Plastic Optical Fibre Gamma Radiation Dosimeter


This project investigates the use of PMMA (polymethyl methacrylate) based Plastic Optical Fibre as ionising radiation sensors, suitable for use in small-field radiotherapy dosimetry. The optical fibre tip is coated with a scintillation material that fluoresces under ionising radiation, with the emitted signal penetrating the fibre and propagating along the fibre for remote monitoring through a spectrometer.


Cancer is the second leading cause of death in the European Union, with more than 2.4 million new cases of cancer (excluding non-melanoma skin cancers) diagnosed within the EU in 2008 [1]. Radiation therapy is involved in the treatment of over 40% of cancer patients [2]. In addition to cancer treatment, radiotherapy also plays an important role in palliative care [3]. With the increasing use of radiation therapy, comes the need for improved radiation monitoring systems. Ensuring safe operating and working conditions for both recipients of ionising radiation in radiotherapy applications, and for those who work and operate in ionising radiation affected environments, is of extreme importance. Radiotherapy is delivered in the form of External Beam Radiotherapy, using linear accelerators, or Brachytherapy, which involves the delivery of miniature radio-active ‘seeds’’ that are delivered to the cancerous area directly using hypodermic needle-like applicators. Radiation therapy destroys cells in a precisely controlled manner in an area being treated, referred to as the “target tissue”, by damaging the genetic material of the tumour, making it impossible for these cells to continue to grow and divide. In reality, some surrounding healthy cells also get damaged and so it is important that, during radiotherapy, damage to nearby healthy cells is minimised.

Sensor Design

The optical fibre sensor, described by figure 1, is constructed by coating the end of an exposed PMMA optical fibre, after the cladding was removed, with a specific radiation sensitive scintillating material. The scintillating phosphor material, an inorganic phosphor, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), supplied by Phosphor Technologies [4], is mixed with an epoxy mix and injected into a cylindrical mould containing the exposed PMMA fibre optic core and allowed to cure. The complete fabrication process is described in more detail by McCarthy et al [5]. The radiation sensitive scintillating material tip of the sensor fluoresces on immediate exposure to ionising radiation. The resultant emitted fluorescent light penetrates the PMMA optical fibre and propagates along the fibre to a distal scientific-grade spectrometer from Ocean Optics, where the intensity of the peak wavelength of the fluorescent light is measured.  


Trials were undertaken at the Galway Private Clinic, Ireland and at the University of California, Los Angeles, USA to demonstrate the suitability of the optical fibre based system to monitoring radiation during radiotherapy dosimetry.

There is a distinct, measurable signal emitted at 544nm on exposure to ionising radation that can be used to monitor the amount of radiation a patient in receiving. The optical fibre set-up allows for real-time monitoring of the radiation, for improved patient safety. The current set-up could be used to monitor radiation externally on the patient, with its small size making it particularly suitable for monitoring critical areas, such as around the eyes.  Future work will be directed towards detailed characterisation of the sensor to test for issues, such as rise and fall times, repeatability and reproducability, and long term stability under a range of conditions and energy levels.  

PUBLICATION LIST (relevant to the project objectives)


  • O'Keeffe, S., Lewis, E., “Polymer Optical Fibre for In Situ Monitoring of Gamma Radiation Processes”. International Journal on Smart Sensing and Intelligent Systems, 2009. 2(3): p. 490-502.
  • G. Leen, E. Lewis, U. Timm, G. Dooly, S. O’Keeffe, D. Heffernan, A. Amanatiadis, A.Gasteratos, A. Athinelis, E. Giannaka, M. Bakopoulos, S. Tsekeridou, G. Markarian, A. Zvikhachevskaya, D. G. Perez, D. Anava and A. Moss “Novel personal digital support systems for Emergency Responders to a crises occurring in a Critical Infrastructure”, IEEE Pervasive Computing. Under Review.
  • McCarthy D., O’Keeffe S., Lewis E. Sporea D., Sporea A., Tiseanu I.  “Radiation dosimeter using an extrinsic fibre optic sensor “, IEEE Sensors Journal. Under Review.


  • McCarthy D., O’Keeffe S., Lewis E. P. Woulfe, J. Cronin, Sporea D., Sporea A., Tiseanu I. “Optical fibre radiation dosimeter for radiotherapy applications”. IEEE Sensors 2012 Conference, Taipei, Taiwan, 28-31 October 2012.
  • D. McCarthy, S. O'Keeffe, P. Woulfe, J. Cronin, E. Lewis, "Scintillating optical fibre sensor for radiotherapy dosimetry",OFS-22, 22nd International Conference on Optical Fiber Sensors, Beijing, China, October 2012.
  • D. McCarthy, S. O'Keeffe, P. Woulfe, J. Cronin, E. Lewis, “Optical Fibre Based Scintillation Probe for Radiotherapy Dosimetry”, OSA Applied Industrial Optics: Spectroscopy, Imaging, and Metrology (AIO) 2012, Monterey, California, USA, June 2012.
  • McCarthy D., O’Keeffe S., Lewis E. Sporea D., Sporea A., Tiseanu I. “Optical fibre X-ray radiation dosimeter sensor for low dose applications”. IEEE Sensors 2011 Conference, Limerick, Ireland, 28-31 October, 2011. pp. 121-124.
  • S. O’Keeffe, K. Bremer, U. Timm, D. McCarthy, G. Leen, E. Lewis, “Advances in All-Optical Sensors for Biomedical Monitoring”, IEEE Biophotonics Workshop 2011, Parma, Italy. (INVITED)
  • D. McCarthy, S. O’Keeffe, E. Lewis, “Optical fibre radiation dosimetry for low dose applications”, IEEE Sensors Conference 2010, Hawaii, US, October 2010.
  • D. McCarthy, S. O'Keeffe, E. Lewis, “Plastic optical fibre X-Ray dosimeter for real-time clinical dosimetry applications”. Fifth IEEE Sensors Applications Symposium (SAS-2010), 23rd-25th February, 2010. Limerick, Ireland. pp. 158-161.
  • O’Keeffe S., Lewis E., Santhanam A., Rolland J.P., “Variable Sensitivity Online Optical Fibre Radiation Dosimeter”, The Eighth IEEE Conference on Sensors (IEEE Sensors Conference), October 25th-28th, 2009, Christchurch, NewZealand.
  • O’Keeffe S., Lewis E., Santhanam A., Winningham A., Rolland J.P., “Low dose plastic optical fibre radiation dosimeter for clinical dosimetry applications”, The Eighth IEEE Conference on Sensors (IEEE Sensors Conference), October 25th-28th, 2009, Christchurch, New Zealand.
  • S. O’Keeffe, E. Lewis, A. Santhanam, J.P. Rolland, “Low Dose Radiation Monitoring Based on PMMA Optical Fibres for Radiotherapy Dosimetry”, in International Conference On Advanced Infocomm Technology 2009. IEEE: Xi'an, China, July 2009.

Book Chapters:

  • D Sporea, A Sporea, S O’Keeffe, D McCarthy, E Lewis, “Optical fibers and optical fiber sensors used in radiation monitoring” in Optical Fibers: Book 4, InTech Publisher, ISBN 979-953-307-653-8. IN PRESS


  • S. O’Keeffe, E. Lewis, A. Santhanam, J.P. Rolland, “PMMA based optical fibre radiation dosimeter for clinical applications”, National Institute of Health Sciences Research Bulletin, June 2009


IEEE Sensors Council Early Career (GOLD) Award 2012 was presented to Dr Sinéad O’Keeffe

“for contributions to optical fiber sensors for radiation monitoring, particularly in patient monitoring during radiotherapy, and leadership in European efforts to develop reliable and standardized optical fiber sensors for safety and security applications.”


[1]      Ferlay J, Shin HR, Bray F, Forman D, Mathers C and Parkin DM. “GLOBOCAN 2008 v1.2, Cancer Incidence and Mortality Worldwide: IARC CancerBase No. 10”. (Lyon, France: International Agency for Research on Cancer; 2010). Available from: http://globocan.iarc.fr, accessed on 16/02/2012.

[2]      Murray, L.J. and Robinson, M.H., “Radiotherapy: technical aspects”, Medicine, 39(12): 698-704, December 2011.

[3]      Ferris FD, Bezjak A, Rosenthal SG., “The palliative uses of radiation therapy in surgical oncology patients.”, Surg Oncol Clin N Am. 2001 Jan;10(1):185-201.

[4]      Phosphor Technology Ltd. Available from: http://www.phosphor-technology.com, accessed on 14/02/2012.

[5]   D. McCarthy, D. et al, “Optical Fibre X-Ray Radiation Dosimeter Sensor for Low Dose Applications”, IEEE Sensors Conference 2011, October 2011, Limerick.