Lucy 3D QA Phantom - Frequently Asked Questions

Frequently Asked Questions

Do I need both the Standard Base and a specific frame interface when I purchase the Lucy Phantom?

The Standard Base that comes with the Lucy Phantom is ideal for use with frameless linac based stereotactic radiosurgery QA. Accessories for Mask adaptors are available should you use this positioning fixation. If your facility utilizes a frame based stereotactic program it is advisable to purchase the specific frame interface for your system. These interfaces are designed to position the Lucy Phantom precisely within your specific system’s coordinate space so that the center of the phantom is at the 0,0,0 position (this point is described as 100,100,100 in some systems).

What is meant by end-to-end QA of my stereotactic system?

There are many systems involved in the planning and treatment of a patient with stereotactic radiosurgery. The patient will be imaged utilizing CT, MR and/or PET imaging. A treatment planning system (TPS) will then be used to create a treatment plan based on the images or fused sets of images from different systems. The plan will then be delivered on the treatment machine. At each step in this process it is critical to verify the precision and accuracy so that small cumulative errors do not add up to be significant. The Lucy 3D QA Phantom utilizes an innovative design that incorporates interchangeable inserts allowing you to assess each stage giving you end-to-end QA of the entire treatment process to within 0.1mm. All cumulative uncertainties are assessed from imaging through delivery ensuring confidence in your overall stereotactic program.

How accurate is the Lucy 3D QA Phantom?

The Lucy 3D QA Phantom is manufactured so that all critical components are accurate to a tolerance of 0.1 mm or less. Rameseshan and Heydarian were able to, “successfully demonstrate that a comprehensive quality assurance program could be developed and performed using a commercially available high precision Lucy phantom.”1 Please contact Standard Imaging for a copy of the paper.

What slice thickness should I use with the Lucy 3D QA Phantom?

It is advisable to scan the Lucy phantom with a similar setup as that used clinically. It has been shown that scanning the phantom with alternate slice thicknesses can shed light on issues that can arise from these different setups such as the ability of the treatment planning system to reproduce target volumes. Performing tests at different thicknesses could allow the user to determine an optimal slice thickness for their purposes.

Can I use the Lucy 3D QA Phantom to verify that my imaging isocenter is the same as my treatment isocenter?

The Lucy 3D QA Phantom includes several inserts that can be used to verify that the imaging isocenter coincides with the treatment beam isocenter. To do this a CT scan is performed with the insert in place. The image set is then imported into the treatment planning system where the absolute center of the phantom is determined and aligned with isocenter of a simple plan. DRR images in the plane(s) of the imaging system are created and saved. The phantom is then positioned in the head frame or aligned to lasers using the Standard Base and images are acquired. These images are then compared to the DRR from the planning system and a 2D/2D match is performed to determine the coincidence.

What size film does the Lucy 3D QA Phantom require?

Most of the inserts that will accept film use 2.5 x 2.5 cm film. Gafchromic film is available in 5.0 x 5.0 cm sheets which can then be cut into four-2.5 x 2.5 cm pieces suitable for use with the Lucy inserts.

How was the size of the sphere chosen?

The 14 cm diameter is the same diameter as one of the original developers head measured at the temples.

How can I register images that I have taken of the Lucy 3D QA Phantom in the different systems I will be viewing and manipulating them in?

The Lucy 3D QA Phantom features a single imbedded fiducial marker in the sphere that indicates the position of the phantom in images. This marker indicates the bridge of the nose for cranial treatments but may be used as a point in space for extracranial treatment.

When would I use the Standard Base with the Lucy 3D QA Phantom?

The Standard Base is used when doing QA for frameless stereotactic radiosurgery. Precision leveling and rotational alignment allows the simulation of patient positioning for frameless cranial or body SRS. The three dimensional geometry of the patient set-up can be examined through 360 degrees of rotation in the transverse, sagittal and coronal planes. The Standard Base can also be utilized with the Mechanical Alignment Pointers for tests such as the Winston-Lutz test for verification of the radiation isocenter for individual stereotactic radiosurgery treatments.

How can I position Lucy in an MRI machine?

The Lucy 3D QA Phantom and frame interfaces are designed without any ferrous materials included. As long as your stereotactic frame is free of ferrous metals you should be able to position the phantom using your frame system. You can also utilize the head pillow or rest that comes with your MRI system to set the Lucy Sphere on for imaging.
1. Ramaseshan R, Heydarian M Comprehensive quality assurance for stereotactic radiosurgery treatments Phys. Med. Biol. 48 (2003) N199-N205

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