Journal of Medical Physics
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Year : 2012  |  Volume : 37  |  Issue : 1  |  Page : 4-7

Dose linearity and monitor unit stability of a G4 type cyberknife robotic stereotactic radiosurgery system

1 Department of Radiotherapy, Apollo Speciality Hospital, Chennai, India
2 Department of Medical Physics, Anna University, Chennai, India

Correspondence Address:
H Sudahar
Department of Radiotherapy, Apollo Speciality Hospital, 320, Padma complex, Mount Road, Chennai - 600 035
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-6203.92714

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Dose linearity studies on conventional linear accelerators show a linearity error at low monitor units (MUs). The purpose of this study was to establish the dose linearity and MU stability characteristics of a cyberknife (Accuray Inc., USA) stereotactic radiosurgery system. Measurements were done at a depth of 5 cm in a stereotactic dose verification phantom with a source to surface distance of 75 cm in a Generation 4 (G4) type cyberknife system. All the 12 fixed-type collimators starting from 5 to 60 mm were used for the dose linearity study. The dose linearity was examined in small (1-10), medium (15-100) and large (125-1000) MU ranges. The MU stability test was performed with 60 mm collimator for 10 MU and 20 MU with different combinations. The maximum dose linearity error of −38.8% was observed for 1 MU with 5 mm collimator. Dose linearity error in the small MU range was considerably higher than in the medium and large MU ranges. The maximum error in the medium range was −2.4%. In the large MU range, the linearity error varied between −0.7% and 1.2%. The maximum deviation in the MU stability was −3.03%.

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