Cancer Physics is a term used to describe the application of physics to the diagnosis and treatment of cancer. Diagnostic imaging is used to identify the location of a tumour, radiation therapy is used to destroy the tumour.

What is Radiation Therapy?

Radiation Therapy (or radiotherapy) is the medical use of ionizing radiation as part of cancer treatment. DNA in cancer cells which enables the cancerous cells to reproduce is damaged by radiation therapy.  When the damaged cells die, the body eliminates them.  Normal cells which may have been effected by radiation can repair themselves. Treatment can be delivered external to the body, (i.e. external beam radiation therapy) or internally by placing the radiation treatment source into or near the cancer site. It may be used alone or in combination with surgery and/or chemotherapy. It may also be palliatively to relieve symptoms in patients with incurable cancers. Total body irradiation is used to prepare the body for a bone marrow transplant. Approximately half of all cancer patients will be recommended radiation therapy.

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External Beam Radiation Therapy is the most frequently used form of radiotherapy. The patient generally lies on a couch and an external source of radiation is pointed at a particular part of the body. Kilovoltage (also known as, superficial) X-rays are generally used for treating skin cancer and superficial structures, megavoltage (or deep)  X-rays are used to treat deep-seated tumours (eg bladder, bowel, prostate, lung, brain). External Beam radiotherapy is generally delivered over a number of days (termed fractions), with each fraction often utilising a number of beam trajectories, although each fraction may only take a few minutes to deliver.

3D-Conformal Radiotherapy has revolutionized treatment planning by enabling tumors and adjacent normal structures to be delineated in three dimensions, using specialized Computed Tomography (CT) and/or Magnetic Resonance Imaging (MRI) scanners and planning software. The profile of each radiation beam is shaped to best fit the the shape and location of the tumour and healthy tissues. 

Intensity-Modulated Radiation Therapy (IMRT) is an advanced type of 3D-Conformal Radiotherapy by enabling higher radiation doses to be delivered to the tumour, sparing healthy tissue. Specific applications include cases where the tumor is wrapped around a vulnerable structure such as the spinal cord or a major organ or blood vessel. 

Image-Guided Radiation Therapy (IGRT) may be used immediately prior to the delivery of an external beam radiation therapy fraction to ensure that the patient and their treatment plan are accurately aligned. Tumours and organs move during treatment.  This can be due to breathing, bladder fullness and a full stomach.  IGRT is conformal therapy guided by images derived from imaging equipment such as CT and X-Ray.  These images are taken immediatlely prior to the patient presenting at the treatment room.  The images are compared to digital information from CT scans taken at the initial onset of treatment planning.  The images are 'merged' enabling the radiation oncology team to better target the tumour without effecting surrounding tissue and organs.  Sometimes a fudicial marker is implanted to help localise the tumour during treatment.

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Radiosurgery (or Stereotactic Radiotherapy), is a medical procedure which allows non-invasive treatment of small area benign and malignant tumours by means of directed beams of ionizing radiation. It is a relatively recent technique (1951), which is used to ablate, by means of a precise dosage of radiation, intracranial and extracranial tumors and other lesions that could be otherwise inaccessible or inadequate for open surgery. In addition to the precision of the beam, added accuracy of delivery is enabled by immobilising the patient through the use of a head frame for instance in the case of a brain tumour.

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Proton Therapy is a type of particle therapy which utilizes a beam of protons to irradiate diseased tissue, most often in the treatment of cancer. Due to their relatively enormous mass, protons scatter less easily in the tissue and the beam stays focused on the tumor shape without much lateral damage to surrounding tissue. All protons of a given energy have a certain range; no proton penetrates beyond that distance. Furthermore, the dosage to tissue is maximum just over the last few millimeters of the particle’s range.It is therefore possible to focus the cell damage due to the proton beam at the very depth in the tissues where the tumor is situated; tissues situated before the Bragg peak receive some reduced dose, and tissues situated after the peak receive none. For this reason, it is favored for treating certain kinds of tumors where conventional X-ray radiotherapy would damage surrounding radio-sensitive tissues to an unacceptable level. This is of particular importance in the case of pediatric patients where long term side effects such as residual occurrence of secondary tumors resulting from the overall radiation dose to the body are of great concern. Because of the lower dose to healthy tissue protons have less severe collateral side-effects than conventional radiation therapy.

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Fast Neutron Therapy utilizes high energy neutrons typically greater than 20 MeV to treat cancer. Most fast neutron therapy beams are produced from proton beams impinging upon beryllium targets. The biological effect of neutrons or X-rays is due almost completely to the secondary electrons that they produce when they interact with a patient's tissue. One a few centres around the world have used fast neutrons for treating cancer. Due to lack of funding and support, at present only 2 are active in the USA.

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