Thermoluminescence response of flat optical fiber subjected to 9 MeV electron irradiations

Radiation Physics and Chemistry 106 (2015) 46–49

Contents lists available at ScienceDirect

Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem

Thermoluminescence response of flat optical fiber subjected to 9 MeV electron irradiations S. Hashim a,b,n, S.S. Che Omar a, S.A. Ibrahim a, W.M.S. Wan Hassan a, N.M. Ung c, G.A. Mahdiraji d, D.A. Bradley e,f, K. Alzimami g a

Department of Physics, Universiti Teknologi Malaysia, 81310, Skudai, Johor Darul Takzim, Malaysia Oncology Treatment Centre, Sultan Ismail Hospital, 81100 Johor Bahru, Malaysia c Clinical Oncology Unit, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia d Department of Electrical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia e Department of Physics, University of Surrey, Guildford GU2 7XH, UK f Department of Physics, Universiti Malaya, 50603 Kuala Lumpur, Malaysia g Department of Radiological Sciences, Applied Medical Sciences College,King Saud University,P.O. Box 10219, Riyadh 11433 Saudi Arabia b

H I G H L I G H T S







TL performance of pure silica flat optical fiber (FF) and TLD-100 rod to electron. TL glow curve with a single prominent peak between 230 and 255 1C. The sensitivity of FF is approximately 16% than TLD-100. The minimum detectable dose was 0.09 mGy for TLD-100 rod and 8.22 mGy for FF.

art ic l e i nf o

a b s t r a c t

Article history: Received 14 November 2013 Accepted 30 June 2014 Available online 9 July 2014

We describe the efforts of finding a new thermoluminescent (TL) media using pure silica flat optical fiber (FF). The present study investigates the dose response, sensitivity, minimum detectable dose and glow curve of FF subjected to 9 MeV electron irradiations with various dose ranges from 0 Gy to 2.5 Gy. The above-mentioned TL properties of the FF are compared with commercially available TLD-100 rods. The TL measurements of the TL media exhibit a linear dose response over the delivered dose using a linear accelerator. We found that the sensitivity of TLD-100 is markedly 6 times greater than that of FF optical fiber. The minimum detectable dose was found to be 0.09 mGy for TLD-100 and 8.22 mGy for FF. Our work may contribute towards the development of a new dosimeter for personal monitoring purposes. & 2014 Elsevier Ltd. All rights reserved.

Keywords: Thermoluminescent Flat optical fiber Sensitivity Minimum detectable dose

1. Introduction Many radiation detectors have been developed over the last few decades and some are being used routinely for environmental and personnel dose control. Some detectors make use of materials that emit light when heated after exposure to radiation. This technique is known as thermoluminescence dosimetry (TLD). Because of its simplicity and suitability for automation much research and development work has been put into this type of dosimetry, which has also turned out to be useful in fields other than radiation protection (Bradley et al., 2012).

n

Corresponding author. E-mail address: [email protected] (S. Hashim).

http://dx.doi.org/10.1016/j.radphyschem.2014.06.028 0969-806X/& 2014 Elsevier Ltd. All rights reserved.

In radiotherapy the aim of dosimetry is to make sure that the dose to the tumour is as prescribed while minimizing the dose to the surrounding normal tissue. The most commonly used energy range for electrons in radiotherapy is 6–20 MeV. At these particular energies, the electron beams are used to treat superficial tumors that are located down to 5 cm in depth. For instance, the treatment of skin or lip cancers, chest wall irradiation for breast cancer and the treatment of head and neck cancers. Electron beam irradiation is preferably compared to superficial X-rays, brachytherapy or tangential photon beams to treat these tumors, since it offers several advantages such as dose uniformity in the target volume and the ability to minimize dose to deeper tissues. (Khan, 2003, Wagiran et al., 2012). The potential use of commercially available single mode doped SiO2 optical fibers has been investigated by a number of workers, for

S. Hashim et al. / Radiation Physics and Chemistry 106 (2015) 46–49

photons (Abdulla et al., 2001, Abdul Rahman et al., 2011; Issa et al., 2011), electrons (Hashim et al., 2009; Yaakob et al., 2011; Abdul Rahman et al., 2011 and Alawiah et al., 2013), protons (Hashim et al., 2006), alpha particles (Ramli et al., 2009), fast neutrons (Hashim et al., 2010) and synchrotron radiation (Abdul Rahman et al., 2010). In all such studies the TL performances of irradiated fibers have shown considerable potential for dosimetric applications. The Ge-doped optical fibers show linear dose response for 6, 9 and 12 MeV electron irradiations up to 4 Gy, encompassing the range of fractionated doses normally used in radiotherapy (Hashim et al., 2009). The Ge-doped optical fiber exhibits sensitivity 23 times higher than the Al-doped fiber (Yaakob et al.,2011). The electron response of both Al- and Gedoped fibers was found to be about 1.3 times that of photon irradiation over the dose range 0.2–4.0 Gy, due to the greater linear energy transfer (LET) of the electrons in the doped fibers compared to photons.(Wagiran et al., 2012). With regard to energy response, a slight reduction in TL yield is observed for the electron beams, decreasing by 11% when comparing the TL yield at 16 MeV with that at 9 MeV for a dose rate of 400 cGy min  1 (Abdul Rahman et al., 2011). The optical fibers also demonstrated good reproducibility (7 1.5%), low residual signal and minimal fading (Abdul Rahman et al., 2011). The pure silica FF preform is a hollow silica tube that contains the core and cladding deposited layers. FF has been fabricated to combine the structural advantages of optical fibers and the functional benefits of planar devices. The ribbon-like planar shapes, with an extended length and flexibility, can be used to develop multiple functional optical components such as splitters, couplers and multiplexers. On the other hand, FF offers a platform for the multi-functionality of integrated optics, while trying to retain many mechanical, chemical and optical properties characteristic of the optical fiber (Dambul et al., 2012). Herein, we report the efforts made by our group in introducing the FF as a new TL media. The comparison being made with the commercially available radiation dosimeter i.e. TLD-100. The present work describes several attractive features of the proposed dosimeters such as dose response, TL glow curve and minimum detectable dose subjected to 9 MeV electron irradiations.

2. Materials and methods 2.1. Sample preparation The dosimetry system herein was based on TLD-100 rods size with the dimension of 1 mm  6 mm and FF with dimension of approximately 3.9 mm  3.9 mm  0.9 mm (Table 1). The FF is fabricated using a conventional 5 m fiber drawing tower located at the Flat Fiber Laboratory, Department of Electrical Engineering, Universiti Malaya (UM), Malaysia. Unlike normal optical fiber preform that resembles a solid rod, the FF preform is a hollow silica tube that contains the core and cladding deposited layers (Fig. 1(i)). Table 1 shows the dimensions of the FF used in this study shown in Fig. 1(ii). In this work, the preform (outer diameter¼26.5 mm, inner diameter¼ 22.8 mm and length¼60 mm) used is a commercially available uncollapsed silica tube. The temperature of the furnace was initially set at 2100 1C, which is silica's melting temperature. When the temperature of the furnace Table 1 Dimension details of pure silica FF in Fig. 1(ii). Parameter

Dimension (mm)

Outer thickness (a) Inner thickness (b) Length (L) Width (W)

1.0 0.8 3.9 3.9

47

Fig. 1. (i) The cross-sectional area of FF (ii) The FF is a hollow silica tube that contains the core and cladding deposited layers (Alawiah et al., 2013).

reaches silica's melting temperature, the preform starts to drop. Then, a capillary cane with a diameter of 2-3 mm was pulled from the bottom of the furnace. The capillary cane was then re-pulled to form the desired FF by applying a low vacuum pressure from the top of the capillary, while the furnace temperature was maintained at 2000 1C. A review of the facilities offered by the UM fiber drawing tower is covered in Chow et al., 2012 and Alawiah et al., 2013. The mass of FF and TLD-100 were determined using an analytical balance BSA224S-CW, (Germany) obtaining values equal to 18.74 mg and 23.62 mg (7 0.05 mg), respectively. The measured TL yield was normalized to unit mass of the TL media. Vacuum tweezers were used for handling and grouping of TL materials (Hashim et al., 2009). 2.2. Annealing The fibers were annealed in a furnace (Harshaw) in order to standardize their sensitivities and background. The fibers, retained inside an alumina container were oven annealed at 400 1C for 1 h. Following the annealing cycle fibers were kept inside the oven allowing their natural cooling down for 24 h to avoid thermal stress, finally the samples were equilibrated at room temperature (Hashim et al., 2010). After cooling, the samples were placed inside an opaque plastic container in order to minimize exposure to potentially high ambient light levels (which could promote detrapping, otherwise referred to as bleaching), both prior to and after irradiation. 2.3. Irradiation The electron irradiations were conducted at Universiti Malaya Medical Centre (UMMC) using a Linear Accelerator (LINAC) Varian Model 2100C. The samples were irradiated using the most commonly used electron energies for radiotherapy at this centre i.e. 9 MeV; doses in the range 1 to 4 Gy were delivered to the TL materials. These samples were sandwiched between slabs of a solid water phantom. The solid water phantom is a soft matter medium that can be considered to be a standard tissue-equivalent medium for use in radiation dosimetry. The field and applicator size was set to 10  10 cm2 and positioned at the standard Source-Surface Distance (SSD) of 100 cm. The dose delivered by LINAC is set at a constant dose rate of 600 MU min  1, where MU signifies Monitor Units with 1 MU being equivalent to 1 cGy. 2.4. TL measurements In the present TL measurements, a Harshaw 3500 TL reader (USA) was used together with WinREMS software, enabling one dosimeter to be read out per loading. During readout the following parameters were used: preheat temperature of 50 1C for 10 s

48

S. Hashim et al. / Radiation Physics and Chemistry 106 (2015) 46–49

(Yaakob et al., 2011b); acquisition temperature 300 1C for 14 s and a heating rate cycle of 25 1C s  1. These settings have been shown to provide an optimal glow curve, free of the effects of superficial traps i.e. flushed out by the pre-heat cycle (Hashim et al., 2014). Finally, in the present investigations, an annealing temperature of 300 1C was applied for 10 s to sweep out any residual signal (Hashim et al., 2014).

glow curve remains unchanged by repeating the cycles of annealing and irradiation at various doses. By comparison, the TLD-100 has five typical peaks at 65 1C, 120 1C, 160 1C, 195 1C and 210 1C (Portal, 1981). Our findings agrees closely with the TL glow peak of SiO2 optical fibers at 230 1C subjected to 60Co gamma radiation (Espinosa et al., 2006), Ge-doped fibers broad component peaking at 257 1C after X-ray irradiation (Benabdesselam et al., 2013) and the unknown doped INO-optical fiber had one well-defined glow peak at 32772 1C from a MeV electron beams linear accelerator (Ong et al., 2009).

3. Results and discussions 3.2. Dose response

The important physical factor in order to determine the stability of the TL material for dosimetry is the temperature at which the peak of the glow curve occurs. Most commercially available TL dosimeters have high glow peak temperatures (i.e. deep electron traps), so that they are stable for several months or years. An example of a TL glow curves obtained from FF after 9 MeV electron irradiations is shown in Fig. 2. This typical pattern of the glow curves obtained from FF is the representation of all those measured fiber samples. It is composed of a broad, dominant peak located between 230–255 1C, which is sensitive to the amount of absorbed dose. This convenient position at relatively high temperature allows us to measure absorbed dose, both at room and high temperature. The general structure of the TL

The sensitivity of a TLD material can be expressed in one of two ways, namely, by the TL yield normalized to the mass of dosimeter or by the TL yield normalized to the mass of the dosimeter and its absorbed dose (McKeever et al., 1995). In this work, the latter approach was utilized to determine the TL sensitivity (TL response.mg  1 Gy  1). Fig. 3 shows the TL dose response of TL materials to electron irradiations. The TL response of the FF was relatively small compared to that of TLD-100 i.e. the change in TL yield per unit absorbed dose or slope for FF and TLD-100 are 21.43 mg  1 Gy  1 and 132.20 mg  1 Gy  1,,respectively. We found that the FF sensitivity is approximately 16% of TLD100 media. This clearly indicates that the TLD-100 rod has a better sensitivity and capability in producing higher TL signals compared to FF (by a factor of 6). Our result was comparable with the TL sensitivity of TLD-100 subjected to electron irradiation of 6-, 15- and 21 MeV i.e. 5 times that of FF (Alawiah et al., 2013). Fig. 4 shows the f (D) supralinearity function of FF where f (D) is a measure of deviation from linearity, given by Eq. (1):

TL Intensity (normalized to unit mass)

3.1. TL glow curve

45

4.0 Gy

40

3.0 Gy

35

2.0 Gy 1.0 Gy

30

f ðDÞ ¼

25 20 15 10 5 0

0

50

100

150

200

250

300

350

400

Temperature (°C)

Linear ( TLD 100 )

400

Linear (FF)

TLD-100: y = 132.2x -0.090 R² = 0.996

350 300

where F(D) is the TL signal intensity as a function of dose D and F(Dl) is measured at low dose Dl, i.e. somewhere in the linear region of F(D) (Mahajna and Horowitz, 1997). By using Eq. (1), the linear behavior is achieved when f (D)¼ 1; supralinearity f (D)41 and in sublinearity the f (D)o1. Fig. 4 shows the data point is clustered close to 1 for doses of 1 Gy up to 2.5 Gy. Then, supralinearity (f (D)41) appears to start at doses greater than 3 Gy. Each data point in Fig. 4 is obtained by taking an average of three individual fiber readings. The linear/supralinear behavior may be attributed to the non-uniform spatial ionization density following electron irradiation. This phenomenon have been successfully introduced as the Unified Interaction Model (UNIM) (Horowitz, 2014). In TLD-100, f (D)¼ 1 only up to a few gray. Above this we have f (D)41 (supralinearity) reaching values as high as ten at approximately 100 Gy. At even higher doses f(D) decreases due to recombination, saturation and/or radiation damage and reaches 1.5

FF: y = 21.43x + 1.117 R² = 0.980

250

ð1Þ

1

200 f(D)

TL Response (normalized to unit mass)

Fig. 2. The TL glow curve of FF at various radiation exposures.

FðDÞ=D FðDl Þ=Dl

150 100

0.5

50 0 -50

0.0

0.5

1.0

1.5

2.0

2.5

Dose (Gy)

Fig. 3. TL response of FF optical fibers and TLD-100 at 9 MeV electron versus dose.

0

0

0.5

1

1.5

2

2.5

Dose(Gy) Fig. 4. Supralinearity function of FF subjected to 9 MeV electron irradiations.

3

S. Hashim et al. / Radiation Physics and Chemistry 106 (2015) 46–49

values substantially less than unity in the 103–105 Gy dose region (Horowitz, 1981). 3.3. Minimum detectable dose The minimum detectable dose (MDD) is important in low dose measurements where the signal of an irradiated TLD is almost the same as the background. The MDD was calculated from Eqs. (2) and (3) (Khan, 2003). Do ¼ ðBmean þ 2σÞF

ð2Þ

F ¼ 1=m

ð3Þ

The Bmean is the TL background signal obtained from the TL samples annealed but not irradiated, σ is the standard deviation of the mean background, and F is the TL system calibration factor for each type of the TL media expressed in Gy nC  1. The value of F is the reciprocal of the slope, m obtained from the dose response graph (Fig. 3) of each particular TL material. In the present work, the MDD was found to be 0.09 mGy and 8.22 mGy for TLD-100 and FF, respectively. 4. Conclusion We have investigated the performance of FF and TLD-100 subjected to 9 MeV electron irradiations including TL glow curve, dose response, sensitivity, linearity and minimum detectable dose. The present dosimeter shows a broad glow curve with a single prominent peak between 230–255 1C i.e. depends on the radiation doses being delivered to the FF. The sensitivity of FF is approximately 16% than TLD-100. The TL yield versus dose dependence has been observed to be linear over the dose range up to 2.5 Gy. The MDD value for FF and TLD-100 was 8.22 mGy and 0.09 mGy, respectively. The literature indicates that radiation dosimetry can be divided into two regions, i.e. for personal dosimetry, demanding high sensitivity at very low doses, and a second region for radiation processing, which require dosimeters capable to measure very high doses. The quest for new, improved TLD materials moves on in terms of dose response and the simple glow curve analysis. In conclusion, the FF shows several promising dosimetric features to be introduced as a new TL material. Acknowledgments The authors would like to acknowledge the MOHE HIR Grant numbers A000007-50001, H-21001-00-F000033 and Universiti Teknologi Malaysia for providing financial assistance through Research University Grant Scheme (RUGS), Project number (Q.J130000.2526.03H27). This research project was partially supported by The Strategic Technologies Program, National Plan for Science, Technology and Innovation (NPSTI) in The Kingdom of Saudi Arabia under Contract no. 11-MED1977-02. References Abdulla, Y.A., Amin, Y.M., Bradley, D.A., 2001. The thermoluminescence response of Ge-doped optical Fibre subjected to photon irradiation. Radiat. Phys. Chem. 61, 409–410.

49

Abdul Rahman, A.T., Bradley, D.A., Doran, S.J., Thierry, B., Bräuer-Krisch, E., Bravin, A., 2010. The thermoluminescence response of Ge-doped silica Fibres for synchrotron microbeam radiation therapy dosimetry. Nucl. Instrum. Methods in Phys. Res. Sect. A: Accel. Spectrom. Detect. Assoc.Equip. 619, 167–170. Abdul Rahman, A.T., Nisbet, A., Bradley, D.A., 2011. Dose-rate and the reciprocity law: TL response of Ge-doped SiO2 optical fibers at therapeutic radiation doses. Nucl. Instrum. Methods in Phys. Res. Sect. A: Accel. Spectrom. Detect. Assoc. Equip. 652, 891–895. Alawiah, A., Intan, A. M., Bauk, S., Abdul Rashid, H. A., Yusoff, Z., Mokhtar, M. R., Wan Abdullah, W. S., Mat Sharif, K. A., Mahdiraji, G. A., Mahamd Adikan, F. R, Tamchek, N., Noor, N. M., Bradley, D., 2013. Thermoluminescence of flat optical fiber in radiation dosimetry under different electron irradiation conditions. Proc. SPIE8775, Mirco-structured and Specialty Optical Fibres II, 87750 S (May 3, 2013). Benabdesselam, M, Mady, F, Girard, S., 2013. Assessment of Ge-doped optical fiber as a TL mode detector. J. Non-Cryst. Solids 360, 9–12. Bradley, D.A., Hugtenburg, R.P., Nisbet, A., Abdul Rahman, A.T., Issa, F., Mohd Noor, N., Alalawi, A., 2012. Review of doped silica glass optical fiber: their TL properties and potential applications in radiation therapy dosimetry. Appl. Radiat. Isot.71 (Supplement: 2–11). Chow, D.M., Tee, D.C., Sandoghchi, S.R., Mahamd Adikan, F.R., 2012. Direct UV Written Wavegiude's Dispersion in Flexible Silica Flat Fibre Chip (Bragg Gratings, Photosensitivity and Poling in Glass Waveguides). Colorado Springs, Colorado United States (June 17–20, 2012. SM2E.4). Dambul, K.D., Mahdiraji, G.A., Amirkhan, F.A., Chow, D., Gan, G., Wong, W.R., Abu Hassan, M.R., Tee, D.C., Ismail, S., Ibrahim, S.A., Tamchek, N., Mahamd Adikan, F.R., 2012. “Fabrication and development of Flat Fiber,”. Proc. PGC 1 (3), 13–16. Espinosa, G., Golzarri, J.I., Bogard, J., García-Macedo J. 2006. Commercial optical fiber as TLD material. Radiation Protection Dosimetry. 119, 197-200. Hashim, S., A.T. Ramli, D.A. Bradley & Wagiran, H. 2006. The thermoluminesce response of Ge-doped optical Fibre subjected to proton irradiation. In:Proceedings of the 5th National Seminar On Medical Physics, 2006 Kuala Lumpur: Malaysia. Medical Physics Association. Hashim, S., Al-Ahbabi, S., Bradley, D.A., Webb, M., Jeynes, C., Ramli, A.T., Wagiran, H., 2009. The thermoluminescence response of doped SiO2 optical Fibres subjected to photon and electron irradiations. Appl. Radiat. Isot. 67, 423–427. Hashim, S., Bradley, D.A., Saripan, M.I., Ramli, A.T., Wagiran, H., 2010. The thermoluminescence response of doped SiO2 optical Fibres subjected to fast neutrons. Appl. Radiat. Isot. 68, 700–703. Hashim, S., Ibrahim, S.A., Che Omar, S.S., Alajerami, Y.S.M., Saripan, M.I., Noor, N.M., Ung, N.M., Mahdiraji, G.A., Bradley, D.A., Alzimami, K., 2014. Photon irradiation response of photonic crystal fibres and flat fibres at radiation therapy doses. Appl. Radiat. Isot. 90, 258–260. Horowitz, Y.S., 2014. Thermoluminescence dosimetry: state-of-the-art and frontiers of future research. Radiat. Meas. , http://dx.doi.org/10.1016/j.radmeas.2014. 01.002. Horowitz, Y.S., 1981. The theoretical and microdosimetric basis of thermoluminescence and applications to dosimetry. Phys. Med. Biol. 26 (4), 765–824. Issa, F., Latip, N.A. A., Bradley, D.A., Nisbet, A., 2011. Ge-doped optical Fibres as thermoluminescence dosimeters for kilovoltage x-ray therapy irradiations. Nucl. Instrum. Methods in Phys. Res. Sect. A: Accel. Spectrom. Detect. Assoc. Equip. 652, 834–837. Khan, F.M., 2003. The Physics of Radiation TherapyWilliam & Wilkin, USA: Lippincott. Mahajna, S., Horowitz, Y.S., 1997. The unified interaction model applied to the gamma ray induced supralinearity and sensitization of peak 5 in LiF:Mg, Ti (TLD-100). J. Phys. D: Appl. Phys. 30, 2603–2619. McKeever, S.W.S, Moscovitch, M., Townsend, P.D., 1995. Thermoluminescence Dosimetry Materials: Properties and Uses. Nuclear Technology Publ, Kent (UK) (1870965191204). Ong, C.L., Kandaiya, S., Kho, H.T., Chong, M.T., 2009. Segments of a commercial Gedoped optical fiber as a thermoluminescent dosimeter in radiotherapy. Radiat. Meas. 44, 158–162. Portal, G, 1981. Preparation and properties of principal TL products. In: Oberhoffer, M., Schermann, A. Bristol (Eds.), Applied Thermoluminescence Dosimetry. Adam Hilger Ltd., pp. 97–122. Ramli, A.T., Bradley, D.A., Hashim, S., Wagiran, H., 2009. The thermoluminescence response of doped SiO2 optical Fibres subjected to alpha-particle irradiation. Appl. Radiat. Isot. 67, 428–432. Wagiran, H., Hossain, I., Bradley, D., Yaakob, A.N. H., Ramli, T, 2012. Thermoluminescence responses of photon and electron irradiated Ge- and Al-doped SiO2 optical Fibres. Chin. Phys. Lett. 29 (2), 027802. Yaakob, A.N. H., Wagiran, H., Hossain, I., Ramli, A.T., Bradley, D., Hashim, S., Ali, H., 2011. Electron irradiation response on Ge and Al-doped SiO2 optical fibres. Nucl. Instrum. Methods Phys. Res. A 637, 185–189.