Comparison of the alanine response to clinical proton and carbon ion beams

Hadrontherapy with proton and carbon ion scanning beams is an advanced radiation treatment modality mainly exploiting the finite range of those particles in the matter, to better spare critical organs close to the tumor volume as compared to photons. However, its complexity requires careful management of dosimetric uncertainties to guarantee patient safety. This study aims to reassess the suitability of alanine-based dosimetry for modern hadrontherapy applications.

Alanine pellets based on electron spin resonance (ESR) were used as dosimeters. The response was taken from the peak-to-peak amplitude and compared to the ionization chamber one. Dose response and dependence on energy, beam direction, and linear energy transfer (LET), for both pristine Bragg peak and spread-out Bragg peak (SOBP) were evaluated. The ESR ratio x/y was evaluated as a function of LET and microwave power. Photon irradiations were performed with a 6 MV linear accelerator at the San Matteo Hospital, while with charged particles at CNAO, both located in Pavia, Italy.

Alanine showed a linear dose-response for both protons and carbon ions in the range of 10-45 Gy. For carbon ions, a pronounced quenching effect in the Bragg peak and energy dependence were observed. Alanine effectiveness was reduced by up to 30% due to LET effects. Moreover, the use of the x/y ratio showed potential for LET differentiation.

Alanine may be a promising dosimeter for hadrontherapy. However, further studies are required to investigate factors of correction due to the effects of LET and energy dependence.