Abstract Book

S931

ESTRO 37

Purpose or Objective The aim of the study is a development of a phantom capable of testing Smart Deviceless4D(SD4D) 4DCT system, to evaluate the system and to compare it to the Advantage4D(A4D) system. Material and Methods The scanning and registration methods were tested on Dynamic Phantom Model008A (CIRS, Norfolk, USA)(DPM) and the cone-shaped phantom (CSP), specially made for the purpose of presented study, as well as on radiotherapy patients scans. Delineations of structures 'External”, 'Lung” and 'Target” were made using Oncentra MasterPlan (Nucletron, Columbia, USA). The analysis of the obtained values were made using the volume of structures and Dice similarity coefficient (DSC). Results During testing of the systems with DPM, it turned out that the Maximum Intensity Projection (MIP) volume of the Target in the soft tissue window was 29,98ccm for A4D and 18,46ccm for SD4D. SD4D eliminates the need for an external surrogate by using a proprietary algorithm based upon internal anatomical features (i.e. change of the body and lung area and change in the density) (fig1).

calculated using clinically reasonable, but simplified, assumptions. The simplified clinical assumptions we considered were: (1) that the material can be considered to be water equivalent, (2) that the CT calibration curve accurately predicts the material density, (3) that the average density for a material can be used for any block of that material, and (4), that individual block correction factors are applied to determine the correct density. Results The average HU measurements of individual blocks of PLA, ABS, NinjaFlex, and Cheetah varied by as much as 121, 30, 178, and 30 HU, respectively. Figure 1 shows the standard CT calibration curve plotted as a solid line, with each block represented as different symbols. Note that for all materials, the CT calibration curve underestimates their actual material density. The HU variation for individual blocks over 5 weeks was very small for all materials, regardless of storage environment. The magnitude of clinical depth errors depended strongly on the material, energy, and assumptions, but some were as large as 9.0 mm. Table 1 shows the errors for just PLA for each energy considered depending on the four assumptions we examined. As can be seen in Table 1, the best case is to apply individual correction factors, and the worst case is to assume water equivalence. Figure 1:

Table 1:

fig1 Diagram of the Smart Deviceless 4D workflow (GE Healthcare) As the DPM has a fixed body, therefore SD4D was unable to properly create MIP reconstruction of the phantom. This led to the construction of the CSP(fig2).

fig2 Axial, sagittal, coronal and 3D reconstruction of the CSP phantom Reconstructed Target volume of the CSP using SD4D in each phase remains within the range of 0,39% to 13,04% difference from the known value (4 ccm) while A4D ranged from 0,06% up to 19,63% difference in the "20%" phase reconstruction. At the point where the enlargement of the volume occurred, there was a stitching point of two cine-scan blocks, in which images were merged in slightly different moments of the cycle. The minimum volume of the "Lung" and "External" structures were for A4D respectively 320,78±0,03ccm and 649,08±0,05ccm in the '50%” phase. As for SD4D respectively 321,18±0,20ccm and 649,77±0,29ccm. The maximum of the volume

Conclusion If proper quality assurance steps are taken, 3D-printed objects can be used accurately and effectively in radiation therapy. It is critically important, however, that the properties of any material being used in patient care be well understood and accounted for. EP-1739 Phantom capable of testing Smart Deviceless4D – four-dimensional CT (4DCT) – system development. T. Kostecki 1 , A. Giłka 1 , A. Kawa-Iwanicka 1 , M. Stefańczyk 1 1 NU-MED CDiTO Katowice, Radiotherapy, Katowice, Poland