Auto-segmentation of head and neck organs at risk in radiotherapy and its dependence on anatomic similarity

PURPOSE: The aim is to study the dependence of deformable based auto-segmentation of head and neck organs-at-risks (OAR) on anatomy matching for a single atlas based system and generate an acceptable set of contours. METHODS: A sample of ten patients in neutral neck position and three atlas sets consisting of ten patients each in different head and neck positions were utilized to generate three scenarios representing poor, average and perfect anatomy matching respectively and auto-segmentation was carried out for each scenario. Brainstem, larynx, mandible, cervical oesophagus, oral cavity, pharyngeal muscles, parotids, spinal cord, and trachea were the structures selected for the study. Automatic and oncologist reference contours were compared using the dice similarity index (DSI), Hausdroff distance and variation in the centre of mass (COM). RESULTS: The mean DSI scores for brainstem was good irrespective of the anatomy matching scenarios. The scores for mandible, oral cavity, larynx, parotids, spinal cord, and trachea were unacceptable with poor matching but improved with enhanced bony matching whereas cervical oesophagus and pharyngeal muscles had less than acceptable scores for even perfect matching scenario. HD value and variation in COM decreased with better matching for all the structures. CONCLUSION: Improved anatomy matching resulted in better segmentation. At least a similar setup can help generate an acceptable set of automatic contours in systems employing single atlas method. Automatic contours from average matching scenario were acceptable for most structures. Importance should be given to head and neck position during atlas generation for a single atlas based system.

Magnetic resonance image guidance in external beam radiation therapy planning and delivery.

The use of magnetic resonance (MR) imaging in radiation oncology is improving dramatically. This review article discusses the necessity of image guidance and how MR finds a significant place in radiotherapy planning and delivery. The challenges to and current solutions for an in-house MR simulation, dedicated MR simulator, estimation of electron density using MR image sets and development of MR-compatible treatment planning systems are presented. This article also reviews the feasibility, advantages and limitations of MR image-guided radiation therapy (MR-IGRT) and its drive toward the integration of radiation beams with MR technology. Specifications of Co-60 MR technology and three other MR-linac projects worldwide are presented. Online and real-time MR guidance is also discussed.