Temperature Equilibrium 5
2 Operation
Temperature Equilibrium
The MapCHECK 3 should be at the same temperature as the treatment room before use. If the
MapCHECK 3 is not stored at treatment room temperature, allow the device to reach temperature
equilibrium before acquiring measurements.
Temperature in the MapCHECK 3 detector array will remain stable when the device is continuously
connected to AC power; the device can remain connected to AC power in the treatment room
provided that the electronics area of the device does not receive direct radiation.
MapCHECK 3 measures temperature change in the detector array and applies temperature
correction to dose calculations.
Background Measurement
A background measurement is collected at software launch to establish the background
correction factor for each detector. SNC Patient software also evaluates MapCHECK 3
measurements while the beam is off and updates background correction factors if beam off
intervals of sufficient duration are found.
After background is completed and stored, the Background box displays “Yes” in green text. If the
‘Background’ box in the toolbar displays “No” in red text, collect a background measurement by
selecting Setup > Collect Background from the menu. The background period can be anywhere
from 30 to 300 seconds.
Ensure that the beam is off when measuring background. If the radiation measurement threshold
is exceeded during background measurement, the process stops and the previous approved
background is applied.
Array Calibration
Array calibration determines relative sensitivity differences between MapCHECK 3 detectors and
stores them as individual correction factors to be applied to the raw net measurement signals
from each detector.
Array Calibration Conditions
For optimal results, it is recommended to perform one array calibration per beam energy and with
the same buildup planned for measurement.
Array Calibration Modes
SNC Patient for MapCHECK 3 has three array calibration modes:
• Standard (IMRT) — Select this option for QA measurements collected with the beam
normal to the surface of the device and exposure for all angles administered at the same
angle i.e., beam straight down, anteroposterior (AP).
• Rotational (VMAT) — Select this option for QA measurements of IMRT or rotational
deliveries. This mode includes the same steps as Standard (IMRT) array calibration as
well as the following steps:
• Posteroanterior (PA) measurements to generate angular dependence correction factors.
• Open field measurements with MapCHECK 3 in MapPHAN.
• MapPHAN Factor — Select this option to modify the last two steps of a completed VMAT
array calibration for one of the following reasons:
• To generate a VMAT array calibration for each MapPHAN accessory (5 cm and 10 cm).
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