Therapeutic Equipment Questions and Answers

Answer: D

The Gamma Knife uses cobalt-60.

The Leksell Gamma Knife holds about 192 to 201 cobalt-60 sources arranged in a hemisphere. Their gamma beams (about 1.17 and 1.33 MeV) are collimated to meet at a single focal point, delivering a high dose to a small intracranial target while the dose to surrounding brain falls off steeply.

It uses no laser and no ultrasound. Machines that use X-rays from a linear accelerator for radiosurgery exist, such as the CyberKnife, but the Gamma Knife is defined by its cobalt-60 gamma sources.

Answer: B

The therapy is brachytherapy.

In brachytherapy (Greek brachys, short) sealed radioactive sources such as iridium-192, iodine-125 seeds or cesium-137 are placed inside or right next to the tumour. Because dose falls steeply with distance, the tumour gets a high dose while nearby normal tissue is spared. It is widely used for cervical and prostate cancer.

Teletherapy is external beam therapy from a distance, for example a linear accelerator or cobalt unit. Chemotherapy uses drugs and immunotherapy uses the immune system, and neither involves radioactive material.

Answer: D

Fractionation is preferred because it allows repair of normal tissues.

Dividing the total dose into many small daily fractions lets normal tissues repair sublethal DNA damage between fractions, and they do this better than most tumours. Fractionation also lets hypoxic tumour cells reoxygenate and cycling cells move into more sensitive phases. These are part of the four Rs of radiobiology: repair, redistribution, reoxygenation and repopulation.

Fractionation cannot guarantee that a tumour never recurs, it does not remove the need for chemotherapy, and more sessions usually cost more, not less.

Answer: C

The modality is stereotactic radiosurgery.

Stereotactic radiosurgery delivers a single high dose to a small, sharply defined target. Many beams converge from different angles under stereotactic localisation, using a frame or image guidance, so the dose outside the target falls off steeply. The Gamma Knife and linac-based radiosurgery are examples.

Conventional external beam radiotherapy is normally given in many fractions over weeks. Brachytherapy places sources inside the tumour. Proton therapy is a particle type that can be used in several schedules, and the single-session multi-angle description defines radiosurgery.

Answer: D

Shortwave diathermy works at about 27.12 MHz.

Shortwave diathermy heats deep tissue with a high-frequency electromagnetic field. It uses the frequencies set aside for industrial, scientific and medical use, and 27.12 MHz (wavelength about 11 m) is by far the most common, with 13.56 and 40.68 MHz also allowed.

2.45 GHz is the microwave diathermy frequency. 50 Hz is mains frequency, which would stimulate nerves and muscle instead of heating. Around 100 kHz is far below the shortwave band.

Answer: B

Laser therapy is mainly used for tissue repair and pain reduction.

Low-level laser therapy (photobiomodulation) uses red or near-infrared light at low power, which causes no heating. It is thought to act on mitochondrial cytochrome c oxidase, and it is used in physiotherapy to speed wound and soft-tissue healing and to relieve pain and inflammation.

Lasers are not used for nerve blocking, which is done with local anaesthetics, or for blood purification, which is dialysis. They have no role in enhancing X-rays.

Answer: A

A defibrillator's function is to restore normal heart rhythm.

In ventricular fibrillation or pulseless ventricular tachycardia the heart muscle fires chaotically and pumps no blood. A defibrillator passes a brief high-energy shock (typically 120-200 J biphasic) through the chest. This depolarises a critical mass of the myocardium at once, ending the chaotic activity so that the SA node can take over again.

Defibrillators often include an ECG monitor to decide when to shock, but measuring the ECG is not their function. Recording EEG is a different instrument, and muscle stimulation is done with low-energy stimulators.