ESTRO 36 Abstract Book

S952 ESTRO 36 _______________________________________________________________________________________________

proton beams. H&N/brain audit is more complex than prostate one, and chamber cavity volume is taken into account more carefully which enables to keep tight tolerances. Results Centres which participated in the previous run did not perform better than centres which participated for the first time in prostate audit. However, results were sufficient in all cases. There was not significant improvement in results with installations of new linac and TPS. Better MLC performance was observed but CT number to RED was still the problematic point. Differences in planning approaches can be seen. Weakest point for the head audit was the phantom positioning on the couch (despite using IGRT). Tolerances for film evaluation depend on the dose gradient in the direction perpendicular to the film plane. We use 95% or 90% (4%/3mm) for gamma index for prostate/ H&N or brain plans respectively. In future, pseudo-3D gamma analysis will be implemented. Conclusion It is not straighforward to identify the causes of deviations, especially when they lie within tolerance limits. Nevertheless, it is possible to identify systematic errors which might be vendor dependent, user dependent, or TPS dependent. These can help to optimise the national quality standard in radiotherapy. We recommend not to use rigid marks on phantom but let the centre apply their own fixation and positioning procedure. We recommend to include CT scanning process and identical „patient“ set- up procedure employing RTTs. When designing audit methodology, it is necessary to analyze pilot run results first and then optimise procedure dependent tolerances. This work has been supported by the project No. TB04SUJB001 and by the Ministry of Interior of the Czech Republic, project No. MV-25972-53/OBVV-2010. EP-1732 Treatment planning of dose escalation for anal cancer in the PLATO trial N.L. Abbott 1 , D. Christophides 2 , M. Robinson 3 , J. Copeland 4 , R. Adams 5 , M. Harrison 6 , M. Hawkins 3 , R. Muirhead 3 , D. Sebag-Montefiore 2 1 Velindre Cancer Centre, National Radiotherapy Trials QA group, Cardiff, United Kingdom 2 University of Leeds, Leeds Cancer Centre- St James University Hospital & Leeds CRUK Centre, Leeds, United Kingdom 3 University of Oxford, CRUK/MRC Oxford Institute for Radiation Oncology, Oxford, United Kingdom 4 University of Leeds, Clinical Trials Research Unit, Leeds, United Kingdom 5 Velindre Cancer Centre, Cardiff, United Kingdom 6 The Hillingdon Hospital NHS Foundation Trust, Uxbridge, United Kingdom Purpose or Objective P ersona L ising A nal cancer radiotherapy d O se (PLATO) is a complex integrated protocol, including ACT5 for high risk patients. ACT5 compares standard and dose escalated radiotherapy. As part of trial development a planning study was carried out by lead centres to determine the impact of dose escalation on OAR sparing. Following this study a benchmark planning case was selected and sent to fifteen UK centres as part of the radiotherapy quality assurance programme (RT QA), co-ordinated by the national QA group. These centres will randomsie the first 60 patients in a pilot phase of the trial. We report the results of the planning study and benchmark planning case with respect to achievable OAR sparing with ACT5 dose escalation.

Figure 1: Planning Study target doses Material and Methods

Eight clinical cases were identified as part of the initial planning study and independently re-planned per the RT trial protocol with and without dose escalation by two experienced IMRT planners. A single (female) case was then selected representative of a typical yet challenging case and used as the planning benchmark. Ten of the fifteen centres participating in the pilot phase of the trial completed the benchmark planning case, planning with dose escalation only. All pilot centre data was processed with CERR [1] software enabling dose distribution and dose volume histograms to be assessed. Results Dose escalated plans for the initial eight cases showed no statistically significant increase in dose to the OAR with dose escalation (p-value>0.1) whilst maintaining PTV coverage (D95%>95%). Ten centres participating in the pilot phase completed the pre-trial exercise. A range of plan beam configurations were used: 1x 2arc 6 flattening filter free (FFF) MV, 2x 3arc 6MV, 2x 7-field IMRT 6MV, 2x2arc 6MV, 2x Tomotherapy and 1x 4arc 6MV. All centres met all trial mandatory dose objectives for the benchmark planning case and the vast majority of optimal constraints, see table 1 .