EBRT is delivered via a linear accelerator. The linear accelerator is an ionising, radiation-generating machine capable of producing radiation energies 1000 times greater than a conventional diagnostic x-ray unit. X-rays (also called photons) used in radiotherapy are in the magnitude of mega-volts (MV - millions of volts).27 Electrons, the most common particle beam produced by linear accelerators, are used to treat superficial disease.14 Photon or electron beams produced by a linear accelerator can be projected into a person from any angle. Photons, significantly more penetrating than electrons, are used to treat deep tumours.14
Types of EBRT
3D conformal radiotherapy (3DCRT) is used to tailor a conformal dose to a tumour, reducing the exposure of proximal normal tissues to as low a dose as possible.32, 33 This technique is always planned using a planning CT scan and a 3D treatment planning system. The complexity of treatment field arrangements and dose calculations for this type of treatment means significantly more time must be spent to complete the planning procedure.
Intensity-modulated radiotherapy (IMRT) is a specialised EBRT technique ideally suited to delivering radiation to tumours that are close to or surrounding highly radiosensitive critical organs, such as the spinal cord, optic nerves or the rectum.34-36 Treatment of these tumours with 3D conformal radiotherapy requires extremely complex field arrangements that require lengthy planning and may still not be able to deliver a high enough radiation dose to the tumour without risking unacceptable morbidity to proximal normal body tissues.33, 34
The most common conceptualisation of IMRT is multiple 'beamlets' added together for each treatment field, which results in a radiation beam with varied intensities. IMRT is delivered using a linear accelerator. Prostate and head and neck cancers are more commonly being treated with IMRT.34
Image guided radiotherapy is the term used to describe images taken before and during treatment.22, 37 Image guided radiotherapy for prostate cancers can involve the implantation of gold seed markers directly into the prostate before treatment planning and treatment. Gold seed markers can be seen on the pre-treatment images and are used to track the position of the prostate relative to the treatment field positions to ensure that the tumour is accurately targeted throughout treatment.38
Total body irradiation (TBI) delivers a relatively uniform amount of radiation to the whole body, and can be used as part of the conditioning regimen for individuals before haematopoietic stem cell transplantation.39
Hemibody radiation delivers radiation to a large proportion of either the upper or lower body, in either a single fraction or over several fractions.39 Uses include:39
- the management of individuals with widespread bony metastases
- the management of uncontrolled pain
- disseminated diseases such as mycosis fungoides.
Stereotactic radiosurgery is a 3D technique that targets intracranial lesions and delivers a desired dose in one fraction.40 Radiosurgery techniques use a stereotactic frame fixed to the persons skull to provide immobilisation and accurate landmarks for localisation of the intracranial targets.41 High doses of radiation are delivered to small or multiple intracranial lesions via the gamma knife, a cyclotron producing charged particle beams, or modified linear accelerator.42, 43
Intraoperative radiation therapy (IORT) is a single-fraction, external beam radiation treatment or high-dose-rate brachytherapy administered at the time of surgery. IORT enables a surgically exposed tumour or tumour bed to be treated while protecting surrounding organs and tissues. IORT may be used for tumours which cannot be resected effectively.44
Stereotactic body radiotherapy (SBRT) is a hypofractionated delivery of radiotherapy. The total dose of radiation is delivered in only one to five treatments. Defining characteristics of SBRT include:38
- precise immobilisation
- the ability to reproduce accurate position from simulation to treatment
- the ability to minimise normal tissue exposure
- precise accounting of organ motion
- extremely accurate targeting of the tumour and surrounding critical structures to avoid using stereotactic coordinates within the tumour or on the individual
- ablative dose fractionation delivered with sub centimeter accuracy.
Prominent sites of treatment studied to date include medically inoperable stage 1 NSCLC, as well as lung, liver and spinal metastases. Further clinical trials are needed to determine the optimal prescription, dose distribution and normal tissue constraints.38
Describe the rationale for TBI in conditioning regimens before haematopoietic stem cell transplantation.
Outline components which would be included in an education session with a person before TBI.
Summarise the common acute and chronic effects of TBI and interventions to prevent and manage these effects.
Discuss the implications of new radiotherapy procedures which reduce treatment duration and consequently nursing contact with the person affected by cancer.