ESTRO 2023 - Abstract Book

S1735

Digital Posters

ESTRO 2023

Fig. 2 illustrates the high dose area for the brainstem, optic chiasm and optic nerves. While the difference to the manual plans is not significant, we observe a trend where (by design) the KBP model strongly tries to push the max dose to these organs below 54Gy while the manual planner allowed higher doses in some cases. This could potentially explain the lower min point doses observed in the KBP plans.

Conclusion A KBP model was developed and demonstrated to produce clinically viable plans for brain and BOS IMPT. In some cases lower min doses and higher hot spots are observed, but target coverage is comparable. The KBP model was built to strongly push for sparing of critical OARs. As with all plans intended to treat patients, KBP plans need careful evaluation and may require manual adjustment in order to achieve the desired compromise of target coverage and OAR sparing. Following the results of the evaluation, the model has been employed clinically.

PO-1969 Microdosimetric approach for treatment planning in proton therapy

P. Pisciotta 1 , J. Magini 2 , E. Traneus 3 , M. Hussein 4 , S. Both 1 , G. Schettino 2 , F. Romano 5

1 University Medical Center Groningen, Department of Radiotherapy, Groningen, The Netherlands; 2 University of Surrey, Department of Physics, Guildford, United Kingdom; 3 RaySearch Laboratories, -, Stockholm, Sweden; 4 National Physical Laboratory, -, Teddington, United Kingdom; 5 Istituto Nazionale di Fisica Nucleare, Catania Division, Catania, Italy Purpose or Objective The use of stochastic measurable microdosimetric quantities, like the energy deposition at a micrometric scale, can lead to a better radiobiological prediction for densely ionizing radiation such as protons. Accurate microdosimetric calculation can currently only be achieved with general purpose Monte Carlo simulation which is extremely slow, limiting clinical adoption. To improve the calculation accuracy within a clinical TPS, workaround need to be elaborated. This work attempts to implement microdosimetric quantities for proton treatment planning via look-up tables(LUTs) to be linked with a TPS. This is of fundamental importance in the view of achieving biological optimization through the microdosimetric kinetic model (MKM) or similar based on microdosimetric means, in a TPS. Materials and Methods The LUTs include the microdosimetric mean quantities(ȳD, ȳF and y*) of monoenergetic proton beams as a function of their kinetic energy. These tables were obtained from a monoenergetic beam impinging perpendicularly on a 1 µ m thick sensitive volume using Geant4. Kinetic energy values were sampled in a logarithmic scale and associated with ȳD, ȳF and y*. As a first step, the consistency of the proposed approach was validated by determining ȳD, ȳF and y* at different depths in water, using the previously calculated LUTs. The obtained quantities were compared with those retrieved at the same depths in water using a “full” Geant4 simulation, considered as a reference. To achieve this, a 150MeV monoenergetic