title: Dosimetry of stereotactic radiosurgery using lithium formate EPR dosimeters.
abstract: Small lithium formate EPR (electron paramagnetic resonance) dosimeters (diameter 3 mm, height 2 mm) were produced and employed for 2D dosimetry of stereotactic radiosurgery (SRS). An anthropomorphic head phantom with an in-house made insert holding 45 lithium formate dosimeters was used. A spherical target was outlined centrally in planning CT images of the head and an SRS dose plan with three arcs was made using the iPlan planning system. Beam collimation was achieved with the BrainLAB m3 micro-MLC. The minimum target dose was 15 Gy. The planned dose distribution was compared to measurements. For dosimetry, a dosimeter calibration series was generated with doses from 1 to 20 Gy. At the treatment unit, three replicate measurement series were performed. The measurements gave on average 2.2% lower dose at the plateau of the dose distribution compared to the dose plan. Larger differences were seen in the penumbra, where the dose plan underestimated the dose gradients. By repeated measurements, the systematic and random error in the SRS delivery was estimated to less than 1 mm. In conclusion, the planning system produced an intracranial dose distribution with tolerable accuracy. Furthermore, small lithium formate EPR dosimeters were useful for measuring SRS dose distributions.
authors.affiliation: Department of Medical Physics, Division for Cancer Medicine and Radiotherapy, The Radium Hospital, Oslo University Hospital, Montebello, N-0310 Oslo, Norway. einar.waldeland@oslo-universitetssykehus.no
authors.forename: Einar
authors.initials: E
authors.lastname: Waldeland
authors.forename: Magnus
authors.initials: M
authors.lastname: Hörling
authors.forename: Eli Olaug
authors.initials: EO
authors.lastname: Hole
authors.forename: Einar
authors.initials: E
authors.lastname: Sagstuen
authors.forename: Eirik
authors.initials: E
authors.lastname: Malinen
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005561:Formates; D006801:Humans; D019047:Phantoms, Imaging; D011874:Radiometry / Q000295:instrumentation*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results
chemical_list: D005561:Formates; C030544:formic acid