattering material behind the DQA3 device during use to minimise any variations which might occur from these backscattering effects.

Keywords: Radiotherapy; Quality assurance; Dosimetry; X-rays


The dosimetry of eye shields for kilovoltage X-ray beams by D. Wang; M. Sobolewski; R. Hill (pp. 491-495).
The objective of this work was to evaluate the dosimetry of tungsten eye shields for use with kilovoltage X-ray beam treatments. The eye shields, originally designed for megavoltage electron beams, were made of 2 mm tungsten thickness and inside diameters of 11.6 and 15.0 mm with optional aluminium caps of 0.5 and 1 mm thickness. The relative dosimetry of the eye shields were examined by measurement of transmission doses with full scatter conditions, central axis depth doses and beam profiles underneath the eye shield. The X-ray beams used in this study ranged in energy from 50 to 280 kVp. Transmission measurements were performed using an Advanced Markus ionisation chamber located at the surface of an RMI457 Solid Water phantom with a 3 cm diameter applicator flush against the phantom surface. Depth doses and profiles measurements were performed in a PTW MP3 scanning water tank with a PTW diamond detector. Results for transmission doses for the medium size eye shield increased from 1 to 22 % for 50–280 kVp while for the smaller eye shield the percentage dose increased from 3.5 to 30 % for the same energy range. There were minimal differences between using the 0.5 and 1 mm aluminium caps. Central axis depth doses measured with and without the eye shields demonstrated the 125 and 180 kVp beams had higher peak doses behind the eye shields. These results show that these tungsten eye shields are suitable for use with kilovoltage X-ray beams. However, the clinical impact needs to be considered for the higher X-ray beam energies.

Keywords: Eye shields; Kilovoltage X-rays; Radiation dosimetry; Ionisation chamber


Radiotherapy Monte Carlo simulation using cloud computing technology by C. M. Poole; I. Cornelius; J. V. Trapp; C. M. Langton (pp. 497-502).
Cloud computing allows for vast computational resources to be leveraged quickly and easily in bursts as and when required. Here we describe a technique that allows for Monte Carlo radiotherapy dose calculations to be performed using GEANT4 and executed in the cloud, with relative simulation cost and completion time evaluated as a function of machine count. As expected, simulation completion time decreases as 1/n for n parallel machines, and relative simulation cost is found to be optimal where n is a factor of the total simulation time in hours. Using the technique, we demonstrate the potential usefulness of cloud computing as a solution for rapid Monte Carlo simulation for radiotherapy dose calculation without the need for dedicated local computer hardware as a proof of principal.

Keywords: Cloud computing; Monte Carlo; GEANT4; Radiotherapy


Development of a surgical instrument for measuring forces applied to the ossicles of the middle ear by Michael Sheedy; Mike Bergin; Grant Wylie; Peter Ross; Richard Dove; Phil Bird (pp. 503-510).
Surgery of the middle ear is a delicate process that requires the surgeon to manipulate the ossicles, the smallest bones in the body. Excessive force applied to the ossicles can easily be transmitted through to the inner ear which may cause a permanent sensorineural hearing loss. An instrument was required to measure the forces applied to cadaveric temporal bone ossicles with the vision of measuring forces in vivo at a later stage. A feasibility study was conducted to investigate a method of measuring force and torque applied to the ossicles of the middle ear. Information from research papers was gathered to determine the expected amplitudes. The study looked at commercially available transducers as well as constructing an instrument using individual axis transducers coupled together. A prototype surgical instrument was constructed using the ATI industrial automation Nano17 six axis transducer. The Nano17 allows for the measurement of force and torque in the X, Y and Z axis to a resolution of 1/320 N. The use of the Nano17 enabled rapid development of the surgical instrument. It meets the requirements for its use on cadaveric models and has the potential to be a useful data collection tool in vivo.

Keywords: Middle ear; Surgical instrument; Force; Nano17
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