Types of radiation therapy
What devices are used for radiotherapy?
Due to the energy of the radiation beam, radiotherapy is divided into:
- megavolt radiotherapy, using high energy radiation beams> 1MV produced in various types of devices:
- cobalt bombs (radiation energy 1.25 MV) containing the Co60 cobalt isotope and the largest part of the energy depositing at a depth of approx. 5 mm; are no longer used in human and animal radiotherapy in Europe,
- accelerators (linear accelerators), most often used in medicine, machines producing a beam of high-energy radiation (4-25 MV), the penetration of which allows irradiation of any place in the patient’s body,
- tomotherapy devices allowing for spiral irradiation with high doses with simultaneous verification of the current anatomical conditions and the patient’s position; are used occasionally to treat animals in the US,
- a cybernetic knife, which is a small linear accelerator located on a robotic arm; so far, such devices are used sporadically to irradiate animals in the USA,
- a gamma knife, i.e. a device that uses cobalt 60 radiation contained in many capsules for very precise irradiation of human nervous system neoplasms,
- ortovoltaic radiotherapy using X-ray machines producing low-energy beams of 100-500 kV radiation with penetration limited in therapeutic ranges to superficial tissues; in such situations there is no need to perform complex irradiation plans; Such devices are currently used in humans only in dermatology, and in animals in a few centers for the treatment of superficial neoplasms.
At the RTWet, we use the Varian Clinac 600 CD linear accelerator (accelerator), which allows us to perform megavolt radiotherapy treatments on our patients.
What are the basic differences between megavolt and ortvoltage radiotherapy?
- Due to the difference in the energy of the beam, the transmittance of the radiation differs.
- The ortovoltaic apparatus is an X-ray apparatus that produces low-energy radiation beams in the range of 100-500 kV, so the therapeutic scope of such a device covers only superficial tissues. For example, with a device power of 300 kV, the therapeutic range is limited to 2-3 cm.
- An orvoltage device is very useful for treating superficial changes.
- Since the maximum dose of the radiation of the ortvolt apparatus is deposited in the skin, the dermatological side effects are definitely more intense compared to the mega-volt apparatus.
- Due to the biological photoelectric effect caused by ortovolta radiation, bones preferentially absorb energy, which reduces the amount of energy deposited in the underlying tissue and an increased risk of bone necrosis complication of late radiotherapy.
- Only superficial lesions are treated with ortvolts, so there is no need for complicated treatment plans.
- Due to the “Compton effect” of the megavolt radiation, the penetration of the radiation beam through the bones and soft tissues is similar, in other words the energy does not decrease significantly after passing through the bone.
- The therapeutic beam produced by the mega-volt apparatus is deposited in the deep tissues of the patient, thanks to which the therapeutic scope of this type of apparatus is not limited in any way.
- The use of a mega-volt apparatus requires the construction of specialized rooms (bunkers) to ensure safety.
- When working with a mega-volt apparatus, it is usually necessary to make a three-dimensional irradiation plan based on tomographic images in a special computer system.