A REAL-TIME PHOTOGRAMMETRIC SYSTEM FOR PATIENT POSITIONING IN PROTON THERAPY 
G. van der Vlugt 
H. 
Rüther 
Professor and Head of Department 
Department of Surveying and Geodetic Engineering 
University of Cape Town 
Republic of South Africa 
Commission V 
ABSTRACT 
Traditionally mechanical devices have been used to position patients with intracranial lesions for proton beam 
therapy. A novel real-time photogrammetric method (Adams and Rüther, 1989) has been developed to replace these 
techniques with the objective of improving positioning efficiency and patient comfort. This paper reports on 
the realisation of the initial concepts and describes principles, system hardware, software and operational 
procedures. Finally, system test results and precisions are discussed. At the time of the formulation of this 
paper the system is already installed and undergoing testing in the treatment vault of the National Accelerator 
Centre (NAC), at Faure near Cape Town. 
KEY WORDS: Digital Photogrammetry, Real-Time Photogrammetry, Proton Therapy, Automated Positioning. 
INTRODUCTION 
One of the methods employed in the treatment of 
patients suffering from intracranial lesions is the 
exposure of the lesion to a proton beam. For this 
purpose it is not only necessary to locate the 
lesion, but also to place the patient in a position 
guaranteeing correct alignment of the lesion in the 
treatment beam. The equipment used for locating and 
positioning the lesion is typically found in 
different rooms of the same institution or in 
different institutions. This necessitates the use of 
a common reference to relate the two coordinate 
systems employed in these different stages. 
When the construction of a proton treatment clinic at 
the NAC in Faure near Cape Town was discussed, it was 
recommended by Adams (1989) to use digital 
photogrammetry based on an existing digital camera 
system (Rüther and Parkyn, 1990) for the patient 
positioning component. This approach was accepted as 
the most economical solution to the problem. Closely 
associated with this system is the development of a 
computer controlled patient support chair by the 
Department of Mechanical Engineering at the 
University of Cape Town. 
Having adopted digital  photogrammetry as the 
positioning principle, the patient positioning 
problem can now be seen as comprising two principal 
components: 
i. Medical imaging component 
The lesion is located relative to the 
reference system by means of a medical imaging 
process, such as the CT (Computer Tomography) 
or MRI (Magnetic Resonance Imaging) scan. 
2. Digital photogrammetry component 
Digital photogrammetry is applied to position 
the lesion into the proton beam and to monitor 
the patient's movements. 
The digital photogrammetry component of the procedure 
can be divided into camera calibration, system check, 
patient positioning and patient monitoring. 
In this paper these digital photogrammetric 
components will be discussed together with software 
and hardware aspects of the system. A brief overview 
of the lesion location stage (although not part of 
this research) is also included in order for the 
reader to fully comprehend the entire treatment 
procedure. 
THE LESION LOCATION STAGE 
Using medical images in conjunction with a technique 
reported by Adams (1990), the position of the 
intracranial lesion is determined relative to 
reference points attached to the patient's head. 
These reference points are later used to establish 
the relative position of the lesion with respect to 
the permanently fixed horizontal beam line in the 
treatment vault. The lesion and reference targets are 
simultaneously imaged on the CT or MRI scan. At 
present, small ball bearings serve as reference 
targets in.the CT scan, while for the MRI scan small 
plastic capsules filled with fish oil are utilised. 
These scans have the capability of allowing the 
determination of three-dimensional coordinates of the 
lesion and targets in the reference coordinate system 
(referred to as the scan coordinate system). 
According to Adams (1990) "it is possible to derive 
three-dimensional coordinates of well defined targets 
to a vector precision of approx. 1.5 mms” for CT 
scans. 
Once the lesion is located, medical specialists 
decide on suitable beam entry points in positions 
which ensure that no sensitive areas of anatomy (eg 
optic nerve or spinal cord) are passed through by the 
beam line. These unmarked points are also coordinated 
in the scan system. The vectors between beam entry 
points and the lesion must be aligned with the beam 
before therapy can commence. 
The reference points on the patient's head are later 
targeted with  retro-reflective markers for the 
digital photogrammetry process. In order to guarantee 
reproducibility of the target positions between 
treatment stages, the points can be tattooed onto the 
patient's skin. Another option under consideration is 
the use of a personalised patient mask with 
permanently attached reference targets. 
SYSTEM HARDWARE AND CONFIGURATION 
Before describing the hardware of the photogrammetric 
patient positioning system (PPPS), it is necessary to 
outline its relationship with the other modules of 
the proton treatment system. Figures 1 and 2 show 
the hardware configurations of the overall treatment 
system and the PPPS respectively.