ESTRO 2022 - Abstract Book

S645

Abstract book

ESTRO 2022

Purpose or Objective While radiation therapy beam orientation selection has a strong impact on treatment quality, it is often difficult to find better set of beam orientations in large number of available beam parameters. Conventional heat map methods are an effective approach for beam orientation selection, but these maps cannot rank beam orientations with respect to realistic dosimetric features. This study proposed a novel dosimetric feature-based heat map calculation method, which is called single-field dosimetrics (SFD), and applied this method on a C-shaped phantom and a head and neck patient in intensity- modulated radiation therapy (IMRT). Materials and Methods The SFD heat map was calculated from clinically-achievable dose distributions. For each beam orientation set of gantry angle and isocenter position, fluence intensity of beamlets was modulated to deliver the maximum dose to the target without exceeding the tolerance doses of other sensitive organs. These dose distributions did not represent the final dose distributions. Instead, they represented the degree of freedom of fluence intensity modulation. An empirical scoring function was then applied for the dose distributions to obtain the SFD heat map score values. Finally, the final IMRT dose distributions were calculated with “good” beam orientations selected from the SFD heat maps by using an open-source treatment planning system. For evaluation, the IMRT dose distributions with the beam orientations selected by the SFD method were compared with those by two conventional heat map methods (ray-tracing and beam’s-eye view dosimetrics). 4 different quality measures (homogeneity index, conformation number, dose coverage, and dose gradient) were used to quantitatively analyze the dose distributions. Results The calculated SFD heat maps effectively ranked beam orientations, while another heat map indicated the identical score value at multiple orientations (Figure 1). The SFD scores provided the similar dosimetric features to those found in the previous manual beam orientation selection studies. Moreover, the calculated IMRT dose distributions with the SFD-selected gantry angles and isocenter positions had better dosimetric quality than those with the conventional heat map methods (Figure 2). Homogeneity index, conformation number, dose coverage and dose gradient of the C-shaped phantom were improved from 0.0787, 0.425, 0.431 and 4.83 for the single-isocenter, equi-spaced dose distribution to 0.0688, 0.433, 0.468 and 4.68 for the SFD dose distribution, respectively.

Conclusion SFD provides a simple and heuristic approach to extract dosimetric features for beam orientation selection. This technique can be performed for any orientation parameters (i.e. beam directions, isocenter positions, etc.) and radiation therapy platforms. The proposed method will be useful for patient-specific precise treatment planning.

PD-0733 Parameters influencing inter-Institute variability in KB plan prediction models for whole breast RT

A. tudda 1 , R. Castriconi 1 , G. Benecchi 2 , E. Cagni 3 , F. Dusi 4 , P.G. Esposito 1 , G. Rambaldi Guidasci 5 , M. Guernieri 6 , A. Ianiro 7 , V. Landoni 7 , A. Mazzilli 2 , E. Moretti 6 , C. Oliviero 8 , L. Placidi 9 , T. Rancati 10 , V. Trojani 3 , A. Scaggion 4 , C. Fiorino 1