ESTRO 36 Abstract Book

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fields. Treatment was delivered with a Novalis- TrueBeam™ STx Linac (Palo Alto, CA, USA). IGRT was achieved with ExacTrac® (version 6.0). ExacTrac® documented the eye position before and after each irradiation field. Results No local failure and no case of enucleation have been seen at a median follow-up time of 329 days (range 98 – 678). Complications observed so far were impairment of visual acuity in half of the cases, intraocular haemorrhage (1 pts.), xerophthalmia (2 pts.), or keratritis (2 pts). The minimal, mean, and maximal doses within the target volumes were 86.3 (± 5.2)%, corresponding to V 95% = 98.3 (± 1.4)%, 100.0 (± 0.4)%, and 103.4 (± 1.1)%, respectively. The conformity index was 1.23 ± 0.16 and the homogeneity index was 0.04 ± 0.01. Mean dose applied to the ipsilateral eye lens, cornea, normal tissue of the involved eye, and the lacrimal gland were 12.1 (± 17.7) Gy, 6.8 (± 11.5) Gy, 18.1 (± 9.2) Gy, and 10.7 (± 7.6) Gy, respectively. Maximal dose of the ipsilateral optic nerve was 31.7 (± 15.9) Gy. Doses delivered to the contralateral eye, lens, optic nerve, and lacrimal gland were less than 0.6 (± 0.7) Gy, 0.2 (± 0.1) Gy, 1.3 (± 1.6) Gy, and 0.2 (± 0.1) Gy, respectively. The doses given to the chiasma did not exceed 1.3 (± 1.5) Gy; the pituitary gland 0.9 (± 1.4) Gy, and the maximal dose to the brain did not exceed 11.1 (± 4.9) Gy. The ITV did not exceed 2mm. Conclusion HybridArc® in combination with peritumoral tissue markers for image-guidance provides highly conformal and homogenous doses distributions for the treatment of small and moving target volumes. OC-0351 Analysis of concordance in multicentre adaptive bladder trials quality assurance E. Parsons 1 , D. Megias 1 , A. Baker 1 , S. Hafeez 2 , E. Hall 2 , H. McNair 3 , Y. Tsang 1 , R. Huddart 3 1 Mount Vernon Hospital, National Radiotherapy Trials Quality Assurance Group, Northwood- Middlesex, United Kingdom 2 The Institute of Cancer Research, Clinical Trials Unit, Sutton- Surrey, United Kingdom 3 Royal Marsden Hospital, Radiotherapy, Sutton- Surrey, United Kingdom Purpose or Objective HYBRID (CRUK/12/055) and RAIDER (CRUK/14/016) are two randomised phase II multi-centre clinical trials investigating the use of adaptive 'Plan of the day” (POD) bladder radiotherapy. In order to promote accurate POD selection across multiple recruiting centres, a pre-accrual assessment for adaptive plan selection was developed as part of an IGRT QA credentialing programme (3 rd ESTRO Forum 2015-OC0564). The purpose of this study was to establish whether the pre-accrual POD assessment is a feasible QA process and investigate whether the POD can be consistently selected by individuals across all recruiting centres. Material and Methods Twelve bladder CT/CBCT image pairs were made available to individuals to register according to protocol. Individuals recorded the most appropriate POD selection from a library of three possible plans and submitted to a central QA group for review. In order to receive QA approval to select the POD for HYBRID/RAIDER, individuals were required to achieve an assessment score of ≥83% (10/12) agreement with the expert consensus answers. It was a pre-requisite of HYBRID and RAIDER that centres already have an appropriate IGRT competency framework for bladder CBCT in place prior to trial recruitment. The assessment was first piloted for 10 centres recruiting to Proffered Papers: Adaptive strategies

the HYBRID trial in November 2013 and then utilised for a further 14 RAIDER centres in June 2015. The Mann-Whitney U test and Kruskal-Wallis test were used to investigate if there were any significant difference in assessment scores between the two trials and individual staff grading respectively. Results The POD assessment was completed by 244 individuals (HYBRID=73, RAIDER=171) from 24 recruiting centres. The median assessment score was 92% (range: 25-100%) and 86% of individuals achieved the score required for QA approval on their first attempt. The distribution of assessment scores in RAIDER was found to be significantly different to HYBRID (p=0.034). Individuals would be more likely to achieve a score ≥83% for RAIDER (90%) than HYBRID (77%). Each centre had an average of 10.2 (Range 3-23) individuals complete the POD assessment. There was no statistically significant difference in assessment scores between different staff grades (p=0.713). The median assessment scores varied between recruiting centres, with a range between 83% and 100%. Conclusion A high median score was achieved by the individuals that completed the assessment indicating consistent POD selection with the expert consensus answers across individuals and centres. The POD assessment proved to be a feasible way of credentialing multiple individuals across all recruiting centres. Differences in assessment scores between HYBRID and RAIDER trials likely reflect the increased experience with pelvis CBCT in UK centres between 2013 and 2015. Individuals of all grades were able to successfully complete the assessment indicating the importance of appropriate local IGRT training rather than staff seniority when choosing the POD. OC-0352 CBCT-guided evolutive library for cervix adaptive IMRT B. Rigaud 1,2 , A. Simon 1,2 , M. Gobeli 3 , C. Lafond 1,3 , D. Williaume 3 , J. Leseur 3 , J. Castelli 1,2,3 , P. Haigron 1,2 , R. De Crevoisier 1,2,3 1 INSERM, U1099, Rennes, France 2 Université de Rennes 1, LTSI, Rennes, France 3 Centre Eugene Marquis, Radiotherapy Department, Rennes, France Purpose or Objective In the context of locally advanced cervix carcinoma adaptive radiation therapy (ART), this study aimed to simulate five treatment strategies, including an original CBCT-guided evolutive library. We compared geometrically the strategies by considering the coverage by the simulated PTVs for both CTV and OARs. Material and Methods Sixteen patients having received a total dose of 45 Gy by IMRT for locally advanced cervix carcinoma were included. Each patient had: three planning CTs corresponding to three bladder volumes (empty (EB), intermediate (IB) and full (FB)), a CT scan at 20 Gy and bi-weekly CBCTs for 5 weeks. The CTV and the OARs were manually delineated on each CT and CBCT. Five radiotherapy (RT) strategies were investigated (Figure 1): (1) “Standard RT” based on one planning CT with IB and considered as reference, (2) “ITV-based RT” with an ITV built from the three planning CT scans, (3) “RT with one midtreatment replanning” corresponding to the standard RT with replanning at 20 Gy, (4) “Pretreatment library ART” using the three planning CTs (EB, IB, FB) to define the plan of the day by a CTV overlapping criteria, and (5) “Evolutive library RT” corresponding to the 4 th strategy enriched by including CBCTs anatomy in the pretreatment library if the daily CTV shape was highly different (overlap scores between the library and the daily CTV). For each strategy, two PTV margins were used (7 and 10 mm). All the strategies were geometrically compared by considering, on the CBCTs, the percentage of coverage of the CTV or the OAR by the