Advancing Treatment Accuracy of Accelerated Partial Breast Irradiation

Accelerated partial breast irradiation (APBI) has been clinically demonstrated as a new and advantageous breast radiotherapy approach. Contrary to standard-of-care whole breast radiotherapy (WBRT), APBI focuses radiation to the tumour bed with a small surrounding margin. To ensure successful treatment outcomes, these precise treatment techniques require a higher level of treatment accuracy than WBRT. The purpose of this thesis is to inform and advance treatment accuracy of external beam APBI. This is achieved through two main approaches. First, 3D printing was utilized to construct phantoms for assessing image fidelity and measuring geometric distortions on multiple radiological imaging modalities used in target delineation during high-precision radiotherapy treatment planning. The proof of concept was demonstrated using a small version of the phantom and with co-registered helical computed tomography (CT), cone beam computed tomography (CBCT), and magnetic resonance imaging (MRI) image sets, which are routinely employed during target delineation of certain cranial diseases for high-precision, high-accuracy radiotherapy. The second part of this work was motivated by the fact that MRI offers excellent soft tissue visualization, which can be particularly advantageous for APBI. In MRI, the breast is positioned at the lateral parts of the imaging field-of-view where geometric distortion increases. Methods demonstrated for the cranial site were further developed to construct a modular, large 3D printed phantom. Radiological image geometric distortion was measured on image sets acquired with MRI sequences often utilized for clinical breast imaging. Results showed that errors arising from geometric distortions can be sufficiently significant to consider in margins for APBI. Second, a novel, realistic, deformable breast phantom was developed for multi-modality imaging, radiation absorption measurements, and surgical simulation applications. The phantom's properties were optimized to match human breast tissues'. Mechanical properties were validated through mechanical and shear-wave ultrasound elastography testing. Radiation absorption was determined through empirical calculations, experimental measurements, treatment planning system calculations, and EGSnrc Monte Carlo simulations. Surgical simulation validation was confirmed by surgeons. Finally, a set of breast phantoms were used to simulate various oncoplastic breast surgery (OBS) techniques. This study provided new insight on OBS and showed how OBS can potentially impact patient eligibility for APBI.