ESTRO 36 Abstract Book

S184 ESTRO 36 2017 _______________________________________________________________________________________________

The uni- and multi-variate analysis showed statistical significance for all parameters except lesion location (table 1).

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 high coefficient associated to the peripheral character is probably due to the EPL un-modelled lateral electron equilibrium caused by the prevalent presence of low density lung tissues surrounding the peripheral lesion, thus greatly impacting dose calculation differences. Based on the multivariate analysis predictive nomogram was generated (R²=0.58, Figure 1).

Dose to OARs calculated with EPL and MC showed strong linear correlation (R²=0.99-1.00). The dose constraints decreased by 1% in the heart (D10cc), great vessels (D10cc) and spinal cord (D0.25cc), 2% in the oesophagus (D5cc), 5% in the ribs (D5cc) and 16% in the trachea (D4cc). . Conclusion The differences between MC and EPL are significantly impacted by dose, tracking, location and the volume of the lesion. Predictive nomogram helps to estimate the differences on GTV D50. EPL to MC OAR dose tolerance limit proved to have a strong linear correlation with conversion factors ranging from 0.84 to 0.99. Based on our model, re-prescription value can be estimated and, if required, used to further restrict the constraints on the OARs during EPL optimization. OC-0350 ExacTrac®-based Fractionated Radiosurgery (fSRS) of Choroidal Melanoma (CM) M. Wösle 1 , P. Goldschmidt 1 , G. Lohm 1 , L. Grajewski 2 , L. Krause 2 , I. Ciernik 1 1 Dessau City Hospital, Radiation Oncology, Dessau, Germany 2 Dessau City Hospital, Ophthalmology, Dessau, Germany Purpose or Objective Proton therapy (PT) has been a standard for treating choroidal melanomas for the last three decades. However, PT is not easily available for the majority of patients. Advances in photon therapy allow highly conformal dose delivery while sparing normal tissue. However, fSRS for small moving target volumes, such as CM, has remained a challenge. Material and Methods Since December 2014, we treated 40 patients with central choroidal tumors with fSRS. Radiotherapy plans were obtained with iPlan® RT (Version 4.5.3, Brainlab, Feldkirchen, D) after placement of 4 Tantalum clips (Altomed Ltd., U.K.) a week prior the planning CT/MRT. Thirteen cases have been reanalysed: ten treated with 10 Gy x 5 for CM, one case of haemangioma treated with 14,5 Gy in one fraction, and 2 cases of breast cancer metastasis treated with 6 Gy x 5 and 4. iPlan® RT uses HybridArc™ as field configuration with three to six dynamic conformal arcs complemented with five to seven dynamic IMRT