Unit 15 - Medical Physics PDF

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Summary

Applications of physical theory in medical use. Distinction received....

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Medical Physics Kate Seeley 19/09/2019

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Introduction The medical field has many uses for applied physics and theories found therein. The following report describes varying physics applications used in diagnosis and treatment in healthcare; the nature of atomic structure; the nature of high-energy radiation and how it can be used safely in treatment and diagnosis; how certain isotopes can be used in diagnosis; the health applications of the electromagnetic spectrum; and how ultrasonic sound can be used in treatment and diagnosis. Sources, diagrams and tables are from online articles, online revision hubs and educational videos, as well as study materials provided via ePearl, to present my understanding of medical physics.

Contents

Title Page Introduction Contents Section 1 – Understand Atomic Structure 1.1 Sub-Atomic Particles

Section 2 – Understand the nature of alpha, beta and gamma radiation, and X-rays 2.1 Explain how the range in air and penetrating powers of alpha, beta, gamma and x-rays are related to their nature and properties 2.2 Explain the safety procedures followed when using alpha, beta and gamma radiation and x-rays

Section 3 – Understand the main uses of ionising radiation in monitoring and treatment 3.1 Explain the use of the Barium meal for soft body imaging 3.2 Explain the use of γ-rays in imaging 3.3 Explain the use of internal sources of radiation in treatment procedures

Section 4 – Understand how radio isotopes are used in healthcare 4.1 Explain how technetium-99m is generated 4.2 Explain the use of Iodine-131 in thyroid investigations

Section 5 – Understand the health applications of a selected part of electromagnetic spectrum 5.1 Explain medical uses of parts of the electromagnetic spectrum

Section 6 – Understand how ultrasound is used in healthcare 6.1 Explain the use of ultrasonics in medical imaging and treatment

Conclusion Recommendations References list Bibliography

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3 Understand atomic structure 1.1 Sub-Atomic Particles Atoms are kept stable by having the same amount of protons and electrons within an atom. Protons are individual units of positive charge and electrons are individual units of negative charge. Having opposing charges creates an attraction needed to hold all particles together to form the atom. Neutrons are neutral particles, having no charge, but prevent protons from repelling each other due to the amount of positive charge they create together.

Figure 1 - Reynolds, 2018

If the atom’s number of protons were to change it would become a different element and if the electrons changed it would become an ion, having become ‘ionised’.

The structure of any atom is basically the same, but get larger and more numerous as the atomic number increases. Take figure 1 as an example. We can tell for certain that it has seven electrons over two orbital shells, meaning it must have seven protons, making the atom nitrogen. Nitrogen has a relative mass of 14.007. Each proton (7) and neutron (7) have a relative mass of 1, equalling 14. The .007 is the relative mass of the total electrons, each of which has approximately 1/1840 the mass of one proton or neutron. Understand the nature of alpha, beta and gamma radiation, and X-rays 2.1 Explain how the range in air and penetrating powers of alpha, beta, gamma and x-rays are related to their nature and properties Alpha radiation could be immensely dangerous if it didn’t lose energy so quickly. It has a strong ionising power but is not penetrative being easily stopped by a sheet of paper or skin and unable to travel more than 5cm (BBC Bitesize). It is deflected by magnetic fields, making it the heaviest and most magnetically-charged radioactive particle (FuseSchool). It is essentially a helium atom with no electrons, and a positive charge ( 42 He+2 ). The beta particle is a single negative charge ( −10 β ) and can retain energy for longer than the alpha particle. Beta particles can travel up to a metre but stopped by a 5mm aluminium sheet. Beta radiation is can also be deflected by magnetic fields (FuseSchool). Gamma rays ( 00 γ ) are high energy electromagnetic waves with a small wavelength and high frequency, able travel further than a kilometre. They are able to penetrate metal and concrete, stopping at lead. The three all come from ionising radiation emitted from decaying

Figure 2 - Nave, 2016

4 atomic nuclei. While it is possible to predict roughly when these processes discharge, it can random and not completely dependable. X-rays are also high energy electromagnetic waves, having longer wavelength and lower frequency than gamma waves. The difference lies in how they are produced. Gamma waves come from the atom nucleus. X-rays are produced by high energy photon release when electrons are passed between orbital shells. The orbital shells can be disrupted by bombarding a metal surface with electrons from a high voltage filament (figure 2) (Bodicoat, 2.1). 2.2 Explain the safety procedures followed when using alpha, beta and gamma radiation and x-rays Ionising radiation, while useful in diagnostic and treatment processes, is also able to alter cell structure and DNA, causing mutations and cancers. This is why dosages and exposure limitation of radiation is extremely important. The radiation exposure from a dental x-ray is the equivalent exposure of one day’s natural background radiation and an abdominal CT scan would provide around four and half years of background radiation over the course of a single procedure (Public Health England). As a patient, radiation exposure at such concentrations are mostly a rare occurrence. Imaging technicians and other medical staff experience the machines on a near daily basis, so the risk of exposure is much larger and must take precautions to limit absorption over their careers. There are three main ways to control limiting exposure:   

Limiting exposure time Increasing distance from source Using appropriate protective equipment

Instant readings can be provided by Geiger counters, but dosimeter badges (figure 3) are commonly used as a cost-effective way to monitor exposure over an extended period. These use x-ray film which darkens dependent on time and distance in proximity to a radioactive source.

Figure 3 - Landauer.com Lead-lined barriers are typically built into imaging suites to protect operators, and wearable protective equipment is provided by law. This includes aprons, masks, gloves, boots and particularly lead-lined collars designed to guard the thyroid glands. This is not just for machines emitting radiation, but also radioactive isotopes delivered directly into the body. These require absolute minimum contact. Understand the main uses of ionising radiation in monitoring and treatment 3.1 Explain the use of the Barium meal for soft body imaging Barium meal, or barium swallow, is a test used to help determine the cause of issues within the digestive tract. As the digestive tract is made up of soft tissue it cannot show up on an x-ray. By introducing a heavy metal-based suspension to coat the inside of the soft tissue, it now makes it possible to contrast the internal organs and view organs via x-ray. This falls into a category of medicines known as radiopaque contrast media (MedlinePlus). Barium sulphate (or barite) is a non-toxic, odourless compound which can absorb x-rays and when added to water it takes on a thick milk-like consistency.

5 Barium is ideal for use in imaging as it is not an element found in anything humans would consume naturally and cannot be absorbed by the body. This makes any trace of the solution in the body relevant to the image. It is later eliminated from the body by excretion. 3.2 Explain the use of γ-rays in imaging Gamma rays can also be intentionally given to patients to gather images of soft tissue organs. These are known as radioactive tracers. These can be injected, ingested or inhaled into the body, and specific radionuclides can target specific organs, systems or types of cell. Gamma ray imaging is particularly useful as targeted body parts can be recorded by a gamma camera to record footage of internal functions in real time. For example, the heart can be dosed with gamma and then recorded to show if there’s an issue with ventricles pumping blood. As a tracer travels to its targeted area, it emits radiation that can be tracked by sensors (Bodicoat, 3.2). This process uses a collimating grid which collects photons emitted by the radiation to relay an electrical signal to a monitor for observation (Mussadiq, 2009).

Figure 1 - Musaddiq, 2009

3.3 Explain the use of internal sources of radiation in treatment procedures Radiotherapy is the use of radiation as a treatment. As mentioned earlier, radiation can alter cells making them irregular and harmful. The correct dosage of different radioisotopes can counteract previous damage by killing off cancer cells and shrinking tumours. Dosages are adjusted by monitoring tumour reaction to the medicine, i.e. if a tumour doesn’t decrease in size at the expected rate and healthy cells are coping, the radiation dosage can be increased. Radiation treatments can be delivered by: 

External beam radiotherapy – high energy gamma or x-rays targeted externally on the body.

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Internal radiotherapy – can be done in a few ways. Via metal implants, placed into the affected organ which emit radiation. For example, a seed implant (brachytherapy) into the prostate gland for prostate cancer. Or via liquid ingested or injected. For thyroid cancer, radioactive iodine can be given to directly target the thyroid glands. Selective internal radio therapy (SIRT) – radiologists can map out blood vessels in and around affected organs, placing a catheter to deliver beads of yttrium-90 to kill cancer cells from inside the tumour (Bodicoat, 3.3).

All of these versions of treatment are about keeping radiation as close to the cancer cells as possible, instead of broadly delivering radiation to the entire body.

Understand how radio isotopes are used in healthcare 4.1 Explain how technetium-99m is generated Technetium-99m is the most commonly used medical radioisotope, used as tracer. Its widespread use is down to the fact it emits gamma rays with a similar photon energy comparable to xray and a very short half-life of 6 hours.

Figure - NRC

This short half-life makes storage impossible, so it’s generated from molybdenum-99 which comes before technetium on the periodic table. Molybdenum-99’s half-life is 66 hours, so once it’s contained in a technetium generator it can undergo a round of decay, losing a beta particle and gaining a proton and electron turning it into technetium-99m

(figure 5). 4.2 Explain the use of Iodine-131 in thyroid investigations Iodine is essential in the production of thyroid hormones, so if it’s introduced to the body that’s where it’ll gather. Only a few radioactive atoms of iodine-131 are needed to give an accurate image of the glands’ functions and as it creates regulatory hormones for metabolism, if something is awry it becomes simple to find where the issues lie (Bodicoat, 4.2). This radioisotope is rarely given purely as diagnostic, instead given as therapeutic for several thyroid conditions (such as iodine deficiency) and imaging is done as a follow up (en.wikipedia.org). As with other tracers, it emits just enough gamma rays to be detected by gamma cameras, but also gives off beta particles which can be used for killing off cancer cells at the same time.

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Understand the health applications of a selected part of electromagnetic spectrum 5.1 Explain medical uses of parts of the electromagnetic spectrum

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Understand how ultrasound is used in healthcare 6.1 Explain the use of ultrasonics in medical imaging and treatment

9 Ultrasound is the sound frequency above 20,000Hz. It’s inaudible to humans, but all sound creates vibrations which can reflect back to us, like an echo. Ultrasound equipment uses the same principal to create visual images which can be used in diagnosis and treatment. As ultrasound frequency is much higher than we can hear, the vibrations can take on physical properties. When pressed against the skin, it can increase blood flow, abating swelling and localised pain, making it useful for soft tissue injuries.

Figure - Wikipedia/Ultrasound need for surgical intervention (Wikipedia).

Ultrasound vibrations can also be used to locate and breakdown nutsized lithiases, or stones. They can be found in multiple parts of the body, commonly in kidneys, bladder and gallbladder. Once broken down, they can usually be passed eliminating

Ultrasound is most commonly used as the safest tool for checking progression foetal development during pregnancy (figure 6). It is essentially echolocation, without need for radiation, and strong enough to create an image of baby’s bones and organs.

Conclusion So many principles of physics have found their way into common usage in a medical setting. The use of radiation can seem intimidating, but rest assured, dosing specific to the patient is carefully formulated by professionals. Uses can be risky in treatment, but when weighed against possible outcomes without it, many of us would take the chance for a cure or extra time. The dosing of a single diagnostic procedure is also daunting, but when one can accept low-level radiation is everywhere always, it’s justifiable.

Recommendations This assignment was very much a “greatest hits” of previous assignments, which really drove the recently learned information out of me and into this report. It’s reassuring to know I can recall what was recently added to my knowledge-base. Having so many sections to write and only a few words per section has been a terrific handicap. I could’ve easily used up another 1000 words just to get all points across.

References list

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BBC Bitesize, Radioactive decay [Online] Available at: https://www.bbc.com/bitesize/guides/z3tb8mn/revision/ (Accessed September 2019) Bickle, I. (2017), From the case: Normal barium swallow [Online] Available at: https://radiopaedia.org/images/30793391 (Accessed September 2019)

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Bodicoat, M., Medical Physics, [Online] Available at: https://www.epearl.co.uk/studymaterial/4581 (Accessed September 2019)

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En.wikipedia.org (2019), Calculus (medicine) [Online] Available at: https://en.wikipedia.org/wiki/Calculus_(medicine) (Accessed September 2019)

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En.wikipedia.org (2019), Iodine-131 - Medical Use [Online] Available at: https://en.wikipedia.org/wiki/Iodine-131#Medical_use (Accessed September 2019)

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En.wikipedia.org (2019), Ultrasound [Online] Available at: https://en.wikipedia.org/wiki/Ultrasound (Accessed September 2019)

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FuseSchool – Global Education (2012), Types of Radiation | Physics | Fuse School [Online video] Available at: https://www.youtube.com/watch?v=5oUagoF_viQ (Accessed September 2019) Landauer, Luxel+, [Online] Available at: https://www.landauer.com/luxel-radiationdosimeter-badges (Accessed September 2019) MedlinePlus (2016), Barium sulfate [Online] Available at: https://medlineplus.gov/druginfo/meds/a606010.html (Accessed September 2019) Mussadiq, M. (2009), Gamma Camera [Online] Available at: https://www.slideshare.net/musadiq/gamma-camera (Accessed September 2019)

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National Research Council Committee (2009) 2 Molybdenum-99/Technetium-99m Production and Use [Online] Available at: https://www.ncbi.nlm.nih.gov/books/NBK215133/ (Accessed September 2019)

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Nave, R. (2016), X-Ray Tube, [Online] Available at: http://hyperphysics.phyastr.gsu.edu/hbase/quantum/xtube.html (Accessed September 2019) O’Doherty, J., et al (2018) The real-life radioactive men: The advantages and disadvantages of radiation exposure [Online] Available at: https://www.researchgate.net/publication/329168876_Reallife_radioactive_men_The_advantages_and_disadvantages_of_radiation_exposure (Accessed September 2019) Public Health England, (2008), Patient dose information: guide [Online] Available at: https://www.gov.uk/government/publications/medical-radiation-patient-doses/patientdose-information-guidance (Accessed September 2019)

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Reynolds, B. (2018), What are the components of the Atomic Structure?, [Online] Available at: https://sciencing.com/components-atomic-structure-14117.html (Accessed September 2019)

Bibliography 

Australian Radiation Protection and Nuclear Safety Agency, Gamma radiation , Australian Government, viewed September 2019 https://www.arpansa.gov.au/understandingradiation/what-is-radiation/ionising-radiation/gamma-radiation

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BBC Bitesize, Radiation and risk, BBC Bitesize, viewed September 2019 https://www.bbc.co.uk/bitesize/guides/zwb3h39/revision/

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BBC Bitesize, Radioactive decay, BBC Bitesize, viewed September 2019 https://www.bbc.com/bitesize/guides/z3tb8mn/revision/

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Bickle, I., 2017, From the case: Normal barium swallow, Radiopaedia.org, viewed September 2019 https://radiopaedia.org/images/30793391

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Bodicoat, M., Medical Physics, ePearl, viewed September 2019, https://www.epearl.co.uk/study-material/4581

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En.wikipedia.org, 2019, Calculus (medicine), Wikipedia.org, viewed September 2019, https://en.wikipedia.org/wiki/Calculus_(medicine) En.wikipedia.org, 2019, Iodine-131, Wikipedia.org, viewed September 2019, https://en.wikipedia.org/wiki/Iodine-131 En.wikipedia.org, 2019, Ultrasound, Wikipedia.org, viewed September 2019, https://en.wikipedia.org/wiki/Ultrasound FuseSchool – Global Education, 2012, Types of Radiation | Physics | Fuse School, YouTube, viewed September 2019, https://www.youtube.com/watch?v=5oUagoF_viQ Landauer, Luxel+, Landauer, viewed September 2019, https://www.landauer.com/luxelradiation-dosimeter-badges

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MedlinePlus, 2016, Barium Sulfate, National Institutes of Health, viewed September 2019, https://medlineplus.gov/druginfo/meds/a606010.html

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Musaddiq, M., 2009, Gamma Camera, SlideShare, viewed September 2019, https://www.slideshare.net/musadiq/gamma-camera

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National Research Council Committee, 2009, 2 Molybdenum-99/Technetium-99m Production and Use, NCBI, viewed September 2019, https://www.ncbi.nlm.nih.gov/books/NBK215133/

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Nave, R., 2016, X-Ray Tube, Georgia State University, viewed September 2019, http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/xtube.html O’Doherty, J., et al, 2018, Real-life radioactive men: The advantages and disadvantages of radiation exposure, Researchgate.net, viewed September 2019, https://www.researchgate.net/publication/329168876_Reallife_radioactive_men_The_advantages_and_disadvantages_of_radiation_exposure

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Public Health England, 2008, Patient dose information: guide, gov.uk, viewed September 2019, https://www.gov.uk/government/publications/medical-radiation-patientdoses/patient-dose-information-guidance

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Reynolds, B., 2018, What are the components of the Atomic Structure?, Sciencing.com, viewed September 2019, https://sciencing.com/components-atomic-structure-14117.html...