ESTRO 2021 Abstract Book

S1519

ESTRO 2021

PO-1793 Quantifying the oxygen fixation mechanism in charged particle beams F. Van den Heuvel 1 , A. Vella 2 , F. Fiorini 3 , M. Brooke 2 , M. Hill 2 , T. Maughan 2 1 Zuidwest Radiotherapeutisch Instituut, Radiatiotherapy, Vlissingen, The Netherlands; 2 University of Oxford, Oncology, Oxford, United Kingdom; 3 Rutherford Cancer Centre, Physics, Reading, United Kingdom Purpose or Objective To develop a framework to include oxygenation effects in radiation therapy treatment planning which is valid for all modalities, energy spectra and oxygen levels. The framework is based on predicting the difference in DNA--damage resulting from ionising radiation at variable oxygenation levels. Materials and Methods Oxygen fixation is treated as a statistical process in a simplified model of complex and simple damage. We show that a linear transformation of the microscopic oxygen fixation process allows to extend this to all energies and modalities, resulting in a relatively simple rational polynomial expression. The model is expanded such that it can be applied in for polyenergetic beams. The methodology is validated using microdosimetric Monte Carlo simulations and an implementation is developed for a clinically relevant proton beam. In addition double strand break induction as calculated by this methodology is compared to published proton experiments at low energies (high LET). Results For all modalities (electrons, protons, Helium ions, and Carbon ions), the damage categorised as complex could be predicted to within 0.3\% of the value calculated using Monte Carlo. The proton beam implementation showed some variation in oxygen enhancement ratios which differed

slightly depending on where the assessment was made; before the SOBP, mid-- SOBP or at the distal edge. Figure 1: Oxygen enhancement ratio's based on differences in induced DNA- damage. For resp. 0.1% and 10% pO2 oxygenation, in a clinical proton treatment plan (IBA). The plan is a 10cm SOBP using a 10cm x 10cm field. The SOBP is generated by a sum of pencil

beams. We note that the OER diminishes in the SOBP and reduces even further at the end of the range due to increased contribution of high LET protons. For illustration we add the dose deposition of the beam normalised at 1Gy (right y-axis).

Table: Comparison of OER calculated and published.

Conclusion An analytic expression calculating complex damage depending on modality, energy spectrum, and oxygenation levels was shown to be effective and can be readily incorporated in treatment planning software, to take into account the impact of variable oxygenation, forming a first step to an optimised treatment based on biological factors. PO-1794 Features robustness in the radiomic workflow: the impact of software choice on feature variability M. Zaffaroni 1 , G. Carloni 2 , S. Volpe 1,3 , C. Garibaldi 4 , G. Marvaso 5,3 , S. Gandini 6 , C. Rampinelli 7 , G. Petralia 8,3 , E. Cassano 9 , M. Bellomi 10 , M. Cremonesi 4 , V. Positano 2,11 , R. Orecchia 12 , B.A. Jereczek-Fossa 1,3 1 IEO European Institute of Oncology, IRCCS, Radiation Oncology, Milan, Italy; 2 University of Pisa, Information Engineering, Pisa, Italy; 3 University of Milan, Department of Oncology and Hemato-Oncology, Milan, Italy; 4 IEO European Institute of Oncology, IRCCS, Unit of Radiation Research, Milan, Italy; 5 IEO European Institute