Treatment of Liver Metastases Using an Internal Target Volume Method for Stereotactic Body Radiotherapy

The overall goal of this motion management and image guided technique is to use stereotactic body radiotherapy or SBRT to treat liver metastases. This measure can help make SBRT a significantly more feasible and accessible option for treating liver metastases. The main advantages of this technique are that it is non-invasive, does not require extensive training, and has more manageable treatment and it work for us for both patients and the staff.

We first had the idea when we compare fiducial marker, air breath control and full-dimensional computed tomography or CT with abdominal compressor use in the irradiation of hepatocellular carcinomas. Demonstrating the procedure will be Yang-Bin Lin, a technician from our department. To begin place the patient in the supine position, head first with the arms over the head, and secure the patient onto the couch.

Make a personalized evacuated vacuum bag according to the patient’s position and body shape, and cover the patient with the cover sheet. Apply an abdominal compressor, and mark the depth of the compressor. Then, place a breath tracking sensor on the chest wall, and monitor the respiratory wave form.

To acquire CT images for radiotherapy treatment planning, first select the 4D-CT mode with a three millimeter slice thickness. Click go on both the screen and the control panel to conduct a SERV-U scan for obtaining both anterior, posterior, and lateral views of the patient. On the helical scan page, set the CT scanning coverage area to extend from the apex of both lungs to five centimeters from the caudal border of the liver.

On the pulmonary gating scan page, set the 4D-CT scanning field to cover the liver, extending three to five centimeters from both the cranial and caudal liver borders. When the respiratory wave form has been stable for three minutes, inject 100 milliliters of an appropriate contrast agent through an 18 gauge IV catheter into the antecubital vein At a rate of four to five milliliters per second. 15 seconds after all of the agent has been injected, conduct a contrasted contiguous helical CT scan.

Then, click next series to conduct a 4D-CT scan. For radiotherapy treatment planning, first import the images from the CT simulation and diagnostic scans into the planning system. To contour the metastatic tumors into gross tumor volume and adjacent organs at risk, first select an organ of interest, and a contour tool to select the organ in each slice of the CT slice.

The gross tumor volume can be determined using the diagnostic images from the CT scan, MRI, and opaque scans. As well as the contrast images from the CT simulation. Next, contour the internal target volume of the tumors according to the organ motion observed on the dynamic tracking images adding a five millimeter margin to the internal target volume to obtain the planning target volume.

Observe all of the dynamic images of the entire liver area to ascertain the tumor and liver movement during respiration. Then contour the internal target volume in all of the dynamic slices to encompass the entire tumor motion. On the day of the treatment, first identify the patient by name, birth date, and ID card.

Position the patient in the vacuum bag. Place the cover sheet, and fix the abdominal compressor as just demonstrated. When the patient is ready, acquire a 4D cone beam CT image, and adjust the couch to corelate the target location obtained on the 4D cone beam CT image to that obtained on the simulation CT images.

At the end of the scan, load the image into the image guided radiotherapy system. The upper left and lower right images are from the CT simulation for the contouring and treatment planning. The upper right and lower left images are from the 4D cone beam CT.Compare the difference of patient position according to images from CT simulation, and confirm treatment location daily.

Then, manually adjust the couch position to eliminate set-up error of patient position. Record and print out the parameters for daily adjustment. Then, confirm the treatment plan and the system configuration, and click go to start the treatment, monitoring the patient during the entire treatment using real-time cameras to ensure patient safety.

In this study, an SBRT treatment plan demonstrated successful radiotherapy planning for two hepatic metastatic tumors for which surgery or another local ablation therapy was not feasible. The two metastatic tumors were three centimeters and 4.3 centimeters in length with 13 cubic centimeter and 22 cubic centimeter volumes respectively. The prescribed dose was 50 grays in five fractions, and the four partial beam arcs were directed to avoid the organs at risk.

These dose volume histograms illustrate the coverage over both of the tumors with 100%of the volume of the planning target volume covered by greater than 95%of the prescribed dose, and with the radiation doses to the organs at risk, within an appropriately restricted range. Once mastered, the CT simulation and image guidance before each fraction steps, can be completed in 10 minutes each if they are performed properly. While attempting this procedure, it’s important to remember to monitor the patient’s condition to confirm that they can tolerate and breathe normally under the abdominal compression.

After its implementation, this technique has paved the way for radiation oncologists in the inspiration of exerting local control of all local metastases in the liver without invasive motion management or inconvenient image guidance techniques in SBRT. After watching this video, you should have a good understanding of how to adapt a 4D-CT scan with abdominal compressor in image guided radiotherapy and the internal target volume in SBRT for liver metastasis. As not every patient is eligible for or willing to have an invasive procedure, this technique provides a non-invasive convenient option that requires minimal training for local operation for a oligometastasis in the liver.