Dosimetry calibration for low-energy protons produced in the ECU accelerator laboratory

Abstract

Large doses of ionizing radiation are routinely employed in radiation therapy to destroy malignant tumor cells. Among the available modalities, proton and heavy-ion beams produced by particle accelerators have been widely recognized as highly effective techniques for cancer treatment. A key advantage of these particle beams is their ability to deposit the majority of their energy within a well-defined and localized volume inside the body, thereby maximizing tumor dose while minimizing irradiation of surrounding healthy tissues. Despite these advantages, continued experimental and methodological studies are required to further refine dose delivery, improve biological effectiveness, and reduce uncertainties associated with particle-beam therapy. In this context, ongoing experiments in the accelerator laboratory at East Carolina University (ECU) are focused on investigating the biological effectiveness of low-energy proton beams in inducing cell damage and tumor cell killing. Accurate interpretation of these radiobiological experiments critically depends on precise knowledge of the radiation dose delivered to the cellular targets. Even relatively small uncertainties in dose determination can lead to significant ambiguities in the assessment of biological response, underscoring the need for robust and well-validated dosimetric techniques. The primary objective of this dissertation is to test, develop, and validate accurate methods for measuring the radiation dose delivered during cell irradiation experiments conducted in the ECU accelerator laboratory. Multiple independent dosimetry techniques are systematically evaluated, including Gafchromic film dosimetry, and solid-state detectors. Experimental dose measurements obtained with these detectors are compared directly with calculated dose values derived from Monte Carlo simulations using the Geant4 toolkit, providing a quantitative framework for cross-validation. Results obtained from experiments using Gafchromic films demonstrate that careful, proton-specific calibration is a critical factor in achieving reliable dose measurements. In particular, the dose response of Gafchromic films is strongly dependent on proton energy and linear energy transfer (LET), and inappropriate calibration can introduce substantial systematic errors. Consequently, this work emphasizes the development of a physically consistent calibration strategy and a comprehensive validation methodology, forming a solid dosimetric foundation for current and future proton-based radiobiology studies at ECU.