Design of spread-out Bragg peaks in hadron therapy with oxygen ions.

Aim: Design of a numerical method for creating spread-out Bragg peak (SOBP) and evaluation of the best parameter in Bortfeld Model to this aim in oxygen ion therapy.

Background: In radiotherapy, oxygen ions have more biological benefits than light beams. Oxygen ions have a higher linear energy transfer (LET) and larger relative biological effectiveness (RBE) than lighter ones.

Materials and methods: For the design of the spread-out Bragg peak (SOBP) for oxygen beam, we designed a numerical method using the Geant4 Monte Carlo simulation code, along with matrix computations.

Results: The profiles of the Bragg Peak have been calculated for each section in the target area by the Geant4 tool. Then, in order to produce SOBP smoothly, a set of weighting factors for the intensity of oxygen ion radiation in each energy was extracted through a numerically designed method. This method was tested for producing SOBP at various widths and at different depths of a phantom. Also, weighting factors of intensity for producing a flat SOBP with oxygen ions were also obtained using the Bortfeld model in order to determine the best parameters. Then, the results of the Bortfeld model were compared with the outcomes of the method that was developed in this study.

Conclusions: The results showed that while the SOBP designed by the Bortfeld model has a homogeneity of 92-97%, the SOBP designed by the numerical method in the present study is above 99%, which in some cases even closed to 100%.