ESTRO 2022 - Abstract Book

S176

Abstract book

ESTRO 2022

Results The proton radiographs showed minor improvement in noise (<1 mm standard deviation in WET) but a larger benefit was seen in helium radiographs (~4 mm standard deviation in WET) due to better filtering of secondary fragments (Fig. 1). The tomographic data shows significantly reduced noise for both ions with relative stopping power (RSP) noise of approximately 0.02 in the uniform part of the phantom (Fig. 2). The prior filter enabled greatly reduced imaging dose without relevant loss in image quality: even a reduction of the number of proton histories by a factor of 9, reducing the imaging dose to ~0.5mGy, only doubled RSP noise. For comparison, with the current state-of-the-art filtering technique, the same reduction resulted in a factor 8 increase in noise.

Fig 1. Noise profiles generated by averaging the standard deviation in each bin along the Y-axis for simulated radiographs of the XCAT phantom using the 3 σ and prior filter. The No Filter plot is split across axes to better visualise the profiles of the filtered data.

Fig 2. Central slice of the proton and helium CT of the CTP404 Sensitometry module (right) and noise profiles (left) with the prior filter and the 3 σ filter applied . The dashed line indicates the position on the phantom. Conclusion The prior filter significantly reduced image noise compared to the current state-of-the-art filter in helium radiography whereas, its performance in proton radiography is comparable. However, noise is significantly reduced for both proton and helium tomographic imaging. The filter’s design overcomes one of the drawbacks of the 3 σ filter: its need to have a representative distribution of ions in every bin. The filter is adjustable and could be optimised for bespoke applications including providing opportunity for low dose online imaging for ion therapy.

Mini-Oral: 06: GI

MO-0219 Quality assurance of preoperative radiotherapy in the CRITICS-II gastric cancer trial

A. Slagter 1 , M. Verheij 2 , J. Buijsen 3 , E. Hendriksen 4 , M. Hulshof 5 , S. Mook 6 , K. Neelis 7 , V. Oppedijk 8 , T. Rozema 9 , M. van der Sangen 10 , E. Jansen 11 1 Netherlands Cancer Intitute, Radiation Oncology, Amsterdam, The Netherlands; 2 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 3 Maastro, Radiation Oncology, Venlo, The Netherlands; 4 Medisch Spectrum Twente, Radiation Oncology, Enschede, The Netherlands; 5 Amsterdam University Medical Centers, Radiation

Made with FlippingBook Digital Publishing Software