Radiation Therapy

Radiation Therapy is a highly specialised area of the radiation sciences. It is a scientific and clinical profession dedicated to the management of patients with benign and malignant disease.
The ionising radiation in its commonest form for treatment is photons (x-rays). The radiation can be used on its own, or in combination with other cancer management strategies such a surgery or cytotoxic chemotherapy. This depends on many factors including the histological diagnosis, how advanced the disease is and the health of the patient.
The radiation can be delivered with one of two intensions radical and palliative. Radical intent is where high doses of radiation (depending on the histological diagnosis) are delivered with the intent to cure, and palliative intent is treatment in order to provide relief from cancer symptoms. One of the main considerations in managing cancer with radiation (as with any other treatment) is maintenance of quality of life for the patient.

The following steps constitute the radiation therapy process:

Localisation

This is the initial step in the radiotherapy process. At this point the exact position of the tumour is located by utilising diagnostic image acquisition techniques such as plain radiographs, CT, MRI and PET. Simulation of the treatment area may also occur where the treatment ‘set up’ is reproduced and radiographic images of this are acquired and recorded. These images are then interpreted and used to configure individual treatment plans for each patient and also for comparison during treatment itself.
Integration of the above modalities in the localisation of the treatment ensures that even microscopic tumour cells and/or lymph nodes that are positively identified as having tumour present are included.

Planning

The tumour/site of original tumour and an area of tissue surrounding it are treated to the highest possible dose. This combined site of tumour and normal cells is known as the Tumour Volume.
Radiation therapy planning utilises sophisticated computer systems to maximise tumour dose and minimise the dose to healthy surrounding tissues. A computer is used to generate a pictorial arrangement of the distribution of the radiation dose that the tumour and surrounding organs will receive.


This is imperative because organs such as the spinal cord or lungs can only tolerate minimal doses of radiation before irreparable damage occurs.
For any one particular treatment site the radiation beam can be directed towards the patient from a number of angles (fields) in order to reduce the dose to radiosensitive organs and ensure a high dose region around the tumour volume.

Treatment

There are a variety of radiation modalities available for treatment. The choice of radiation/particle type (photon, electron, proton, neutron, beta and gamma) and energy depends on a number of factors such as how ‘deep seated’ the tumour is and the nearby radiosensitive structures.


Radiation can be administered externally with machines that work at either Kilovoltage energies (used for treating superficial tumours) or Megavoltage energies (Linear Accelerators which are used to treat deep seated tumours).
Internal radioactive sources are also used to treat tissues and organs such as the tongue, cervix or prostate gland.

Daily treatment has to be both accurate and reproducible. This means that the patient needs to be immobilised in exactly the same position every day. Precise measurements are used to align the radiation beam with the specific area of the body being treated. The treatment area itself can be verified on the treatment machine before, during or after the daily treatment is delivered. These images can then be matched with those from the original planning procedure using sophisticated computer equipment.


Prior to any patients being treated all equipment must go through rigorous quality assurance procedures in order to ensure it is operating safely.


The technology within the field of radiation therapy is constantly developing with the view of achieving optimal conformation of the radiation beam to the tumour volume. Utilisation of Intensity Modulated Radiation Therapy (IMRT) is the closest the technology has got to achieving this.


ref.:      http://www.med.monash.edu.au/radiography