Phantoms for Linac Radiosurgery and the Gamma Knife

Spherical phantom ST-1100A
For Checking Mechanical and Dosimetric Parameters of Treatment Units

STandard Cone

This is a dry-water cone, which fits precisely in a recess in the sphere. It accepts the dosimetric cylinder (TLD or film). It houses the dosimetric cylinder at the center of the sphere.

Optional Cone

This is molded to locate the measuring volume of an ion chamber at the center of the sphere. This cone is custom molded to suit the particular ion chamber specified by the customer.

Dosimetry in the Sperical Phantom

When the center of the sphere is used as the target for testing the treatment unit, it must indicate the relationship between the point of maximum dose and the target. These should closely coincide for an accurate system.

A three-dimensional dosimetry cylinder at the center of the sphere measures both the deviation of the maximum dose from the target and the gradient of the dose along the three orthogonal axes of the sphere.

The TLD Dosimetric Cylinder ST-1103

The TLD dosimetric cylinder is a stack of dry-water disks of 44 mm in diameter. Seven of the disks have concentric rings of holes for TLD rods, 1 mm in diameter and 3 mm long. Disk #4 is in the central plane of the cylinder. A smaller target disk is at the center of this disk. It has a Hounsfield number of about 130 for visibility in a CT scan.

The disks are assembled tightly by two nylon rods and round, blind nuts, which locate the cylinder precisely, linearly and angularly, in both sphere and head.


 
 
 

The Film Dosimetric Cylinder ST-1116

This is an optional cylinder, interchangeable with the TLD cylinder. It is built up of 11 film disks and 12 dry-water disks with the same nylon assembly rods and blind nuts.

A simple fixture is supplied so the user can punch the film disks from film sheets.


 
 
 
 

Head Phantom for Stereotactic Radiosurgery ST-1150A
to Check Accuracy of the Treatment

The Sphere was designed in conjunction with Timothy D. Solberg, Ph.D.

Dosimetry in the Head Phantom

Provisions are made for installation of the dosimetric cylinder at two locations in the cranium. One is on the CC axis of the head close to the apex. The other is near one side of the head at about ear level. Both cylinders are perpendicular to the transverse planes of the head.

Since the dose at only one location is to be measured at a time, the other location is filled with a dry-water cylinder with no dosimetric provisions. The target can be located uniquely by an initial CT scan.

Disc with TLD Rods

Disc with TLD Rods
Two-dimensional dose distribution (measured in the central plane using 1 x 3 mm TLD rods)

Two-dimensional dose distribution
(measured in the central plane using 1 x 3 mm TLD rods)

Catalog Numbers for Linac Radiosurgery & Gamma Knife

ST-1100A Spherical Phantom System
Includes the following:
ST-1101 Sphere with Standard Recess for Truncated Cones
ST-1102 Truncated Cone for TLD and Film Dosimetry
ST-1103 TLD Dosimetric CylinderST-1104 Adaptor for Dosimetric Cylinder
Includes 4 Spare Nylon Assembly Rods and 8 Spare Blind Nylon Nuts.

Options
ST-1106 Truncated Cone for Ion Chamber (includes molding or machining to install ion chamber at center of sphere to user’s specification)
ST-1116 Film Dosimetric Cylinder
NOTE: If both the sphere and head are purchased, only one dosimetric cylinder is needed.


ST-1150A Head Phantom
Includes:
Includes one TLD Dosimetric Cylinder and one One-Piece, Dry-Water Cylinder to Fill Other Cavity.
Includes 4 Spare Nylon Assembly Rods and 8 Spare Blind Nylon Nuts.

OPTIONS
ST-1115 Punch for film
ST-1116 Film Dosimetric Cylinder
The Sphere was designed in conjunction with Timothy D. Solberg, Ph.D.
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