ESTRO 2023 - Abstract Book

S1556

Digital Posters

ESTRO 2023

body and PTV structures, respectively (see figure).

Conclusion The PRIMO MC software is a valuable tool for dosimetric verification of clinical plans during the commissioning of the primary TPS, as well as to perform independent verifications of the plans in the clinical practice.

PO-1826 Dosimetric verification of small field SBRT plans using a new enhanced leaf model for VarianTruebeam

M. Oellers 1 , A. Swinnen 1 , F. Verhaegen 1

1 MAASTRO, Medical Physics, MAASTRICHT, The Netherlands

Purpose or Objective Supported by better diagnostic imaging, there is an increasing trend in radiation oncology to treat smaller tumors with a high dose in few fractions. Nevertheless hypofractionation in lung cancer remains challenging especially for very small targets with diameters below 1 cm. Current advanced dose algorithms like Acuros XB still have its limitations in predicting dose within 5% for small fields where for example inaccuracies in the MLC model may be amplified in the final dose prediction [1]. A way to improve the dose accuracy is by improving the current MLC model and more specific the way the leaf tips are modelled in Eclipse. A more realistic modelling of the leaf tips will most probably lead to a more accurate prediction of dose in very small targets. Materials and Methods A pre-release of Acuros XB (version 18) with the new enhanced model (ELM) was used to determine new dosimetric leaf gap (DLG) values in Eclipse for Truebeam STx (Table 1). With these values the plans described in [1] were recalculated in