Users Manual Part 2

Clinical User’s Guide IBA | 15-3|
Volume 1 - Treatment Session
|Part II - Using Treatment Room Equipment Resetting a Dose Counter Electronic Unit |
The DCEU also emits beeps while the dose is being delivered. A number of audible
pulses are emitted with a frequency proportional to the momentary dose rate. The
DCEU contains a volume adjustment control and a nominal dose rate selector.
The normal end to an irradiation is determined by the Therapy Control System(TCS),
which also receives input from the ionization chambers to monitor the dose.
Because the DCEU serves as a redundant device, the target dose entered on the
DCEU is normally slightly higher than the required dose entered on the TCS.
X-ray images taken with the retractable X-ray tube located inside the nozzle,
accumulate counts on the DCEU. Therefore, the DCEU must be reset following all
irradiations in order to avoid reaching the required dose during the patient setup
procedure. If the required dose is reached during the patient setup procedure, the
nozzle preparation procedure will be canceled.
In addition to entering a target dose on the DCEU, the counters shall be reset before
an irradiation can begin. The TCS provides the enabling signal for resetting and will
not allow the beam to enter a TR until the DCEU counters have been reset.
To reset the DCEU:
1. When the led next to red Reset button is lit (green), press the Reset button.
2. Use the buttons of the Preset display to set the counter to a value that is slightly
higher (e.g., 105%) than the required dose. There is a button to count up (above
the display) and a button to count down (below the display).
Important Enter the maximum preset Monitor Units (MU) value on the Dosimetry
Counter Electronic Unit (DCEU) front panel before irradiation.
The maximum preset MU value depends on the treatment mode, as
follows:
Pencil Beam Scanning:
 a MU value equal to 105% of the prescribed MU
WARNING Be aware that two types of DCEU exist: one where you set the actual
MU value, indicated by the
Preset [MU] label below the Preset display
(see Figure 15-1), and one where you set the MU value divided by 10,
indicated by the
Preset [x10MU] label below the Preset display (see
Figure 15-1).
Take a close look at the DCEU in your TCR to ascertain that you have to
enter either the actual MU value, or the MU value divided by 10.