A Novel Dosimetry System for Computed Tomography using Phototransistor

Computed tomography (CT) dosimetry normally uses an ionization chamber 100 mm long to estimate the computed tomography dose index (CTDI), however some reports have already indicated that small devices could replace the long ion chamber to improve quality assurance procedures in CT dosimetry. This paper presents a novel dosimetry system based in a commercial phototransistor evaluated for CT dosimetry. Three detector configurations were developed for this system: with a single, two and four devices. Dose profile measurements were obtained with them and their angular response were evaluated. The results showed that the novel dosimetry system with the phototransistor could be an alternative for CT dosimetry. It allows to obtain the CT dose profile in details and also to estimate the CTDI in longer length than the 100 mm pencil chamber. The angular response showed that the one device detector configuration is the most adequate among the three configurations analyzed in this study.

Authors:

• C. M. M. Paschoal
• M. L. Sobrinho
• D. do N. Souza
• J. Antônio Filho
• L. A. P. Santos

Keywords:

• Computed tomography
• dosimetry
• photo-transistor

References:

[1] Aoyama, L., Koyama, S., Kawaura, C., 2002. An in-phantom dosimetry
system using pin silicon photodiode radiation sensors for measuring
organ doses in X ray CT and other diagnostic radiology. Med. Phys. 29,
1504-1510.
[2] Dixon, R.L., 2003. A new look at CT dose measurements: Beyond
CTDI. Med. Phys. 30, 1272-1280.
[3] Hansson, J.; Eriksson, S.; Klang, A. T.; Bath, M., 2010. Comparison of
three methods for determining CT dose profile: presenting the tritium
method. Radiat. Prot. Dosim. 139, 434-438.
[4] Herrnsdorf, L., Björk, M., Cederquist, B., Mattsson, C. G., Thungström,
G., Fröjdh, C., 2009. Point dose profile measurements using solid-state
detectors in characterization of Computed Tomography systems. Nucl.
Instrum. Methods Phys. Res. A 607, 223-225.
Mettler Jr, F.A., Wiest, P. W., Locken, J. A., Kelsey, C. A., 2000. CT
scanning: patterns of use and dose. J. Radiol. Prot. 20, 353-359.
[5] Mori, S., Endo, M., Nishizawa, K., Tsunoo, T., Aoyoma, T., Fujiwara,
H., Murase, K., 2005. Enlarged longitudinal dose profiles in cone-beam
CT and the need for modified dosimetry Med. Phys. 32, 1061-1069.
[6] Nachonechny, K.D., Fallone, B. G., Rathee, S., 2005. Novel methods of
measuring single scan dose profiles and cumulative dose in CT. Med.
Phys. 32, 98-109.
[7] Rosenfeld, A.B., 2006. Electronic dosimetry in radiation therapy. Radiat.
Meas. 41, S134-153.
[8] Santos, L.A.P., Magalhães, C. M. S., Silva, J. O., Antônio Filho, J.,
Silva Jr., E., Santos, W. M.., 2008. A feasibility study of a
phototransistor for the dosimetry of computerized tomography and
stereotactic radiosurgery beams. Radiat. Meas. 43, 904-907.
[9] Shrimpton, P. C., Hillier, M. C., Lewis, M. A., Dunn, M., 2006.
National survey of dose from CT in the UK: 2003. J. Radiol. 79, 968-
980.