1. Technical development of a high resolution CCD-based scanner for 3-D gel dosimetry: (I) Scanner construction S J Doran, K K Koerkamp*, M A Bero, P Jenneson, E J Morton and W B Gilboy S Department of Physics, University of Surrey, Guildford, GU2 7XH, UK Department of Physics University of Surrey Department of Applied Physics University of Twente, NL * S J Doran, K K Koerkamp M A Bero, P Jenneson, E J Morton, W B Gilboy Dept of Applied Physics, University of Twente, Enschede, NL

2. Structure of talk Historical perspective and context of the research Original scanner Components of the new scanner  Light source  Collimation  Tank  Stepper motors  Detection

3. Historical perspective Colour-change gels introduced in 1991 (Appleby and Leghrouz, Med. Phys. 18, 309-312, 1991) 2-D imaging of radiation dose with CCD (Tarte et al. Med. Phys. 24(9), 1521-1525, 1997) Pencil-beam, laser-based systems Typically one plane in ~15 mins. (Kelly et al. Med. Phys. 25(9), 1741-1750, 1998) Imaging of stacked gels (Gambarini et al. DOSGEL ’99) First CCD tomography scanners (Wolodzko et al., Bero et al., DOSGEL ’99) Typically 512 planes in ~30 mins.

4. X-ray tomography lab at UniS The University of Surrey Physics Department already has a large investment in experimental X-ray computed tomography (Dr E Morton). Optical tomography fits perfectly into this scheme.

5. Original scanner: DOSGEL ’99 First image obtained in 1999 with the simple setup below demonstrates principle, but images not adequate. Scanning tankReconstructed OT image of optical density Optical density profile

6. Premise for further development Up until now optical dosimetry has been seen as a cheap alternative to MRI. In designing the original CCD scanner, we originally tried to prove the principle on an ultra-low budget (< £5000). To obtain a credible medical instrument, one must purchase components with a higher specification. The key question is “How expensive does it need to be?” Strategy is to upgrade components gradually and evaluate which ones make the greatest difference.

7. New scanner schematic Hg lamp Cylindrical lens, pinhole and filter  pseudo point-source Lens  parallel beam Scanning tank with matching medium Exposed gel Unexposed gel Diffuser screen on which real shadow image forms CCD detector Standard 50mm camera lens PC with frame- grabber card Turntable controlled by acquisition computer via stepper motors

8. New scanner

9. Light source: mercury vapour lamp The mercury emission spectrum contains a number of strong emission lines in the visible. In particular, there are lines on either side of the isobestic point. Wavelength / nm  (optical absorbance) / cm -1 FXG spectral dose-response

10. Collimation of light source Short dimension of discharge tube Circular converging lens Collimating aperture Light source (elongated discharge tube) Cylindrical lens, focussing dimension Cylindrical lens, non-focussing dimension Long dimension of discharge tube Filter Cylindrical lens Pinhole Filter 7 cm Aim is to produce large diameter, parallel light beam. Hence, need good point source.

11. Scanning tank Purpose-built perspex tank, 30 cm 3 Turntable attached to “rotation table” below (Time and Precision, Basingstoke, UK, model TR48) via watertight seal Projection screen stuck to back face of tank

12. Stepper motors Motor controllers (Parker Hannifin Corporation, Rohnert Park, CA, USA, model 6K4)  precision 0.05° in rotation table positioning Ethernet interface to host computer

13. Signal detection 50 mm camera lens Off-the-shelf CCD detector (RS ~£120) CCIR framegrabber (Matrox pulsar, ~£1000) Acquisition PC, Visual Basic

14. Conclusions The new tomography scanner operates on the same principles as the previous prototype, but each of the components now has a higher specification. As will be shown subsequently, further improvement is needed in the CCD detector and projection screen.