A comparison of extra-cranial radiation exposure during Gamma Knife Stereotactic Radiosurgery between Model C and Perfexion©

Keywords: radiosurgery, Brain Tumors, Dose Prescription, physics, absorbed dose

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     Different radiosurgical devices may have different body exposure characteristics.
To compare superficial doses on four body regions — lens, thyroid, sternum, genitals — following Gamma Knife Radiosurgery (GKR) performed with Gamma Knife Model C and Gamma Knife Perfexion©.
     Thermoluminescent LiF-GR200A dosimeters were used. At first, they were applied on the surface of an Alderson-Rando anthropomorphic phantom and standard treatment plan for a mesial occipital lesion was simulated. Afterwards, the same batches were used for measuring the superficial doses to lens, thyroid, sternum and genitals on 52 patients who underwent GKR with Model C and 51 patients who underwent GKR with Perfexion© for intracranial tumors and functional disorders.  In both series similar treatment parameters were administered: prescription dose range was 10-45 Gy and prescription dose volume range 0.09-28.5 cm3. Following the same methods, we measured the absorbed dose values after a simulated stereotactic radiosurgical treatment with a LINAC — Clinac 2100 Varian — reproducing the same conditions for dose planning previously performed with GK.
     The values of mean absorbed dose for different body regions are 28.51 cGy for lens, 5.67 cGy for thyroid, 4.51 cGy for sternum, 0.83 cGy for genitals with Gamma Knife Model C and 17.41 cGy for lens, 0.81 cGy for thyroid, 0.32 cGy for sternum, < TLD lower limit detectable for genitals with Gamma Knife Perfexion©.   The measured absorbed doses for the simulated Linac radiosurgery treatment on Alderson-Rando phantom were: 59.61 cGy for lens, 37.9 cGy for thyroid, 10.34 for sternum and 0.68 cGy for genitals.
     Using these techniques we could compare radiation administration to the body using different radiosurgical devices.
     These data may serve as a benchmark.


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