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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, #3)

Proton therapy: decisions, decisions by Juergen Meyer (pp. 253-256).

Generating fuzzy rules for constructing interpretable classifier of diabetes disease by Nesma Settouti; M. Amine Chikh; Meryem Saidi (pp. 257-270).

Diabetes is a type of disease in which the body fails to regulate the amount of glucose necessary for the body. It does not allow the body to produce or properly use insulin. Diabetes has widespread fallout, with a large people affected by it in world. In this paper; we demonstrate that a fuzzy c-means-neuro-fuzzy rule-based classifier of diabetes disease with an acceptable interpretability is obtained. The accuracy of the classifier is measured by the number of correctly recognized diabetes record while its complexity is measured by the number of fuzzy rules extracted. Experimental results show that the proposed fuzzy classifier can achieve a good tradeoff between the accuracy and interpretability. Also the basic structure of the fuzzy rules which were automatically extracted from the UCI Machine learning database shows strong similarities to the rules applied by human experts. Results are compared to other approaches in the literature. The proposed approach gives more compact, interpretable and accurate classifier.

Keywords: Interpretable classification; Fuzzy rules; FCM; Neuro-fuzzy ANFIS; UCI machine learning database

Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study by J.-H. Kim; R. Hill; Z. Kuncic (pp. 271-282).

In this study, we assessed the accuracy of surface doses determined by direct measurement and treatment planning system (TPS) calculations, relative to benchmark Monte Carlo (MC) doses calculated at 70 μm for a 6 MV, 10 × 10 cm clinical radiotherapy beam. In a homogeneous phantom with both open and fixed wedged fields, we found that the relative dose measured with an Attix chamber underestimates the MC calculated surface dose by 2.9 %, while the relative dose measured with EBT2 Gafchromic film overestimates the MC surface dose by 0.9 %. There was a significant over-response of up to 20 % in doses calculated at <2 mm depth with the Eclipse analytic anisotropic algorithm (AAA) compared to corresponding MC doses for an open field. This drops to <2 % at 2 mm depth. In a heterogeneous phantom, EBT2 film overestimates relative dose by up to 3.1 % compared to the MC calculated surface dose. The AAA relative dose calculated in a heterogeneous phantom at 2 mm depth agrees to within 1.5 % with the MC doses calculated at the same depth, but overestimates the MC surface dose (at 70 μm) by up to 2.5 %. Our results suggest that TPS doses evaluated near the surface be reported with a depth that should be at least 2 mm and this should be taken into consideration in the planned target volume for treatments where surface dose is a constraining factor. Our study demonstrates the usefulness of EBT2 film for measuring surface dose: under homogeneous conditions, the effective point of measurement of EBT2 film can be considered equivalent to the clinical skin depth of 70 μm.

Keywords: Surface dosimetry; Monte Carlo simulation; Treatment planning system; Gafchromic EBT2 film

A robotic catheter system with real-time force feedback and monitor by Nan Xiao; Jian Guo; Shuxiang Guo; Takashi Tamiya (pp. 283-289).

This paper presents a robotic catheter system with force sensors, monitor and a master–slave remote control system. We developed micro force sensors and applied them in the system to guarantee the operation safety in intravascular neurosurgery applications, and employed a camera to monitor the operation. Two kinds of force information are obtained through force sensors when the catheter contacted the blood vessel. The experiment shows that the proposed force sensors-based catheter system works well through force feedback and remote control. The system can facilitates the operation and avoid potential damages.

Keywords: Robotic catheter mechanism; Force sensor; Force monitoring

Experimental determination of dosimetry parameters for Sinko ¹²⁵I seed source using a modified polystyrene phantom by Yuting Duan; Menglong Zhang; Gang Wang; Liqing Du (pp. 291-296).

Successful treatment for permanent implant brachytherapy is based on accurate measurement of dosimetry parameters for the seed sources. Literature describes the application of various types of phantom to determine the AAPM TG-43 dosimetry parameters for permanent implant seeds. Previously we created a new type of phantom used to measure the dosimetry parameters of a high dose-rate ¹⁹²Ir source. In this study, we modified the phantom to suit to a common type of ¹²⁵I seed source (Sinko BT-125-1). The dose-rate constant, radial dose function and anisotropy function of this source were measured in detail and compared with the published values of other similar in-design ¹²⁵I seed sources. The experimental results exhibit fairly small measurement uncertainties and good self-consistency. The modified phantom is demonstrated on the measurement of dosimetry parameters for the Sinko BT-125-1 ¹²⁵I seed, however, it could easily be used for similar measurements of other permanent implantation seed sources.

Keywords: Brachytherapy; ¹²⁵I seed; TG43 parameters; Modified phantom

Assessment of Occupational Exposure Among Pakistani Medical Staff During 2007–2011 by Khalid Masood; Munir Ahmad; Junaid Zafar; Mumtaz ul Haq; Afshan Ashfaq; Haroon Zafar (pp. 297-300).

The data analysis of occupationally exposed medical workers in Nuclear Medicine (NM), Radiotherapy (RT) and Diagnostic Radiology (DR) at the Institute of Nuclear Medicine and Oncology (INMOL), Pakistan is presented for the time interval (2007–2011). The whole-body exposure doses of the workers were measured by using the Film Badge Dosimetry technique. The annual average effective doses in NM, RT and DR have been found well below the permissible annual limit of 20 mSv (averaged over a period of 5 consecutive years), with no over-exposure detected. This declining trend of annual average effective dose is the consequence of improved radiation protection practices at INMOL during the recent years.

Keywords: Nuclear Medicine; Radiotherapy; Dosimetry

Polymer gels impregnated with gold nanoparticles implemented for measurements of radiation dose enhancement in synchrotron and conventional radiotherapy type beams by Wan Nordiana Rahman; Christopher James Wong; Trevor Ackerly; Naoto Yagi; Moshi Geso (pp. 301-309).

Normoxic type polyacrylamide gel (nPAG) dosimeters are established for dose quantification in three-dimensions for radiotherapy and hence represent an adequate dosimeter for quantification of the dose variation due to the existence of the gold nanoparticles (AuNPs) in the target during irradiation. This work compared the degree of polymerisation in gel doped with nanoparticles (nPAG–AuNP) with control gel samples when irradiated by various sources. Samples were irradiated with a synchrotron radiation source of mean energy 125 keV, 80 kV X-ray beams from superficial therapy machine (SXRT), 6 MV X-rays and 6 MeV electron beams from linear accelerator. Analysis of the dose–response relation was used to determine a dose enhancement factor (DEF) of 1.76 ± 0.34 and 1.64 ± 0.44 obtained for samples irradiated with kilovoltage X-rays energy from synchrotron source and SXRT respectively. Similarly, including AuNPs in gel results in a DEF of approximately 1.37 ± 0.35 when irradiated by an electron beam and 1.14 ± 0.28 for high energy X-ray beams. The results demonstrate the use of AuNPs embedded in polymer gels for measuring the enhancement of radiation caused by metallic nanoparticles.

Keywords: Gold nanoparticles; Radiotherapy; Polymer gel dosimeter; Synchrotron radiation

Evaluation of automated image registration algorithm for image-guided radiotherapy (IGRT) by Shamurailatpam Dayananda Sharma; Prabhakar Dongre; Vaibhav Mhatre; Malhotra Heigrujam (pp. 311-319).

The performance of an image registration (IR) software was evaluated for automatically detecting known errors simulated through the movement of ExactCouch using an onboard imager. Twenty-seven set-up errors (11 translations, 10 rotations, 6 translation and rotation) were simulated by introducing offset up to ±15 mm in three principal axes and 0° to ±1° in yaw. For every simulated error, orthogonal kV radiograph and cone beam CT were acquired in half-fan (CBCT_HF) and full-fan (CBCT_FF) mode. The orthogonal radiographs and CBCTs were automatically co-registered to reference digitally reconstructed radiographs (DRRs) and planning CT using 2D–2D and 3D–3D matching software based on mutual information transformation. A total of 79 image sets (ten pairs of kV X-rays and 69 session of CBCT) were analyzed to determine the (a) reproducibility of IR outcome and (b) residual error, defined as the deviation between the known and IR software detected displacement in translation and rotation. The reproducibility of automatic IR of planning CT and repeat CBCTs taken with and without kilovoltage detector and kilovoltage X-ray source arm movement was excellent with mean SD of 0.1 mm in the translation and 0.0° in rotation. The average residual errors in translation and rotation were within ±0.5 mm and ±0.2°, ±0.9 mm and ±0.3°, and ±0.4 mm and ±0.2° for setup simulated only in translation, rotation, and both translation and rotation. The mean (SD) 3D vector was largest when only translational error was simulated and was 1.7 (1.1) mm for 2D–2D match of reference DRR with radiograph, 1.4 (0.6) and 1.3 (0.5) mm for 3D–3D match of reference CT and CBCT with full fan and half fan, respectively. In conclusion, the image-guided radiation therapy (IGRT) system is accurate within 1.8 mm and 0.4° and reproducible under control condition. Inherent error from any IGRT process should be taken into account while setting clinical IGRT protocol.

Keywords: OBI; IGRT; Evaluation; Image registration

Measurement and effects of MOSKIN detectors on skin dose during high energy radiotherapy treatment by Hani Alnawaf; Martin Butson; Peter K. N. Yu (pp. 321-328).

During in vivo dosimetry for megavoltage X-ray beams, detectors such as diodes, Thermo luminescent dosimeters (TLD’s) and MOSFET devices are placed on the patient’s skin. This of course will affect the skin dose delivered during that fraction of the treatment. Whilst the overall impact on increasing skin dose would be minimal, little has been quantified concerning the level of increase in absorbed dose, in vivo dosimeters produce when placed in the beams path. To this extent, measurements have been made and analysis performed on dose changes caused by MOSKIN, MOSFET, skin dose detectors. Maximum increases in skin dose were measured as 15 % for 6 MV X-rays and 10 % for 10 MV X-rays at the active crystal of the MOSKIN device which is the thickest part of the detector. This is compared to 32 and 26 % for a standard 1 mm thick LiF TLD at 10 × 10 cm² field size for 6 and 10 MV X-rays respectively. Radiochromic film, EBT2 has been shown to provide a high resolution 2 dimensional map of skin dose from these detectors and measures the effects of in vivo dosimeters used for radiotherapy dose assessment.

Keywords: Radiochromic film; Skin dose; Radiotherapy; X-rays; MOSFET; Medical physics; Dosimetry

A CAD interface for GEANT4 by C. M. Poole; I. Cornelius; J. V. Trapp; C. M. Langton (pp. 329-334).

Often CAD models already exist for parts of a geometry being simulated using GEANT4. Direct import of these CAD models into GEANT4 however, may not be possible and complex components may be difficult to define via other means. Solutions that allow for users to work around the limited support in the GEANT4 toolkit for loading predefined CAD geometries have been presented by others, however these solutions require intermediate file format conversion using commercial software. Here within we describe a technique that allows for CAD models to be directly loaded as geometry without the need for commercial software and intermediate file format conversion. Robustness of the interface was tested using a set of CAD models of various complexity; for the models used in testing, no import errors were reported and all geometry was found to be navigable by GEANT4.

Keywords: Monte Carlo; GEANT4; Computer aided design; CAD; Geometry

A phantom for verification of dwell position and time of a high dose rate brachytherapy source by M. Madebo; J. Pillainayagam; T. Kron; R. Franich (pp. 335-339).

Accuracy of dwell position and reproducibility of dwell time are critical in high dose rate (HDR) brachytherapy. A phantom was designed to verify dwell position and dwell time reproducibility for an Ir-192 HDR stepping source using Computed Radiography (CR). The central part of the phantom, incorporating thin alternating strips of lead and acrylic, was used to measure dwell positions. The outer part of the phantom features recesses containing different absorber materials (lead, aluminium, acrylic and polystyrene foam), and was used for determining reproducibility of dwell times. Dwell position errors of <1 mm were easily detectable using the phantom. The effect of bending a transfer tube was studied with this phantom and no change of clinical significance was observed when varying the curvature of the transfer tube in typical clinical scenarios. Changes of dwell time as low as 0.1 s, the minimum dwell time of the treatment unit, could be detected by choosing dwell times over the four materials that produce identical exposure at the CR detector.

Keywords: Phantom; Dwell time; Dwell position; HDR

A new approach of QRS complex detection based on matched filtering and triangle character analysis by Yanjun Li; Hong Yan; Feng Hong; Jinzhong Song (pp. 341-356).

QRS complex detection usually provides the fundamentals to automated electrocardiogram (ECG) analysis. In this paper, a new approach of QRS complex detection without the stage of noise suppression was developed and evaluated, which was based on the combination of two techniques: matched filtering and triangle character analysis. Firstly, a template of QRS complex was selected automatically by the triangle character in ECG, and then it was time-reversed after removing its direct current component. Secondly, matched filtering was implemented at low computational cost by finite impulse response, which further enhanced QRS complex and attenuated non-QRS regions containing P-wave, T-wave and various noise components. Subsequently, triangle structure-based threshold decision was processed to detect QRS complexes. And RR intervals and triangle structures were further analyzed for the reduction of false-positive and false-negative detections. Finally, the performance of the proposed algorithm was tested on all 48 records of the MIT-BIH Arrhythmia Database. The results demonstrated that the detection rate reached 99.62 %, the sensitivity got 99.78 %, and the positive prediction was 99.85 %. In addition, the proposed method was able to identify QRS complexes reliably even under the condition of poor signal quality.

Keywords: Electrocardiogram; QRS complex detection; Matched filter; QRS triangle

Evaluation of detector material and radiation source position on Compton camera’s ability for multitracer imaging by C. Z. Uche; W. H. Round; M. J. Cree (pp. 357-364).

We present a study on the effects of detector material, radionuclide source and source position on the Compton camera aimed at realistic characterization of the camera’s performance in multitracer imaging as it relates to brain imaging. The GEANT4 Monte Carlo simulation software was used to model the physics of radiation transport and interactions with matter. Silicon (Si) and germanium (Ge) detectors were evaluated for the scatterer, and cadmium zinc telluride (CZT) and cerium-doped lanthanum bromide (LaBr₃:Ce) were considered for the absorber. Image quality analyses suggest that the use of Si as the scatterer and CZT as the absorber would be preferred. Nevertheless, two simulated Compton camera models (Si/CZT and Si/LaBr₃:Ce Compton cameras) that are considered in this study demonstrated good capabilities for multitracer imaging in that four radiotracers within the nuclear medicine energy range are clearly visualized by the cameras. It is found however that beyond a range difference of about 2 cm for ^113mIn and ¹⁸F radiotracers in a brain phantom, there may be a need to rotate the Compton camera for efficient brain imaging.

Keywords: Compton camera; GEANT4; Multitracer imaging; Brain imaging

Abstracts of the 2011 South East Asian Congress of Medical Physics (SEACOMP 2011) (pp. 365-387).

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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, #3)

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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, #3)