|Year : 2022 | Volume
| Issue : 2 | Page : 215-218
Professor, Medical Physics Unit, IRCH, AIIMS, New Delhi, India
|Date of Submission||24-Jun-2022|
|Date of Decision||01-Jul-2022|
|Date of Acceptance||04-Jul-2022|
|Date of Web Publication||5-Aug-2022|
Medical Physics Unit, IRCH, AIIMS, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kumar P. News. J Med Phys 2022;47:215-8
| Magnetic Resonance Elastography and Brain Tumor|| |
Researchers from the University of Leipzig and Charite – Universitatsmedizin in Germany have discovered that metastasizing capability of brain tumors may be linked with the mechanical properties of the tumor cells and suggest that the changes in elasticity of cells may impact the prognosis. Magnetic resonance elastography (MRE) uses low-frequency vibrations combined with magnetic resonance imaging (MRI) to measure softness and viscosity. The researcher also used optical stretcher which is an optical trap that uses two laser beams to deform single cells to measure their viscoelastic properties. They found that glioblastoma, a highly malignant brain tumor, is softer but less viscous than a benign tumor. Glioblastoma infiltrates by spreading tinny fingers into the surrounding tissues. It is similar to the viscous fingers phenomenon when less viscous liquid is injected into another liquid. Four patients with a benign brain tumor and four with brain cancer (three were glioblastoma) underwent MRE and their tumor cells were subjected to the optical stretcher. Malignant tumors were softer and less viscous (more fluidity) but their cells individually were not less viscous. It was found that the elasticity (and not the viscosity) of the cells were correlated with the fluidity of the tissue. It was surmised that a tumor to squeeze (flow) into the surrounding tissue, the cells must squeeze past each other, making elasticity a parameter which mediates the infiltration. Tumor cells also showed much wider range of mechanical properties than benign ones. The researchers have postulated that such heterogeneity may permit the part of the tumor to flow and spread, whereas the other part maintains the rigidity of the cancer tumor.
Details may be seen at:
| Flash Radiotherapy and Plastic Scintillator Detector|| |
FLASH radiotherapy is ultra-high dose rate (UHDR) radiotherapy using electron, proton, or photon beams with about 40 Gy/s or higher dose rate in the preclinical stage or preliminary clinical stage. UHDR is supposed to reduce damage and toxicity in normal tissues while retaining the antimalignant action. X-ray Cancer Imaging and Therapy Experimental (XCITE) Lab, University of Victoria, Canada, has developed an economical in vitro UHDR irradiation facility for small samples (maximum size 6 mm) which may be exposed to dose rate up to 118 Gy/s by employing X-ray tube-based system using beam shutter. The exposure time is of the order of 1 ms. The sample is held very close to the X-ray tube window. The group used real-time small field dosimetry using a plastic scintillator detector (PSD) developed by Medscint. PSD has the advantage of near-water equivalence, nanosecond response, high spatial resolution, and resistance to radiation damage. PSD does not need a small field correction factor to characterize its response and shows a linear response to dose and dose rate for a wide dynamic range of low-dose rate to UHDR. The researchers have developed PSD of 0.5 mm × 0.5 mm size which suits small-field dosimetry. XCITE researchers are using fruit fly larvae as small animal experiments along with online real-time tiny PSD. They are also planning to irradiate normal and malignant skin cells fabricated with a three-dimensional (3D) printing method. These cells are called multicellular cell spheroids which may be grown in a very uniform fashion and may be used to measure interspheroid dose delivery difference of <1.1%. XCITE group is also involved in designing an electron-to-photon converter to deliver UHDR 10 MV photon beam with a dose rate of 200 Gy/s. They are also working on spatially fractionated radiation therapy (SFRT) where a single high-dose fraction is delivered deliberately in heterogeneous fashion. In SFRT, a high dose is given within the target volume and in the region of underdosing and may hold a promise of minimizing the side effects.
Details may be seen at:
| Photobiomodulation May Heal Radiation Damage|| |
Researchers at the University of Buffalo are toying with the idea of healing the radiation damage in normal tissues as well as chronic wounds using a low dose of optical light. The technique has been termed photobiomodulation (PBM). In brachytherapy, radioactive seeds are implanted within the cancer tumor. Such implanted seeds deliver a high radiation dose to the target tumor with a minimal dose to nearby healthy tissues and hence minimizing the risk of side effects. However, implantation of radioactive seeds may cause local radiodermatitis and radionecrosis which may be healed by PBM. Researchers carried out the experiments in mice which were divided into four groups. One group received only brachytherapy seed implantation, the second group received brachytherapy and PBM, the third group received only PBM, and the fourth group served as control. The second group was further subdivided into PBM with red light and PBM with near-infrared light. A similar subdivision was made for the third group as well. In total, 18 mice were implanted with brachytherapy 125I seeds subcutaneously. PBM therapy used red light (660 nm) or near-infrared (880 nm) generated by light-emitting diodes with a 1 cm2 spot and irradiance of 40 mW/cm2 along with the fluency of 20 J/cm2. PBM was given once per week over the site of seed for 60 days. All mice with brachytherapy developed radionecrosis at 21 days when the dose delivered was about 8.5 × 104 Sv. Digital image analysis of wound revealed that PBM reduced the incidence and severity of skin damage. This was especially true for PBM with red light. Wounds took an average of 61 days to heal without any assistance. For PMB with near infrared, this healing time was on average 49 days, and with PBM with red light, the same was 42 days. Laser Doppler flowmetry and thermal imaging were done to assess the blood flow every week since radiation damage tends to reduce blood perfusion resulting in prolonged inflammation. It was found that at 42 days, the skin damage was maximum in brachytherapy seed alone group but PBM-treated mice showed improved blood perfusion and significantly reduced inflammation. Irradiation impacts tissue metabolism. Therefore, the researchers evaluated metabolism (tracer uptake) around 125I seeds at 42 days using μ-positron emission tomography/computed tomography with tracer 18F-fluorodeoxyglucose and found it significant in only brachytherapy seed group with respect to PBM group indicating much-reduced metabolism in the latter. The reduced side effects of brachytherapy-like inflammation and tissue damage in PBM group were finally confirmed by histology by sacrificing one mouse from each group at 42 days.
Details may be seen at:
| American College of Radiology - American Association of Physicists in Medicine Radiation Safety Officer Resources|| |
The American College of Radiology (ACR) and the American Association of Physicists in Medicine have revised its Radiation Safety Officer (RSO) resource document. The document was first published in April 2015 and was revised in January 2017. It is popular reference material and is viewed about a hundred times every month at the ACR website. The compendium has been prepared to help radiologists to comprehend the role of a RSO for X-ray equipment, unsealed radiopharmaceuticals, and sealed sources used in medical imaging. The resource is limited to medical imaging and some radionuclide therapy but does not include radiation therapy. This is a 104-page document spanning over nine chapters. Chapters have been divided into sections and subsections. It is an overall view of the framework of RSO in diagnostic and nuclear medicine imaging. It explains the role and responsibility of RSO, details of the radiation protection program, dose limits, safety policies, shielding, etc. Radioactivity-related issues have also been covered widely. Although it does not give very detailed nitty-gritty of all the quality assurance tests, it is an overall good RSO resource.
The PDF file of the resources is freely downloadable at:
| International Atomic Energy Agency Safety Guide on Leadership, Management, and Culture for Safety in Radioactive Waste Management|| |
The International Atomic Energy Agency (IAEA) establishes a standard of safety for the protection of health in the form of the Safety Standards Series (SSS) which has three categories of documents such as Safety Fundamentals, Safety Requirements, and Safety Guides. The present publication is General Safety Guide (GSG)-16 which has been published in January 2022. This supersedes IAEA SSS No GSG-3.3, the management system for the processing, handling, and storage of radioactive waste and GSG-3.4, the management system for the disposal of radioactive waste. The present GSG-16 provides recommendations on developing and implementing a system for safety during all steps of radioactive waste management like processing (including pretreatment, treatment, and conditioning), storage, and disposal but does not include transport. The publication emphasizes the effective leadership and development of a culture of safety. The book has seven sections. The first section is an introduction, whereas the second section identifies the characteristics of radioactive waste management that influence leadership, management, and work culture. Sections 3, 4, 5, and 6 provide the recommendation on the responsibility of safety, leadership of safety, management for safety, and culture for safety, respectively. The final section provides recommendations on the measurement, assessment, and improvement of the management system. This publication may be useful for regulatory bodies and the organization which direct, plan, or manage radioactive waste. Supplier or provider of safety-related services and products that support the management of radioactive waste may also be benefited from this publication.
The publication may be downloaded free at:
| International Atomic Energy Agency Issues TECDOC on Assessment of Prospective Cancer Risk from Occupational Exposure|| |
IAEA has developed a technical document in collaboration with the International Labour Organization on the assessment of the risk of contracting cancer due to occupational exposure to radiation among various types of workers. Radiation workers are supposed to be monitored for their occupational radiation dose using personnel dosimeters such as thermoluminescent dosimeters or optically stimulated luminescence badges. There are over 24 million workers who are monitored for their radiation dose while working in the diverse fields of nuclear application, radioactivity-related engagement, miners, air crews, industrial workers, researchers, health-care professionals, etc. These people face radiation risk due to their occupation and measures for radiation protection need to be taken. IAEA has released a tech doc entitled “assessment of prospective cancer risks from occupational exposure to ionizing radiation” which would help in managerial decisions related to controlling exposure of these workers. It enumerates specific guidance on how to assess the risk of cancer induction in such workers who are exposed to radiation in the course of their occupation. The publication takes into account the various factors which influence the probability of contracting malignancy by the radiation worker. These factors include the way an occupational worker is exposed (like inhalation by miner, external exposure to radiologists, and radiographers), type of radiation, duration of radiation exposure, worker's age, etc. The publication enumerates relevant theories and models along with a methodological framework to assess the cancer risk prospectively. It shall help the managerial decisions on limiting and controlling occupational radiation exposure. The publication does not cover medical and public exposure as they are not deemed to be occupational exposures. There are seven chapters encompassing details of cancer risk, dosimetry in such situations, various risk models, methods for the calculation of risk, sources of uncertainties in such methods, etc. spanning over 79 pages.
The free soft book may be downloaded from:
| Laser-Generated High-Energy Ion Beam|| |
Physicists at Osaka University, Japan, have been successful in generating high-energy proton and carbon ion beams by firing a laser pulse at a target made of two layers of graphene. The presence of noise in the laser beam tends to destroy the thin target made from conventional material. This noisy prepulse arrives at the target before the main peak of laser intensity and may ruin the target which is micrometer thick. However, the thin targets do not need super-intense laser and hence preferable. Scientists found some solutions to this problem of destruction of thin target by the laser in so-called “plasma mirror” which forms due to ionization of the target at the leading edge of the laser pulse. The ionized material forms a surface which reflects the laser's high-intensity peak (and hence called mirror) but allows entry to the noisy prepulse. Making micrometers thin target from the conventional 3D materials and their surfaces flat enough (to form plasma mirror) are expensive. The researchers at Osaka University used graphene as target since graphene is a two-dimensional sheet of carbon just one atom thick. Graphene is the thinnest, lightest, strongest, and most transparent material with comparable thickness. Scientists developed a large area of suspended graphene (LSG) with a double layer of graphene 2 nm thick. Simulation studies have indicated that pre-pulse would make the graphene melt before the arrival of main laser peak and the resulting plasma would interact with the relativistic part of the pulse generating MeV beams of protons and carbon ions without forming a plasma mirror. The durable LSG target would help laser-driven ion acceleration to be utilized in targeted cancer therapy, laser-driven nuclear fusion, and laboratory-based simulations of astrophysics events.
Details may be seen at:
| Magnetic Resonance Navigation and Magnetic Thermoablation|| |
Scientists at University College, London, have developed a Minimally INvasive IMage-guided Ablation (MINIMA) where ferromagnetic thermoseed is guided by magnetic resonance navigation through the tissues to the target tumor. Once in the intended place, the thermoseed may be heated remotely to a high temperature by applying an alternating magnetic field which kills the cancer cells by thermoablation. The steering of the thermoseed in the body is done using imaging gradient coil of MRI which may also image it in real time. The seed may be navigated through the target tissue to carry out thermoablation at multiple points, leading to ablation of the whole region. After the procedure, the seed may be navigated back to the entry point of the body and removed. The researchers applied MINIMA in ex vivo brain tissue experiments with 0.3 mm accuracy and also in a mouse model. The thermoseed was a chrome steel sphere of 2 mm diameter as this size is comparable to a brain biopsy needle and chrome steel has high saturation magnetization, leading to increased translational force and hence tissue penetrability. The spherical shape of the thermoseed facilitated easy movement in all directions. Navigation experiments were carried out in a 9.4 T preclinical MRI as well as in a 3T clinical MRI. The location of the seed was tracked using image distortion artifacts around the seed. Heating of the seed was achieved by MRI-compatible magnetic alternating current hyperthermia system. It was found that the distance moved by the seed in tissue increased as gradient strength increased. Tissue penetration and efficiency in the movement of seed through the tissue improved with an increase in seed diameter and the duty cycle as well. Cell culture in mice indicated that the duration of heat might control ablation volume. The new MINIMA technique holds good potential as an alternative to surgery or radiotherapy in brain and prostate cancer. The high precision of the technique may reduce the damage to the surrounding normal tissues and hence may reduce the side effects. It may also be used to treat a nonmalignant condition like drug-resistant epilepsy.
Details may be seen at:
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