ESTRO 2020 Abstract Book

S1007 ESTRO 2020

Material and Methods Three groups of three female Fischer rats were treated with a single radiation dose of 25, 30 and 35 Gy respectively, using a micro-irradiator (X-RAD SmART) with micro-CBCT guidance. The radiation beam was conveyed to the bladder by a 3-fields overlap as delineated on micro- CT. 3D and longitudinal scans (Vevo 2100) were acquired at different bladder fullness conditions before and 4 days after radiation. Empty, half-filled and full-filled bladder volumes were determined for four not-irradiated rats of the sample by measuring transverse and longitudinal bladder axes from 3D US image and applying the ellipsoid volume formula. Mean BWT was estimated for both ventral and dorsal bladder sides throughout the measurement of the bladder wall area along a segment of 4-mm in the central longitudinal scan for the different filling conditions; similarly, the area inside bladder was measured in order to estimate the mean diameter of the organ. This procedure was intended to minimize the dependence on contour delineation and on vessels that locally thickened the wall. Mean BWT against volume and mean diameter were plotted and fitted. Mean BWT and diameter were quantified to highlight a possible bladder wall thickening due to acute radiation effects. Image analysis was performed using ImageJ. Results Fig.1 shows the relationship between the mean BWT measured either on dorsal and ventral sides against bladder volume. For bladder volume >1.5 ml, BWT are almost constant and equal to 0.34 mm with maximum variations of about 20%.

inflammatory response and fluid extravasation which could be achieved at different times during the RT treatment according to the number of fractions the dose/fraction and type of radiation.

Conclusion The study represents a first step towards the challenging objective of understanding, and describing in a mechanistic way the effect of radiation on the vascular microenvironment. The code is already able to model a realistic 3D network. Shift to 3D network will be performed after the tuning of the parameters which will be accomplished through in vitro (microfluidic chip) and in vivo (sublingual microscope in head&neck cancer patients) measurements. Simulations can be also extended to deal with an already impaired vasculature (e.g. hypertension, smoke, diabetes). PO-1805 PM014 improves radiotherapy in an orthotopic lung cancer mouse model by alleviating PO-1806 Early radio-induced bladder wall thickening in rats: optimizing the methodology and first evidences A. Spinelli 1 , A. Bresolin 2 , S. Zuppone 3 , G. Fallara 3 , R. Vago 3 , C. Fiorino 2 , C. Cozzarini 4 1 San Raffaele Scientific Institute, Experimental Imaging Centre, Milano, Italy ; 2 San Raffaele Scientific Institute, Medical Physics, Milan, Italy ; 3 San Raffaele Scientific Institute, Urological Research Institute, Milan, Italy ; 4 San Raffaele Scientific Institute, Radiation Oncology, Milan, Italy Purpose or Objective The main goal of this work is to present a non-invasive imaging method based on ultrasounds (US) to investigate radiation induced changes of bladder wall thickness (BWT) using a rat model. First step consisted in the assessment of the relationship between BWT and bladder filling in order to assess the best filling conditions for reproducible measurements. The approach was then applied to irradiated rats to quantify this effect early after irradiation. Abstract withdrawn

An example of US images of the bladders before and after irradiation is shown in Fig.2. Fully-filled bladders of rats irradiated with 25, 30 and 35 Gy always showed volumes above 1.5 ml, confirming the reliability of the BWT measurements. The average ratios between BWT-post and BWT- pre irradiation were equal to 1.13 ± 0.11, 1.68± 0.16 and 1.35 ± 0.36 for 25, 30 and 35 Gy respectively; of note, 4/6 rats treated with 30-35 Gy showed BWT ratios >1.5, in contrast to rats irradiated with 25 Gy.