The precision of modern radiation therapy techniques is limited by the motion and deformation of tumours and surrounding anatomy. Dr Yeo has developed the world's first deformable three-dimensional radiation dose detector. He used it to experimentally validate a mathematical modelling approach to accounting for deformation in radiotherapy of liver cancer. His work is recognised by numerous citations of many of his publications in international peer-reviewed journals. This book is a collection of his findings during his PhD research. Yeo's work continuously focuses on developing tissue-equivalent deformable phantoms, validating mathematical deformation models, and clinically implementing deformation adaptive approach for cancer diagnosis, image-guided therapies, and treatment evaluation/assessment.