Nine; 9 questions out of the 35 questions in the Radiation Protection and Quality Assurance content area come from the Equipment Use and Quality Assurance sub-topic.
Components and Operation
In radiotherapy, most equipment used for treatment use x-rays or radionuclides. Example of radiotherapy equipment:
Modern treatment planning highly depends on imaging. Imaging units include Computed Tomography (CT), Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET). Each imaging equipment has a unique role in defining and localizing target volumes. CT scanners have been used in treatment planning for many years. They have the ability to image patient anatomy and gross tumor slice by slice. These images can be processed to be viewed in 3-dimensions. The CT numbers can be correlated with tissue density, pixel by pixel, allowing heterogeneity corrections in treatment planning.
Most of the modern institutions are now using PET imaging units. This is because PET images allow differentiation between benign and malignant tissues. PET images can also be used to follow up changes in tumors during treatment. PET images can be combined with CT images to provide physiologic imaging, allowing differentiation of malignant tissues (tumors) from the normal tissues on the basis of their metabolic differences.
MRI uses powerful magnetic fields to produce detailed pictures of soft tissues, body organs and bones. These images help in diagnosing and in monitoring of a treatment.
A linear accelerator is an accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear beamline. They are commonly used for external beam radiation treatments to deliver high-energy x-rays or electrons to cancer tumors or targeted areas. It customizes the high-energy x-rays or electrons to conform to a tumor’s shape and size, in order to kill the tumor and spare the surrounding normal tissues. It has some built-in safety measures to ensure it will not deliver higher doses than prescribed. It treats tumors in all body sites using the following techniques; convectional techniques, Intensity-Modulated Radiation Therapy (IMRT), Image-Guide Radiation Therapy (IGRT), Volumetric Modulated Arc Therapy (VMAT), Stereotactic Radiosurgery (SRS) and Stereotactic Body Radio Therapy (SBRT).
Cobalt 60 units
In Cobalt-60 units or Cobalt therapy, the radioisotope cobalt-60 is used in external beam radiotherapy machines to produce a beam of gamma rays for treating cancer tumors. Although, nowadays cobalt units are partly being replaced by the linear accelerators which can generate higher-energy radiation without producing radioactive wastes. Cobalt-60 machines are relatively reliable and easy to maintain than linear accelerators.
Caesium-137 therapy units
Caesium-137 is a by-product of nuclear fission process in nuclear reactions like nuclear bombs, nuclear weapon testing and nuclear reactor operations. It emits gamma rays, hence it is commonly used in hospitals as a source of gamma rays. It is used in calibration of medical radiotherapy devices for treating cancer and in calibration of radiation detection instruments that are used to monitor the radiation received by patients and radiation workers.
Low-to-High X-rays units
X-ray units have a range of energies to allow treatment of tumors in different locations. Deep-seated tumors such as pelvis or abdomen, require high-energy beams while shallow to moderately deep tumors such as head and neck, breast and extremities require low-energy beams.
Brachytherapy is a procedure of delivering radiation to tumors by placing a radioactive material within or immediate to the tumor. It can be used alone or in combination with external beam radiation therapy, surgery or/and chemotherapy. Brachytherapy unit plays a great role in radiotherapy because some tumors such as gynecologic malignancies, prostate cancer, oral cancers and brain cancers can only be best treated using brachytherapy. Brachytherapy is classified according to; location of the plant, type of loading, dose rate, duration of treatment and type of emission. Sources used in brachytherapy unit includes iridium-192, caesium-137, iodine-125 and palladim-103.
1. Faiz M. Khan, John P. Gibbons, Paul W. Sperduto. 2016. Treatment Planning in Radiation Oncology.
2. OECD. 2017. Radiotherapy Equipment. Retrieved from data.oecd.org on 2018/12/18.
3. Wikipedia. 2018. Cobalt Therapy.