Several trials using radiofrequency ablation (RFA) have reported clinical effectiveness in early stage inoperable NSCLC. As larger tumours or centrally located tumours are more likely to recur following either RFA or SRT, further studies are currently underway investigating the use of combined RFA and SRT to improve local control.
LIVER Surgery is the treatment of choice for both primary liver tumours and limited liver metastases. However, for patients who are not suitable for surgery due to the extent of disease or medical condition, alternative strategies have been investigated. Conventional radiotherapy techniques can offer only palliation as the radiosensitivity of normal liver tissue limits the dose that can be delivered. SRT techniques enable ablative doses to be delivered to metastatic liver lesions, but long term published data with respect to outcomes are still lacking. SRT is generally used to treat primary liver lesions if other treatment modalities are not suitable, or in the event of recurrence.
RFA is now widely used for smaller lesions (<3cm) and has shown local control rates comparable to surgery29
. RFA is, however, unsuitable for tumours situated close to the diaphragm, or large vessels and, in these cases, SRT would be the treatment of choice.
PROSTATE Hypofractionated radiotherapy is emerging as an alternative treatment for early stage prostate cancer, potentially offering an increase in tumour control and patient survival compared to conventional radiotherapy30
. Conventional radiotherapy is an accepted
treatment option for a growing number of patients diagnosed with prostate cancer who are medically inoperable. However, the effectiveness is limited by the negative effects of the radiation on surrounding normal tissue.
The low alpha/beta ratio for prostate cancer suggests high dose hypofractionated radiotherapy will result in a favourable biological response. Data from the use of high dose rate (HDR) brachytherapy in prostate cancer support this theory and have shown positive results31
these technologies do not address the issue of intrafractional motion. Due to the tracking ability that the CyberKnife system offers, target motion can be identified and corrections applied accordingly, ensuring accurate target coverage despite recurrent and unpredictable prostate motion.
Long term follow up data are still required to confirm effectiveness and late toxicities of stereotactic radiotherapy. If these data demonstrate that stereotactic radiotherapy is as effective as other modalities such as surgery, brachytherapy and cryotherapy, then stereotactic radiotherapy may become the treatment of choice for prostate cancer because it offers a non-invasive alternative with short treatment duration.
CONCLUSION In the future, we are likely to see continued technological advancements and developments further improving the radiotherapy delivery systems that have contributed to the success of stereotactic radiotherapy. Conventional radiotherapy will continue to be suitable for many indications. However, effectiveness will always be limited by the negative effects of the radiation on the volume of surrounding normal tissue. In some circumstances, stereotactic radiotherapy may prove beneficial when used as a boost following radiotherapy.
The benefits offered by stereotactic radiotherapy include accuracy, potentially reduced incidence of treatment related toxicity due to its high conformity, and improved outcomes with dose escalation. It also offers a highly efficient treatment delivery in a small number of fractions. Patient selection is important and stereotactic radiotherapy is most suitable for smaller localised tumour volumes. Patients with distant active metastatic disease may not be appropriate, unless good local control is important for palliation.
. However, the HDR procedure is invasive, requires anaesthetic,
the use of a catheter and hospitalisation. Stereotactic radiotherapy is the optimum external beam technique to deliver large doses per fraction, minimising the risks to surrounding normal tissue, and can offer a non-invasive alternative while applying the same dosimetric and biological considerations32
studies have demonstrated improved effectiveness and reduced toxicity with focused, high dose radiation treatments delivered in three to four treatment sessions with compensation for tumour motion, using stereotactic radiosurgery.
While improvements in treatment delivery techniques, such as Intensity modulated radiotherapy (IMRT), Intensity modulated arc therapy (IMAT) and SRT have enabled an increased dose per fraction to be delivered without increasing toxicity to normal tissue, and IGRT technologies including CBCT offer pre-treatment image guidance,
Further studies are required in both the curative and palliative settings to investigate quality of life, symptom control, disease free interval, late effects and survival. Direct comparisons with alternative methods of treatment are also necessary to clarify the relative role of SRT in the overall management of malignant disease.
. Furthermore, several recent published
In conclusion, CyberKnife is a unique stereotactic platform and published data so far are encouraging with good local control being achieved in numerous tumour sites. However, large phase III studies are required if the true potential of stereotactic radiotherapy is to be established in both a palliative and curative setting.
27 2011
IMAGING & ONCOLOGY
Alexandra Aitken is principal radiographer, and Dr Nihal Shah, Dr Pete Ostler and Professor Peter Hoskin are consultant clinical oncologists at Mount Vernon Cancer Centre, Northwood, Middlesex, United Kingdom. Mount Vernon was the first National Health Service centre with CyberKnife.
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