engleski

Peripheral Doses in Children Undergoing Gamma Knife Radiosurgery

It has been known for a long time that patients treated with ionizing radiation carry a risk of developing cancer in their lifetimes. Radiotherapy treatments typically involve the delivery of doses of tens of Gray to the target volume, whilst delivering lower doses to all other parts of the body. The carcinogenic properties of ionising radiation thus lead to a probability of inducing a second cancer in the irradiated patient. Factors contributing to the recently renewed concern about the radiation induced secondary cancer include improved cancer survival rate, younger patients population as well as emerging treatment modalities that can potentially elevate secondary exposures to healthy tissues distant from the target volume. Gamma Knife radiosurgery stereotactically delivers a high single dose of external radiation to a small well-defined intracranial lesions. Due to a large amount of dose delivered in a single fraction (10 – 30 Gy) in stereotactic radiosurgery, dose outside the treatment volume is an important issue. The aim of study was to measure the out-of-field doses during the Leksell Gamma Knife Model C radiosurgery for children. The children population was chosen due to their higher susceptibility to radiation. Also, due to smaller size of their bodies, the larger doses are expected to all out-of-field tissues and organs than for adults for the same irradiation conditions. The purpose was to identify doses delivered to the eye lens, thyroid glands, breasts, sternum, upper abdomen and gonads from the doses measured with dosimeters placed on the some positions on the surface of the patients. The relation of the organ doses and doses on the surface was determined by measurements using the anthropomorphic phantom (CIRS, ten-year old child). Additionally, surface doses were measured on the patients ; there were 5 patients between 4 and 14 years old. At the every point of measurement two types of thermoluminescent dosimeters were placed, LiF:Mg, Ti and LiF:Mg, Cu, P and two radiophotoluminescent glass dosimeters (GD-352M). The agreement between three types of dosimeters was on average within 6 %. Doses on the patients have shown large dissipation for the same positions above specified organs. This is due to different influential parameters (position and volume of the target, height and weight of patient, irradiation dose). For example, doses to the eyes and gonads varied from 0.7% to 2.55% and from 0.05% to 0.22% of the mean target dose, respectively. Results of organ dose measurements in the phantom and on the surface of the phantom show uncertainty of about 20 % of the organ dose estimations from the surface dose measurements.

Gamma Knife; Peripheral doses; LiF:Mg; Ti; LiF:Mg; Cu; P; RPL (GD-352M); child phantom

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