The isotope of which one among the following elements is used in the treatment of cancer?
- (a)Uranium
- (b)Cobalt
- (c)Iodine
- (d)Fluorine
Correct — B, Cobalt. Cobalt-60 is the isotope used in radiotherapy. It is made by neutron irradiation of natural cobalt-59 in a reactor, has a half-life of about 5.27 years, and decays by beta emission to nickel-60 with the prompt release of two gamma photons of 1.17 and 1.33 million electronvolts. Those penetrating gamma rays are what the treatment uses: a shielded cobalt-60 source in a teletherapy unit is rotated about the patient so that the beams cross at the tumour, delivering a high dose there while spreading the dose to healthy tissue over a wide arc. Cobalt-60 teletherapy is the mainstay of external-beam radiotherapy wherever a linear accelerator is not available.
- (a)Uranium — Uranium is a nuclear fuel, not a therapeutic source. Its alpha emissions have almost no penetrating power outside the body, and uranium is chemically toxic to the kidneys, which rules it out as a medical isotope.
- (c)Iodine — Iodine is not the best answer here, though it has a genuine medical role. Iodine-131 is used against thyroid disorders and thyroid cancer because the thyroid concentrates iodine, and iodine-125 is used in some implanted seeds. Neither is the general-purpose external-beam source that the question is reaching for, and neither is used outside those organ-specific applications.
- (d)Fluorine — Fluorine has no therapeutic isotope in this sense. Fluorine-18 is used in positron emission tomography scans, which is diagnostic imaging rather than treatment.
Radioisotopes are used in medicine in two distinct ways. In diagnosis a short-lived, weakly penetrating tracer is given to the patient and its emissions are imaged from outside — technetium-99m and fluorine-18 are the standard examples. In therapy a strongly penetrating emitter is used to destroy dividing cells: either as an external beam, where a shielded cobalt-60 source or a linear accelerator directs radiation into the tumour, or as an internal source, where a substance the body concentrates in one organ carries the isotope there.
The item is a one-name recall, and the intended answer is cobalt because cobalt-60 teletherapy is the classic textbook case. Iodine is the option that deserves a second look — iodine-131 genuinely treats thyroid cancer — but it works only for one organ, whereas the question asks in general terms about the treatment of cancer. Where a candidate has to choose, cobalt is the answer every syllabus intends. Present-day practice has moved on in the better-equipped hospitals: linear accelerators have replaced many cobalt units because they can be switched off and need no radioactive source, though cobalt teletherapy is still widely used in India.
- Cobalt-60 is produced by neutron irradiation of cobalt-59 and has a half-life of about 5.27 years.
- It emits gamma photons of 1.17 and 1.33 million electronvolts, which are penetrating enough to reach deep tumours.
- Iodine-131 is used against thyroid disorders and thyroid cancer, because the thyroid takes up iodine selectively.
- Technetium-99m and fluorine-18 are diagnostic imaging isotopes, not therapeutic ones.
- Cobalt-60 also sterilises medical supplies and preserves food by irradiation.
- Choosing iodine because iodine-131 and the thyroid are the more memorable pairing.
- Assuming any radioactive element can serve as a therapeutic source.
- Confusing diagnostic tracers with therapeutic sources.
A single-element recall item. The examiner offers one general-purpose therapeutic isotope and three elements with either no medical role or an organ-specific one.
Cobalt-60 is commonly used in radiation therapy because it emits
- (a) alpha rays
- (b) beta rays
- (c) gamma rays
- (d) X-rays
Answer(c) gamma rays
The next question down the same chain. That item assumes you already know cobalt-60 is the therapy isotope and asks which radiation makes it useful; this one asks for the element itself. The two together are the whole fact.
Which one of the following element's isotope is used in the treatment of cancer?
- (a) Uranium
- (b) Cobalt
- (c) Sodium
- (d) Iodine
Answer(b) Cobalt
The same question with one option changed. Uranium, cobalt and iodine appear in both lists, and cobalt is again what survives — useful confirmation that the examiners want the general-purpose teletherapy source rather than the organ-specific one.
- practice — not a real PYQ
Iodine-131 is used mainly in the treatment of disorders of which organ?
- (a)Liver
- (b)Thyroid gland
- (c)Kidney
- (d)Pancreas
Answer(b) Thyroid gland — it is the one organ that concentrates iodine from the blood.
- practice — not a real PYQ
Cobalt-60 is valued in radiotherapy chiefly because it emits
- (a)alpha particles
- (b)neutrons
- (c)gamma rays
- (d)positrons
Answer(c) gamma rays — two photons of 1.17 and 1.33 MeV, penetrating enough to reach deep tissue.