Evaluation of Novel Cone-Beam CT for Guidance and Adaptation of Precision Radiotherapy

This is a feasibility study investigating the image quality of a new, high-performance cone beam CT (CBCT) used for on-couch imaging during radiotherapy treatments.

This study focuses on potential benefits of a high performance cone beam CT (CBCT) image guidance system for improved precision in the delivery of radiotherapy. CBCT is currently used during radiation therapy to align the patient to their original treatment plan to increase the precision of radiation delivery. Current CBCT imaging technology requires approximately a minute to acquire an image. In order to acquire images with sufficient quality to allow accurate targeting, the patient may need to perform multiple breath hold maneuvers to "freeze" the motion of tumors that move with the breathing cycle (e.g. lung, liver, and breast tumors). The new high-performance CBCT can acquire an image in approximately 6 seconds, potentially enabling acquisition of images with a single breath hold. Improved motion compensation algorithms used in image reconstruction may allow acquisition of good quality images even while a patient is not holding their breath. The methodology for the subject's treatment setup, CT simulation, treatment planning, image guidance and treatment delivery will be determined by the subject's treatment team and is not specified by this study. Enrollment in the study may occur after treatment delivery has started but must be prior to the fifth fraction. Following completion of informed consent to participate in this study, high-performance CBCT imaging will be scheduled immediately before or after one of the subject's first five scheduled radiation treatment fractions. Two research CBCT images will be acquired, one with breath hold, the other with free breathing. With minimal disruption for participating patients, this study will enable a comparison of (i) the subject's treatment planning fan-beam CT and (ii) the conventional CBCT acquired on an existing treatment unit with (iii) the high-performance CBCT. Image quality of the high performance CBCT image data will thereby be compared to both a best-case standard (fan-beam) and the status-quo for on-couch imaging to isolate and identify improvements.

This is a single-site study designed to generate data describing the quality and applicability of on-couch high-performance CBCT imaging for anatomy visualization and radiation treatment dosimetry planning.

The quality of fan-beam CT, standard CBCT and high-performance CBCT will be evaluated by calculating contrast, noise, resolution, Hounsfield Unit accuracy and artifact reduction. Furthermore, the three image sets will be evaluated qualitatively by multiple observers with training in radiation oncology and image-guided radiation therapy, who will rank the images acquired for each subject by perceived quality/usefulness for structure contouring and RT guidance.

Dose-volume histograms for key target structures and organs at risk will be calculated from both the high-performance and standard CBCT images and compared to those from the existing dosimetric plan for each subject to determine the accuracy of the dosimetric calculations based on the CBCTs.

The patient experience with CBCT image acquisition will be determined through the use of a questionnaire comparing elements of the standard CBCT image acquisition process to that of the high-performance CBCT process.

Inclusion Criteria: Subject is scheduled for treatment on one of the five TrueBeam platforms at the NS Health QE2 site. Subject is receiving radiation therapy using a breath-hold technique (for example, lung, liver and left breast cancers). Exclusion Criteria: Patient is pregnant or has plans for pregnancy during the period of treatment. Patient is unwilling to consent to participating to the study, or for whom informed consent is not possible.