Radiation Therapy : Calibration & verification


Precision Densitometer for Radiosensitive Film

UW–Madison researchers have developed a radiosensitive film densitometer that reduces light scattering and heat problems often encountered during scanning.

The device provides ‘point-to-point’ scanning in which the laser source and detector are moved in tandem over the film. The detector measures the light that is transmitted through the film at different locations and provides a signal at each location. A set of density values based on these signals then is output.

The film is supported in a holder only at its edges to remove scattering and interference caused by the glass support bed. Highly repeatable 25 micrometer resolution density measurements may be obtained.

IsoPhantom: A Customizable 3-D Phantom for Improved Radiation Dosimetry

A UW–Madison researcher has developed a system and method for utilizing available detector arrays with a highly configurable 3-D phantom to acquire accurate 3-D dosimetry information. This radiation dosimetry quality assurance system is configured to measure actual radiation dose delivered by the radiation delivery system during a planned medical procedure.

The system consists of a 3-D phantom extending along a longitudinal axis to form an exterior surface and an interior volume, a passage that extends the interior volume of the phantom to receive a detector array, an angular-compensation system coupled to the surface of the 3-D phantom to control any angular dependence of the detector array during dose measurement and a detector-angle adjustment system to allow positioning of the detector array with respect to the radiation source (see the figure below for a general schematic of the system). The system: 1) corrects for device-dependent angular dependence, 2) optimizes the measurement plane(s) to any plane rotated about the longitudinal axis to maximize sensitivity specific to each radiation plan, and 3) is capable of serving all 2-D dosimetry arrays. The system can be utilized with flexible analysis software to integrate 2-D array measurements into a 3-D analysis engine and graphical user interface.

Radiation Therapy Volume Phantom Using Film

UW-Madison researchers have developed a novel volume phantom for radiation therapy treatment verification. The phantom uses a single sheet of spirally rolled radiation-sensitive film to provide dose measurements in a volume. The rolled film is held within an equalizing ring of attenuating material, which provides greater uniformity in radiation measurement. The ring may also be extended to a hemisphere for improved modeling and simulation of treatments in a patient’s head region. The phantom also has an optical guidance system composed of four spheres, which is located on a frame on the dome and is placed into the patient’s mouth during treatment.