Springer Science and Business Media LLC

This study investigates the characteristics and application of the optically-stimulated luminescence dosimeter (OSLD) in cobalt-60 high dose rate (HDR) brachytherapy, and compares the results with the dosage produced by the treatment planning system (TPS). The OSLD characteristics comprised linearity, reproducibility, angular dependence, depth dependence, signal depletion, bleaching rate and cumulative dose measurement. A phantom verification exercise was also conducted using the Farmer ionisation chamber and in vivo diodes. The OSLD signal indicated a supralinear response (R2 = 0.9998). It exhibited a depth-independent trend after a steep dose gradient region. The signal depletion per readout was negligible (0.02%), with expected deviation for angular dependence due to off-axis sensitive volume, ranging from 1 to 16%. The residual signal of the OSLDs after 1 day bleached was within 1.5%. The accumulated and bleached OSLD signals had a standard deviation of ± 0.78 and ± 0.18 Gy, respectively. The TPS was found to underestimate the measured doses with deviations of 5% in OSLD, 17% in the Farmer ionisation chamber, and 7 and 8% for bladder and rectal diode probes. Discrepancies can be due to the positional uncertainty in the high-dose gradient. This demonstrates a slight displacement of the organ at risk near the steep dose gradient region will result in a large dose uncertainty. This justifies the importance of in vivo measurements in cobalt-60 HDR brachytherapy.

A new technique for measuring hand volumes using Archimedes principle is described. The technique involves the immersion of a hand in a water container placed on an electronic balance. The volume is given by the change in weight divided by the density of water. This technique was compared with the more conventional technique of immersing an object in a container with an overflow spout and collecting and weighing the volume of overflow water. The hand volume of two subjects was measured. Hand volumes were 494±6 ml and 312±7 ml for the immersion method and 476±14 ml and 302±8 ml for the overflow method for the two subjects respectively. Using plastic test objects, the mean difference between the actual and measured volume was -0.3% and 2.0% for the immersion and overflow techniques respectively. This study shows that hand volumes can be obtained more quickly than the overflow method. The technique could find an application in clinics where frequent hand volumes are required.

With the increasing demand for coagulation POCT for patients in the surgery department or the ICU, rapid coagulation testing techniques and methods have drawn widespread attention from scholars and businessmen. This paper proposes the use of electromagnetic induction sensor probe for detection of dynamic process causing changes in the blood viscosity and density before and after coagulation based on the damped vibration principle, in order to evaluate the coagulation status. Utilizing the dynamic principle, the differential equation of vibration system comprising elastic support and electromagnetic induction device is established through sensor dynamic modeling. The structural parameters of elastic support are optimized, and the circular sheet spring is designed. Furthermore, harmonic response analysis and vibration fatigue coupling analysis are performed on the elastic support of the sensor by considering the natural frequency of the system, and the electromagnetic induction sensor testing device is set up. Using the device and coagulation reagent, the standard curve for coagulation POCT is plotted, and the blood sample application in clinical patients is established, which are methodologically compared with the imported POCT coagulation analyzer. The results show that the sensor designed in this paper has a first-order natural frequency of 11.368 Hz, which can withstand 5.295 × 102 million times of compressions and rebounds. Its correlation with the results of SONOCLOT analyzer reaches 0.996, and the reproducibility 0.002. The electromagnetic induction coagulation testing sensor designed has good elasticity and anti-fatigue, which can meet the accuracy requirement of clinical detection. This study provides the core technology for developing the electromagnetic induction POCT instrument for dynamic testing of coagulation process.

Trong xử lý tín hiệu điện não đồ (EEG) và từ não đồ (MEG), bộ tạo chùm song scalar là một kỹ thuật phổ biến để tái tạo quá trình theo thời gian của một nguồn não trong một chuỗi thời gian đơn. Tuy nhiên, một điều kiện tiên quyết cho các bộ tạo chùm scalar là hướng của nguồn phải được biết hoặc ước lượng, trong khi trên thực tế, hướng của nguồn não thường không được biết trước và các kỹ thuật hiện tại để ước lượng hướng nguồn não chỉ hiệu quả đối với các nguồn não có tỷ số tín hiệu trên nhiễu (SNR) cao. Do đó, các bộ tạo chùm vector được áp dụng, không cần biết hướng của nguồn và tái tạo quá trình theo thời gian của nguồn trong ba phương hướng trực giao (x, y, và z). Để thu được một chuỗi thời gian duy nhất, độ lớn vector của ba đầu ra trực giao của bộ tạo chùm có thể được tính toán tại mỗi điểm thời gian (thường gọi là chỉ số hoạt động thần kinh, NAI). Tuy nhiên, NAI lại khác so với quá trình theo thời gian thực tế của một nguồn vì nó chỉ chứa các giá trị dương. Hơn nữa, khi ước lượng độ lớn của nguồn mong muốn, hoạt động nền (các tín hiệu không mong muốn) trong các đầu ra bộ tạo chùm cũng trở thành tất cả các giá trị dương, dẫn đến việc khi được cộng vào nhau, làm giảm SNR. Điều này trở thành một vấn đề nghiêm trọng khi nguồn mong muốn yếu. Chúng tôi đề xuất áp dụng phân tích thành phần độc lập (ICA) trên các chuỗi thời gian trực giao của một voxel não, được tái tạo bởi bộ tạo chùm vector, để tái tạo lại quá trình theo thời gian của một nguồn mong muốn trong một chuỗi thời gian đơn. Cách tiếp cận này cũng cung cấp một ước lượng tốt về hướng dipole. Dữ liệu EEG mô phỏng và thực tế đã được sử dụng để chứng minh hiệu suất của voxel-ICA và được so sánh với bộ tạo chùm scalar và chuỗi thời gian độ lớn của bộ tạo chùm vector. Cách tiếp cận này đặc biệt hữu ích khi nguồn mong muốn yếu và hướng của nguồn không thể được ước lượng bằng phương pháp khác.

Some serious radiation accidents have occurred around the world during the delivery of radiotherapy treatment. The regrettable incident in Panama clearly indicated the need for independent monitor unit (MU) verification. Indeed the International Atomic Energy Agency (IAEA), after investigating the incident, made specific recommendations for radiotherapy centres which included an independent monitor unit check for all treatments. Independent monitor unit verification is practiced in many radiotherapy centres in developed countries around the world. It is mandatory in USA but not yet in Australia. This paper describes development of an independent MU program, concentrating on the implementation of the Enhanced Dynamic Wedge (EDW) component. The difficult case of non centre of field (COF) calculation points under the EDW was studied in some detail. Results of a survey of Australasian centres regarding the use of independent MU check systems is also presented. The system was developed with reference to MU calculations made by Pinnacle 3D Radiotherapy Treatment Planning (RTP) system (ADAC-Philips) for 4MV, 6MV and 18MV Xray beams used at the Newcastle Mater Misericordiae Hospital (NMMH) in the clinical environment. A small systematic error was detected in the equation used for the EDW calculations. Results indicate that COF equations may be used in the non COF situation with similar accuracy to that achieved with profile corrected methods. Further collaborative work with other centres is planned to extend these findings.

The quality of a prostate implant using radioactive I-125 seeds can be assessed by performing post-implant dosimetry, which therefore has to be a reliable evaluation tool. At the RAH, we have noticed large variations in post-implant dosimetric parameters compared to the pre-implant data. The purpose of this study was to investigate the cause of these differences. Post-implant dosimetry was performed 4 weeks after implant on 15 prostate cancer patients. The CT images of the pelvis were exported to the planning system, where contouring of the target (prostate) was executed by 6 clinicians, followed by the post-implant dosimetry performed by a physicist. Pre- and post-implant dosimetric parameters were analyzed and compared. The average target volume based on the ultrasound measurements was 35.8 cc. Post-implant CT volumes were determined and averaged over the 15 patients by each clinician, and their average values vary from 28.9 cc to 67.9 cc. Beside the under/overestimation of the target on the CT there was also a ‘shift’ in the target base on the ultrasound image. By comparing pre-implant and post-implant dosimetric parameters we have encountered a significant discrepancy between target volumes based on ultrasound image and CT image. It was concluded that the accuracy of target coverage was partially connected to the poorer quality of the CT image compared to the ultrasound scan, patient’s anatomy, but mostly to the poor implantation of the base.

The most widely accepted method for shielding design of X-ray facilities is that contained in the National Council on Radiation Protection and Measurements Report 147 whereby the computation of the barrier thickness for primary, secondary and leakage radiations is based on the knowledge of the distances from the radiation sources, the assumptions of the clinical workload, and usage and occupancy of adjacent areas. The shielding methodology used in this report is complex. With this methodology, the shielding designers need to make assumptions regarding the use of the X-ray room and the adjoining areas. Different shielding designers may make different assumptions resulting in different shielding requirements for a particular X-ray room. A more simple and practical method is to base the shielding design on the shielding principle used to shield X-ray tube housing to limit the leakage radiation from the X-ray tube. In this case, the shielding requirements of the X-ray room would depend only on the maximum radiation output of the X-ray equipment regardless of workload, usage or occupancy of the adjacent areas of the room. This shielding methodology, which has been used in South Australia since 1985, has proven to be practical and, to my knowledge, has not led to excess shielding of X-ray installations.