Elekta Synergy S Linear Accelerator Lab Analysis

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Elekta Synergy S linear accelerator (LINAC) was used to produce the 6, 10, and 15MV photon beams for measurements. The accelerator is fitted with the new Agility multileaf collimators (MLC) thinner than the previously used MLC’s to improve a field definition (Kantz et al. 2015; Thompson et al. 2014). The quality assurance was carried out monthly to ensure the LINAC response does not vary from the commissioning data (CPQR 2013). The LINAC has been calibrated to 100 cGy/MU at Dmax for a 10×10 cm2, and daily output checking was performed to ensure that LINAC operated within the ±3% limit (Andreo et al. 2006). 3.2 Film
3.2.1 Kodak X-OMAT V/EDR2 film
3.2.2.1 Calibration curve
The radiographic EDR2 films which were used for investigation of PDD,
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The right image shows the sensitive volume of a diode or diamond detector
The detectors were aligned visually with the cross hairs (centre of the beam, CAX), and then the OmniPro software is used to correct the positioning of the detector. The servo measured a depth dose curve to find the position of Dmax and 40 % of a maximum dose. Then in-line and cross-lines profiles are measured at these depths, and the position of the 50% level was determined for these profiles. The positions of the 50% for the profiles are compared and the offsets are then displayed.
3.3.2.2 Voltage
Diode and micro-diamond detectors are semiconductor detectors thus no voltage is applied, CC01 required 300 volts to allow for optimal data
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The two detector method employs the use of a field and a reference detector. The reference detector is used to minimize the effect of dose rate fluctuations (Das et al. 2008). The single detector method utilizes the step-by-step mode of data collection, this mode moves the detector at specified step sizes and stops for a specified time. This minimizes the linac dose rate fluctuation which is the same function performed by the reference detector. The pause time was determined by comparing the profiles obtained from two detector method and the single detector method to optimize both the beam on time and the noise.
The single detector mode is further optimized by utilizing two algorithms that are within the Omnipro software. The gradient algorithm is used in measuring beam profiles as the detector’s step sizes alter if two positions have a difference that is more than predicted. The breakpoint algorithm was used for PDD measurements, as the algorithm changed the step sizes after a certain depth was reached. The output factors were measured by collecting signals with the sensitive volume of the detector placed at 10cm

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