DosimetryA methodology for dosimetry audit of rotational radiotherapy using a commercial detector array
Section snippets
Methods and materials
Ten UK cancer centres that had already begun treating with a form of rotational radiotherapy (Varian RapidArc, Elekta VMAT or Helical Tomotherapy) were visited in the period between June 2011 and November 2011. Of those centres, five used Varian RapidArc, two centres used Pinnacle SmartArc (Philips Healthcare, Eindhoven, Netherlands) delivered on Elekta and three had Helical Tomotherapy. One centre also chose to use Pinnacle SmartArc, in addition to RapidArc, delivered on a Varian linear
Results
In total, 36 2D-Array and Gafchromic film planes were measured, as well as 72 ionisation chamber points and 40 sets of alanine measurements. After processing the film, it was discovered that 9 out of the 36 (25%) appeared to have significant artefacts that were traced back to a single batch. These films were subsequently discounted from further analysis. The difference between the standard ion chamber output measured by the audit team and host centre was within ±1% in all cases.
Discussion
This study demonstrates that, in a direct comparison, the 2D-Array agrees and correlates well with both ion chambers and alanine for dose point measurements. This is shown by the strong concordance correlation coefficients being >0.998 in all cases and this strong trend can be seen in the scatter plots in Fig. 3. However, the corresponding Bland–Altman plots in Fig. 3 indicate that there was a systematic tendency for the 2D-Array to under-respond relative to ion chambers and alanine, and that
Conflicts of interest
The authors have no conflicts of interest to declare.
Acknowledgments
We would like to thank all staff at the ten visited centres for their hard work and cooperation: Addenbrookes Hospital, Christie Hospital, Clatterbridge Cancer Centre, Ipswich Hospital, James Cook University Hospital, Northern Centre for Cancer Care, Royal Marsden Hospitals (London and Sutton sites), Royal Surrey County Hospital and University College London Hospital. We are grateful to the London Clinic for the initial test run of the audit. The authors wish to acknowledge the financial
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