On-line dosimetry for radiotherapy using non-invasive optical fibre sensors with Al2O3:C OSL detectors (PhD)

In vivo dosimetry at the tumour site is an ultimate goal in radiation therapy. The development of treatment techniques such as hadron therapy introduces new challenges and requirements, such as the need to provide real-time dosimetry devices with high spatial resolution, sensitivity and accuracy. An optical-fibre radiation dosimeter system, based on radioluminescence (RL) and optically stimulated luminescence (OSL) from carbon-doped aluminium oxide (Al₂O₃:C) can be used for these purposes.

Study, develop and apply an on-line dosimetry system using an optical fibre with Al₂O₃:C OSL detector in hadron therapy

Hadron therapy is a form of radiation therapy using strongly interacting particles like protons and heavier ions. Proton therapy is the most common hadron therapy in use. This is in general characterized by a better dose conformation to the tumour and, at the same time, a lower dose to healthy tissue, when comparing to photon therapy. Heavy ions therapy uses particles heavier than protons, such as carbon ions. Compared to protons, carbon ions have the advantage on being more effective on killing the tumour, due to the higher density of ionization at the end of their range, which makes it harder for the cancerous cells to repair their damaged DNA (higher Relative Biological Effectiveness, RBE).

OSL detectors have been used successfully for many years in personal, space and retrospective dosimetry, with increasing applications also in the medical field. The high sensitivity of Al₂O₃:C for OSL and the possibility of having very small detectors, make it a good candidate for high precision dosimetry, with the possibility on using Al₂O₃:C single crystals or crystalline powder. The Al₂O₃:C OSL readout is quite simple with the possibility of re-estimating the absorbed dose, the material has no fading for at least 100 days after irradiation, the signal can be cleaned by bleaching or annealing and the dose response is linear from 10 mSv to in excess of 10 Sv. OSL materials can be used for on-line monitoring by coupling them to a reader through an optic fiber. Sometimes, even the fiber itself can have luminescent properties that can be used for real-time dosimetry.

The necessity of an in vivo dosimetry system is extremely high for radiotherapy, and, in particular, in hadron therapy, which requires dosemeters having a reliable response and behavior under different energy ranges and particle types. An important challenge for these devices, in hadron therapy, is that dose variations are very steep, which makes the dosimetry applications more complicated. The possibility of using OSL for precise dosimetry in hadron therapy has yet to be demonstrated, although some first steps have been taken in conventional radiotherapy.

The use of an optical fibre with an OSL-RL (radioluminescence) detector can give the advantage of acquiring the dose rate and absorbed dose at the same measurement. The dose rate is measured during irradiation of the fiber itself using the RL signal, and the absorbed dose is calculated by the OSL signal in the crystalline detector. The OSL readout can be performed in several ways, for instance with continuous wave (CW), pulsed or linear modulation stimulation (LM), where different aspects of the OSL curve can be explored. 

            The proposal to use non-invasive optical fibre sensors with Al₂O₃:C OSL detectors in dosimetry for radiotherapy applications is very interesting for SCK-CEN. The RDC group has experience both in research in the medical domain (also radiotherapy) and  in new dosimetry techniques, like the OSL technique. Furthermore, the SCK-CEN is involved in the Belgian Hadron Therapy Consortium. There is also a possibility of cooperation between the RDC group and ARI group that has experience using optical fibre types in nuclear environments.