Sains Malaysiana 53(6)(2024): 1377-1387

http://doi.org/10.17576/jsm-2024-5306-12

Characterization and Correction of Fading Effects in GeDOFs Microdosimeter for Absorbed Dose Measurements

(Pencirian dan Pembetulan Kesan Pudar dalam Mikrodosimeter GeDOFs untuk Pengukuran Dos Serap)

NORAMALIZA MOHD NOOR¹, NIZAM TAMCHEK², UNG NGIE MIN³, MOHD TAUFIK DOLAH⁴ & MUHAMMAD SAFWAN AHMAD FADZIL^5,*

¹Department of Radiology, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

²Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

³Clinical Oncology Unit, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia

⁴Radiation Safety and Health Division, Malaysian Nuclear Agency, Bangi, 43000 Kajang, Selangor, Malaysia

⁵Diagnostic Imaging and Radiotherapy Program, Centre for Diagnostic, Therapeutic and Investigative Studies, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia

Received: 8 October 2023/Accepted: 2 May 2024

Abstract

This study investigates the thermoluminescence (TL) fading of fabricated germanium-doped optical fibers (GeDOFs) with a focus on TL signal intensity, glow curve, best-fit curve, and correction factor. Two distinct GeDOFs geometries, cylindrical fiber (CF) and flat fiber (FF), were compared for TL intensity decay under 6 MV and 10 MV photon beams. TL intensity measurements were recorded from the first day post-irradiation to the 106^th day and a comparison of two fading curve-fitting approaches was carried out. Fading correction factor () was derived, and the corresponding uncertainties were calculated. Over time, GeDOFs exhibited a decline in TL intensity, with a notably rapid decay occurring in the initial 30 days after irradiation. The most substantial TL intensity loss was observed in FF, with values of 58.9% for 6 MV and 63.4% for 10 MV. The evaluation of curve fitting showed that the best conformity was achieved through a single exponential decay equation model. The area under the glow curve decreased as the time between GeDOFs irradiation and TL readout increased. was determined by comparing the fading function of reference GeDOFs to that of the measured ones. The estimated uncertainties associated with  were found to be 0.06% for CF and 0.12% for FF, respectively. GeDOFs exhibit fading characteristics influenced by TL readout interval time and radiation energy. When quantifying the absorbed dose from photon beams, it is crucial to account for the fading correction factor to ensure the precise and accurate measurement of the dose.

Keywords: Correction factor; dosimetry audit; fading; Ge-doped optical fibres

Abstrak

Kajian ini meneliti kemerosotan termopendarcahaya (TL) gentian optik dop Ge yang difabrikasi (GeDOFs) dengan tumpuan diberikan kepada keamatan isyarat TL, lengkungan bara, lengkungan padanan terbaik dan faktor pembetulan. Dua geometri GeDOFs yang berbeza, gentian silinder (CF) dan gentian leper (FF) dibandingkan tahap kemerosotan keamatan TL di bawah sinaran foton 6 MV dan 10 MV. Pengukuran keamatan TL direkodkan dari hari pertama selepas penyinaran hingga hari ke-106 dan perbandingan antara dua pendekatan padanan lengkungan kemerosotan telah dijalankan. Faktor pembetulan kemerosotan signal ( ) diterbitkan dan ketidakpastian yang berkaitan telah dihitung. Seiring berjalannya masa, GeDOFs menunjukkan penurunan keamatan TL dengan kemerosotan yang ketara berlaku dalam tempoh 30 hari pertama selepas penyinaran. Kehilangan keamatan TL yang paling ketara diperhatikan pada FF, dengan nilai pengurangan sebanyak 58.9% untuk 6 MV dan 63.4% untuk 10 MV. Penilaian padanan lengkungan menunjukkan bahawa padanan terbaik dicapai melalui model persamaan kemerosotan eksponensial tunggal. Kawasan di bawah lengkungan bara berkurang apabila masa antara penyinaran GeDOFs dan pembacaan TL meningkat.  ditentukan dengan membandingkan fungsi kemerosotan signal GeDOFs rujukan dengan yang diukur. Anggaran ketidakpastian yang berkaitan  berada pada kadar 0.06% untuk CF dan 0.12% untuk FF. GeDOFs menunjukkan ciri kemerosotan signal yang dipengaruhi oleh selang masa bacaan TL dan tenaga sinaran. Apabila mengukur dos terserap daripada sinaran foton, adalah penting untuk mempertimbangkan faktor pembetulan kemerosotan signal untuk memastikan pengukuran dos yang tepat.

Kata kunci: Audit dosimetri; faktor pembetulan; gentian optik dop Ge; kemerosotan signal

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*Corresponding author; email: safwanfadzil@ukm.edu.my