Medical Physics

  Journal of Diagnostic Imaging in Therapy

Medical physicists are concerned with the clinical services of Nuclear Medicine and Radiology Departments including technological advancement of new instruments and procedures in the following areas: Diagnostic Imaging, Radiation Therapy and Dosimetry with the aim of ALARA, which is a radiation safety term that stands for As Low As Reasonably Achievable. It simply means that radiation exposure should be at a minimum towards medical personnel and patients within a reasonable effort by the organisation.

The medical physicist plays an integral part of the patient treatment plan, especially in the area of diagnosis and therapy.  The role of the medical physicist is to interact with physicians especially in the oncology setting:  their critical role is to devise a safe treatment plan which involves administering the correct radiation dose to the cancer patient.  Consequently, complex calculations are required for the external radiation beams or internal radioactive sources. The most important factor is to derive accurate calculations involving the radiation output from the sources employed at the various cancer stages.

Treatment planning systemTreatment planning system
(Nishiyama S, Yoda K, Komatsu T. J Diagn Imaging Ther. 2015; 2(2): 35-40. CrossRef)

The reirradiation of spinal metastases requires previous knowledge of the delivered dose to the spinal cord. This information is necessary to minimise further exposure to the dose delivery. In most cases the reirradiation of spinal metastases is performed by cyberknife or tomotherapy. Cyberknife procedures require the patient to remain still for longer time periods.  This can induce stress in the patient. Therefore, the radiation dose transferred to the patient is performed by the principles of tomotherapy.  This approach uses rotational beams of radiation and thus limits the damage to the surrounding organs. Furthermore, the application of stereotactic body radiotherapy is employed for the reirradiation. This allows for high radiation doses to the target while sparing the spinal cord and neighbouring organs.

Dose distributionDose distribution
(Nishiyama S, Yoda K, Komatsu T. J Diagn Imaging Ther. 2015; 2(2): 35-40. CrossRef)

The medical physicist is central to nuclear medicine either in a regulatory capacity or for consultation with other medical colleagues.  Nuclear medicine uses radionuclides for internal delineation of organs and to decide the most significant physiological variables. These may include metabolic rates and blood flow analysis.

Another area which involves the physicist is equipment performance, writing standard operating procedures (SOPs), quality control in imaging systems and input into the design of radiation installations.  In addition, the physicist has a role in radiological protection and the control of radiation exposure to medical staff and patients. The medical physicist in most cases is part of the clinical and scientific advice board to help solve and analyse problems arising in specialised medical areas.

Advancing Medical Physics

Medical physicists have a vital role in the medical research team. They have numerous responsibilities in the fields of oncology, cardiology, and neurology amongst others.  In oncology departments, they work mostly with radiation and are interested in the mechanism of biological change after irradiation. Further technological advances are paving the way for high-energy machines to treat patients and also new techniques to determine the exact measurement of radiation.  The design of computer software based on more advanced algorithms is used to calculate the correct dose for patient treatment.  An active area of research is particle irradiation applied to biological systems compared to photon therapy.

The medical physicists play a significant role in patients with heart disease by measuring the blood flow and levels of oxygenation. In mental health patients, they interpret the evoked potential (EP) tests due to the electrical activity of the brain which is also an application used in multiple sclerosis patients. Medical physicists are also interested in the application of digital computers in medicine and information systems.  In addition to the concept of diagnostic problems which include processing, data storage and accessing medical images. Furthermore, to measuring the amount of radioactivity in the patient and studying the behaviour of radioactive substances in the body.  Medical physicists are an integral part in the development of instrumentation and technology applied to theranostic medical imaging.

Consequently, this involves the use of magnetic and electro-optical storage devices for the manipulation of X-ray images.  Furthermore, the physicist has a role in the quantitative analysis of both static and dynamic images using digital computer techniques. In addition, to radiation methods for the analysis of various tissue characteristics.  With the expanding areas of MRI-CT scanners used to generate cross-sectional images of the human body: medical physicists engage in research and development on imaging procedures, utilising infrared and ultrasound sources.

Image Quality Phantom
Image Quality Phantom
(Ferrando O, et al. J Diagn Imaging Ther. 2015; 2(1): 18-29. CrossRef)

The IEC Image Quality Phantom conforms with the NEMA 2012 standard and is applied in the simulation of whole-body PET imaging and camera-based coincidence imaging techniques. In addition to the evaluation of reconstructed image quality in whole-body PET and camera-based coincidence imaging.  The IEC Quality Phantom determines the coincidence count rate characteristics for both the brain and cardiac imaging. Furthermore, the IEC Quality Phantom is important in the evaluation of the relationship between true coincidence count rate and radioactivity. Also, to the determination of the address, errors caused by address pile up and finally to the assessment of the count loss correction scheme.

Medical Imaging Physics

Medical imaging physics deals with areas of testing, optimization and quality assurance especially in the fields of diagnostic radiology physics including radiographic X-rays, fluoroscopy, mammography, angiography and computed tomography.  Medical imaging physics is important also in the area of non-ionizing radiation modalities such as ultrasound (US) and MRI.

The duties of the medical physicist include radiation protection procedures, radiation monitoring including dosimetry. A current role of the medical imaging physicist includes the responsibility of PET and SPECT imaging and hybrids with MRI and CT scanners.

Functional magnetic resonance imaging (fMRI) began in the 1990s by Ogawa and Kwong.  This technique is used to measure brain activity and works by detecting the changes in the oxygenated blood and response to neural activity.  Imaging studies have shown when the brain area becomes more active it consumes more oxygen.  Therefore, to keep up with this demand the blood flow increases in these active regions of the brain. fMRI can be used to produce various activation maps showing which parts of the brain are active. fMRI is part of the medical imaging apex, including positron emission tomography (PET) imaging and near-infrared spectroscopy (NIRS).  These two techniques are involved in the study of blood flow and oxygen metabolism of brain activity.  fMRI of the brain has several key benefits including the non-invasive procedure and does not involve radiation.  Both of these provide safety towards the patient and medical personnel. Also, it produces excellent spatial and good temporal resolution.

Radiation Therapeutic Physics

Radiation therapeutic physics (radiotherapy physics or radiation oncology physics) is concerned mostly with linear accelerator (Linac) systems and kilovoltage X-ray treatment units.  In addition to more advanced modalities such as tomotherapy, gamma knife, cyberknife, proton therapy, and brachytherapy.

Therapeutic physics may include boron neutron capture therapy, sealed source radiotherapy and terahertz radiation systems. Therapeutic physics also involves high-intensity focused ultrasound, optical radiation lasers, ultraviolet and amongst others. Furthermore, extending to photodynamic therapy including nuclear medicine using unsealed source radiotherapy and photomedicine.

Nuclear Medicine Physics

Nuclear Medicine is a discipline that uses radiation to gain information about the functioning of the human body’s organs to diagnose disease and to apply appropriate therapy treatments.  The information generated helps the physicians to make a reasonable and accurate diagnosis of the patient’s disease state.

The organs of the human body which can easily undergo imaging include thyroid, bones, heart, liver amongst others. Another use of radiation is its ability to treat diseased organs and/or tumours. Radiotracers in medicine are widely used throughout the World healthcare organisations and this extends to mobile facilities. About 10,000+ hospitals worldwide use radioisotopes in medicine for diagnosis and therapy procedures.  The most diverse radioisotope used in diagnosis is technetium-99m.  This radionuclide accounts for over 30 million procedures per annum and accounts for 80% of all nuclear medicine procedures.  In context, the USA, produces some 18 million nuclear medicine procedures per year. In Europe, there is about 10 million procedure from a population of 500 million people. Marketing suggests that the use of radiopharmaceuticals in diagnosis is growing at a rate of 10% per annum.

Nuclear medicine which began in the 1950s by physicians investigating the endocrine system using iodine-131 to diagnose and treat thyroid disease. The medical physicist liaises with a radiologist due to the hybrid PET-CT systems. CT scanning and nuclear medicine contribute to over a third of the total radiation exposure.  The average total yearly radiation exposure in the USA per person is 6 mSv per year.

The responsibility of the Health Physicist (Radiation Safety or Radiation Protection Officer) is with the evaluation and control of health hazards associated with the safe handling of radiation sources. Therefore, the supervision and monitoring of radionuclides or ionising radiation in the clinical setting is of paramount importance to regulatory requirements.

The application of more advanced computer systems is to enable processes to analysis complex driven by the generation of computer algorithms for the delineation of anatomical structures.  For example, image segmentation plays a central role in various biomedical imaging applications.  These include quantification of tissue volumes, diagnosis and localization of pathology.

In addition, to the study of anatomical structure, treatment planning and computer-integrated surgery, the application of a 3-D volume extraction algorithm was suggested for the segmentation of cerebrovascular structure for the brain.  Previous knowledge of the cerebrovascular structure and multiple seed voxels are identified on the initial image.

In light of the preserved voxel connectivity, the seed voxels were grown within the cerebrovascular structure area throughout the 3-D volume extraction procedure.  This algorithm improved the segmentation results compared to other methods such as the histogram approach.  Furthermore, this 3-D volume extraction algorithm is also applicable to segment tree-like organ structures. For example, the renal artery and coronary artery can be derived from these medical imaging modalities.