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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.36, #1)
March 2013 editorial: Operational Statistics for the APESM Journal (Jan 2012–Feb 2013)
by Martin Caon (pp. 5-7).
International Organization for Medical Physics: policy statement and editorial (reprinted from Medical Physics 40(4) 2013)
by William Hendee (pp. 9-10).
Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation by Jiří Barilla; Miloš Lokajíček; Hana Pisaková; Pavel Simr (pp. 11-17).
Mathematical analytical model of the processes running in individual radical clusters during the chemical phase (under the presence of radiomodifiers) proposed by us earlier has been further developed and improved. It has been applied to the data presented by Blok and Loman characterizing the oxygen effect in SSB and DSB formation (in water solution and at low-LET radiation) also in the region of very small oxygen concentrations, which cannot be studied with the help of experiments done with living cells. In this new analysis the values of all reaction rates and diffusion parameters known from literature have been made use of. The great increase of SSB and DSB at zero oxygen concentration may follow from the fact that at small oxygen concentrations the oxygen absorbs other radicals while at higher concentrations the formation of oxygen radicals prevails. It explains the double oxygen effect found already earlier by Ewing. The model may be easily extended to include also the effects of other radiomodifiers present in medium during irradiation.
Keywords: Radiobiological mechanism; Chemical phase; DSB formation; Oxygen effect
Australian diagnostic reference levels for multi detector computed tomography by Anna Hayton; Anthony Wallace; Paul Marks; Keith Edmonds; David Tingey; Peter Johnston (pp. 19-26).
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) is undertaking web based surveys to obtain data to establish national diagnostic reference levels (DRLs) for diagnostic imaging. The first set of DRLs to be established are for multi detector computed tomography (MDCT). The survey samples MDCT dosimetry metrics: dose length product (DLP, mGy.cm) and volume computed tomography dose index (CTDIvol, mGy), for six common protocols/habitus: Head, Neck, Chest, AbdoPelvis, ChestAbdoPelvis and Lumbar Spine from individual radiology clinics and platforms. A practice reference level (PRL) for a given platform and protocol is calculated from a compliant survey containing data collected from at least ten patients. The PRL is defined as the median of the DLP/CTDIvol values for a single compliant survey. Australian National DRLs are defined as the 75th percentile of the distribution of the PRLs for each protocol and age group. Australian National DRLs for adult MDCT have been determined in terms of DLP and CTDIvol. In terms of DLP the national DRLs are 1,000 mGy cm, 600 mGy cm, 450 mGy cm, 700 mGy cm, 1,200 mGy cm, and 900 mGy cm for the protocols Head, Neck, Chest, AbdoPelvis, ChestAbdoPelvis and Lumbar Spine respectively. Average dose values obtained from the European survey Dose Datamed I reveal Australian doses to be higher by comparison for four out of the six protocols. The survey is ongoing, allowing practices to optimise dose delivery as well as allowing the periodic update of DRLs to reflect changes in technology and technique.
Keywords: Diagnostic reference level; Computed tomography; Effective dose
Straightened cervical lordosis causes stress concentration: a finite element model study by Wei Wei; Shenhui Liao; Shiyuan Shi; Jun Fei; Yifan Wang; Chunyue Chen (pp. 27-33).
In this study, we propose a finite element analysis of the complete cervical spine with straightened and normal physiological curvature by using a specially designed modelling system. An accurate finite element model is established to recommend plausible approaches to treatment of cervical spondylosis through the finite element analysis results. There are few reports of biomechanics influence of the straightened cervical curve. It is difficult to measure internal responses of cervical spine directly. However, the finite element method has been reported to have the capability to quantify both external and internal responses to mechanical loading, such as the strain and stress distribution of spinal components. We choose a subject with a straightened cervical spine from whom to collect the CT scan data, which formed the basis of the finite element analysis. By using a specially designed modelling system, a high quality finite element model of the complete cervical spine with straightened curvature was generated, which was then mapped to reconstruct a normal physiological curvature model by a volumetric mesh deformation method based on discrete differential properties. Then, the same boundary conditions were applied to do a comparison. The result demonstrated that the active movement range of straightened cervical spine decreased by 24–33 %, but the stress increased by 5–95 %. The stress was concentrated at the facet joint cartilage, uncovertebral joint and the disk. The results suggest that cervical lordosis may have a direct impact on cervical spondylosis treatment. These results may be useful for clinical treatment of cervical spondylosis with straightened curvature.
Keywords: Biomechanics; Finite element method; Cervical Lordosis; Cervical spondylosis treatment
Performance of spinal cord injury individuals while standing with the Mohammad Taghi Karimi reciprocal gait orthosis (MTK-RGO) by Mohammad Taghi Karimi; Pouya Amiri; Amir Esrafilian; Jafar Sedigh; Francis Fatoye (pp. 35-42).
Most patients with spinal cord injury use a wheelchair to transfer from place to place, however they need to stand and walk with orthosis to improve their health status. Although many orthoses have been designed for paraplegic patients, they have experienced various problems while in use. A new type of reciprocal gait orthosis was designed in the Bioengineering Unit of Strathclyde University to solve the problems of the available orthoses. Since there was no research undertaken regarding testing of the new orthosis on paraplegic subjects, this study was aimed to evaluate the new orthosis during standing of paraplegic subjects. Five paraplegic patients with lesion level between T12 and L1 and aged matched normal subjects were recruited into this study. The stability of subjects was evaluated during quiet standing and while undertaking hand tasks during standing with the new orthosis and the knee ankle foot orthosis (KAFO). The difference between the performances of paraplegic subjects while standing with both orthoses, and between the function of normal and paraplegic subjects were compared using the paired t test and independent sample t test, respectively. The stability of paraplegic subjects in standing with the new orthosis was better than that of the KAFO orthosis (p < 0.05). Moreover, the force applied on the crutch differed between the orthoses. The functional performance of paraplegic subjects was better with the new orthosis compared with normal subjects. The performance of paraplegic subjects while standing with the new orthosis was better than the KAFO. Therefore, the new orthosis may be useful to improve standing and walking in patients with paraplegia.
Keywords: Standing; Spinal cord injury; Functional hand task; Orthosis
Effects of fatigue on microstructure and mechanical properties of bone organic matrix under compression by Hanna Trębacz; Artur Zdunek; Justyna Cybulska; Piotr Pieczywek (pp. 43-54).
The aim of the study was to investigate whether a fatigue induced weakening of cortical bone was revealed in microstructure and mechanical competence of demineralized bone matrix. Two types of cortical bone samples (plexiform and Haversian) were use. Bone slabs from the midshaft of bovine femora were subjected to cyclical bending. Fatigued and adjacent control samples were cut into cubes and demineralized in ethylenediaminetetraacetic acid. Demineralized samples were either subjected to microscopic quantitative image analysis, or compressed to failure (in longitudinal or transverse direction) with a simultaneous analysis of acoustic emission (AE). In fatigued samples porosity of organic matrix and average area of pores have risen, along with a change in the pores shape. The effect of fatigue depended on the type of the bone, being more pronounced in the plexiform than in Haversian tissue. Demineralized bone matrix was anisotropic under compressive loads in both types of cortical structure. The main result of fatigue pretreatment on mechanical parameters was a significant decrease of ultimate strain in the transverse direction in plexiform samples. The decrease of strain in this group was accompanied by a considerable increase of the fraction of large pores and a significant change in AE energy.
Keywords: Acoustic emission; Anisotropy; Bovine cortical bone; Fatigue; Image analysis
An Australian secondary standard dosimetry laboratory participation in IAEA postal dose audits by J. B. Davies; J. Izewska; H. Meriaty; C. Baldock (pp. 55-58).
For over 30 years, the International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) have jointly monitored activities of secondary standard dosimetry laboratories (SSDLs) through postal dose audits with the aim of achieving consistency in dosimetry throughout the world. The Australian Nuclear Science and Technology Organisation (ANSTO) maintains an SSDL and is a member of the IAEA/WHO SSDL Network. Postal dose audit results at this Australian SSDL from 2001 to 2011 demonstrate the consistency of absorbed dose to water measurements, underpinned by the primary standard maintained at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).
Keywords: TLD; Dose audit; SSDL network
Evaluation of GAFCHROMIC EBT2 dosimetry for the low dose range using a flat-bed scanner with the reflection mode by Tatsuhiro Gotanda; Toshizo Katsuda; Takuya Akagawa; Rumi Gotanda; Akihiko Tabuchi; Kenyu Yamamoto; Tadao Kuwano; Hidetoshi Yatake; Koichi Yabunaka; Yoshihiro Takeda (pp. 59-63).
Recently developed radiochromic films can easily be used to measure absorbed doses because they do not need development processing and indicate a density change that depends on the absorbed dose. However, in GAFCHROMIC EBT2 dosimetry (GAF-EBT2) as a radiochromic film, the precision of the measurement was compromised, because of non-uniformity problems caused by image acquisition using a flat-bed scanner with a transmission mode. The purpose of this study was to improve the precision of the measurement using a flat-bed scanner with a reflection mode at the low absorbed dose dynamic range of GAF-EBT2. The calibration curves of the absorbed dose versus the film density for GAF-EBT2 were provided. X-rays were exposed in the range between ~0 and 120 mGy in increments of about 12 mGy. The results of the method using a flat-bed scanner with the transmission mode were compared with those of the method using the same scanner with the reflection mode. The results should that the determination coefficients (r 2 ) for the straight-line approximation of the calibration curve using the reflection mode were higher than 0.99, and the gradient using the reflection mode was about twice that of the one using the transmission mode. The non-uniformity error that is produced by a flat-bed scanner with the transmission mode setting could be almost eliminated by converting from the transmission mode to the reflection mode. In light of these findings, the method using a flat-bed scanner with the reflection mode (only using uniform white paper) improved the precision of the measurement for the low absorbed dose range.
Keywords: Radiochromic film; Flat-bed scanner; Transmission mode; Reflection mode; Density resolution