Stereotactic body radiotherapy in prostate cancer: is rapidarc a better solution than cyberknife?
OBJECTIVE
There is increasing interest in stereotactic body radiotherapy (SBRT) for the management of prostate adenocarcinoma, with encouraging initial biological progression-free survival results. However, the limited literature is dominated by the use of the Cyberknife platform. This led to an international phase III study comparing outcomes for Cyberknife SBRT with both surgery and conventionally fractionated intensity-modulated radiotherapy (the PACE study). We aim to compare Cyberknife delivery with Rapidarc, a more widely available treatment platform.


METHODS
The scans of six previous prostate radiotherapy patients with a range of prostate sizes were chosen. The clinical target volume was defined as the prostate gland, with 3 mm added for the Cyberknife planning target volume (PTV) and 5 mm for the Rapidarc PTV. Accuray multiplan v. 4.5 was used for planning with delivery on a Cyberknife VSI system v9.5; Varian Eclipse v10 was used for Rapidarc planning with delivery using a Varian 21EX linear accelerator. Both systems attempted to deliver at least 35 Gy to the PTV in five fractions with PTV heterogeneity <12%.


RESULTS
All organ at risk (OAR) constraints were achieved by both platforms, whereas the Cyberknife failed to achieve the desired PTV homogeneity constraint in two cases. In other OARs without constraints, Cyberknife delivered higher doses. The volume of the 35 Gy isodose was slightly larger with Rapidarc, but conversely at doses <35 Gy normal tissues received higher doses with Cyberknife. The mean planning and delivery time was in favour of Rapidarc.


CONCLUSIONS
We have shown that there is no discernible dosimetric advantage to choosing Cyberknife over Rapidarc for SBRT delivery in prostate cancer. Given the significant benefits of Rapidarc in terms of availability, planning and delivery time, the authors suggest that phase III trials of SBRT should include Rapidarc or equivalent rotational delivery platforms.
Radiotherapy Physics, St. Bartholomew's Hospital, London, UK; Institute of Cancer, Queen Mary, University of London, London, UK.
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Macdougall
Radiotherapy Physics, St. Bartholomew's Hospital, London, UK; Institute of Cancer, Queen Mary, University of London, London, UK.
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Dean
The Gray Institute of Radiation Oncology and Biology, Oxford, UK. Electronic address: rebeccamuirhead@hotmail.com.
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Muirhead
D000230:Adenocarcinoma / Q000601:surgery*; D018572:Disease-Free Survival; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000601:surgery*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods
Cyberknife; SBRT; hypofractionation; prostate; rapidarc