Linac Radiosurgery Phantom

Linac Radiosurgery and the Gamma Knife Phantom

SPHERICAL PHANTOM to Check Mechanical and Dosimetric Parameters of Treatment Units

	Homogenous dry water phantom with precise spherical shape – 16 cm diameter
	Displacement of maximum dose from center of sphere shows degree of accuracy and stability of the system
	Checks the dose-calculation algorithm for a homogenous sphere

Dosimetry in the Spherical 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 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

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.

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.

Head Phantom to Check Accuracy of the Treatment

	Total System Quality Assurance
	Checks the dose calculation algorithm with and without correction for tissue heterogeneities
	Measures the dose delivered to intracranial lesions

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.

Catalog Numbers

ST-1100A	SPHERICAL PHANTOM SYSTEM Includes the following:	ST-1150A HEAD PHANTOM Includes
ST-1101	Sphere with Standard Recess for Truncated Cones	Includes one TLD Dosimetric Cylinder and one One-Piece, Dry-Water Cylinder to Fill other Cavity
ST-1102	Truncated Cone for TLD and film Dosimetry	Includes 4 Spare Nylon Assembly Rods and 8 Spare Blind Nylon Nuts
ST-1103	TLD Dosimetric Cylinder
ST-1104	Adaptor for Dosimetric Cylinder	Options
	Includes 4 Spare Nylon Assembly Rods and 8 Spare Blind Nylon Nuts	ST-1115 Punch for Film
Options		ST-1116 Film Dosimetric Cylinder
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

Copyright © 2004 JZ Imaging & Consulting Last modified: 07/18/11

Copyright © 2004 JZ Imaging & Consulting
Last modified: 07/18/11