Cancer is an umbrella term used to describe a collection of related diseases involving the uncontrolled growth and division of rogue body cells. The treatment for cancer often involves a combination of surgery, immunotherapy, chemotherapy, and/or radiotherapy. Oncologists decide which treatment to use depending on the type and staging of cancer.
In radiation therapy (or radiotherapy), high energy radiation (such as MeV x-rays) or particles (such as electrons or protons), are directed at tumours with the aim of eliminating, shrinking or stopping the progression of cancerous cells.
Medical physicists in radiotherapy are responsible for the technical aspects that are involved when using high energy beams. These include the acceptance, commissioning and quality control of linear accelerators, imaging equipment for treatment simulation (CT, PET-CT, MRI) and treatment planning systems. Such systems need to be maintained and calibrated to a precise degree (sub-mm accuracy) to ensure the proper delivery and reproducibility of radiotherapy treatments.
Medical physicists liaise with clinical oncologists to prepare patient specific treatment plans with the aim of delivering the prescribed dose to the tumour, whilst simultaneously preserving healthy tissue. The medical physicist checks that the planned dose distribution is accurate and agrees with the delivered dose. All treatment plans are independently cross-checked by a second physicist for verification. Radiotherapy medical physicists work closely with radiographers in order to ensure that the patient is scanned and treated in an adequate way throughout all of the treatment sessions.
The contribution of medical physicists to complex radiotherapy techniques such as IMRT (Intensity-Modulated Radiation Therapy), IGRT (Image-Guided Radiation Therapy), VMAT (Volumetric- Modulated Arc Therapy) and SABR (Stereotactic Ablative Body Radiotherapy), result in significant improvements to the patients since toxicity is decreased.
In another type of radiotherapy technique called Brachytherapy, radioactive sources are inserted within the tumour itself, in order to maximize the delivery of the administered treatment. In brachytherapy, the Medical Physicist is responsible for handling these sources safely and for planning the precise positioning and timing of the sources inside the patient to obtain a suitable dose distribution to treat the patient whilst minimizing the dose to surrounding healthy tissue. Moreover, the Medical Physicist is also responsible for the acceptance testing, commissioning and quality assurance of Brachytherapy related equipment such as afterloaders and applicators.