Dosimetry
A methodology for dosimetry audit of rotational radiotherapy using a commercial detector array

https://doi.org/10.1016/j.radonc.2013.05.027Get rights and content

Abstract

Purpose

To develop a methodology for the use of a commercial detector array in dosimetry audits of rotational radiotherapy.

Materials and methods

The methodology was developed as part of the development of a national audit of rotational radiotherapy. Ten cancer centres were asked to create a rotational radiotherapy treatment plan for a three-dimensional treatment-planning-system (3DTPS) test and audited. Phantom measurements using a commercial 2D ionisation chamber (IC) array were compared with measurements using 0.125 cm3 IC, Gafchromic film and alanine pellets in the same plane. Relative and absolute gamma index (γ) comparisons were made for Gafchromic film and 2D-Array planes, respectively.

Results

Comparisons between individual detectors within the 2D-Array against the corresponding IC and alanine measurement showed a statistically significant concordance correlation coefficient (both ρc > 0.998, p < 0.001) with mean difference of −1.1 ± 1.1% and −0.8 ± 1.1%, respectively, in a high dose PTV. In the γ comparison between the 2D-Array and film it was that the 2D-Array was more likely to fail planes where there was a dose discrepancy due to the absolute analysis performed.

Conclusions

It has been found that using a commercial detector array for a dosimetry audit of rotational radiotherapy is suitable in place of standard systems of dosimetry.

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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