As treatment planning and delivery techniques in radiation therapy have developed with the evolution of more advanced technology, the aim has become to maximise the dose to the tumour while minimising the dose to the surrounding healthy tissue.
However, tumours can move, both during a radiation treatment session and from one treatment session to another, as a result of normal internal organ function (digestion, elimination, and breathing) and small differences in the way the patient is positioned for treatment. If these changes in position move the tumour out of the planned treatment range, the tumour may not receive the full amount of radiation that it should, or normal tissues may receive more radiation than they can tolerate.
IGRT techniques are used to verify the tumour location each day. An On-Board Imager®, an automated system for delivering IGRT treatment, allows the radiation therapist to:
IGRT enables the clinical team to locate the tumour while the patient is in the treatment position, and to minimise the volume of healthy tissue exposed to radiation during treatment.
An alternative approach is to produce a computed tomography (CT) image of the patient using the ‘cone beam’ technique. The linear accelerator rotates around the patient for a full arc allowing a full 3D volume to be imaged and analysed, with the patient’s position adjusted if necessary before treatment is delivered.
IGRT has allowed for the safe delivery of higher doses of radiation therapy to more precise targets within the body, improving the efficacy of treatment while sparing more healthy tissue.