Introduction
Radioisotopes and radiopharmaceuticals play a crucial role in modern diagnostic imaging and cancer therapy. Understanding their production, biological behaviour, radiation effects, and dose calculations is essential for students studying nuclear medicine, radiography, and medical physics. This assignment systematically demonstrates key concepts aligned with academic learning outcomes.
Q1 AC 1.1: Radioisotope and Radiopharmaceutical definitions
A radioisotope is an isotope of an element that has some of its particles disintegrate and emit alpha or α, beta or β, or gamma or γ radiation in their effort to achieve the state of stability. It helps in determination of the half-life, being the time it takes for half of the atoms of a given element to decay. Alpha particles are heavy and less penetrating, raining refers to beta particles as electrons or positrons have moderate penetrating ability while gamma rays are electromagnetic waves with high penetration power (George et al. 2021). A radiopharmaceutical could be defined as the drug including a radioisotope which serves for diagnostic or therapeutic purposes like 99mTc for imaging and 131I for treatment of thyroid.
Q2: AC 1.2: Radioisotopes production
- Technetium-99m (99mTc) Production
This one is obtained from Molybdenum-99 (99Mo) using a radioisotope generator.
The production process is initiated with Molybdenum-99 (99Mo) that is obtained by neutron irradiation of uranium-235 in a nuclear reactor. It is a product of molybdenum-99 which decays through beta decay with half life of about 66 hours, and produces Technetium-99m or 99m Tc. Technetium generator is a device used for obtaining 99Tc which is added to prepare radiopharmaceuticals used in exams.
Another benefit of carbon-99 toward technetium-99 is that it has a shorter half-life of 6 hours though it is relatively rich in energy that enhances the quality of imagery used in diagnoses.
- Cobalt-60 (60Co) Production
Cobalt-60 is a gamma-ray gamma-emitting radioisotope mostly used in the treatment of cancer and as a sterilizing agent.
The method of producing cobalt 60 involves exposure of the Cobalt-59(59 Co) to neutron beams in a nuclear reactor to produce Cobalt-60(60Co). Cobalt-60 then emits beta particles and turns into Nickel sixty; the gamma rays emitted have an energy of about 1.17MeV as well as 1.33 MeV.
Cobalt-60 is normally applied for irradiation in cancer therapy when the beam of radiation is used from outside the body.
- Iodine-131 (131I) Production
Iodine-131 is also known to be used in imaging and treatment of thyroid cancer more frequently than any other cancer type.
This isotope is synthesised through neutron irradiation of Tellurium-130 (130Te) in nuclear reactors. The reaction produces Iodine-131, which is a radioactive material that undergoes beta decay, and it has a half-life of eight days besides emitting gamma rays.
The advantage of using Iodine-131 is that it is naturally taken up in the thyroid glandular system thus used in both diagnoses.
Q3 AC 1.3 Radiological and Biological Properties of Radionuclides
(a) Radiological Properties
Themost appropriate radiation types and half-lives should be possessed by the radionuclides used in medical application. An isotope called Technetium-99m (99m Tc) is used for diagnoses, the gamma emission of which lasts for only 6 hours, allowing for a perfect view without excessive exposure (Poletto et al. 2022). 131I is a radioactive isotope of iodine that gives off both the beta and gamma rays with a half-life of 8 days which is ideal for the therapy. Cobalt-60 is used as a source of radiotherapy since it has high gamma emissions energy, and its half-life is 5.3 years, making it suitable for constant use in treatment of cancer.
(b) Biological Properties
The biological type characteristics involved in radionuclides dictates the manner in which it responds within the human body. Iodine-131 has the natural tendency to concentrate in the thyroid tissue enabling the treatment to be focused. Xenon-133 or 133Xe on the other hand remains dissolved in lung tissue and therefore is good for imaging of the respiratory system. Technetium-99m has the ability to attach to different tissues of the human body for efficient organ scans. Biological type half-life or rate of excretion that mainly influences radiation dose along with patient safety.
Q4 AC 2.1: Function and Working of a Gamma Camera
A gamma camera is a device also known as a scintillation camera which is a medical imaging system that is used in nuclear medicine to detect gamma radiation emitted inside the human body from radionuclides. It assists in showing the processes of the organs and differentiation of the irregularities. The camera is made up of a collimator that only allows in a certain amount of radiation, a scintillation crystal that translates the gamma rays into light as well as photomultiplier pipes or PMTs that amplify the signal (Nunes et al. 2022). All the detected signals are then converted into an image in a computer. However, sectarianism as well as the readiness of legumes continue to grow, push themselves forward, do their thing and make life miserable and unpredictable for everyone forced to interact with them.
Q5 AC 2.2: Comparison of Radioisotopes in Imaging
Thallium-201 (201Tl) is MIA that emits low energy gamma photons that can be used in cardiac imaging by imitating potassium uptake of tissues in the heart. This is why Xenon-133 (133Xe) is the kind of gas that is used in lung ventilation scans. 99mTc is preferred for these organ scans because of its ideal gamma-emitting energy of 140 keV and favourable half life of 6 hours (Naskar and Lahiri, 2021). Imaging equipment are gamma cameras as well as SPECT scanners. These isotopes are different in terms of their decay mode and this determines the imaging properties that are seen when used in PET scans instead of Fluorine-18 (18F).
Q6 AC 2.3: Comparison of Radioisotopes in Imaging
The treatment for many small tumors is systemic radionuclide therapy with either Iodine-131 or ¹³¹I and Lutetium-177(¹⁷⁷Lu) because it can be administered intravenously and accumulates in cancer cells. Shallow isolated tumors are treated through brachy radiotherapy where the radioactive source like Iridium-192 or ¹⁹²Ir is placed near to the tumor mass. For tumors adjacent to radiosensitive organs, for example in the chest or the abdomen, the EBRT with high energy X-rays or protons is used to avoid damaging the healthy tissue in the region (Banerjee et al. 2022). It is based on the location, size and radiation sensitivity of the tumor for the better treatment with minimal side effects.
Q7 AC 3.1: Effects of Radiation on Animal Cells
Radiation goes on animal cells by stochastic and deterministic effects. Stochastic effects are probabilistic and can include randomness of DNA mutations that may lead to cancer or genetic disorders (Uccelli et al. 2022). Deterministic effects also depend on the dose, resulting in a change in the number or alteration of normal cells or tissues at high doses, cell death, burns or failure of organs or tissues. Low doses can cause DNA repair mechanisms, while high doses cause the cell to undergo apoptosis or necrosis. Dosimeters are used most commonly when there is radiation protection in order to avoid taking too much radiation (Hansen and Bender, 2022). Alpha particles produce massive local effects, beta particles get into the tissues while gamma rays go deep into the tissues.
Q8 AC 3.2: Radiation Damage to Cells
Radiation affects molecules by ionizing them and this affects the DNA, leading to cell death or formation of cancer cells. Somatic cells (body cells) in patients are affected at high doses in a deterministic fashion and this causes burns, tissue fibrosis, and organ failure . It also takes into consideration the lagged and stochastic effects that may lead to getting cancer in the future years (Vallabhajosula, 2023). Somatic cells are not able to undergo the processes of mitosis and are developed from germ cells which can be changed and lead to birth defects or inherited diseases. High concentrations cause chromosome mutations while low levels may be corrected by the DNA repair mechanism. It further depends on the type of the radiation, the dosage received and the time the affected party was exposed (Pant et al. 2024). Selective shielding, dose measurement and controlled exposure are important techniques in order to reduce potential impacts in the clinical and working environment.
Q9 AC3.3: Calculating Number of Decays per Day
To estimate the number of decays per day, we use the activity equation:
A=λN
where:
- A is the activity
- λ is the decay constant,
- N is the number of radioactive nuclei.
The decay constant is mainly given below.
λ=ln(2)/(T1/2)
where T1/2 is mainly the half-life of the isotope.
(a) Diagnostic Radioisotope with the particular Activity 52 MBq
Since 1 MBq = 10^6 Bq, the activity is given below.
A=52×106 Bq
The number of decays per day:
Decays per day=A×86400 = (52×106)×86400 =4.4928×1012 decays per day
(b) Therapeutic Radioisotope with the particular Activity 3800 TBq
Since 1 TBq = 10^{12} Bq, the activity is given below.
A=3800×1012 Bq
The number of decays per day:
Decays per day=A×86400 = (3800×1012)×86400 = 3.2832×1021 decays per day
The diagnostic isotope mainly undergoes 4.49×1012 decays per day while the therapeutic isotope specifically undergoes 3.28×1021 decays per day.
Q10 AC3.3: Absorbed Dose Calculation
The absorbed dose or D is mainly calculated utilizing the formula given below.
D=E/m
where:
- D is the absorbed dose in Gray or Gy,
- E is the energy absorbed in Joules or J,
- m is the mass of the affected tissue in kg.
Given data:
- Energy absorbed: E=18J
- Tumor mass: m=175g=0.175kg
Calculation is mainly given below.
D=18/0.175
D=102.86 Gy
The absorbed dose mainly received through the help of the tumor is 102.86 Gy.
Q11 AC3.3: Radiation Dose Calculation
Given Data are given below.
- Absorbed dose from the overall gamma rays are 15 mGy = 0.015 Gy
- Absorbed dose from the overall alpha particles are 7 mGy = 0.007 Gy
- Radiation weighting factor (Wr):
- Gamma rays: Wr=1
- Alpha particles: Wr=20
- Factor of tissue weighting for lungs (Wt): 0.12
(a) Calculation of Total Equivalent Dose
The equivalent dose or H is calculated using the formula given below.
H = D×Wr
For gamma rays are given below.
Hγ=0.015×1=0.015 Sv
For alpha particles:
Hα=0.007×20=0.14 Sv
Total equivalent dose:
Htotal = Hγ+Hα = 0.015+0.14 = 0.155 Sv
(b) Effective Dose Calculation
The effective dose or E is mainly calculated utilizing the formula given below.
E=Htotal×Wt
E=0.155×0.12
E=0.0186 Sv or 18.6 mSv
The total amount of equivalent dose is 0.155 Sv and the total effective dose mainly received by the lungs is defined as 18.6 mSv.
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Reference List
Journals
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Naskar, N. and Lahiri, S., 2021. Theranostic terbium radioisotopes: challenges in production for clinical application. Frontiers in medicine, 8, p.675014.
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