Improving the quality of head and neck radiotherapy CT images using a second image reconstruction set.

Purpose: To improve the quality of radiotherapy head and neck CT images through use of an additional image set reconstructed from the raw data of the primary scan, thus allowing parameters such as reconstruction field-of-view (FOV) and kernel to be optimised without impacting on the images used for treatment planning dose calculations.

Methods: Using a Catphan image quality phantom and a Toshiba Aquilion LB CT scanner, qualitative and quantitative measurements were made for different reconstruction kernels and FOV diameters. The preferred FOV diameter and kernels were selected.

Can different Catphan phantoms be used in a multi-centre audit of radiotherapy CT image quality?

Purpose: To determine the variation between Catphan image quality CT phantoms, specifically for use in a future multi-centre image quality audit.

Method: 14 Catphan phantoms (models 503, 504 and 604) were scanned on a Canon Aquilion Prime CT scanner using a single scan protocol. Measurements were made of noise in the uniformity section, visibility of low contrast targets and contrast, x-ray attenuation and CT number for 5 materials in the sensitometry section.

Radiation dosimetry changes in radiotherapy treatment plans for adult patients arising from the selection of the CT image reconstruction kernel.

Objective: The reconstruction kernel used for a CT scan strongly influences the image quality. This work investigates the changes in Hounsfield units (HUs) which can arise when altering the image reconstruction kernel for planning CT images and the associated changes in dose in the radiotherapy treatment plan if the treatment planning system (TPS) is not re-calibrated.

Methods: Head and neck, prostate and lung CT images from four centres were used.

IPEM topical report: the first UK survey of dose indices from radiotherapy treatment planning computed tomography scans for adult patients.

CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for the calculation of dose in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance in the literature on dose levels in radiotherapy CT imaging either within the UK or internationally.

Assessment of the variation in CT scanner performance (image quality and Hounsfield units) with scan parameters, for image optimisation in radiotherapy treatment planning.

Purpose: To define a method and investigate how the adjustment of scan parameters affected the image quality and Hounsfield units (HUs) on a CT scanner used for radiotherapy treatment planning. A lack of similar investigations in the literature may be a contributing factor in the apparent reluctance to optimise radiotherapy CT protocols.

Method: A Catphan phantom was used to assess how image quality on a Toshiba Aquilion LB scanner changed with scan parameters.

Can CT scan protocols used for radiotherapy treatment planning be adjusted to optimize image quality and patient dose? A systematic review.

This article reviews publications related to the use of CT scans for radiotherapy treatment planning, specifically the impact of scan protocol changes on CT number and treatment planning dosimetry and on CT image quality. A search on PubMed and EMBASE and a subsequent review of references yielded 53 relevant articles. CT scan parameters significantly affect image quality.