Enabling state of the art radiotherapy
On-board kV imaging
Modern linear accelerators have on-board kV imaging equipment. This enables image guided radiation therapy (IGRT), using either kV or CBCT. Implanted fiducial markers makes it easy and safe for the medical staff to determine the need for patient repositioning prior to each fraction (interfraction motion management).
Matching kV to DRR
The fastest and easiest method is to capture two orthogonal kV images and compare them to Digitally Reconstructed Radiographs (DRRs). The two sets of images are blended over each other and moved so that the markers in the kV image overlap with the corresponding structure in the DRR. Images courtesy of Dr Marcio Fagundes.
Matching CBCT to CT
It is sometimes beneficial to also visualize soft tissue using cone beam computed tomography (CBCT). The CBCT is then compared to CT. The two image sets then have to be compared in all three dimensions. Images courtesy of Dr Marcio Fagundes.
Fiducial markers makes positioning more precise
A recent study, with corresponding author from the Icahn School of Medicine at Mount Sinai, compared 2-dimensional kV orthogonal imaging with fiducial markers (kV-FM) and soft-tissue CBCT (ST-CBCT) for IGRT of prostate.
They concluded that “The kV-FM-based daily image guided alignment for IMRT of prostate cancer is more precise than ST-CBCT, as assessed by a physician’s ability to reproducibly align images. Given the magnitude of the error introduced by inconsistency in making ST-CBCT alignments, these data support a role for daily kV imaging of FM to enhance the precision of external beam dose delivery to the prostate.”
Source: Goff PH, Harrison LB, Furhang E, et al. 2D kV orthogonal imaging with fiducial markers is more precise for daily image guided alignments than soft-tissue cone beam computed tomography for prostate radiation therapy. Learn more.
Elekta XVI seed match
Some accelerators have software that can be used to automatically identify implanted markers in CBCT and CT. It may then also be possible to capture CBCT with lower imaging dose. Note: Elekta is a registered trademark of Elekta AB.
Varian TrueBeam Auto Beam Hold
Varian’s Advanced IGRT & Motion package includes the Auto Beam Hold (ABH) feature. ABH is an imaging technique that monitors the patient during radiation treatments. This is achieved by detecting implanted fiducials in radiographic images acquired during treatment. The treatment beam is paused when ABH observes a discrepancy between the planned markers positions and the detected positions. Learn more
We believe that the combination of Gold Anchor and ABH creates unprecedented opportunities to provide safe and economical radiotherapy with high accuracy and precision.
Gold Anchor fiducial markers in prostate.
Gold Anchor fiducial markers in liver.
Gold Anchor fiducial markers in prostate, automatically detected by Varian TrueBeam®. Images courtesy of the Sahlgrenska University Hospital.
Note: Varian and Varian Medical Systems are registered trademarks, and TrueBeam® is a trademark of Varian Medical Systems, Inc.
“We have used Gold Anchor with TrueBeam triggered images in prostate and liver since the spring of 2019. By implementing automatic marker detection with periodic kV imaging we can now monitor intrafraction motion during radiotherapy. This provides a new level of confidence when adopting more hypofractionated treatments.”
Gold Anchor is great for proton therapy
- The thinner (0.28 mm diameter) Gold Anchor markers cause very little dose perturbation when they are implemented with a line shape.
- The high density material – gold – provides good visibility with kV imaging.
- The film measurements below show dose perturbation for a Gold Anchor implanted with a line-shape (assumed to form more of a zigzag shape) vs. regular gold markers.
Dose perturbation downstream of the markers with the markers oriented perpendicular to the beam axis near the end of the SOBP (Spread-Out Bragg Peak). The dose is normalized to an unperturbed region.
Source: Extract from “Investigation of dosimetric effects of radiopaque fiducial markers for use in proton beam therapy with film measurements and Monte Carlo simulations”
Gold Anchor can be tracked with the Cyberknife® system
- It is recommended to insert Gold Anchor as a ball shaped or tadpole shaped marker.
- However, 10 mm Gold Anchor markers can also be tracked when inserted as a line shape marker.
Gold Anchor has so far been used for Cyberknife® treatments of lung, liver, pancreas, adrenal gland, and prostate.
- CyberKnife-based prostate cancer patient radioablation – Article (Gliwice, Poland)
- CyberKnife markers visible on CT and MRI – Poster at the SRS/SBRT Scientific Meeting 2014 (Austin CyberKnife)
- Using foldable Gold Anchor markers for fiducial tracking with the CyberKnife – Presentation at the 2011 CyberKnife® Robotic Radiosurgery Summit (Philadelphia CyberKnife)
Note: Cyberknife is one of the trademarks and/or registered trademarks of Accuracy Incorporated in the United States and other countries.
Gold Anchor enables a safer and easier radiation process.
Man weighing 170 kilograms, 375 pound, with kidney cancer.
Pancreatic cancer. Circles indicates five days inter-fraction tumor movement.
Gold Anchor as a reference for an earlier field border in a new metastasis close to earlier treatment.
Gold Anchor as a reference for the caudal field border in a rectal cancer treatment.
- More accurate and precise than the frame technique – the marker indicates the true position.
- Reduced setup time in the treatment room compared to the xyz coordinate fram technique – better throughput.
- Intuitive and easy matching of orthogonal or CBCT images to DRR’s – increased safety and reduced risk of treatment errors.
Gold Anchor can be used be used with TomoTherapy® system
The best visibility is achieved by implanting a 0.4x20mm marker (GA200-20-B) with a ball shape.
These images show a Gold Anchor used for positioning of a liver SBRT patient. The CT study from the treatment planning step. The MVCT image was acquired with the TomoTherapy® Hi Art® treatment system immediately prior the treatment.
Note: TomoTherapy® and Hi Art® are registered or common law trademarks of TomoTherapy Incorporated in the United States and other countries.