Investigation of In-Field and Out-of-Field Radiation Quality With Microdosimetry and Its Impact on Relative Biological Effectiveness in Proton Therapy

Marta Missiaggia; Giorgio Cartechini; Francesco Tommasino; Emanuele Scifoni; Chiara La Tessa

doi:10.1016/j.ijrobp.2022.11.037

Investigation of In-Field and Out-of-Field Radiation Quality With Microdosimetry and Its Impact on Relative Biological Effectiveness in Proton Therapy

Int J Radiat Oncol Biol Phys. 2023 Apr 1;115(5):1269-1282. doi: 10.1016/j.ijrobp.2022.11.037. Epub 2022 Nov 25.

Authors

Marta Missiaggia¹, Giorgio Cartechini², Francesco Tommasino², Emanuele Scifoni³, Chiara La Tessa⁴

Affiliations

¹ Department of Physics, University of Trento, Trento, Italy; Trento Institute of Fundamental Physics and Applications (INFN-TIFPA), Trento, Italy; Department of Radiation Oncology, University of Miami, Miami, Florida.
² Department of Physics, University of Trento, Trento, Italy; Trento Institute of Fundamental Physics and Applications (INFN-TIFPA), Trento, Italy.
³ Trento Institute of Fundamental Physics and Applications (INFN-TIFPA), Trento, Italy.
⁴ Department of Physics, University of Trento, Trento, Italy; Trento Institute of Fundamental Physics and Applications (INFN-TIFPA), Trento, Italy; Department of Radiation Oncology, University of Miami, Miami, Florida. Electronic address: cxl1666@miami.edu.

PMID: 36442542
DOI: 10.1016/j.ijrobp.2022.11.037

Abstract

Purpose: Using microdosimetry, this study investigated the relative biological effectiveness (RBE) and quality factor (Q¯) variations in field and out of field as a function of radiation quality for clinical protons.

Methods and materials: A water phantom with a spread-out Bragg peak (SOBP) was irradiated to acquire microdosimetric spectra at several distal and lateral depths with a tissue equivalent proportional counter. The measurements were used as inputs to microdosimetric kinetic and Loncol models to determine the RBE spatial distribution and compare it with predictions from the dose-averaged linear energy transfer-based McNamara model. Q¯ values and biological and dose equivalent values were also calculated.

Results: The data demonstrated that radiation quality changed more rapidly with depth than lateral distance from the SOBP. In beam, y_D ranged from approximately 4 keV/μm at the entrance to 8 keV/μm at the SOBP far end, reaching approximately 15 keV/μm at the penumbra. Out of field, the overall highest value of 23 ± 2 keV/μm was observed at the beam-edge penumbra. Radiation quality changes caused RBE deviations from the clinical value of 1.1, whose extent depends on the approach used for assessing radiation quality as well as on the radiobiological model. For RBE₁₀, microdosimetry-based models appeared to better reproduce the radiobiological data than the dose-averaged linear energy transfer model. Out of field, both the RBE and Q¯ values appeared to have limitations in describing the radiation biological effectiveness. This research also presents a first comprehensive benchmark of TOPAS code against in-field and out-of-field microdosimetric spectra of therapeutic protons.

Conclusions: Further investigation will be necessary to evaluate the quantitative effects of RBE variations on treatment planning and assess the clinical consequences in terms of both tumor control and normal-tissue toxicity. The achievement of this goal calls for accurate radiobiological data to validate the RBE models.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Humans
Neoplasms*
Proton Therapy* / adverse effects
Protons
Radiometry / methods
Relative Biological Effectiveness

Substances

Protons