Dosimetric characteristics of a new linear accelerator under gated operation

Abstract

Respiratory gated radiotherapy may allow reduction of the treatment margins, thus sparing healthy tissue and/or allowing dose escalation to the tumor. However, current commissioning and quality assurance of linear accelerators do not include evaluation of gated delivery. The purpose of this study is to test gated photon delivery of a Siemens ONCOR Avant‐Garde linear accelerator. Dosimetric characteristics for gated and nongated delivery of 6‐MV and 15‐MV photons were compared for the range of doses, dose rates, and for several gating regimes. Dose profiles were also compared using Kodak EDR2 and X‐Omat V films for 6‐MV and 15‐MV photons for several dose rates and gating regimes. Results showed that deviation is less than or equal to 0.6% for all dose levels evaluated with the exception of the lowest dose delivered at 25 MU at an unrealistically high gating frequency of 0.5 Hz. At 400 MU, dose profile deviations along the central axes in in‐plane and cross‐plane directions within 80% of the field size are below 0.7%. No unequivocally detectable dose profile deviation was observed for 50 MU. Based on the comparison with widely accepted standards for conventional delivery, our results indicate that this LINAC is well suited for gated delivery of nondynamic fields.PACS numbers: 87.56‐By, 87.66‐Cd, 87.66‐Jj

Time delays and margins in gated radiotherapy

“…Overall, linear accelerators appear very accurate at delivering dose in gated modes, for static as well as dynamic deliveries. ( 8 , 14 – 18 ) Our results are consistent with these findings. A few articles have addressed the measurement of time delays.…”

Gating characteristics of an Elekta radiotherapy treatment unit measured with three types of detector

“…Thus these measurements are consistent with the Varian data. Kriminski et al (2006) studied gating of the Siemens ONCOR system. They also studied a range of gating periods with 50 % duty cycle.…”

“…Previous authors have reported gating results for three manufacturers: Varian Wang 2000 andJin andYin 2005); Siemens (Kriminski et al 2006 andWeibert et al 2009) and Brainlab (Hugo et al 2003 andVerellen et al 2003). The Varian system uses a gridded gun for gating.…”

Dosimetry of a linear accelerator under respiratory gating

“…Nevertheless, since dose calculations for treatment planning are usually based on data gained for ungated irradiation, it is very important to check whether gating influences the beam characteristics of the linear accelerator before introducing respiratory gating into clinical routine [18][19][20][21].…”