Essential Radiotherapy Techniques – Stereotactic Radiotherapy

What is a stereotactic treatment?

A highly specialised and complex delivery of external beam radiation therapy called stereotactic radiation uses focused radiation beams targeting a well-defined tumour, relying on detailed imaging, computerized three-dimensional treatment planning and precise treatment set-up to deliver a much higher radiation dose than standard radiotherapy with extreme accuracy.

There are two types of stereotactic radiation

• Stereotactic radiosurgery (SRS) refers to a single or several stereotactic radiation treatments of the brain or spine. Dedicated equipment is required, which could be either a CyberKnife or Linac that has been specially modified with small sized collimators. Specific planning systems are required for this treatment delivery in all such cases.

• Stereotactic body radiation therapy (SBRT) refers to one or several stereotactic radiation treatments with the body, excluding the brain or spine.

Conditions treated with stereotactic radiation

Stereotactic radiosurgery (SRS) is used to treat conditions involving the brain or spine including:

• Primary brain tumours

• Brain metastases

• Benign tumours arising from the membranes covering the brain (meningiomas)

• Benign tumours of the inner ear (acoustic neuromas)

• Abnormal blood vessels in the brain (arteriovenous malformations)

Stereotactic body radiation therapy (SBRT) is used to treat small tumours in the chest, abdomen or pelvis that cannot be removed surgically or treated with conventional radiation therapy, including:

• Small lung cancers

• Lung metastases

• Liver metastases

These lists cover commonly treated conditions but cannot include every possibility.

Stereotactic services across Australia¹⁴

Stereotactic radiotherapy is offered in 11 centres (21%) nationally. 82% of stereotactic equipment is located in the public sector, while the remaining 18% is located at privately owned facilities. Australian Capital Territory, Northern Territory and Tasmania do not offer any stereotactic services.

Stereotactic equipment distribution

Trends and issues arising

Demand for stereotactic services is difficult to measure because in the absence of stereotactic radiotherapy treatment patients receive alternative treatments such as surgery for acoustic neuromas and whole brain radiotherapy for solitary brain metastasis. For this reason an increase in stereotactic service provision is important for patient choice and appropriate clinical decision-making. The likelihood of SRS usage will increase from increased patient and referrer demand as the more consistent utilisation of SRS in other countries will resonate with cancer managers and patients here. This will be compounded as oligometastases are increasingly more aggressively managed overseas.

 Continued evolution of stereotactic techniques broadens applicability of stereotactic treatments to extra-cranial sites. This activity is referred to as stereotactic body radiation therapy (SBRT) and this is a fast-developing area, particularly in Europe and North America. SBRT has potential for reduced morbidity, an example being SBRT to liver metastasis as an alternative to surgery. SBRT also holds a promise for durable local control and even cure for patients with solitary (or oligo) metastatic disease.

The capability of linear accelerators to deliver stereotactic radiotherapy is increasing and it is expected that this technique will be applied more widely in the next decade. Highly specialised techniques, such as SRS and SBRT must be provided by centres which have specialist multidisciplinary clinical teams with expertise in the delivery of the stereotactic technique.

The current single fraction Medicare rebate grossly under-reimburses the cost of providing stereotactic radiosurgery, when considered in terms of cost in capital outlays and time taken for planning and treatment. The rebate is based on a single fraction (i.e. one big dose of radiation delivered in one treatment). All stereotactic radiotherapy regardless of its mode of delivery should carry a Medicare rebate that is appropriate for the complexity of planning and delivery. Fractionated delivery of stereotactic radiotherapy (i.e. delivered over multiple treatments) is expected to increase. Research into the radiobiology of cancer supports increased fractionation to allow normal tissue cells time to repair and recover between treatments.