engleski

Out-of-field organ doses and cancer risks for Gamma Knife treatment with and without automatic positioning system

Gamma Knife (GK) radiosurgery is highly precise method for treatment of small intracranial lesions with high single radiation dose. Leksell Gamma Knife unit Model C (Elekta AB, Stockholm, Sweden) contains 201 fixed Co-60 gamma sources arranged in a hemispherical surface. Narrow photon beams are collimated and focused at a single focus (isocenter) by fixed primary and exchangeable secondary collimator system. Secondary collimator system consists of four collimator helmets that produce almost spherical dose distribution of diameter 4, 8, 14 or 18 mm around isocenter. In order to conform radiological dose distribution to the size and shape of a tumour volume and to spare neighboring critical healthy tissues, clinical treatment plans are usually built with more than one collimator helmet, and for each helmet more than one isocenter (i.e. patient’s head has to be repositioned within one helmet so that focus moves to different target points inside tumour). Helmet and/or isocenter exchanges are performed when patient is not in the treatment position. During transportation of the patient in and out of the treatment position additional dose to patient, that is not taken into account by GK treatment planning system, is accumulated. The Leksell Gamma Knife Model C can use for repositioning of the patient’s head robotic automatic positioning system (APS) and in that case couch with patient has to travel only to the defocus position. When APS is not mounted, to change the isocenter position patient has to travel fully out of the treatment unit. In this work comparison of out-of-field organ doses and cancer risks for one GK treatment of the same clinical cases with and without APS will be presented. Out-of-field organ doses were measured with radiophotoluminescent (RPL) dosimeters placed in the organs of an antrompomorphic phantom representing 10 year old child and cancer risks are estimated using methods presented in BEIR VII.

out-of-field organ dose; gamma knife

nije evidentirano