Related Experiment Video
Updated: Sep 15, 2026
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
A Combined Dose and Microdosimetric Modeling Framework Incorporating Volume Effects Correlates with Tissue Sparing in
G Bordieri1, M Missiaggia2, M Battestini1
1Department of Physics, University of Trento, Trento, Italy; Trento Institute for Fundamental Physics and Application (TIFPA), Trento, Italy.
Purpose:
Proton minibeam (pMB) radiation therapy delivers highly heterogeneous dose distributions, alternating high-dose peaks and low-dose valleys. This aims to widen the therapeutic window by improving normal tissue sparing while maintaining the same or even better tumor control. The performance of pMB strongly depends on the collimator design and physical parameters. To better understand the physical and radiobiological drivers of this enhanced therapeutic window, we perform a detailed microdosimetric characterization of pMBs and assess their impact.
Methods And Materials:
We characterize radiation quality with microdosimetry through Monte Carlo simulations. Then we extend the Generalized Stochastic Microdosimetric Model (GSM2) to predict the normal tissue complication probability (NTCP) at different depths in water, 1, 2, and 4 cm, for 100-MeV pMBs realized with varying configurations of the collimator. Results are compared with conventional homogeneous field irradiation after dose normalization to the tumor. The developed model is applied by considering tissues as divided into several functional subunits, connected by introducing a seriality parameter.
Results:
Microdosimetric characterization of pMB irradiation shows differences between peak and valley regions in shaping lineal energy spectra, especially at low depth, whereas radiation quality uniforms progressively closer to the target region (tumor). NTCP calculation results suggest an increased sparing effect for pMB over conventional homogeneous field. A strong dependence is found on the peak-to-valley dose ratio and on the seriality parameter. Predictions indicate substantial sparing from pMB, especially for peak-to-valley dose ratio > 15, including relatively serial organs with seriality around 0.7. All results are consistent with the general trends reported in experimental studies.
Conclusions:
This integrated dose-microdosimetric-biological framework elucidates how spatial fractionation, radiation quality, and organ architecture collectively shape tissue sparing in pMB. The findings identify conditions under which pMB may offer NTCP reduction, highlighting the importance of incorporating microdosimetry and tissue seriality in future optimization and clinical translation efforts.
