CT ventilation imaging

Radiation induced lung toxicity (RILT) involves painful lung inflammation affecting up to 31% of lung cancer patients treated with conventional radiotherapy. Recent studies suggest that RILT could be reduced by avoiding irradiation of healthy (functional) lung. We are investigating computed tomography (CT) ventilation imaging, a new modality that can provide high-quality, accessible functional lung imaging that can be easily incorporated into radiotherapy planning.

At present, our goals are to validate computed tomography (CT) ventilation imaging against nuclear-medicine based methods, and investigate the role of on-line ventilation imaging to measure and adapt for ventilation changes on a day-to-day basis.

How it works

The primary function of the lung is 'ventilation,’ referring to gas-blood exchange at the alveolar level. At present, the clinical standard for lung ventilation imaging is based on nuclear-medicine. CT-ventilation uses advanced image processing techniques to provide high-resolution ventilation images with no extra cost in hardware or imaging dose.

CT ventilation in 3 steps: (i) Image acquisition, (ii) Deformable registration (iii) Analysis

Generation of CT ventilation images in three steps.

CT-ventilation imaging can be performed in three simple steps:

  • (i) Acquisition of CT-images of the lung at exhale and inhale states using breath-hold CT, or respiratory correlated four-dimensional CT (4D-CT).
  • (ii) Deformable image registration (DIR) software is used to determine a spatial mapping ("deformation map") between the exhale and inhale images.
  • (iii) Application of a ventilation metric involves quantitative analysis based on regional lung deformation, and/or changes in image intensity.

The resulting ventilation image can be superimposed directly onto the anatomic image, providing an added dimension of functional information which is easy to understand and can be of direct benefit in planning a radiotherapy treatment.

Clinical study: validating CT-ventilation imaging

Functional planning based on CT ventilation

Comparison of radiotherapy treatment plans based on anatomic data (left) and incorporating functional information (right). Image courtesy of Dr. Tokihiro Yamamoto, University of California-Davis.

We are conducting a clincal study at Royal North Shore Hospital testing the physiological accuracy of CT ventilation imaging for use in lung cancer radiotherapy. The physiological accuracy of CT ventilation imaging will be assessed via a correlation study against the current gold standard for ventilation imaging, nuclear medicine imaging.

We will also quantify the dosimetric impact of CT ventilation imaging for functional avoidance lung radiotherapy. Functional avoidance is a method of treatment planning which tries to avoid irradiation of high-functioning (well-ventilated) lung regions. Our Our functional-based plans will be compared to standard of care, anatomic-based plans.

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On-line CT ventilation imaging

Image showing daily ventilation changes in radiotherapy

Daily ventilation changes during lung cancer radiotherapy; ventilation images in colour, anatomy in greyscale. Patient images courtesy Dr. Geoffrey Hugo, Virginia Commonwealth University.

The efficacy of functional avoidance is diminished if there are temporal changes in the ventilation pattern throughout a course of radiotherapy. This can occur for a number of reasons, for example changing tumour size, disease progression and radiation damage.

To meet this challenge, we are developing 'on-line' ventilation imaging using four-dimensional cone-beam CT (4D-CBCT) images acquired on the radiotherapy treatment machine. 4D-CBCT is itself a rapidly growing modality, used for visualisation of lung (and other) tumour motion in image guided radiation therapy (IGRT). This technology will allow us to track day-to-day changes in lung ventilation, facilitating truly adaptive functional lung avoidance radiotherapy for the first time.

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