A Study on the Peripheral Dose of 6MV X-ray Beam

6 MV X선의 주변선량분포

  • Choi, Doo-Ho (Department of Therapeutic Radiology, College of Medicine, Seoul National University) ;
  • Kim, Il-Han (Department of Therapeutic Radiology, College of Medicine, Seoul National University) ;
  • Ha, Sung-Whan (Department of Therapeutic Radiology, College of Medicine, Seoul National University) ;
  • Park, Charn-Il (Department of Therapeutic Radiology, College of Medicine, Seoul National University)
  • 최두호 (서울대학교 의과대학 치료방사선과학 교실) ;
  • 김일한 (서울대학교 의과대학 치료방사선과학 교실) ;
  • 하성환 (서울대학교 의과대학 치료방사선과학 교실) ;
  • 박찬일 (서울대학교 의과대학 치료방사선과학 교실)
  • Published : 1989.06.20

Abstract

The peripheral dose, defined as the dose outside therapeutic photon fields, was estimated for 6MV X-ray linear accelerator. The measurements were performed using silicon diode detectors controlled by automatic controlled water phantom. The effects of field size, collimator position, presence or absence of wedge filter, and wedge angle were analyzed. The results were as follows 1. The peripheral dose decreases as the distance from field margin increases and it is more than 2.4% of central axis maximum dose even at 15cm distance from field margin. 2. Maximum build-up of peripheral dose is at 2-3 mm from the water surface and drops to a minimum at 1.5cm depth and then the dose increase again. 3. The peripheral dose increases as the field size. increases. At the short distance from field margin, the difference of peripheral dose between 5 $\times\;5cm^2$ and 20 $\times\;20cm^2$ field size reaches more than 2 fold. 4. The peripheral dose is higher along the upper collimator than along the lower collimator. The differences is less than 1%. 5. The presence of wedge filter increases peripheral dose. And the peripheral dose is higher along the blade side of wedge filter than along the ridge side. The difference is about 3% at 5cm distance from the field margin for 15 $\times\;15cm^2$ field size and 60$^{\circ}$ wedge filter. 6. The Peripheral dose of wedge filter increases as the wedge filter angle increases and the increasing ratio is about 2 fold in 60$^{\circ}$wedge filter compared with open field.

Keywords