|Year : 2022 | Volume
| Issue : 4 | Page : 412-416
Professor and Head, Medical Physics Unit, IRCH, AIIMS, New Delhi, India
|Date of Submission||28-Dec-2022|
|Date of Acceptance||29-Dec-2022|
|Date of Web Publication||10-Jan-2023|
Dr. Pratik Kumar
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;47:412-6
| Novel Positron Emission Tomography Tracer for Biology-Guided Radiation Therapy|| |
Researchers at Stanford University, USA, have created a new 89Zr radioisotope-based positron emission tomography (PET) tracer called 89Zr-Panitumumab (89Zr-Pan) which emits positron and may be imaged (tracked) for a longer duration. Biology-guided radiation therapy (BgRT) is an experimental technique in which PET images of the tumor are taken to guide the delivery of the radiation treatment beam. As the radiation treatment of cancer may span over a few weeks, there may be a need to administer the short-lived 18F-fluorodeoxyglucose (half-life 110 min) five-six times during the treatment so that latest shape and size of the tumor is tracked. Researchers at Stanford University instead developed the tracer using 89Zr which has a half-life of 78 h. This novel radionuclide was tagged with antibodies as they show high tumor specificity and uptake. The researchers tested 89Zr-Pan in mice with implanted tumors and administered 5 Gy treatment doses over 6 days and performed sequential PET-computed tomography (PET-CT). There was also a group of control with tumor and tracer administration but was not given any treatment. The treatment group showed good shrinkage in tumor. The signal from the tracer in the treatment group was evaluated from PET images and was found to reduce with time with respect to the control group due to a reduction in uptake which was about 50% of that in untreated mice. However, it was still possible to track the tumor for BgRT even after reduction in the signal. Through the results of animal model cannot be directly applied to humans, the researchers calculated presumably that in equivalent human tumors a single shot of 89Zr-Pan may be imaged for about five consecutive days.
The further details may be seen at https://physicsworld.com/a/long-lived-pet-tracer-could-ease-biology- guided-radiotherapy/.
| The American Association of Physicists in Medicine (AAPM) Task Group Report 303 Guidelines for Implementation of Magnetic Resonance Imaging in High-Dose-Rate Brachytherapy|| |
AAPM task group (TG) report 303 is a detailed recommendation of magnetic resonance imaging (MRI) and quality assurance (QA) for MRI-based high-dose rate (HDR) brachytherapy. The report describes the workflow of HDR brachytherapy and evaluates the practical considerations of implementing the MRI in HDR brachytherapy in case of treatment of gynecologic and prostate cancer. After the advent of brachytherapy, the two-dimensional (2D) imaging was extensively used for image guidance. However, kV X-ray imaging system has limitations in differentiating various types of soft tissues owing to similar attenuation. The arrival of CT and MRI converted the 2D imaging into volumetric imaging, providing better visualization of tumors, nearby normal structures, and organs at risk (OARs). MRI, in conjunction with CT and/or ultrasound has provided better opportunities for image guidance. AAPM TG Report 303 describes the role of MRI, protocols, and methodologies for MR imaging in HDR brachytherapy in details. It incorporates the latest risk-based QA and gives an example of risk-based analysis of MRI-based prostate HDR brachytherapy.
The details may be seen at https://www.aapm.org/pubs/reports/detail.asp? docid = 226#:~:text = Report%20No.%20303%20-%20AAPM%20task%20 group%20report, brachytherapy%E2%80%94Considerations%20from%20simulation%20to%20treatment%20%282022%29%20Category%3A%20Reports.
| Incidence of Early-Onset Cancers is Increasing|| |
A review paper has noticed the shift of the incidence of cancer toward the early years worldwide, that too a bit dramatically. The paper notices that since 1990 the number of adults under the age of 50 years developing cancer has increased sharply and the rate of incidence of such early-onset cancers is increasing despite discounting the effect of the improved facilities for cancer screening. The authors have found that each newer generation (say people born in 1950 vs. those born in 1960) is facing the higher risk of early-onset of cancer. Cancer is known earlier as an old age disease. For example, people over the age of 50 years are more likely to develop cancer. However, this paper cautions that the rate of incidence of cancer for people below the age of 50 years is also increasing. The review paper which indicates that further detailed study is needed to conclude anything, considered the data for 14 cancers (breast, colorectal, endometrial, esophageal, extra hepatic bile duct, gallbladder, head and neck, kidney, liver, bone marrow, pancreas, prostate, stomach, and thyroid) for the people under 50 years of age during 12 years' period (from 2000 to 2012). The paper indicates that we might be looking at the probable global pandemic of early-onset cancers. The authors explain that early-onset colorectal cancers in people under age of 50 years started increasing after 1990s. The authors note the same trend even in those countries where there is no cancer screening program and hence indicating that increased screening cannot explain this shift completely. The paper surmises that the rise of consumption of highly processed foods in a combination of diet, lifestyle, weight, environmental factors, and microbiome in our gut may be the contributing factors. Eight out of 14 cancers which this paper has studied was related with the digestive system. This is a review paper of many other papers and now the researchers plan to include a prospective study of children and following them up to find the impact of a healthier lifestyle in their early years.
The further details may be found at https://www.sciencealert.com/cancers-in-adults-under-50-have-increased- dramatically-around-the-globe.
| Xenon Enhanced Ventilation Computed Tomography may Reduce Toxicity of Radiation Therapy in Lung|| |
For locally advanced non-small cell lung cancer the chemotherapy and radiotherapy are recommended as treatment modalities but the modality is limited by the development of radiation pneumonitis. Currently, RT treatment plan delivers dose to the anatomical stricture of the lung and does not take into account the functional and nonfunctional (due to cancer) part of the lung. The result is that about 30% of patients develop radiation pneumonitis (lung inflammation) after the radiation treatment of lung affecting the quality of life. Researchers at Taiwan used Xenon-enhanced ventilation CT (XeCT) to identify functional and nonfunctional lung areas in a Phase-2 clinical trial of 36 patients and targeted only nonfunctional area of lung with RT. Only 17% of patients developed radiation pneumonitis of Grade 2 or higher which is a significant improvement. The patients first underwent a baseline CT scan of thorax followed by five cycles of respiration with a xenon gas breathing system in which they inhaled a mixture of 70% oxygen and 30% nonradioactive xenon. After inhalation, the XeCT scan was performed at full inspiration breath hold. At the end, the patients washed out xenon gas by inhaling 100% oxygen for a minute and underwent a postwashout XeCT at full inspiration. All these XeCT examinations required about 20–25 min. XeCT images showed the xenon-ventilated areas of the lung in color and areas with poor ventilation as black. The digital subtraction of image yielded xenon-enhanced functional lung areas which was used in Treatment Planning System (TPS) to generate a functional-lung-avoidance plan (fAP). fAP delivered lower doses to the functional areas of lung and OAR in intensity-modulated radiation therapy or volumetric-modulated arc therapy treatment. Overall, the researchers delivered 60 Gy of thoracic irradiation in 30 fractions. The authors report that the functional part of lung which received 20 Gy or more decreased from 23.3% to 20.6%, and the mean lung dose also reduced from 14.3 Gy to 12.4 Gy leading to the reduction of Grade 2 or more radiation pneumonitis from 5.7% to 4%. In total, 5 patients out of 36 developed radiation pneumonitis of Grade 2 and one developed radiation pneumonitis of Grade 3. The researchers have pointed out the limitations as well. Such sparing planning leads to the higher maximal dose within the target and also less conformal dose distributions. XeCT is costly and not easily available at present.
The details may be seen at https://physicsworld.com/a/xenon-enhanced-ventilation-ct-protects-the-lungs-during radiotherapy/?notification = onesignal.
| International Atomic Energy Agency Designates Okayama University Japan as International Atomic Energy Agency Collaborating Centre for Boron Neutron Capture Therapy|| |
The International Atomic Energy Agency (IAEA), Vienna has signed an agreement with Okayama University (OU), Japan, in September 2022 during the 66th General Conference of IAEA to work jointly in the area of Boron Neutron Capture Therapy (BNCT), thus making OU the first IAEA Collaborating Centre for BNCT. The present agreement is a culmination of long-standing collaboration between the two for BNCT, a noninvasive targeted radiotherapy treatment of invasive malignant tumors. IAEA has, at present, 58 collaborating centers in 36 countries working in various areas of research, development, and training. OU which lies around 650 km west of Tokyo, already runs a specialized medical physics course on BNCT. Its agreement with IAEA stipulates to provide assistance to institutions interested in building BNCT facility, provide education and training in BNCT, develop standards for BNCT and encourage the participation of female students in this field. BNCT has received increased global interest of late as compact accelerator-based neutron source has become a reality now. Japan has a regulatory approval in place for cyclotron-based BNCT as medical device and has permitted TPS and a boron-containing pharmaceutical for the clinical treatment of unresectable, recurrent head-and-neck cancer. Today, more than 30 facilities worldwide are active in work related with BNCT. Patients receiving BNCT are administered stable Boron-10 containing pharmaceutical intravenously, and the reagent accumulates in cancer cells. When the accumulated Boron-10 isotopes are bombarded with neutrons, the isotope captures the neutrons leading to a nuclear reaction and the release of alpha particle and lithium nuclei. Alpha and Lithium nuclei expend all their energy within the cancer cells, causing their death. These cancer cells are targeted selectively by the selective accumulation of B-10 and not by the neutron irradiation. BNCT has the potential to spare normal cells and contains high biological effectiveness.
The details may be accessed at https://www.iaea.org/newscenter/news/iaea-japans-okayama-university-to-work-together-on-advancing-boron-neutron-capture-therapy-to-help-fight-cancer.
| A Model for the Risk of Secondary Cancer in Particle Therapy|| |
Researchers at Gesellschaft für Schwerionenforschung (GSI) Helmholtz Centre for Heavy Ion Research, Germany, are in the process of developing a model which may compare the risk of secondary cancers (SC) among particle therapy modalities. Such a model, if effective, may be incorporated into the TPS to incorporate the risk of SC to optimize the treatment further. The model for SC tries to strike a balance between the cell kill and cell transformation effected by the radiation delivered to the patient during the cancer treatment. Cell kill represents the cancer suppression since the radiation kills the transformed cells as well, while cell transformation indicates mutation which may lead to cancer induction. The relation between the radiation dose and the chance that irradiated cells may develop cancer is given by linear-quadratic (L-Q) model for photons. However, in the present model for particle therapy, the researchers used a local effect model (LEM) to predict relative biological effectiveness (RBE). They used ion-beam LQ parameters predicted by LEM to account for the increased RBE of the particle radiation. The researchers experimented with a defined target and defined OAR for proton and carbon ion irradiation. Proton and Carbon ion irradiation revealed that the final results carry complex relationship with various parameters. In general, carbon ion caused a lesser probability of SC due to reduced lateral scattering during the entrance, but it deposited a higher dose behind the target as compared to that of protons. The overall risk for SC varies with the planning as well. For example, the risk of SC for carbon ion was found to be 1.5 times of that for protons when the plan incorporated a single beam. However, the same risk was just 1.16 times for the two opposing beams since the location of the assumed OAR with respect to the target volume influenced the risk. The researchers took 10 cases of prostate cancer already treated with photon radiotherapy and planned treatment with opposing fields with proton as well as carbon ion. The carbon ion treatment plan gave better conformal treatment to target region than that of the proton but delivered large low dose area behind the tumor as well. The risk of SC in OAR in proton therapy was slightly higher for bone and skin (median risk ratio 1.19 for bone and 1.06 for skin) with respect to carbon ion therapy, but it was significantly lower for bladder (0.68) and rectum (0.49). At present, the SC risk models are not incorporated in treatment planning but may gain attention in comparing treatment plans in future.
The details may be seen at https://physicsworld.com/a/proton-versus-carbon-ion-therapy-model-compares- secondary-cancer-risks/.
| American College of Radiology Updates Appropriateness Criteria|| |
The American College of Radiology (ACR) introduced in 1993, appropriateness criteria (AC) which are evidence-based guidelines to assist referring physicians to make appropriate decision regarding medical imaging and treatment for a variety of medical conditions. These guidelines ensure the most efficacious use of medical imaging services which, in turn, enhances the quality of care. It covers diagnostic imaging, radiotherapy protocols, and image-guided interventional procedures. The guidelines are updated annually by expert panels, and it has been revised last in October 2022. At present, AC includes 222 diagnostic imaging and interventional radiology topics with 1050 clinical variants covering more than 3000 clinical scenarios. Last update has added one new topic entitled “Workup of Noncerebral Systemic Arterial Embolic Source” and has revised eight topics such as Chronic Hip Pain, Chronic Shoulder Pain, Lung Cancer Screening, Management of Vertebral Compression Fractures, Monitoring Response to Neoadjuvant Systemic Therapy for Breast Cancer, posttreatment follow-up of Prostate Cancer, Central Venous Access Device and Site Selection, and Right Upper Quadrant Pain. All these topics give elaborate narration, evidence table and a summary of the literature search made in the area of interest. The summaries have been made patient-friendly which may help the general people (patients) to understand which test(s) is/are appropriate for their condition. They are likely to facilitate better communication from referring physicians and radiologists. ACR permits individuals to use ACR AC for research, scientific, and information purpose only. For a purpose other than the above-mentioned, one has to get permission by filling online permission request form.
Details may be accessed at https://www.itnonline.com/content/american-college-radiology-releases-new-and-updated-acr-appropriateness-criteria-0.
| A Diamond-Based Detector Maps Electrical Currents in Heart|| |
Researchers at Tokyo Institute of Technology, Japan, have developed a high-resolution diamond-based detector which may measure the magnetic field created by electrical currents traveling in the heart noninvasively with a resolution of 5.1 mm which is the highest at present. The disease condition of tachycardia and fibrillation arise due to imperfect flow pathways electrical impulses in the heart. Cardiologists use magnetocardiography (MCG) which is contactless and measures the magnetic field produced by electrical currents in the heart remotely. However, the spatial resolution of MCG depends on the size of the sensor and operating temperature. The superconductor-based sensors are good in detecting small magnetic field but have to be at very low temperature and hence away from the heart which compromises its resolution. MCG are unable to resolve the intricate rotational waves produced by ventricular arrhythmias fully. In the latest research, the scientists created nitrogen-vacancy (NV) in diamond by replacing a pair of adjacent carbon atoms with a nitrogen atom and an empty space. NV center is an isolated quantum spin which is quite sensitive to the external magnetic field. Furthermore, it emits fluorescence depending on the intensity and direction of the magnetic field and facilitates an optical readout. The researchers used this diamond-based sensor just a few millimeters from the heart of live rats and NV centers of the sensor were illuminated with a green laser with an arrangement to capture the emitted fluorescence by a photodiode. The researchers developed a model to change the fluorescence measurement into the corresponding magnetic fields, and these data produced a 2D image of the electrical activity of the heart in mice. Further development in this area is on the way, and researchers hope that it may help cardiologists to study the origin and progression of many heart conditions.
Details may be accessed at https://physicsworld.com/a/high-resolution-diamond-sensor-maps-electrical-currents- in-the-heart/?utm_medium=emailandutm_source=iopandutm_term=andutm_campaign=14258-53694andutm_content=Title%3A%20High-resolution%20diamond%20sensor%20maps%20electrical%20currents%20in%20the%20heart%20-%20research_updatesandCampaign + Owner=.
| Burst Wave Lithotripsy as Alternative Treatment for Kidney Stone in Awake Patients|| |
Kidney stones are very common condition of ailment in general population. Smaller stones may pass on their own but larger stones may need treatment. Extracorporeal shock wave lithotripsy (ESWL) is the current treatment modality which uses shock waves to break the stones in the patients who are sedated. Some patients need a repeated appointment for ESWL. ESWL Causes tissue injury which results in bleeding and is generally painful. Researchers at the University of Washington School of Medicine, USA, are developing a new burst wave lithotripsy (BWL) which uses short harmonic bursts of ultrasound energy. BWL takes shorter time and does not need any anesthesia (sedation) to be administered. The researchers have reported BWL to fragment the stones of a variety of sizes, location, and densities to lesser than 2 mm sizes within 10 min with negligible tissue injury. For the human trial, the researchers used ureteroscopy to see the state of stones and tissues after BWL treatment in 19 patients. There were a total of 25 confirmed stones in these 19 patients. BWL pulverized 39% of stones completely, while 52% were fragmented partially. Volume wise, 90% stone volume was broken up completely. Most of the broken pieces were under 2 mm in size. Ureteroscopy revealed mild to no tissue injury which led to the mild bleeding. BWL has the potential to be quicker, in-clinic and economical modality with lower pain than the current ESWL technique.
The details may be seen at https://www.news-medical.net/news/20220322/Burst-wave-lithotripsy-may-provide- an-effective-alternative-for-noninvasive-treatment-of- kidney-stones.aspx.
| AAPM Report 374 Issues Guidelines on AAPM Task Group-51 Reference Dosimetry|| |
The American Association of Physicists in Medicine Task Group 51 (AAPM TG-51) protocol is a clinical reference dosimetry of high energy photon and electron beam which was published in 1999. The addendum was published in 2014 which deals with flattening filter free beam and details the characteristics of reference class ionization chamber. The guidelines define the procedure for the reference measurement of photon and electron beam in terms of absorbed dose to water with the use of calibrated ionization chamber and associated corrections for physical effects. However, there might be alternative methods data which may have a bearing on the accuracy of the dosimetry. The TG-51 does not elaborate on the alternative methods and associated data and hence there is no deliberation on the extent of effect of various methods on the accuracy of the dosimetry. For example, the depth at which absorbed dose becomes 50% of the maximum dose for electron, i.e., R50 as well as photon component of the percent depth dose (PDD) at the depth of 10 cm, %dd (10) x for photon requires measurement as a function of depth in water but there is no detailed description of the method of measurement. Dosimetry may be influenced by the electrometer of the ion chamber, extension cable, measurement set-up and the long term stability of the equipment. Moreover, the ancillary gadget used in dosimetry like triaxial cable, equipment for the measurement of temperature and pressure, and relative humidity may also influence the accuracy of the dosimetry. The new AAPM Report 374 focuses on the procedures of dosimetry to attain the best results. It aims to describe a simplified procedure wherever applicable. In nutshell, the AAPM Report No. 374 presents the practical guidelines for the implementation of AAPM TG-51 in the area of (i) measurement of depth ionization curves for the specifications of the beam quality, (ii) specifications of the reference ion chamber and parameters of the dosimetry system, (iii) commissioning of a dosimetry system, (iv) procedure for setting the water tank and ion chamber for PDD measurement, (v) requirement for ancillary gadgets, and (vi) conversion between dose at reference depth and the depth needed by TPS.
Details may be found at https://www.aapm.org/pubs/reports/detail.asp? docid = 227#:~:text = Report%20No.%20374%20-%20AAPM%20WGTG51%20Report%20374%3A, dosimetry%20of%20external%20 high-energy%20photon%20and%20electron%20beams.