Moving into the 21st century: analysis of inverse planned radiation therapy for breast cancer

Abstract

Planning a course of radiation therapy for a patient with breast cancer is a complex task. This thesis outlines four research phases investigating different treatment modalities and planning techniques for radiation therapy to the intact breast. Phase one involved a systematic review of the literature to inform on the magnitude of inter- and intra-fraction motion during breast radiation therapy treatment. Analysis of the literature world-wide found that the overall magnitude of motion was <5mm. This result demonstrated the feasibility of implementation of intensity modulated radiation therapy (IMRT) modalities and informed planning target volume (PTV) margins and the importance of immobilisation devices. Phase two identified the contouring requirements, prescriptions, and dose endpoints for target volumes, organs at risk (OARs) and planning contours for breast radiation therapy. Adequate contouring guidelines were essential to limit the large inter-observer and intra-observer variability in contouring during breast radiation therapy planning. A hypofractionated dose and simultaneous integrated boost (SIB) were also identified as planning techniques to be utilised for plan comparison. In phase three, tomotherapy, both static and helical, 3D-conformal radiation therapy (3D-CRT) and IMRT planning procedures were developed. These four modalities were compared for dosimetric outcome in phase four and five. The planning comparison in phase four found static tomotherapy preferable to helical tomotherapy treatment due to the large areas of low dose being delivered to the patient during helical tomotherapy. In phase five inversely optimised modalities demonstrated improved dosimetric outcomes compared to the current 3D-CRT modality.