An overview of the current status of SBRT in the UK and the impact of this technique on future oncology services.
Stereotactic Body Radiotherapy (SBRT) was developed in the 1990s at the Karolinska Institute, Sweden and gained worldwide momentum after the phase I/II dose escalation studies by Timmerman1
. The SBRT treatment technique is similar to that used
for intracranial lesions, employing multiple radiation beams to target a tumour with high precision, delivering an ablative dose of radiation, made possible by limiting the treatment volume.
The radiobiological rationale for SBRT is that by delivering a few large fractions in a relatively short overall treatment time, a more potent biological effect is achieved1. Using high dose per fraction for extra-cranial lesions (especially in lung tumours) poses greater challenges due to tumour and organ at risk (OAR) motion both inter and intra- fractionally2
. The advantage of this technique in lung cancer is that patients with early
stage tumours, who are unfit for radical surgery, appear to have improved local control and disease specific survival than conventional radiotherapy3-5 grade 3) reported in the literature is below 5 per cent6
. The serious toxicity (≥ .
It is important to consider that a number of the published studies were done prior to the era of on-line image guidance equipment. The introduction of image guidance techniques has the potential to enhance target localisation and the safety of SBRT treatments. With the increased availability of volumetric imaging on linacs, most centres are now delivering extra-cranial stereotactic radiotherapy in a frameless context, enabling a greater flexibility in the types of patients who can benefit from SBRT.
The implementation of SBRT is a multidisciplinary team effort and needs a clearly defined pathway. The practice of SBRT requires a high level of confidence in the accuracy of the entire treatment delivery process due to the delivery of large doses in a few fractions, and the minimisation of normal tissue toxicity with rapid dose fall off away from the target.
The UK SBRT Consortium was founded in 2008 to ensure safe, consistent implementation of this technique, for lung cancer patients initially, across the UK. Comprehensive guidelines which detail key publications, patient selection criteria, quality assurance recommendations, planning guidelines and dose/fractionation schedules have been issued. The Consortium has played a vital role in ensuring implementation is achieved safely without the infrastructure provided by a clinical trial process. The model used for lung SBRT treatments will be extended to other sites as experience is gained.
Lung was the most common tumour site, followed by liver, spine, prostate, pancreas and paediatric tumours (figure 1).
0 1 2 3 4 5 6 7 8
Currently treating Intending to treat
CURRENT STATUS In June 2010 a questionnaire was circulated by the SBRT consortium to identify the current status of SBRT in the UK and to provide a baseline against which future activity could be measured. Analysis of the questionnaire data was also distributed to the National Radiotherapy Implementation Group SBRT short life working group.
Questions covered tumour sites, patient numbers, equipment utilised, resource implications and quality assurance. At this point there were seven treating centres with a further six centres intending to treat using this technique in the near future.
15 2011
IMAGING & ONCOLOGY
Lung
Pancreas
Spine Site Figure 1 Distribution of tumour site and frequency of centres treating or intending to treat using SBRT (June 2010).
There was a spread of treatment equipment across all manufacturers: Cyberknife, Varian OBI, Elekta XVI and Tomotherapy. The Cyberknife centres, as expected for a product marketed as a radiosurgery system, were treating larger numbers of patients per annum from more anatomical sites.
QUALITY ASSURANCE AND COMMISSIONING GUIDELINES A recent report from the American Association of Physicists in Medicine (AAPM) task group 101[7]
states that:
In SBRT, confidence in the accuracy of the technique requires an integration of the modern imaging, simulation, treatment planning and delivery technologies in all phases of the treatment process.
This has been addressed by the consortium in the production of guidelines detailing
Liver
Prostate
Paediatrics
Number of centres
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