Silvestre Patallo, Ileana; (2024) A roadmap for improving traceable dosimetry of preclinical research with medium energy x-ray irradiators. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Modern preclinical radiotherapy research has advanced with the use of sophisticated small animal irradiation platforms and in vivo preclinical models. However, despite these technological advances, few studies translate into clinical trials. A significant barrier is the lack of standardization in performing and reporting dosimetric aspects of the irradiations. / Aims: To address some of the identified challenges, this thesis proposes improvements to the various stages of the dosimetry chain associated with small-field, medium-energy x-ray preclinical irradiations performed with Image-Guided Small Animal Radiotherapy Platforms. / Methods: An experimental methodology was developed to characterize novel small scintillator detectors for beam parameters measurements and end-to-end dose verification. A new fibre calibration for the Hyperscint scintillator was tested by comparing different spectral components of scintillation emission. A multidetector comparison of small field relative output factors, involving organic and inorganic scintillators, EBT3 films, and Lassena CMOS, was conducted. A new method to determine reference absorbed dose using a small volume ionisation chamber (PTW-31022) traceable to the UK Air Kerma Primary Standard was validated. Additionally, the use of alanine as a transfer detector in medium-energy x-rays was characterized, and a multi-institutional end-to-end dosimetry audit was implemented in the UK. / Results: The scintillators' linearity and dose rate response matched ionization chambers. A new fibre + dose calibration procedure was proposed to Hyperscint manufacturers. Small field output factors measured across detectors agreed within ±4.5%. The PTW-31022 measurements of reference absorbed dose in the machine-specific 10 mm × 10 mm field had an uncertainty of ±3.7%. The end-to-end audit identified commissioning errors at one centre, with dose differences across institutions within ±5%. / Conclusions: This work represents a step forward in the pathway of meeting the increasing requirements for accuracy, adequate quality assurance, and dosimetric validation of preclinical radiation research studies. A multidetector approach is advantageous for measurements in small fields. The new formalism strengthens the dosimetry chain by quantifying uncertainties in traceable reference dose measurements. The audit highlighted the need for independent verification of preclinical treatment planning systems and provided an overview of dose accuracy across research institutions.

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