Comparison of dosimeter response of TLD 100 and ionization chamber for high energy photon beams at KIRAN Karachi in Pakistan The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx C[.]
The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx Contents lists available at ScienceDirect The Egyptian Journal of Radiology and Nuclear Medicine journal homepage: www.sciencedirect.com/locate/ejrnm Original Article Comparison of dosimeter response of TLD-100 and ionization chamber for high energy photon beams at KIRAN Karachi in Pakistan Muhammad Waqar a,d,⇑, Asdar Ul-Haq b, Syed Bilal d, M Masood c a Nuclear Medicine Oncology and Radiotherapy Institute Nawabshah (NORIN), Pakistan Karachi Institute of Radiotherapy and Nuclear Medicine (KIRAN), Pakistan c Pakistan Institute of Nuclear Science and Technology (PINSTECH), Pakistan d Pakistan Institute of Engineering and Applied Sciences (PIEAS), Pakistan b a r t i c l e i n f o Article history: Received 15 October 2016 Accepted 21 January 2017 Available online xxxx Keywords: TLD Dosimeter Ionization chamber Phantom Relative variation a b s t r a c t This study was conducted by measuring point dose at different depths of water phantom by using two types of dosimeters (PTW N30013 ionization chamber and TLD-100 chips) at Karachi institute of radiotherapy and nuclear medicine (KIRAN), Pakistan Two different TLD chips were used (circular pallets and square chips) The main aim of this study was to compare the responses of two different types of dosimeter irradiated with MV X-rays using same parameters Both types of dosimeter were irradiated with different dose value ranging from 25 cGy to 500 cGy The deviation between different shapes of TLD and ionization chamber remained within 5% limit Maximum deviations of circular pallets reading from that of ion chamber are 3.56% at 1.5 cm depth and 4.91% at cm depth For square chips maximum deviation happened to be 4.38% at 1.5 cm depth and 4.23% at cm depth This measurement shows that TLDs are reliable tool for dosimetry regardless of their shape or manufacturer and they can be used as re-validation tool for ion chamber dosimetry Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine Production and hosting by Elsevier This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/) Introduction Inter comparison is an important activity to ensure the consistency of radiation dosimetry [1] The ionization chamber is a benchmark of dosimeter, and had been known to provide the most accurate and reliable results [2] One difficulty with ionization chamber is that the measured dose can be perturbed by volume averaging over their relatively large active volume [3] Practically there are several things to consider, such as the large volume of active and effective point of measurements [4] They can’t be used in anthropomorphic for in vivo measurements When ionization chamber measurements are impractical, it can be replaced by TLD, especially in in vivo dosimetry The small size of TLD allows it to be inserted into an anthropomorphic or water phantom for dosimetry TLDs can be used to measure point doses with greater precision in volume as their active volume can be made very small as compared to ionization chamber For fractional dose measure- Peer review under responsibility of The Egyptian Society of Radiology and Nuclear Medicine ⇑ Corresponding author at: Senior Medical Physicist, Nuclear Medicine Oncology and Radiotherapy Institute Nawabshah (NORIN), Pakistan E-mail address: phy_waqar@yahoo.com (M Waqar) ment, the corrections for energy and dose response are taken into account [5] To achieve dose measurement precision, TLD implementation program requires a rigorous annealing and response measurement protocol, and routine QA of the TLD reader and annealing oven temperature control [6] When radiation is incident on a crystal of thermo luminescent material, it excites it This crystal can’t be de-excited itself and energy of radiation remains trapped If this crystal is heated up to a certain temperature, it is de-excited and releases the trapped energy in the form photon of visible light This light is detected by PMTs The output of PMTs is directly related to the light output of TL crystal, which is itself proportional to the dose absorbed in the crystal by incident radiation If output of PMTs is calibrated against the absorbed dose, TLDs can be used to assess the dose absorbed in TL crystal Once TL dosimeter is read, it can be reused after a process called annealing which eliminates any residual imperfection in crystal [7,8] Thermo-luminescence properties of crystal can be explained theoretically by energy band theory of solids [9] LiF is the most common crystal used for Thermo luminescence dosimetry because of its tissue equivalence (Zeff = 8.2 compared to 7.4 for tissue) and its energy independent response in the range of 100 keV–1.3 MeV [10,11] TLD-100 is LiF crystal doped with http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 0378-603X/Ó 2017 The Egyptian Society of Radiology and Nuclear Medicine Production and hosting by Elsevier This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Waqar M et al Egypt J Radiol Nucl Med (2017), http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 M Waqar et al / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx Magnesium and Titanium and is usually used for dosimetry in radiotherapy The light output of PMTs is plotted against temperature or time that is called glow curve [12] Various curves plotted in glow curve shows the released electrons of different energy, which were trapped in the crystal At room temperature TLD-100 has different peaks corresponding to different electron energy level [13,14] Electrons trapped at lower energy levels are prone to fading, which is loss of trapped charges before readout Factors, which affect the shape of glow curve are annealing, heating rate and its uniformity, size and history of sample, threading instrument TLD-100s are heated before irradiation first at 400 °C for one hour followed by 100 °C for two hours or at 800 °C for 24 h (called annealing) This slow heating relieves trapped electron remained in lower peaks of glow curve by decreasing their trapping efficiency These electrons can also be released by post irradiation annealing by heating at 100 °C for 10 The magnitude of these peaks rapidly decreases with time after irradiation so they can be released at lower temperature after irradiation After removing peaks at lower values of temperature, glow curve shows more predictable behavior [15] The aim of present study is to compare the responses of TLD dosimeters with the other most widely used dosimeters, ion chamber Ion chambers are commonly used for dosimetry in radiotherapy Present study focuses on a point that response of TLD dosimeters is in well agreement with ion chambers and can be used as a re-validation tool for ion chamber dosimetry Materials and Methods In this study, two different batches of TLDs (LiF-Mg-Ti) having different shape, dimensions and manufactured by different wellknown companies (HARSHAW, USA & MTS, Poland) were used First batch comprised of 125 square shape TLD chips (TLD-100) having dimensions of 3.2 3.2 0.9 mm3, manufactured by M/s HARSHAW, USA The second batch comprised of 125 circular pellets (MTS-N) having the dimensions of 4.5 0.9 mm3 manufactured by M/s MTS, Poland The ionization chamber (PTW N30013 Serial number 0114, PTW-FREIBURG Corporation, Germany) with volume 0.6 cm3was used in this study It is often used for absolute dosimetry measurement in radiotherapy because it has flat response and better signal to noise ratio For measurement of the charges produced by photon in water and PMMA solid phantoms, CNMC11 electrometer (model No 5232) was used with IC The ionization chamber was calibrated from Secondary Standard Dosimetry Laboratory (SSDL) PINSTECH, Islamabad Linear Accelerator with of MV fixed energy (Primus plus) manufactured by Siemens Medical systems, USA) and manuallyoperated TLD Reader system (Thermo-Scientific Model 3500) with heating rate 10 °C/s was utilized to carry out this study Before use, TLDs were first grouped according to their Element Correction Factor (ECC) 125 TLDs of each group are randomly selected and their ECC were manually calculated HARSHAW 3500 single chip TLD reader was used for this purpose Around 140 TLDs with their ECC close or equal to unity were selected for the measurement Among 140 TLDs, 70 were square chips and 70 were circular pellets After grouping, TLDs were calibrated After each use, TLDs were annealed in Thermo Lyne 47900 furnace, first at 400 °C for one hour and then at 100 °C for two hours A time gap of almost 48 h is given between exposure and reading the TLD to minimize the fading Background or zero readings were rechecked after annealing, along with test light reading Fig Experimental arrangements A set of annealed TLD-100 were irradiated with field size 10 10 cm2, at 100 cm SSD and at cm depth in a solid water phantom to a dose of 200 cGy with a MV photon beam A calibration factor was measured for each TLD All TLDs were irradiated repeatedly with 50 cGy, 100 cGy and 150 cGy to check the linearity and reproducibility of TLD response All the TLDs showed a linear response with this range of doses The responses of TLD samples and ionization chamber were observed at SSD 100 cm with field size 10 10 cm2 in water phantom at depths of 1.5 cm (Dmax) and cm by varying the doses from 25 cGy to 500 cGy Experimental arrangements are shown in Fig Relative variation of measured TLD readings (DTLD) and Ionization chamber readings (DIC) are calculated using following formula [16]: d ð%Þ ¼ DTLD DIC 100 DIC ð1Þ Results and Discussion In this section, the response of both batches of TLDs against irradiation was compared with the ion chamber response separately It was found that TLD response is in a good agreement with ion chamber readings 3.1 At the Depth of Maximum Dose (1.5 cm) Tables and were the measured dose values of TLDs (DTLD) and IC (DIC) for X-ray beams with energy MV measured at depth of 1.5 cm Average relative variation for square TLD chips from that of IC readings were calculated The maximum and minimum relative variation was found to be 4.41% and 0.29% for the doses of 250 cGy & 500 cGy respectively This data is plotted in Fig Table Responses of TLD (square chips) and Ion chamber dosimeter at the depth of 1.5 cm Dose (cGy) 25 50 100 150 200 250 300 350 400 450 500 Square chips 1.5 cm DTLD (cGy) DIC (cGy) Relative variation (%) 24.49 47.18 96.14 146.50 190.15 234.44 281.43 336.91 376.94 433.16 489.37 24.4 48.97 98.06 147.08 196.11 245.25 294.33 343.36 392.33 441.55 490.77 0.37 3.65 1.95 0.40 3.04 4.41 4.38 1.88 3.92 1.90 0.29 Please cite this article in press as: Waqar M et al Egypt J Radiol Nucl Med (2017), http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 M Waqar et al / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx Table Responses of TLD (circular pellets) and Ion chamber dosimeter at the depth of 1.5 cm Dose (cGy) 25 50 100 150 200 250 300 350 400 450 500 Circular Pellets 1.5 cm Table Responses of TLD (square chips) and Ion chamber dosimeter at the depth of cm Dose (cGy) DTLD (cGy) DIC (cGy) Relative variation (%) 25.05 47.82 97.56 147.45 197.18 253.54 300.03 346.06 397.92 427.95 473.30 24.40 48.97 98.06 147.08 196.11 245.25 294.33 343.36 392.33 441.50 490.77 2.67 2.34 0.51 0.25 0.55 3.38 1.94 0.79 1.42 3.07 3.56 For circular pallets, the maximum and minimum relative variation was found to be 3.56% and 0.25% at dose values of 500 cGy & 150 cGy respectively as tabulated in Table and plotted in Fig For 1.5 cm depth, relative variation for square chips and circular pallets with respect to ionization chamber was observed to be within ±4.5% and ±4% respectively 25 50 100 150 200 250 300 350 400 450 500 Square chips cm DTLD (cGy) DIC (cGy) Relative variation (%) 21.87 43.74 81.92 127.40 164.71 204.40 245.33 285.73 340.05 377.92 417.08 21.2 42.52 85.15 127.79 170.36 212.94 255.73 298.36 341.05 383.68 426.31 3.16 2.87 3.80 0.30 3.31 4.01 4.07 4.23 0.29 1.50 2.16 3.2 At Dose Depth (5 cm) Measurements were also performed at dose depth of cm Dose values of TLD’s (DTLD) and IC (DIC) for X-ray beams with energy MV measured at depths of cm for the square and circular chips with ionization chamber are shown in Tables and Average Fig Comparison of TLD (square chips) and ion chamber response at the depth of 1.5 cm Fig Comparison of TLD (circular chips) and ion chamber response at the depth of 1.5 cm Please cite this article in press as: Waqar M et al Egypt J Radiol Nucl Med (2017), http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 M Waqar et al / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx Table Responses of TLD (circular pellets) and Ion chamber dosimeter at the depth of cm Dose (cGy) 25 50 100 150 200 250 300 350 400 450 500 Circular Pellets cm DTLD (cGy) DIC (cGy) Relative variation (%) 20.30 40.43 82.17 122.59 163.63 219.28 259.92 298.46 352.40 395.27 438.37 21.00 42.52 85.15 127.79 170.36 212.94 255.73 298.36 341.05 384.67 426.31 3.35 4.91 3.49 4.07 3.95 2.98 1.64 0.03 3.33 2.76 2.83 relative variation for square TLD chips from that of IC readings were calculated The maximum and minimum relative variation was found to be 4.23% and 0.29% for the doses of 350 cGy & 400 cGy respectively The data is given in Table and plotted in Fig For cm dose depth, the relative variations within ±4% and ±5% for square chips and circular pellets respectively as shown in Fig While comparing IC response with TLD’s response in water phantom at different depths, it was found that TLD is a suitable detector for quality assurance or re-validation purpose, especially for the energies of therapeutic range, provided that they have been properly calibrated The dose re-validation is very important because of the direct involvement of human beings Very limited and insufficient literature was available to support the procedure adopted in this section Banjade et al [17] proposed that accuracy of better than 5% of measured dose can be achieved He cited the results of Marshall et al for the measurement of depth dose with accuracy of 5.3% According to ICRU recommendation the variation of 3–5% between the delivered and prescribed dose is allowed in radiotherapy [18] At 10 cm depth and energies of MV and 18 MV, variation is shown to about 0.1–1.3% [16] At low energy in mammography the variation of results between ion chamber and TLS is 4–8% [19] Present measurements have shown relative variation within ±4% and ±5% of ion chamber measurement at 1.5 cm & cm respectively It is also suggested that more studies must be conducted, for comparison of these two dosimeters Fig Comparison of TLD (square chips) and Ion chamber response at the depth of cm Fig Comparison of TLD (circular chips) and ion chamber response at the depth of cm Please cite this article in press as: Waqar M et al Egypt J Radiol Nucl Med (2017), http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 M Waqar et al / The Egyptian Journal of Radiology and Nuclear Medicine xxx (2017) xxx–xxx responses at specified depths (1.5 cm & cm), to have a better understanding Conclusion Ion chambers are primary radiation detectors for radiation dosimetry in radiotherapy Their relatively large active volume and their vulnerability to changes in atmospheric conditions, sometimes, make their results unreliable In present study, TLDs showed the results of within 5% deviation from those of ion chamber which is in a good agreement The responses of both types of TLD lie within acceptable limits regardless of shape and manufacturer It can be concluded that TLDs can be used as a re-validation tool for ion chamber dosimetry Conflict of interest Authors have nothing to disclose Acknowledgement The authors are grateful to Mr Muhammad Shahban, NORIN cancer hospital Nawabshah, Mr Shamim Haider and Tauseef Rehman, KIRAN cancer hospital Karachi for their assistance and help References [1] Zˇivanovic´ MZ, Lazarevic´ ÐR, Ciraj-Bjelac OF, Stankovic´ SJ, C´eklic´ SM, Karadzˇic´ KS Intercomparisons as an important element of quality assurance in metrology of ionising radiation Nucl Technol Radiat Prot 2015;30:225–31 [2] Nalbant N Pre-treatment dose verification of IMRT using Gafchromic EBT3 film and 2D array J Nucl Med Radiat Ther 2014;2014 [3] Fitriandini A, Wibowo W, Pawiro S Comparison of dosimeter response: ionization chamber, TLD, and Gafchromic EBT2 film in 3D-CRT, IMRT, and SBRT techniques for lung cancer J Phys: Conf Ser 2016;012006 [4] McEwen M, Kawrakow I, Ross C The effective point of measurement of ionization chambers and the build-up anomaly in MV X-ray beams Med Phys 2008;35:950–8 [5] Olko P Advantages and disadvantages of luminescence dosimetry Radiat Meas 2010;45:506–11 [6] Low DA, Moran JM, Dempsey JF, Dong L, Oldham M Dosimetry tools and techniques for IMRT Med Phys 2011;38:1313–38 [7] Pradhan A, Bakshi A Calibration of TLD badges for photons of energy above MeV and dosimetric intricacies in high energy gamma ray fields encountered in nuclear power plants Radiat Prot Dosim 2002;98:283–90 [8] Rosenwald J-C, Nahum A, Chavaudra J, Carlsson GA, Dance D, Bielajew A, et al Handbook of radiotherapy physics theory and practice; 2008 [9] Siddique R, Uddin Z, Hussain M Dosimetric evaluation and verification of external beam 3-D treatment plans in humanoid phantom using thermoluminescent dosimeters (TLDs) J Basic Appl Sci 2012;8:690–5 [10] Cherry P, Duxbury A Practical radiotherapy: physics and equipment John Wiley & Sons; 2009 [11] Nette H, Onori S, Fattibene P, Regulla D, Wieser A Coordinated research efforts for establishing an in international radiotherapy dose intercomparison service based on the alanine/ESR system Appl Radiat Isot 1993;44:IN1–IN11 [12] Taylor G, Lilley E The analysis of thermoluminescent glow peaks in LiF (TLD100) J Phys D: Appl Phys 1978;11:567 [13] Anacak Y, Arican Z, Bar-Deroma R, Tamir A, Kuten A Total skin electron irradiation: evaluation of dose uniformity throughout the skin surface Med Dosim 2003;28:31–4 [14] Delgado A, Ros JG Evolution of TLD-100 glow peaks IV and V at elevated ambient temperatures J Phys D: Appl Phys 1990;23:571 [15] Derreumaux S, Chavaudra J, Bridier A, Rossetti V, Dutreix A A European quality assurance network for radiotherapy: dose measurement procedure Phys Med Biol 1995;40:1191 [16] Swinnen A Quality assurance in radiotherapy: development and validation of a mailed dosimetry procedure for external audits using a multipurpose phantom and in vivo dosimetry Katholieke Universiteit Leuven; 2005 [17] Banjade D, Raj TA, Ng B, Xavier S, Tajuddin A, Shukri A Entrance dose measurement: a simple and reliable technique Med Dosim 2003;28:73–8 [18] Andreo P, Burns DT, Hohlfeld K, Huq MS, Kanai T, Laitano F, et al Absorbed dose determination in external beam radiotherapy: an international code of practice for dosimetry based on standards of absorbed dose to water IAEA TRS 2000;398 [19] Stanton L, Day J, Brattelli S, Lightfoot D, Vince M, Stanton R Comparison of ion chamber and TLD dosimetry in mammography Med Phys 1981;8:792–8 Please cite this article in press as: Waqar M et al Egypt J Radiol Nucl Med (2017), http://dx.doi.org/10.1016/j.ejrnm.2017.01.012 ... are annealing, heating rate and its uniformity, size and history of sample, threading instrument TLD- 100s are heated before irradiation first at 400 °C for one hour followed by 100 °C for two hours... values of TLDs (DTLD) and IC (DIC) for X-ray beams with energy MV measured at depth of 1.5 cm Average relative variation for square TLD chips from that of IC readings were calculated The maximum and. .. with ionization chamber are shown in Tables and Average Fig Comparison of TLD (square chips) and ion chamber response at the depth of 1.5 cm Fig Comparison of TLD (circular chips) and ion chamber