What is 3-D Conformal Radiation Therapy?
Three dimensional (3-D) Conformal Radiation Therapy (CRT) is a technique where the beams of radiation used in treatment are shaped to match the tumour. Previously, radiation treatment matched the height and width of the tumour, meaning that healthy tissue had to be exposed to the beams. Advances in imaging technology make it possible to locate the tumour precisely.
Conformal radiation therapy uses the targeting information to focus precisely on the tumour while minimizing damage to the healthy surrounding tissue. This exact targeting makes it possible to use higher levels of radiation in treatment, which are more effective in shrinking and killing tumours.
3-D conformal radiation therapy allows shaping of the radiation dose around the target, while minimising the amount of radiation received by normal structures.
3-D conformal radiation therapy is in some ways similar to IMRT both are used to target cancer while sparing healthy tissue. 3DCRT delivers the same dose of radiation to the entire treatment field. IMRT varies the amount/intensity of dose delivered within different segments of the treatment field. Sometimes due to the tumour shape and location, 3-D conformal radiation therapy is best suited to treating a cancer. This determination is made by the radiation oncologist.
How is this procedure done?
The process begins with taking a 3-D image of the tumour, often using computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), or PET-CT imaging. The 3-D image is then analysed by a computer program which designs radiation beams that follow the shape of the tumour.
Planning conformal radiotherapy treatment is very similar to planning other types of external radiotherapy. But planning may take longer. It involves several steps, which usually begin with a virtual simulation session. This session involves
- Planning the radiotherapy to make sure that all the tumour is inside the radiotherapy field
- Making marks on the skin to make sure the same area is treated each session (see skin markings *link*)
- Making moulds to keep certain parts of your body still during treatment
If you are having conformal radiotherapy to your head or neck, you may need to wear a Perspex mould during your treatment. You may hear this called a shell or mask. Some types of mask are see-through, others are not. Moulds can also be used for other parts of the body, such as the breast, limbs and sometimes the whole body. The mould keeps the area completely still so your treatment will be as accurate as possible. These moulds also allow us to make any markings you may need to the mask, instead of your skin.
Having your treatment
Having conformal radiotherapy is very much like having other types of external radiotherapy. The treatment doesn’t hurt and it only takes a few minutes to have your dose of radiotherapy. The Radiation Therapists will spend time helping you lie into the right position and put on any moulds that you may need.
What can I expect from this procedure?
3-D conformal therapy has been shown to improve outcomes for a number of cancer types, including head and neck, lung, liver, prostate and braincancers. This technique is the most widely used for treated cancers with radiation and is the technique available in all cancer centres in Ireland.