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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, #1)

A Computed Tomography (CT) wish list, from a medical physicist’s perspective by Zoe Brady; Paul Einsiedel (pp. 1-5).

Incorrect and inconsistent use of trade marks by contributors to APESM by Chuan-Dong Wen; Trevor Ackerly (pp. 7-8).

Four dimensional CT imaging: a review of current technologies and modalities by J. Moorrees; E. Bezak (pp. 9-23).

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 both during computed tomography (CT) imaging and radiation delivery. This review paper investigates the various technologies which have been developed in the field of CT scanning as well as their accuracy, cost and the implications of their clinical implementation. The scanning modalities covered include: slow CT, breath hold CT, gated CT and retrospectively correlated CT (4DCT). It was found that there are advantages and drawbacks to each of the mentioned techniques relating to patient dose, scan time, extra equipment and workload. Also some scanning techniques are only compatible with certain treatment modalities which would further influence the decision as to which technologies to implement.

Keywords: 4DCT; Review; Four dimensional; Retrospective; Prospective; Gated; Breath hold

Study of chaotic behavior of tremor of some Parkinsonians under deep brain stimulation by Mehrzad SadeghiRazlighi; Amir Homayoun Jafari; Seyyed Mohammad Firoozabadi; Gholam Ali Shahidi (pp. 25-30).

Deep Brain Stimulation, functional neurosurgery for Parkinson’s disease treatment, has three parameters: frequency, pulse width, and voltage. They should be selected appropriately to achieve an effective treatment. In this research, we studied some nonlinear dynamics of Parkinsonian tremor under Deep Brain Stimulation. We recorded finger tremor signals of 8 patients at different voltages as data. To study tremor behavior variation at different voltages, we extracted some nonlinear dynamic features of the data. These features were: embedding space, correlation dimension, largest Lyapunov exponent, entropy and variance of embedding space along x, and y axes. We found that the largest Lyapunov exponents were positive and correlation dimensions of data were not integer, and also all embedding spaces at different voltages had attractors. These observations show that the tremor signal has chaotic behaviors. Also, embedding space variance along x, and y axes in all cases and entropy in the most of them had minimum values at highest voltages in comparison with other voltages. We plotted bar graphs of embedding space variances along x, and y axes at every patient’s recorded voltages. A reduction procedure was seen after a threshold in all graphs. As a result, all the chaotic features change with the voltage variation. In the future, it could be possible to select the optimum stimulation voltages by using chaotic features of tremor.

Keywords: Parkinson’s disease; Tremor; Deep brain stimulation; Nonlinear dynamics; Chaos; Stimulation parameter

Respiration-rate estimation of a moving target using impulse-based ultra wideband radars by Azadeh Sharafi; Mehran Baboli; Mohammad Eshghi; Alireza Ahmadian (pp. 31-39).

Recently, Ultra-wide band signals have become attractive for their particular advantage of having high spatial resolution and good penetration ability which makes them suitable in medical applications. One of these applications is wireless detection of heart rate and respiration rate. Two hypothesis of static environment and fixed patient are considered in the method presented in previous literatures which are not valid for long term monitoring of ambulant patients. In this article, a new method to detect the respiration rate of a moving target is presented. The first algorithm is applied to the simulated and experimental data for detecting respiration rate of a fixed target. Then, the second algorithm is developed to detect respiration rate of a moving target. The proposed algorithm uses correlation for body movement cancellation, and then detects the respiration rate based on energy in frequency domain. The results of algorithm prove an accuracy of 98.4 and 97% in simulated and experimental data, respectively.

Keywords: Wireless detection; Body movement cancellation; UWB; FPGA

Monte Carlo simulation of the effect of focal spot size on contrast-detail detectability by John Poletti; Donald McLean (pp. 41-48).

A contrast-detail experiment was simulated using Monte Carlo methods, to test the hypothesis that quantum limitations lead to an optimum minimum focal spot size below which no further improvement in image quality may be obtained. The simulation included a variable X-ray tube focal spot size, patient equivalent water phantom, X-ray couch, automatic exposure control, anti-scatter grid and indirect digital radiography detector. A number of simplifications were necessary in order to limit the calculation time to 8 days per image. Four images were produced for each focal spot size and these were scored by eight experienced observers. The contrast-detail curves were found to improve monotonically as focal spot size was reduced, with the best images produced by a point source. This contradicts the hypothesis of quantum limitation of focal spot size. We conclude that further work is required on the optimization of focal spot size. To assist with this, a new definition of system detective quantum efficiency is suggested, that includes the focal spot modulation transfer function, but does not include scattered radiation from the patient.

Keywords: Focal spot; Contrast-detail; Quantum noise

A retrospective evaluation of radiation dose associated with low dose FDG protocols in whole-body PET/CT by Kathy P. Willowson; Elizabeth A. Bailey; Dale L. Bailey (pp. 49-53).

The objective of the study is to retrospectively measure patient radiation dose resulting from whole body X-ray CT and FDG PET studies using a low-dose protocol performed on the Siemens Biograph mCT scanner. A total of 483 patient studies were reviewed. For each, the CT dose-length product was used to estimate radiation dose to the patient as a result of the whole body X-ray CT component of the PET/CT study. The net injected FDG dose was used to calculate the whole body effective dose based on ICRP recommendations. Dose calculations were also modified to take into account individual patient weight. The total effective dose received by each patient was taken as the sum of the PET and CT components of the study. The mean effective dose from the CT component of the diagnostic study was found to be 8.2 mSv (3.4–23.4 mSv), for a CT protocol of 120 kV_p and effective tube current–time product of 80 mAs with automatic exposure control. For an average injected FDG activity of 304 MBq the mean PET effective dose was found to be 6.3 mSv when using the ICRP standard models, or 6.0 mSv when scaling effective dose to individual patient weight or patient blood volume. The average total effective dose across the entire patient cohort for a combined PET/CT study was found to be ~14.5 mSv (9.6–29.8 mSv). Low-dose protocols for whole-body PET/CT scanning result in an effective radiation dose to the patient of approximately 14.5 mSv. Additional reductions through the use of iterative CT reconstruction and optimized low-dose FDG protocols could see total effective doses for whole-body PET/CT fall to below 10 mSv.

Keywords: FDG; Dosimetry; PET; CT

The influence of walking with an orthosis on bone mineral density by determination of the absolute values of the loads applied on the limb by Mohammad Taghi Karimi (pp. 55-61).

Spinal cord injury is damage to the spinal cord that results in loss of mobility and sensation below the level of injury. Most patients use various types of orthoses to stand and walk. It has been claimed that walking and standing with orthosis reduces bone osteoporosis, improves joint range of motion and decreases muscle spasm. Unfortunately, there are discrepancies regarding the clinical effects of walking and standing on bone mineral density. The aim of this research was to find the absolute values of the loads transmitted by body and orthosis in walking with use of an orthosis. 5 normal subjects were recruited to stand and walk with a new design of reciprocal gait orthosis. The loads transmitted through the orthosis and anatomy was measured by use of strain gauge and motion analysis systems. It has been shown that the loads applied on the anatomy were significantly more than that transmitted through the orthosis. Moreover, the patterns of the forces and moments of the orthosis and body completely differed from each other. As the most part of the loads applied on the complex transmitted by anatomy in walking with an orthosis, walking with orthosis can influence bone mineral density.

Keywords: Orthosis; Paraplegia; Osteoporosis

¹⁵³Sm-HM for arthritic knee pain. Estimated dosimetry by Alberto E. Hardy-Pérez; Eugenio Torres-García; Consuelo Arteaga-de-Murphy; Martha Pedraza-López; Eleni Mitsoura; Nallely P. Jiménez-Mancilla (pp. 63-69).

Osteoarthritis is the most common type of arthropathy and after cardiovascular diseases is the most disabling disease in developing countries. The dosimetry for the clinical application of 153-samarium-hydroxymacroaggregates (¹⁵³Sm-HM) for radiation synovectomy (RSV) and palliative treatment for arthritic pain, as far as we know, has not been reported. The aim of this research was to estimate the radiation dose necessary for synovial ablation and pain palliation with minimum risk to the patient. ¹⁵³Sm-HM (370 MBq) was administered intra-articularly in a patient with severe knee pain and hindered motility. Regions of interest drawn on sequential, conjugated, anterior and posterior scintigraphy images were used to obtain the respective activity. The data was entered into a knee joint histological-geometric model designed with micrometric dimensions to represent the synovial cell layers. The Monte Carlo code was used to calculate the absorbed dose in each of the 12 model-cells representing the distance from the synovial liquid to the cartilage or bone. The absorbed dose in the synovial cavity was 114 Gy which is sufficient energy for RSV. The treated patient referred little pain and higher motility with no adverse reactions. ¹⁵³Sm-HM is a potentially valid radiopharmaceutical for RSV, which effectively palliates knee pain.

Keywords: ¹⁵³Sm-HM; Arthrosis; Knee dosimetry; Pain palliation; Knee pain

Digital chest radiography image quality assessment with dose reduction by R. K. Grewal; N. Young; L. Collins; N. Karunaratne; R. Sabharwal (pp. 71-80).

A retrospective study of digital chest radiography was performed to compare the image quality and dose parameters from two X-ray rooms in different areas of the same hospital using identical X-ray units but different local protocol for obtaining chest PA and lateral radiographs. Image quality of radiographs was assessed from the printed films using well established European guidelines and modified criteria. Patient entrance surface air kerma was calculated using technical data recorded for each radiograph and measured output of the X-ray unit. Effective dose and dose to radiosensitive organs was estimated using dose calculation software PCXMC. There was no statistical significant difference in the evaluated image quality using either technique, median entrance surface air kerma to the patient reduced significantly with added filtration technique and use of normal density setting. Phantom measurements indicated that an additional filtration of 0.1 mm Cu + 1 mm Al in the X-ray beam alone reduced the entrance surface air kerma by 35%.

Keywords: Chest radiography; Image quality; Dose reduction; Additional filtration

Investigating the effect of dose rate and maximum allowable MLC leaf velocity in dynamic IMRT by S. A. Yoganathan; Karthick Raj Mani; K. J. Maria Das; Arpita Agarwal; C. Kesavan; Shaleen Kumar (pp. 81-84).

The purpose of this study is to analyze the effect of various dose rates (DR) and maximum allowable MLC leaf velocities (MLV) in dynamic Intensity Modulated Radiotherapy (IMRT) planning and delivery of head and neck patients. Five head and neck patients were retrospectively included in this study. The initial dynamic IMRT ‘reference plans’ were created for all these patients, using a DR of 400 MU/min and MLV of 2.5 cm/s. Additional plans were generated by varying the DR and MLV values. The DR value was varied from 100 to 600 MU/min, in increments of 100 MU/min, for a MLV of 2.5 cm/s. Also the MLV was varied from 0.5 to 3 cm/s, in increments of 0.5 cm, for a DR of 400 MU/min. In order to maintain the prescribed dose to the PTV, the DR was allowed to vary (‘beam hold or DR modulation’ during delivery) when the MLV was changed and the MLV was allowed to vary when the DR was changed. The mean doses to the PTV as well as parotids, maximum dose of spinal cord and total MU were recorded for analysis. The effect of DR and MLV on treatment delivery was analyzed using the portal dosimetry for all the above plans. The predicted portal dose fluences of the TPS were compared with the measured EPID fluences using gamma evaluation criteria of 2% dose difference and 2 mm distance to agreement. A small proportional increase in OAR doses with DR was observed. Increases to MLV value resulted in decreases of the OAR doses and this effect was considerable for values below 1.5 cm/s. DR and MLV both resulted in no appreciable dose variation to the target. The total MU to deliver the plan increases with increasing DR and decreasing MLV. When comparing portal images derived from the treatment plans with portal images obtained by delivering the treatments, it was observed that the treatments was most reliably delivered when the DRs were set to lower values and when the MLVs were set to higher values.

Keywords: Dose rate; Intensity modulated radiotherapy; MLC leaf velocity; Dynamic IMRT

A technique for calibrating a high dose rate ¹⁹²Ir brachytherapy source by O. L. Fourie; T. G. Crabtree (pp. 85-92).

The reference air kerma rate of an ¹⁹²Ir high dose rate brachytherapy source is determined based broadly on the International Atomic Energy Agency (IAEA) TECDOC 1274 code of practice. Since the primary standards dosimetry laboratory at the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) does not maintain a standard at ¹⁹²Ir quality, the air kerma calibration coefficient of an IBA FC65-G Farmer type ionisation chamber is calculated using coefficients determined at 300 kV and ⁶⁰Co qualities. The methodology proposed by Mainegra-Hing and Rogers [1] at 250 kV and ¹³⁷Cs qualities is used. The validity of this approach is tested by performing Monte Carlo simulations to determine the chamber’s air kerma calibration coefficient at ¹⁹²Ir quality. Very good agreement is obtained between values using these two methods. The reference air kerma rate is measured using the Farmer chamber in an in air jig. In addition the necessary correction factors are applied to the measured value. The reference air kerma rate determined in this way is compared to the value stated by the vendor of the ¹⁹²Ir source on the source calibration certificate. Differences are with one exception less than 1%. It is concluded that because of the agreement between the values from the methodology used in this study and the source calibration certificate values this methodology can be used clinically.

Keywords: High dose rate brachytherapy; Reference air kerma rate; IAEA TECDOC 1274; IBA FC65-G ionisation chamber

A programmable motion phantom for quality assurance of motion management in radiotherapy by L. Dunn; T. Kron; P. N. Johnston; L. N. McDermott; M. L. Taylor; J. Callahan; R. D. Franich (pp. 93-100).

A commercially available motion phantom (QUASAR, Modus Medical) was modified for programmable motion control with the aim of reproducing patient respiratory motion in one dimension in both the anterior–posterior and superior–inferior directions, as well as, providing controllable breath-hold and sinusoidal patterns for the testing of radiotherapy gating systems. In order to simulate realistic patient motion, the DC motor was replaced by a stepper motor. A separate ‘chest-wall’ motion platform was also designed to accommodate a variety of surrogate marker systems. The platform employs a second stepper motor that allows for the decoupling of the chest-wall and insert motion. The platform’s accuracy was tested by replicating patient traces recorded with the Varian real-time position management (RPM) system and comparing the motion platform’s recorded motion trace with the original patient data. Six lung cancer patient traces recorded with the RPM system were uploaded to the motion platform’s in-house control software and subsequently replicated through the phantom motion platform. The phantom’s motion profile was recorded with the RPM system and compared to the original patient data. Sinusoidal and breath-hold patterns were simulated with the motion platform and recorded with the RPM system to verify the systems potential for routine quality assurance of commercial radiotherapy gating systems. There was good correlation between replicated and actual patient data (P 0.003). Mean differences between the location of maxima in replicated and patient data-sets for six patients amounted to 0.034 cm with the corresponding minima mean equal to 0.010 cm. The upgraded motion phantom was found to replicate patient motion accurately as well as provide useful test patterns to aid in the quality assurance of motion management methods and technologies.

Keywords: Varian Rpm; Motion; Phantom; Radiotherapy; Respiratory motion

Calculation of midplane dose for total body irradiation from entrance and exit dose MOSFET measurements by P. R. Satory (pp. 101-104).

This work is the development of a MOSFET based surface in vivo dosimetry system for total body irradiation patients treated with bilateral extended SSD beams using PMMA missing tissue compensators adjacent to the patient. An empirical formula to calculate midplane dose from MOSFET measured entrance and exit doses has been derived. The dependency of surface dose on the air-gap between the spoiler and the surface was investigated by suspending a spoiler above a water phantom, and taking percentage depth dose measurements (PDD). Exit and entrances doses were measured with MOSFETs in conjunction with midplane doses measured with an ion chamber. The entrance and exit doses were combined using an exponential attenuation formula to give an estimate of midplane dose and were compared to the midplane ion chamber measurement for a range of phantom thicknesses. Having a maximum PDD at the surface simplifies the prediction of midplane dose, which is achieved by ensuring that the air gap between the compensator and the surface is less than 10 cm. The comparison of estimated midplane dose and measured midplane dose showed no dependence on phantom thickness and an average correction factor of 0.88 was found. If the missing tissue compensators are kept within 10 cm of the patient then MOSFET measurements of entrance and exit dose can predict the midplane dose for the patient.

Keywords: In vivo dosimetry; Radiotherapy; Total body irradiation (TBI); MOSFET

The Australian radiation protection and nuclear safety agency megavoltage photon thermoluminescence dosimetry postal audit service 2007–2010 by C. P. Oliver; D. J. Butler; D. V. Webb (pp. 105-108).

The Australian radiation protection and nuclear safety agency (ARPANSA) has continuously provided a level 1 mailed thermoluminescence dosimetry audit service for megavoltage photons since 2007. The purpose of the audit is to provide an independent verification of the reference dose output of a radiotherapy linear accelerator in a clinical environment. Photon beam quality measurements can also be made as part of the audit in addition to the output measurements. The results of all audits performed between 2007 and 2010 are presented. The average of all reference beam output measurements calculated as a clinically stated dose divided by an ARPANSA measured dose is 0.9993. The results of all beam quality measurements calculated as a clinically stated quality divided by an ARPANSA measured quality is 1.0087. Since 2011 the provision of all auditing services has been transferred from the Ionizing Radiation Standards section to the Australian Clinical Dosimetry Service (ACDS) which is currently housed within ARPANSA.

Keywords: Audit; TLD; Quality assurance; Dosimetry

Loredana Marcu, Eva Bezak (eds): Recent advances and research updates, medical physics and radiobiology by Anna Ralston (pp. 109-111).

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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, #1)

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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, #1)