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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, #2)

APSIG at heart by Simon Downes (pp. 113-115).

Comparison of organ dosimetry methods and effective dose calculation methods for paediatric CT by Z. Brady; T. M. Cain; P. N. Johnston (pp. 117-134).

Computed tomography (CT) is the single biggest ionising radiation risk from anthropogenic exposure. Reducing unnecessary carcinogenic risks from this source requires the determination of organ and tissue absorbed doses to estimate detrimental stochastic effects. In addition, effective dose can be used to assess comparative risk between exposure situations and facilitate dose reduction through optimisation. Children are at the highest risk from radiation induced carcinogenesis and therefore dosimetry for paediatric CT recipients is essential in addressing the ionising radiation health risks of CT scanning. However, there is no well-defined method in the clinical environment for routinely and reliably performing paediatric CT organ dosimetry and there are numerous methods utilised for estimating paediatric CT effective dose. Therefore, in this study, eleven computational methods for organ dosimetry and/or effective dose calculation were investigated and compared with absorbed doses measured using thermoluminescent dosemeters placed in a physical anthropomorphic phantom representing a 10 year old child. Three common clinical paediatric CT protocols including brain, chest and abdomen/pelvis examinations were evaluated. Overall, computed absorbed doses to organs and tissues fully and directly irradiated demonstrated better agreement (within approximately 50 %) with the measured absorbed doses than absorbed doses to distributed organs or to those located on the periphery of the scan volume, which showed up to a 15-fold dose variation. The disparities predominantly arose from differences in the phantoms used. While the ability to estimate CT dose is essential for risk assessment and radiation protection, identifying a simple, practical dosimetry method remains challenging.

Keywords: Computed tomography; Paediatric; Organ absorbed dose; Effective dose; Dosimetry

An automated approach for segmentation of intravascular ultrasound images based on parametric active contour models by Alireza Vard; Kamal Jamshidi; Naser Movahhedinia (pp. 135-150).

This paper presents a fully automated approach to detect the intima and media-adventitia borders in intravascular ultrasound images based on parametric active contour models. To detect the intima border, we compute a new image feature applying a combination of short-term autocorrelations calculated for the contour pixels. These feature values are employed to define an energy function of the active contour called normalized cumulative short-term autocorrelation. Exploiting this energy function, the intima border is separated accurately from the blood region contaminated by high speckle noise. To extract media-adventitia boundary, we define a new form of energy function based on edge, texture and spring forces for the active contour. Utilizing this active contour, the media-adventitia border is identified correctly even in presence of branch openings and calcifications. Experimental results indicate accuracy of the proposed methods. In addition, statistical analysis demonstrates high conformity between manual tracing and the results obtained by the proposed approaches.

Keywords: Segmentation; Active contour models; Intravascular ultrasound; Autocorrelation; Texture

Optimisation of exposure conditions for in vitro radiobiology experiments by Elizabeth Claridge Mackonis; Natalka Suchowerska; Pourandokht Naseri; David R. McKenzie (pp. 151-157).

Despite the long history of using cell cultures in vitro for radiobiological studies, there is to date no study specifically addressing the dosimetric implications of flask selection and exposure environment in clonogenic assays. The consequent variability in dosimetry between laboratories impedes the comparison of results. In this study we compare the dose to cells adherent to the base of three types of commonly used culture flasks or plates. The cells are exposed to a 6MV clinical photon beam using either an open or a half blocked field. The depth of medium in each flask is varied with the medium surrounding the flask either water or air. The results show that the dose to the cells is more affected by the scattering conditions surrounding the flasks than by the level of filling within the flask. It is recommended that water or a water equivalent phantom material is used to surround the flasks or plates to approximate full scatter conditions at the cell layer. However for modulated fields, surrounding the 24 well plates with water-equivalent material is inadequate because of the large volume of air surrounding individual wells. Our results stress the importance of measuring the dose for new experimental configurations.

Keywords: Radiobiology; Dosimetry; In vitro; Irradiation; MV

Tools to analyse and display variations in anatomical delineation by Martin A. Ebert; L. N. McDermott; A. Haworth; E. van der Wath; B. Hooton (pp. 159-164).

Variations in anatomical delineation, principally due to a combination of inter-observer contributions and image-specificity, remain one of the most significant impediments to geometrically-accurate radiotherapy. Quantification of spatial variability of the delineated contours comprising a structure can be made with a variety of metrics, and the availability of software tools to apply such metrics to data collected during inter-observer or repeat-imaging studies would allow their validation. A suite of such tools have been developed which use an Extensible Markup Language format for the exchange of delineated 3D structures with radiotherapy planning or review systems. These tools provide basic operations for manipulating and operating on individual structures and related structure sets, and for deriving statistics on spatial variations of contours that can be mapped onto the surface of a reference structure. Use of these tools on a sample dataset is demonstrated together with import and display of results in the SWAN treatment plan review system.

Keywords: Anatomical delineation; Inter-observer variation; Clinical trials; Radiotherapy; Software

Combining the LKB NTCP model with radiosensitivity parameters to characterize toxicity of radionuclides based on a multiclonogen kidney model: a theoretical assessment by Hui Lin; Jia Jing; Liangfeng Xu; Dongsheng Wu; Yuanying Xu (pp. 165-176).

The Lyman–Kutcher–Burman (LKB) normal tissue complication probability (NTCP) model is often used to estimate the damage level to normal tissue. However, it does not manifestly involve the influence of radiosensitivity parameters. This work replaces the generalized mean equivalent uniform dose (gEUD) with the equivalent uniform dose (EUD) in the LKB model to investigate the effect of a variety of radiobiological parameters on the NTCP to characterize the toxicity of five types of radionuclides. The dose for 50 % complication probability (D ₅₀) is replaced by the corresponding EUD for 50 % complication probability (EUD₅₀). The properties of a variety of radiobiological characteristics, such as biologically effective dose (BED), NTCP, and EUD, for five types of radioisotope (¹³¹I, ¹⁸⁶Re, ¹⁸⁸Re, ⁹⁰Y, and ⁶⁷Cu) are investigated by various radiosensitivity parameters such as intrinsic radiosensitivity α, alpha–beta ratio α/β, cell repair half-time, cell mean clonogen doubling time, etc. The high-energy beta emitters (⁹⁰Y and ¹⁸⁸Re) have high initial dose rate and mean absorbed dose per injected activity in kidney, and their kidney toxicity should be of greater concern if they are excreted through kidneys. The radiobiological effect of ¹⁸⁸Re changes most sharply with the radiobiological parameters due to its high-energy electrons and very short physical half-life. The dose for a probability of 50% injury within 5y (D _50/5) 28 Gy for whole-kidney irradiation should be adjusted according to different radionuclides and different radiosensitivity of individuals. The D _50/5 of individuals with low α/β or low α, or low biological clearance half-time, will be less than 28 Gy. The 50 % complication probability dose for ⁶⁷Cu and ¹⁸⁸Re could be 25 Gy and 22 Gy. The same mean absorbed dose generally corresponds to different degrees of damage for tissues of different radiosensitivity and different radionuclides. The influence of various radiobiological parameters should be taken into consideration in the NTCP model.

Keywords: NTCP LKB model; Radiosensitivity parameter; Toxicity evaluation; Radionuclide; Multiclonogen model

A Monte Carlo study on tissue dose enhancement in brachytherapy: a comparison between gadolinium and gold nanoparticles by Mohammad Taghi Bahreyni Toossi; Mahdi Ghorbani; Mohammad Mehrpouyan; Fateme Akbari; Leila Sobhkhiz Sabet; Ali Soleimani Meigooni (pp. 177-185).

The aim of this study was to quantify the dose enhancement by gadolinium and gold nanoparticles in brachytherapy. MCNPX Monte Carlo code was used to simulate four brachytherapy sources: ⁶⁰Co, ¹⁹⁸Au, ¹⁹²Ir, ¹⁶⁹Yb. To verify the accuracy of our simulations, the obtained values of dose rate constants and radial dose functions were compared with corresponding published values for these sources. To study dose enhancements, a spherical soft tissue phantom with 15 cm in radius was simulated. Gadolinium and gold nanoparticles at 10, 20 and 30 mg/ml concentrations were separately assumed in a 1 × 1 × 1 cm³ volume simulating tumour. The simulated dose to the tumour with the impurity was compared to the dose without impurity, as a function of radial distance and concentration of the impurity, to determine the enhancement of dose due to the presence of the impurity. Dose enhancements in the tumour obtained in the presence of gadolinium and gold nanoparticles with concentration of 30 mg/ml, were found to be in the range of −0.5–106.1 and 0.4–153.1 % respectively. In addition, at higher radial distances from the source center, higher dose enhancements were observed. GdNPs can be used as a high atomic number material to enhance dose in tumour volume with dose enhancements up to 106.1 % when used in brachytherapy. Regardless considering the clinical limitations of the here-in presented model, for a similar source and concentration of nanoparticles, gold nanoparticles show higher dose enhancement than gadolinium nanoparticles and can have more clinical usefulness as dose enhancer material.

Keywords: Brachytherapy; Dose enhancement; Monte Carlo simulation; Gadolinium nanoparticles; Gold nanoparticles

Clinical assessment of dynamic coefficient of friction effects in shoe-sole trituration of patients with drop foot by Jamshidi Nima; Salami Firooz (pp. 187-191).

The aim of this study was examining the effect of human factors such as plantar friction, contact period time, and impulse on shoe-sole trituration of drop foot patients. Twenty-five patients with drop foot and twenty normal subjects were recruited in the study. The force plate and its related software’s recorded human factor (coefficient of friction, ground reaction force, time of stance phase) as time dependent parameters. Dynamic coefficient of friction patterns were categorized based on their magnitude versus time when the longitudinal axis of the sole was plotted as the Y-axis and the transverse axis of the sole as X-axis during stance phase. The result of this research indicated that the average coefficient of friction among drop foot patients is 77.53 % (p value <0.05) lower than the normal subjects. Also the time of stance phase among drop foot patients is 7.56 % (p value <0.05) greater than normal subjects. There is no difference in the peaks, of vertical ground reaction force between normal and control group. The findings of this research revealed that the time of stance phase has a key role in shoe-sole trituration of patients with drop foot.

Keywords: Steppage gait; Force plate; Shoe design

Predicting the continuous values of breast cancer relapse time by type-2 fuzzy logic system by Hamid Mahmoodian (pp. 193-204).

Microarray analysis and gene expression profile have been widely used in tumor classification, survival analysis and ER statues of breast cancer. Sample discrimination as well as identification of significant genes have been the focus of most previous studies. The aim of this research is to propose a fuzzy model to predict the relapse time of breast cancer by using breast cancer dataset published by van’t Veer. Fuzzy rule mining based on support vector machine has been used in a hybrid method with rule pruning and shown its ability to divide the samples in many subgroups. To handle the existence of uncertainties in linguistic variables and fuzzy sets, the TSK model of Interval type-2 fuzzy logic system has been used and a new simple method is also developed to consider the uncertainties of the rules which have been optimized by genetic algorithm. B632 validation method is applied to estimate the error of the model. The results with 95 % confidence interval show a reasonable accuracy in prediction.

Keywords: Gene expression profile; Breast cancer; Fuzzy systems; Relapse time

On the accuracy of localization achievable in fiducial-based stereoscopic image registration system using an electronic portal imaging device by N. M. Ung; L. Wee (pp. 205-213).

Portal imaging using electronic portal imaging device (EPID) is a well-established image-guided radiation therapy (IGRT) technique for external beam radiation therapy. The aims of this study are threefold; (i) to assess the accuracy of isocentre localization in the fiducial-based stereoscopic image registration, (ii) to investigate the impact of errors in the beam collimation device on stereoscopic registration, and (iii) to evaluate the intra- and inter-observer variability in stereoscopic registration. Portal images of a ball bearing phantom were acquired and stereoscopic image registrations were performed based on a point centred in the ball bearing as the surrogate for registration. Experiments were replicated by applying intentional offsets in the beam collimation device to simulate collimation errors. The accuracy of fiducial markers localization was performed by repeating the experiment using three spherical lead shots implanted in a pelvic phantom. Portal images of pelvis phantom were given to four expert users to assess the inter-observer variability in performing registration. The isocentre localization accuracy tested using ball bearing phantom was within 0.3 mm. Gravity-induced systematic errors of beam collimation device by 2 mm resulted in positioning offsets of the order of 2 mm opposing the simulated errors. Relatively large inter-portal pair projection errors ranges from 1.3 mm to 1.8 mm were observed with simulated errors in the beam collimation device. The intra-user and inter-user variabilities were observed to be 0.8 and 0.4 mm respectively. Fiducial-based stereoscopic image registration using EPID is robust for IGRT procedure.

Keywords: Electronic portal imaging device; Fiducial markers; Stereoscopic image registration; Systematic and random errors

Paediatric dose measurements for chest X-ray examinations at Maternity and Children Hospital in Najran - Saudi Arabia by M. K. Saeed; J. M. Al-Qahtani (pp. 215-219).

The entrance skin dose (ESD) of chest X-ray examinations for AP and PA projections of paediatric patients at Maternity and Children Hospital in Najran, Saudi Arabia have been obtained using DoseCal software. The majority of the results obtained show low measured ESD for chest X-ray examinations. The mean of ESD for the AP projection was found to be 37.5, 40.5, 41.3, and 52.3 μ Gy for age groups 0−1, >1−5, >5−10, and >10−15 years respectively. However, the ESD for PA projection was found to be 50.7 and 56.7 μ Gy for age groups >5−10, and >10−15 years respectively.

Keywords: X-ray; DoseCal; Chest X-ray; Entrance skin dose

Development of digital reconstructed radiography software at new treatment facility for carbon-ion beam scanning of National Institute of Radiological Sciences by Shinichiro Mori; Taku Inaniwa; Motoki Kumagai; Tsunekazu Kuwae; Yuka Matsuzaki; Takuji Furukawa; Toshiyuki Shirai; Koji Noda (pp. 221-229).

To increase the accuracy of carbon ion beam scanning therapy, we have developed a graphical user interface-based digitally-reconstructed radiograph (DRR) software system for use in routine clinical practice at our center. The DRR software is used in particular scenarios in the new treatment facility to achieve the same level of geometrical accuracy at the treatment as at the imaging session. DRR calculation is implemented simply as the summation of CT image voxel values along the X-ray projection ray. Since we implemented graphics processing unit-based computation, the DRR images are calculated with a speed sufficient for the particular clinical practice requirements. Since high spatial resolution flat panel detector (FPD) images should be registered to the reference DRR images in patient setup process in any scenarios, the DRR images also needs higher spatial resolution close to that of FPD images. To overcome the limitation of the CT spatial resolution imposed by the CT voxel size, we applied image processing to improve the calculated DRR spatial resolution. The DRR software introduced here enabled patient positioning with sufficient accuracy for the implementation of carbon-ion beam scanning therapy at our center.

Keywords: Carbon-ion-beam treatment; Digital reconstructed tomography; Image quality; Scanning irradiation

Investigation of the haemodynamic environment of bifurcation plaques within the left coronary artery in realistic patient models based on CT images by Thanapong Chaichana; Zhonghua Sun; James Jewkes (pp. 231-236).

The aim of this study was to investigate the plaques at the left coronary artery (LCA) and their effect on the haemodynamic and wall shear stress (WSS) in realistic patient models. Three sample patients with left coronary disease were selected based on CT data. The plaques were present at the left anterior descending and left circumflex branches with more than 50 % lumen narrowing. Computational fluid dynamics analysis was used to perform simulation of patient-specific models with realistic physiological conditions that demonstrate in vivo cardiac flow. WSS and blood flow in the LCA were measured during cardiac cycles. Our results showed that WSS was found to increase at the stenotic locations and decrease at pre- and post-plaque locations, whilst the recirculation location was found at post-plaque regions. There is a strong correlation between coronary bifurcation plaques and hemodynamic and WSS changes, based on the realistic coronary disease models.

Keywords: Atherosclerosis; Haemodynamic; Computational fluid dynamics; Coronary artery disease; Plaques

Paperless medical physics QA in radiation therapy by J. Luo; S. Yau; S. White; L. Wilfert (pp. 237-243).

Physics quality assurance (QA) is an integral part of a medical physicist’s role in the radiotherapy centre. Management of physics QA documents is an issue with a long-term accumulation. Storage space, archive administration and paper consumption are just some of the difficulties faced by physicists. Plotting trends and drawing meaningful conclusions from these results can be challenging using traditional QA methods. Remote checking of QA within a hospital network can also be problematic. The aim of this project is introduce a paperless QA system that will provide solutions to many of these issues.

Keywords: Quality assurance; Paperless; Trend; Documentation

Changes to dose at surface and shifts of dose distributions at depth through dry and wet wound dressings for photon and electron beam radiotherapy by Ciara Mac Nally; Simon Woodings (pp. 245-250).

Wound dressings are used during patient radiotherapy treatments, particularly in cases of radiation induced lesions. Potentially, the presence of a dressing may increase the dose to the skin, further aggravating the skin reaction and decrease the dose at depth. The changes are dependent on linear accelerator beam type and beam quality and were determined for 4 and 10 MV photon energies and 6 and 15 MeV electron energies using a slab phantom and fixed separation parallel plate chambers. Since these dressings have been designed to be used on exuding wounds, measurements were taken under eight different wound dressings in both dry and wet state. Irradiations with photon energies increased the skin dose significantly (max. increase: 68.1 %; average increase: 48 %) with little or no change to dose at depth. Electron beam energies showed little or no change to doses at the surface, but the dose distribution was shifted towards the surface. The maximum decrease in dose at depth was 3.6 % for 6 and 15 MeV through all dressings except one and was therefore considered to be clinically insignificant. A change in dose at surface of 9.7 % and at R₅₀ of 25.9 %, equivalent to a shift of dose towards the surface of 7.5 mm, was measured for one dressing. This demonstrates that it is possible for a wet dressing to significantly alter electron beam dosimetry.

Keywords: Wound dressing; Radiotherapy; Dosimetry; Skin dose; Dose at depth; Exuding wounds

L. Marcu, E. Bezak and B. Allen: Biomedical physics in radiotherapy for cancer by Tomas Kron (pp. 251-252).

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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, #2)

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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, #2)