Beam characteristics of megavoltage beams at low monitor unit settings


Kemikler G. , Acun H.

PHYSICA MEDICA-EUROPEAN JOURNAL OF MEDICAL PHYSICS, cilt.27, ss.203-208, 2011 (SCI İndekslerine Giren Dergi) identifier identifier identifier

  • Cilt numarası: 27 Konu: 4
  • Basım Tarihi: 2011
  • Doi Numarası: 10.1016/j.ejmp.2010.10.007
  • Dergi Adı: PHYSICA MEDICA-EUROPEAN JOURNAL OF MEDICAL PHYSICS
  • Sayfa Sayıları: ss.203-208

Özet

Beam characteristics of a linear accelerator are of great importance for intensity-modulated radiation therapy (IMRT) to ensure precise and accurate dose delivery to patients. In step-and-shoot IMRT, each beam is delivered through a series of small, segmented fields at low monitor unit (MU) settings. In this study, the beam characteristics of both static (ST) and segmental intensity-modulated (IM) beams were investigated at various dose rates for 6 and 18 MV at low MU settings.
Abstract

Beam characteristics of a linear accelerator are of great importance for intensity-modulated radiation therapy (IMRT) to ensure precise and accurate dose delivery to patients. In step-and-shoot IMRT, each beam is delivered through a series of small, segmented fields at low monitor unit (MU) settings. In this study, the beam characteristics of both static (ST) and segmental intensity-modulated (IM) beams were investigated at various dose rates for 6 and 18 MV at low MU settings. 

Dose linearity was investigated for both the ST and the IM beams. For the ST beams, standard 10 x 10 cm(2) fields were irradiated with MU values ranging from 1 to 100. For the IM beams, 10 x 10 cm(2) and 15 x 15 cm(2) fields were used as subfields. The normalized dose (ND)/MU was obtained. Beam flatness and symmetry for 2 and 10 MU was measured by in-plane (G-T) and cross-plane (R-L) profiles using Kodak XV films. 

The largest dose/MU discrepancies were observed for 1 MU. For the ST beams, the beam output decreased up to 4.5% for 1 MU at the high dose rates of 6 and 18 MV. Dose variations were less than 1% for doses above 5 MU. No significant variation was observed in the beam profiles of the ST and the IM groups. Beam flatness and symmetry were close to 3% and 2% for 6 and 18 MV, respectively. Our results showed that dose linearity and delivery errors were close to 1% for doses above 5 MU, which is considered acceptable for both 6- and 18-MV ST and IM therapy.