Author ORCID Identifier


Date of Graduation


Document Type

Dissertation (PhD)

Program Affiliation

Medical Physics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Stephen Kry, PhD

Committee Member

Fada Guan, PhD

Committee Member

Phil Taddei, PhD

Committee Member

Oleg Vassiliev, PhD

Committee Member

Christine Peterson, PhD

Committee Member

Rebecca Howell, PhD


Carbon ion radiotherapy is a novel modality used for the treatment of tumors that are unresectable, close to critical structures, or resistant to standard radiotherapy. A unique benefit of this therapy is the relative biological effectiveness (RBE) of the beam (i.e., how biologically potent carbon ions are as compared to x-rays), which is significantly elevated. This RBE also varies as a function of many parameters, and there are currently several models implemented in clinical and research-based treatment planning systems with which to predict RBE. These algorithms are computationally expensive and there are currently no means of validating their implementation within treatment planning systems, meaning that there is no viable means of testing that the dose delivered to patients matches that prescribed. Additionally, uncertainty in RBE by physical parameters and model assumptions have not been well characterized, which makes it difficult to understand where model differences arise.

The aim of this work is to create a robust measurement-based program with which to validate clinical implementation of RBE by each common model. To accomplish this, Geant4 Monte Carlo will be used to simulate a clinically realistic carbon beam incident on a water phantom along with multiple common microdosimeters in the beam line. Input parameters for each RBE model (microdosimetric spectra, kinetic energy spectra, physical dose, double strand break yield) will be calculated throughout the beam line. This data will be used to both compare and evaluate uncertainty in current RBE models and microdosimetry techniques for estimating RBE. Most importantly, this data will be used to create a system of estimating RBE by any common model using exclusively input parameters that can be physically measured.

This will serve as the basis of the first quality assurance audit program for carbon radiotherapy, which will both verify that delivered biological dose matches that prescribed by commercial treatment planning systems and manage RBE comparisons and uncertainties to within a 10% tolerance. This will allow the independent comparison of RBE model and treatment outcome to establish consistency and standardization of clinical practice in the rapidly developing field of carbon radiotherapy.


relative biological effectiveness, carbon radiotherapy, RBE, RBE modelling, microdosimetry, tissue equivalent proportional counter

Available for download on Friday, August 09, 2024