Evaluation of organ dose and image quality metrics of pediatric CT Chest-Abdomen-Pelvis (CAP) examination: an anthropomorphic phantom study

The aim of this study is to investigate the impact of CT acquisition parameter setting on organ dose and its influence on image quality metrics in pediatric phantom during CT examination. The study was performed on 64-slice multidetector CT scanner (MDCT) Siemens Definition AS (Siemens Sector Healthcare, Forchheim, Germany) using various CT CAP protocols (P1–P9). Tube potential for P1, P2, and P3 protocols were fixed at 100 kVp while P4, P5, and P6 were fixed at 80 kVp with used of various reference noise values. P7, P8, and P9 were the modification of P1 with changes on slice collimation, pitch factor, and tube current modulation (TCM), respectively. TLD-100 chips were inserted into the phantom slab number 7, 9, 10, 12, 13, and 14 to represent thyroid, lung, liver, stomach, gonads, and skin, respectively. The image quality metrics, signal to noise ratio (SNR) and contrast to noise ratio (CNR) values were obtained from the CT console. As a result, this study indicates a potential reduction in the absorbed dose up to 20% to 50% along with reducing tube voltage, tube current, and increasing the slice collimation. There is no significant difference (p > 0.05) observed between the protocols and image metrics

Implementation of silicon based dosimeters, the dose magnifying glass and magic plate for the dosimetry of modulated radiation therapy

New cutting edge radiation therapy techniques such as Intensity Modulated Radiation Therapy (IMRT), Stereotactic Radiosurgery (SRS), Helical TomoTherapy and most recently Volumetric Modulated Arc Therapy (VMAT) produce radiation dose maps with high dose modulation and tight gradients between the high and low dose region. Difficulties in the dosimetric verification of these new complex treatment methods using existing dosimeters have led to the need for a new generation of fast responding real time dosimeters with submillimetre precision. This thesis describes two detector systems based on silicon substrates that were developed to address this need. The first detector system was a silicon strip detector called the “Dose Magnifying Glass” (DMG). It consisted of 128 detectors spaced 0.2 mm apart. It was coupled to a TERA ASIC chip that enabled simultaneous readout of multiple channels at high temporal resolution. The first part of the thesis involved investigation of the basic characteristics of the DMG followed by its application in the dosimetric verification of IMRT, SRS and Helical TomoTherapy treatment deliveries. The high spatial resolution of this device was ideal for the measurement of high dose gradients in IMRT and small fields encountered in SRS. When compared with film dosimetry, DMG measurements showed agreements within 3% for a SRS treatment plan. The DMG was also successfully employed as an independent quality assurance tool for the verification of helical Tomotherapy machine binary MLC leaf parameters. The second detector was a two dimensional array detector so named the “Magic Plate” (MP). The diode was based on epitaxial technology and has a very thin sensitive volume of 50 μm. The MP comprised of 11 × 11 epitaxial diodes mounted on a 0.6 mm thick Kapton substrate. This detector was designed to be used either as a transmission detector or to measure dose distributions in a solid water phantom. Preliminary testing of the MP in a clinical IMRT treatment delivery was carried out. The MP measurements demonstrated good agreement (\u3e80%) with conventional EBT2 film dosimetry and with treatment planning system predicted dose distributions using 3%/3mm gamma criteria

Survey of postgraduate medical physics programmes in the Asia-Oceania region

The increased use of medical imaging and radiation therapies has resulted in a high demand for medical physicists. Although medical physics programmes are well established in advanced countries, the same cannot be said for many low- and medium-income countries. In some countries, there may be huge variations in the graduates' skill and quality, which pose a problem in ensuring patient safety, providing quality assurance in treatments, optimisation of protocols and standardisation of quality. It also makes any yet-to-be-established regional peer recognition efforts problematic. In order to understand the depth of this problem, a survey was carried out as part of the home-based assignment under the RAS 6088 IAEA programme. A large diversity in terms of course content, duration, clinical training and student profile could be observed across the Asia-Oceania universities surveyed. Out of 25 programmes, only six received recognition from professional bodies, and they were mostly in Australia and New Zealand. Hence, to ensure quality education, a regional curriculum model needs to be developed to harmonise standards. And there is still a long way to go towards standardizing medical physics education and clinical training in the region. © 2019 Associazione Italiana di Fisica Medic

Dosimetric evaluation near lung and soft tissue interface region during respiratory-gated and non-gated radiotherapy: A moving phantom study

Challenges in treating lung tumours are related to the respiratory-induced tumour motion and the accuracy of dose calculation in charged particle disequilibrium condition. The dosimetric characteristics near the interface of lung and Perspex media in a moving phantom during respiratory-gated and non-gated radiotherapy were investigated using Gafchromic EBT2 and the MOSkin detector. The MOSkin detectors showed good agreement with the EBT2 films during static and gated radiotherapy. In static radiotherapy, the penumbral widths were found to be 3.66 mm and 7.22 mm in Perspex and lung media, respectively. In non-gated (moving) radiotherapy with 40 mm respiratory amplitude, dose smearing effect was observed and the penumbral widths were increased to 28.81 mm and 26.40 mm, respectively. This has been reduced to 6.85 mm and 9.81 mm, respectively, in gate d radiotherapy with 25% gating window. There were still some dose discrepancies as compared to static radiotherapy due to the residual motion. This should be taken into account in the margin generation for the target tumour

Problems and solutions in medical physics : volume 1 : diagnostic imaging physics

xv, 139 p. ; 23 cm

Lipid Alterations in Glioma: A Systematic Review

Gliomas are highly lethal tumours characterised by heterogeneous molecular features, producing various metabolic phenotypes leading to therapeutic resistance. Lipid metabolism reprogramming is predominant and has contributed to the metabolic plasticity in glioma. This systematic review aims to discover lipids alteration and their biological roles in glioma and the identification of potential lipids biomarker. This systematic review was conducted using the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Extensive research articles search for the last 10 years, from 2011 to 2021, were conducted using four electronic databases, including PubMed, Web of Science, CINAHL and ScienceDirect. A total of 158 research articles were included in this study. All studies reported significant lipid alteration between glioma and control groups, impacting glioma cell growth, proliferation, drug resistance, patients’ survival and metastasis. Different lipids demonstrated different biological roles, either beneficial or detrimental effects on glioma. Notably, prostaglandin (PGE2), triacylglycerol (TG), phosphatidylcholine (PC), and sphingosine-1-phosphate play significant roles in glioma development. Conversely, the most prominent anti-carcinogenic lipids include docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and vitamin D3 have been reported to have detrimental effects on glioma cells. Furthermore, high lipid signals were detected at 0.9 and 1.3 ppm in high-grade glioma relative to low-grade glioma. This evidence shows that lipid metabolisms were significantly dysregulated in glioma. Concurrent with this knowledge, the discovery of specific lipid classes altered in glioma will accelerate the development of potential lipid biomarkers and enhance future glioma therapeutics

Medical physicists in Malaysia: A national workforce survey 2019

Objective: Medical physics in Malaysia is still considered a young profession. This workforce survey aims to understand the status, aspirations, motivation and experiences of medical physicists (MPs) in the country. A subsection of this survey also aims to understand the role of women. Method: A survey was carried out between April 20 and May 30, 2018 by a working group under the Medical Physics Division of the Malaysian Institute of Physics (IFM). The survey form was designed using Google Form and sent to various public and private institutions nationwide that employed MPs registered with IFM. Results: A total of 106 responses (28% men and 72% women) were analysed. This represented 30% of the medical physics workforce. Majority of them had postgraduate degrees, but their clinical training is mostly obtained on the job with no certification. The number of low-ranking female MPs was disproportionately high. MPs worked long hours and achieving work-life balance (WLB) was a challenge. Factors that improved their WLB included working close to home, having a supportive manager and flexible working hours. Most MPs aspired to become professional and mentor younger compatriots, besides contributing to patient care and research. Gender discrimination was reportedly low. Conclusion: Medical physics in Malaysia is growing and has a strong representation of women. In future, they would probably take over the top management from their male counterparts, whose number had stagnated. A united effort was essential to set up a proper clinical training system to train clinically qualified MPs. © 2019 Associazione Italiana di Fisica Medic

Characterization of MOSkin detector for in vivo skin dose measurement during megavoltage radiotherapy

In vivo dosimetry is important during radiotherapy to ensure the accuracy of the dose delivered to the treatment volume. A dosimeter should be characterized based on its application before it is used for in vivo dosimetry. In this study, we characterize a new MOSFET-based detector, the MOSkin detector, on surface for in vivo skin dosimetry. The advantages of the MOSkin detector are its water equivalent depth of measurement of 0.07 mm, small physical size with submicron dosimetric volume, and the ability to provide real-time readout. A MOSkin detector was calibrated and the reproducibility, linearity, and response over a large dose range to different threshold voltages were determined. Surface dose on solid water phantom was measured using MOSkin detector and compared with Markus ionization chamber and GAFCHROMIC EBT2 film measurements. Dependence in the response of the MOSkin detector on the surface of solid water phantom was also tested for different (i) source to surface distances (SSDs); (ii) field sizes; (iii) surface dose; (iv) radiation incident angles; and (v) wedges. The MOSkin detector showed excellent reproducibility and linearity for dose range of 50 cGy to 300 cGy. The MOSkin detector showed reliable response to different SSDs, field sizes, surface, radiation incident angles, and wedges. The MOSkin detector is suitable for in vivo skin dosimetry

Zinc-Doped Magnesium Borate Glass: A Potential Thermoluminescence Dosimeter for Extended Range of Dosimetric Applications

In this study, we report the dosimetric properties of zinc-doped magnesium borate (MgB4O7:Zn) glass, which was originally synthesized. MgB4O7:Zn glass was successfully synthesized through the melt-quenching technique. The amorphous nature of the synthesized samples was observed through X-ray diffraction (XRD) analysis and further confirmed through field emission scanning electron microscopy (FESEM) analysis. The glass-forming ability and thermal stability were estimated to be 0.61 and 1.62, respectively. The TL dosimetric characteristics, i.e., dose response, reproducibility, TL sensitivity, minimum detectable dose and signal stability, are reported. The synthesized sample demonstrated a simple glow curve with a single well-defined dosimetric peak at 240 °C with an optimal heating rate of 7 °C s−1. The synthesized glass demonstrated a linear dose response from 3 Gy to 5 kGy. The promising dosimetric characteristics demonstrate the potential of the synthesized glass to be recommended as a TL dosimeter for a wide range of applications