fields (~4-6cm) and low density lung does introduce uncertainties in the dose distribution. Therefore using a type B algorithm (eg Anisotropic Analytical Algorithm, or collapsed cone), which accurately assesses lack of lateral scatter, is strongly recommended.
To keep OAR doses as low as possible, many beams are utilised (nine or more) and it may be advantageous to use a non-coplanar beam arrangement. The use of dynamic arc techniques will produce a more conformal dose distribution, whilst treating a larger volume of the lung to a low dose bath10
. Before implementing such a technique, consideration must be given to the interplay effects between the moving target and the moving leaves11 .
RESOURCE IMPLICATIONS Aside from the tumour, a number of key organs at risk need to be outlined, so that intended radiation dose to the latter can also be accurately ascertained. If available, help from radiology colleagues is invaluable but this increases significantly the outlining time compared to standard treatments. The treatment planning must consider the multiple OARs and the effect of reduced lateral scatter in the lung surrounding a small tumour. As such, it is relatively complex. At Clatterbridge Centre for Oncology (CCO) it is performed by physicists only.
Figure 2 shows a breakdown of the components of the process from seven UK SBRT centres.
In-room timings showed this SBRT technique to be an efficient use of linac time. It also gives the additional advantage of a reduced number of hospital visits for the patient. This is shown in table 2 using data from Clatterbridge Centre for Oncology.
As experience increases, there is a decrease in the time for each step in the process, especially the planning stage, and this is similar to the reductions seen when intensity modulated radiotherapy (IMRT) planning techniques were first implemented. It is expected that when any new site is treated with SBRT, these values may increase during the initial implementation phase.
In-room times are reduced with the use of automatic couch corrections from the treatment consoles. An increased use of rotational techniques such a Volumetric Modulated Arc Therapy and RapidArc will also reduce the treatment time - current nine static field technique 12 min beam on time, if two arcs are used, this could be reduced to two minutes.
DATA COLLECTION When introducing a new technique to your centre, even if the use of the technique has been proven in the literature, we appreciate that it is good practice to collect toxicity and outcome data. This data collection needs to be prospective rather than retrospective. However, the NHS does not provide the funding to support this.
This has been addressed locally by involving the clinical effectiveness team to produce a database of treatment toxicities but this is based on the small number of SBRT patients
currently being treated. Quality of life data are being collected by nurse specialists. There will be additional follow up clinic visits and appropriate diagnostic imaging dependent on the treatment site where this technique is used.
The UK Consortium means to facilitate consistent data collection across the country and aims to establish a national database of SBRT toxicities and outcomes.
QUALITY OF LIFE Reduced treatment visits as a consequence of SBRT may impact positively on the daily life of individual patients. However, the treatment planning and delivery process is prolonged. It is important to manage patient and carer expectations, stressing that they have early disease and the necessary time and care is essential to deliver the best possible treatment.
SBRT appears to be associated with minimal acute and late toxicity. Fatigue is one of the most commonly reported symptoms. The relatively good tolerability of SBRT may result in improved quality of life outcomes which should be formally evaluated.
WORKFORCE DEVELOPMENT Due to the high technical demands of SBRT, the American Society for Radiation Oncology and the American College of Radiology have jointly published practice guidelines that detail recommendations for staffing levels and staff responsibilities for this technique12
.
Currently at CCO, the SBRT clinician will be present at each treatment fraction to approve the soft tissue match on the CBCT and any necessary isocentre corrections. However, we are working towards the SBRT treatment being a radiographer/physicist led Image Guided Radiotherapy process. The SBRT clinician would be available at the verification (day 0) appointment and then would hand over to the SBRT radiographer/physicist team for subsequent treatments. This team would provide expert knowledge of the treatment plan (physicist) and the image guidance method (radiographer) and could therefore make the appropriate decision for required isocentre corrections.
This is a logical progression following the recent increase in use of soft tissue registration as routine practice in the UK, especially for lung cancer patients. The experience gained for routine conformal treatments will lead to a safe delegation of responsibility to competent radiographers. We are working with academic institutions to produce Masters level modules in advanced imaging techniques, which will incorporate a competency assessment for SBRT treatments image evaluation.
The next step would be the establishment of consultant radiographer posts specialising in SBRT with the technical expertise to take responsibility for soft-tissue match during treatment and to co-ordinate the SBRT radiographer team of advanced imaging practitioners required for this technique. They would have their own workload of SBRT patients to provide on-treatment review and follow-up clinics and would assist in the
17 2011
IMAGING & ONCOLOGY
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