Lecture 13 - CBCT SBRT Lung Procedure

ONCOL 306 - Imaging. University of Alberta

what are two indications that the patient must meet to use the CBCT SBRT Lung procedure

Patient must be SBRT Lung and have supine patient position

CBCT Procedure Step 1 - Acquire Low-dose Thorax CBCT

• rationale

low-dose thorax CBCT is a low dose full-scan

CBCT Procedure Step 2 - Assess Quality of CBCT (assess window and level as needed to view ITV)

• rationale

ensure the scan volume is appropriate and you are able to visualize all relevant structures for the CBCT match

• make sure we are in the lung window when doing soft tissue match

• make sure we are in bone window when doing bony match

CBCT Procedure Step 3 - Assess for abnormal anatomy, objects, etc

• what should we be looking for?

pleural effusion, penumothorax, change in mass size or position

• also ensure there is no metal in the field

Tumors in what region of the lung have an increased risk of causing pneumothorax

tumors in the hilar region

CBCT Procedure Step 4 - Automatch to bone

• what does the ROI include

• exclude what as much as possible

• what axes are included

• intensity range

ROI should only include the vertebral bodies, we exclude the ribs in our match

exclude air as much as possible while being within the CBCT scanned area

we include translation axes only (exclude rotational axes as we do not do 6DOF)

intensity range = bones

CBCT Procededure Step 5 - Evaluate pitch, role, and yaw

• what do we do in this step

look at slices in each plane to show bony landmark and use slider bar to quickly contrast postion of bones on CBCT to Sim CT

• any rotations > 3 degrees = reposition patient

CBCT Procedure Step 6 - Evaluate Pretreatment prep

• what prep occurs with SBRT Lung

none

CBCT Procedure Step 7 - intervene if needed

• what interventions may we need to take?

in terms of prep, there are no interventions but we can check for pathologies

• If it’s a small pneumothorax you may still treat it that day , but a collapsed lung + large pathologies may impact the treatment plan / patient health.

  • ROs may still treat patients with old plans until a new plan is made.

  • If it is collapsed lung, definitely should get patient off the bed and get help

CBCT Procedure Step 8 - Automatch to Soft Tissue

• ROI to include

• exclude

• what axes are included

• intensity range

ROI to include GTV/ITV

exclude air outside of body contour while being within CBCT scanned area

include translational axes only

• we may include rotational axes if we do 6DOF

CBCT Procedure Step 9 - Perform Volume Match

• what are we matching to

• ensure mass remains within …

• we match to ITV to ensure primary target remains within the contours

• ensure the mass remains within the ITV to ensure dose to OAR is being limited

  • evaluate position of patient upon matching to target

CBCT Procedure Step 10 - Apply shifts as to RADTH Imaging Guidelines

• Lung SBRT SAL

• Lung SBRT IRAL

SAL = apply all shifts

IRAL = probably 0.4 cm