Stereotactic device for Gamma Knife radiosurgery in experimental animals: technical note

Polymer gel in rat skull to assess the accuracy of a new rat stereotactic device for use with the Gamma Knife

PURPOSE

Accurate targeting is crucial for the irradiation of a small-volume animal brain. We propose an original method, based on a polymer gel, to determine the accuracy and reproducibility of irradiation using a new stereotactic frame.

METHODS

An in-house designed rat stereotactic frame, compatible with the Gamma Knife, was constructed. The rat brain was then removed through a small burr hole and the intracranial cavity was washed and filled with a polymer gel. This "gel brain" was irradiated by Gamma Knife and the irradiated volumes and coordinates were measured after the irradiation.

RESULTS

The position of the polymerized areas revealed that the stereotactic frame was able to accurately reproduce the same position of irradiation in each animal. The small standard deviation demonstrated the high reproducibility.

CONCLUSION

The polymer gel confirmed the ability of the rat stereotactic frame to accurately and reproducibly position a small animal for precise radiosurgery procedures.

Development of a stereotactic device for gamma knife irradiation of small animals

OBJECTIVE

The authors developed a stereotactic device for irradiation of small animals with Leksell Gamma Knife(R) Model C. Development and verification procedures were described in this article.

METHODS

The device was designed to satisfy three requirements. The mechanical accuracy in positioning was to be managed within 0.5 mm. The strength of the device and structure were to be compromised to provide enough strength to hold a small animal during irradiation and to interfere the gamma ray beam as little as possible. The device was to be used in combination with the Leksell G-frame(R) and KOPF(R) rat adaptor. The irradiation point was determined by separate imaging sequences such as plain X-ray images.

RESULTS

The absolute dose rate with the device in a Leksell Gamma Knife was 3.7% less than the value calculated from Leksell Gamma Plan(R). The dose distributions measured with GAFCHROMIC(R) MD-55 film corresponded to those of Leksell Gamma Plan(R) within acceptable range. The device was used in a series of rat experiments with a 4 mm helmet of Leksell Gamma Knife.

CONCLUSION

A stereotactic device for irradiation of small animals with Leksell Gamma Knife Model C has been developed so that it fulfilled above requirements. Absorbed dose and dose distribution at the center of a Gamma Knife helmet are in acceptable ranges. The device provides enough accuracy for stereotactic irradiation with acceptable practicality.