Fast Daily Interfraction and Intrafraction Prostate Repositioning for High Precision Radiotherapy

The research described in this thesis is focused on development and clinical evaluation of image-guidance solutions for correction of both inter- and intrafraction prostate motion in external beam radiotherapy. Corrections are based on planar imaging of implanted gold markers with MV and kV beams. The main advantages of the developed system include (1) high positioning accuracy, (2) minimal increase in fraction duration, (3) high degree of automation, i.e. minimal operator interference, (4) remote controlled couch re-positioning, (5) minimal additional imaging dose. Another important objective of the research was the assessment of residual errors, including organ deformation and rotation, to establish appropriate planning margins. One of the main findings of the research is that implanted gold markers allow for fast daily correction of translational errors in prostate radiation therapy with high accuracy. An investigation of intrafraction positioning errors which occur during the treatment delivery revealed that intrafraction errors partially reproduce from day-to-day, thereby limiting margin reduction in prostate radiotherapy if not corrected. Another finding was that deformation of the seminal vesicles limits margin reduction with daily online translation corrections based on implanted markers. Furthermore, the benefit of rotation corrections in addition to translation corrections was insignificant. Finally, electronic portal imaging devices (EPIDs) have significantly facilitated time and workload efficient strategies for managing daily positioning errors with minimal extra imaging dose to the patient.

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