Types of radiation therapy
What devices are used in radiotherapy?
Due to the energy of the radiation beam, radiotherapy is divided into:
- megavoltage radiotherapy, using high energy radiation beams> 1MV produced in various types of devices:
- cobalt bombs (radiation energy 1.25 MV) containing the isotope of cobalt Co-60 with the largest part of the energy being deposited at a depth of approx. 5 mm. They 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; they 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, a device that uses cobalt-60 radiation placed in many capsules for very precise irradiation of human nervous system neoplasms,
- orthovoltage 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 for the treatment of superficial neoplasms.
At the RTWet Center, we use the Varian Clinac 600 CD linear accelerator, which allows us to perform megavoltage radiotherapy treatments on our patients.
What are the basic differences between megavoltage and orthovoltage radiotherapy?
- Due to the difference of the beam’s energy, the penetration of the radiation differs.
- The orthovoltage machine is an X-ray device that produces low-energy radiation beams in the range of 100-500 kV, so the therapeutic scope covers only superficial tissues. For example, with a power of 300 kV, the therapeutic range is limited to 2-3 cm.
- An orthovoltage device is very useful for treating superficial changes.
- Since the maximum dose of the radiation of the orthovoltage machine is deposited in the skin, the dermatological side effects are definitely more intense compared to the megavoltage machine.
- Due to the biological photoelectric effect induced by orthovoltage radiation, bones preferentially absorb energy, which reduces the energy deposited in the underlying tissue and increases the risk of a bone necrosis as a late complication of radiotherapy.
- Only superficial lesions are treated with orthovoltage therapy, so there is no need for complicated treatment plans.
- Due to the “Compton effect” of the megavoltage 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 megavoltage machine is deposited in the deep tissues, allowing the therapeutic scope of this type of device not to be limited in any way.
- The use of a megavoltage machine requires the construction of specialized rooms (bunkers) to ensure safety.
- It is usually necessary to make a three-dimensional irradiation plan based on tomographic scans in a special computer system while working with a megavoltage machine