ESTRO 36 Abstract Book

S497 ESTRO 36 2017 _______________________________________________________________________________________________

Purpose or Objective MR has the ability to assess numerous physiological and biochemical tumour characteristics. Fractal analysis may provide a better insight into the biology and behaviour of prostate tumour than simplistic comparisons of multiparametric data. In this pilot study, we aim to determine whether fractal and lacunarity analysis can characterize the properties of radio-recurrent prostate cancer, using Apparent Diffusion Coefficient (ADC) MR Images. Material and Methods Retrospective analysis of eight patients with recurrent prostate cancer after previous radical radiotherapy (mean age: 71.25 years), underwent MRI examination for re- staging prior to consideration of salvage therapy. ADC images of the prostate were manually segmented from surrounding tissue and a region of interest (ROI) drawn to distinguish between restrictive diffusion and non- restrictive tissue (figure 1b). Low, medium and high ADC value maps were generated by intensity thresholding the respective restrictive and non-restrictive ROIs. These were processed and converted to 8-bit black and white images (figure 1c, low intensity in restricted diffusion) for application to in-house textural analysis software (image 1d) to estimate (a) fractal dimension (b) fractal abundance and (c) lacunarity Curve1 Figure 1: (a) an ADC image of the prostate gland (b) an ADC image showing areas of restricted diffusion (red) and non-restricted diffusion (blue) (c) shows a binary image used for fractal and lacunarity analysis (d) lacunarity curves from restricted areas (red) and non-restricted areas (blue)

These preliminary data show that fractal and lacunarity analysis may be able to characterise areas of restricted diffusion and non-restrictive diffusion on ADC images. Restrictive diffusion often indicates areas of aggressive prostate tumour. This method could be used in future studies to investigate other MR sequence images where the visual difference between prostate tumour and normal tissue is not so obvious to the naked eye, or where simple analysis of multiparametric data fails to adequately characterise tumour biology. Poster: Physics track: Implementation of new technology, techniques, clinical protocols or trials (including QA &audit) PO-0907 Remote auditing of IMRT/VMAT deliveries N. Miri 1 , K. Legge 2 , J. Lehmann 3 , P. Vial 4 , B. Zwan 5 , P. Greer 6 1 University of Newcastle, School of Mathematical and Physical Sciences, Newcastle- NSW, Australia 2 University of Newcastle, School of Mathematical and Physical Sciences, Newcastle, Australia 3 Calvary Mater Newcastle Hospital, Radiation and Oncology, Newcastle, Australia 4 Liverpool and Macarthur Cancer Therapy Centres, Department of Medical Physics, Sydney, Australia 5 Gosford Hospital, Central Coast Cancer Centre, Gosford, Australia 6 Calvary Mater Newcastle Hospital, Radiation and Oncology departement, Newcastle, Australia Purpose or Objective Purpose: To perform a novel study on remote auditing of dose deliveries of VMAT/IMRT clinical trials of different radiotherapy centres. The assessment is undertaken using EPID images from the centres and a local ‘signal to dose’ conversion model. Material and Methods Methods: The assessment included IMRT deliveries from 12 centres and VMAT deliveries from 6 centres. The centres downloaded benchmarking CT data sets and instructions to produce IMRT/VMAT trial plans, a head and neck (H&N) and post-prostatectomy (P-P) plan. Two virtual phantom data sets were provided for a flat and a cylindrical phantom. Trial plans were transferred to the phantoms; individual field/arcs at gantry zero on the flat phantom and the trial plan at actual gantry angles to the cylindrical phantom. EPID images acquired from a calibration plan were used to align and calibrate the EPID systems and model/correct EPID-linac sag. Integrated images were acquired for IMRT fields and cine images for VMAT arcs each cine image encompassing approximately 5 degrees. For 2D and 3D analysis, the images were converted to dose inside respectively the virtual flat and cylindrical phantom. The dose conversion was performed using an established model. To assess the delivered doses, the modelled dose was compared with corresponding TPS dose using the gamma function with all doses greater than 10% of the global maximum dose assessed. Results At 3%/3mm, 2D analysis of the H&N plan resulted in 99.6% (SD: 0.1) and 99.1% (SD: 0.1) mean pass rates for respectively IMRT and VMAT deliveries. Similarly, the P-P plan analysis resulted in 99.7% (SD: 0.2) and 99.6% (SD: 0.3) mean pass rates for corresponding deliveries over the centres. 3D analysis, on the other hand, resulted in slightly lower pass rates. H&N deliveries resulted in 98.3% (SD: 0.2) and 96.4% (SD: 2.6) mean pass rates. The P-P plan assessment resulted in 98.3% (SD: 1.5) and 97.2% (SD: 1.3) mean pass rates. Using a more stringent criteria, 3%/2mm, the H&N analysis resulted in 92.2% (SD:1.9) and 93.3% (5.4) mean pass rates and the P-P plan resulted in 94.0% (SD:4.3) and 95.6% (SD: 1.8) mean pass rates for respectively IMRT and VMAT deliveries. For VMAT

Results The average fractal characteristics are summarised in table 1 with the fractal dimension between areas of restricted diffusion and non-restrictive diffusion of the low and medium intensity images being of significant difference (p=0.0014 and 0.0023 respectively). The fractal abundance of the medium intensity image between the restricted diffusion and non-restrictive diffusion was also significant (p=0.0012).

Conclusion