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CHAIR 
CONTROL 
MONITOR 
Fig.1. Hardware configuration of the 
proton treatment system 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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3 power = 3 
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cameras units = monitors 
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Fig.2. Hardware components of PPPS 
The system components are 
1. Photogrammetric Patient Positioning System 
(PPPS) 
1.1 Three Philips CCD video cameras, power 
supply units (PSU) and a signal 
processor interface (SPI). 
1.2 Matrox MVP-AT frame-grabber and image- 
processing card (512 by 512 by 8 bits 
image formats) 
1.3 Unisys 386 PC with an 8087 Math 
coprocessor 
1.4 Three external Philips video monitors 
2. Patient support chair system 
2.1 Computer controlled chair 
2.2 Computer for chair control 
2.3 Manual controller 
3. Dose control computer 
4. Interlock and control computer 
The PPPS computer (which is responsible for all the 
digital photogrammetry procedures) is connected to 
the chair computer through its communication port, 
and to the interlock and control computer through a 
relay. 
The chair can be controlled by a hand-held unit, for 
provisional positioning by the operator, and 
automatically by the PPPS (through the chair’s 
computer), for the fine positioning. 
The interlock and control system controls the 
activation and deactivation of the proton beam. 
Before the beam is activated the system ensures that 
all necessary safety procedures have been completed. 
These procedures include activating various switches, 
passing check points, closing safety gates and 
various other precautionary measures. These must be 
strictly adhered to by the operators in the interest 
of patient and staff safety. The interlock and 
control system will also deactivate the beam if the 
PPPS detects any intolerable patient movement. 
The dose control computer, which regulates the 
radiation exposure, is a separate unit connected to 
the interlock and control computer. 
The frame-grabber simultaneously captures three 
images and stores them in three frame buffers, each 
with a 512 by 512 by 8 bits format. A fourth frame 
buffer of equal size is available for image 
processing operations. From Figure 2 it can be seen 
that of the four input channels on the MVP-AT frame- 
grabbing and image-processing card, channels 0 - 2 
receive the video signals from the three black and 
white CCD (Charged Coupled Device) cameras. Channel 
3 is used for the synchronisation (sync) input. The 
power supply units (PSU) provide power for the 
cameras as well as  sync-signals. Originally, 
difficulties were encountered with the 
synchronisation of the three cameras. These were 
overcome by introducing a signal processor interface 
(SPI) designed by the Department of Electrical and 
Electronic Engineering at UCT. The SPI acts as a 
distribution amplifier bringing the sync and video 
signals up to the required amplitude and waveshape, 
and isolating the input from the output. Double 
terminations are thus avoided and perfect matching 
(75 Ohms) is obtained (Private communication, J. 
Hesselink). 
To enable the system operator to efficiently respond 
to the image information received from the cameras, 
the MVP outputs the video images to the three analog 
output monitors as shown in Figure 2. 
CAMERA/OBJECT CONFIGURATION 
It was decided to install a total of eight cameras at 
eight camera stations, uniformly distributed around 
the patient chair (Figs. 3 and 4). The configuration 
was designed to allow for different patient treatment 
positions. Four stations are located at the level of 
the beam-line and four at approximately a 45 degrees 
angle above the horizontal. The stations are all 
roughly 2.5m away from the lesion point, where the 
lesion point is defined by the intersection of the 
vertical chair axis and the beam line. 
  
  
beam-line 
  
  
Fig.3 Plan view of camera station positions.