Technical note: On the reliability of laboratory beta-source calibration for luminescence dating

The dose rate of the 90Sr / 90Y beta source used in most luminescence readers is a laboratory key parameter. There is a well-established body of knowledge about parameters controlling accuracy and precision of the calibration value but some hard-to-explain inconsistencies still exist. Here, we have investigated the impact of grain size, aliquot size and irradiation geometry on the resulting calibration value through experiments and simulations. The resulting data indicate that the dose rate of an individual beta source results from the interplay of a number of parameters, most of which are well established by previous studies. Our study provides evidence for the impact of aliquot size on the absorbed dose in particular for grain sizes of 50–200 µm. For this grain-size fraction, the absorbed dose is enhanced by ∼ 10 %–20 % as aliquot size decreases due to the radial increase of dose rate towards the centre of the aliquot. The enhancement is most variable for 50–100 µm grains mounted as aliquots of < 8 mm size. The enhancement is reversed when large grains are mounted as small aliquots due to the edge effect by which the dose induced by backscattered electrons is reduced. While the build-up of charge dictates the increase of absorbed dose with the increase of grain size, this principle becomes more variable with changing irradiation geometry. We conclude that future calibration samples should consist of subsamples composed of small, medium, large and very large quartz grains, each obtaining several gamma doses. The calibration value measured with small, medium and large aliquots is then obtained from the inverse slope of the fitted line, not from a single data point. In this way, all possible irradiation geometries of an individual beta source are covered, and the precision of the calibration is improved.

Radiation Dose Enhancement in Megavoltage Radiation Therapy using Au, Gd, Pt, Ag, and Bi Nanoparticles of Various Concentration Level

A digital phantom was created from a CT scan of a patient’s head and employed together with GATE 8.2 Monte Carlo modeling of a linear accelerator of nominal 6 MV energy to simulate an irradiation geometry for a typical tumor volume centrally within the brain region. Although simplistic in arrangement, this setup was considered appropriate to demonstrate the dose enhancements that may be expected for megavoltage external beam radiation therapy for nanoparticles (NP) of different elemental composition and concentration. Ag, Gd, Pt, Au and Bi were modeled in concentrations varying from 15 mg NP / gram tissue to 70 mg NP / gram tissue. The maximum Average Dose Enhancement Factor (ADEF) to the Gross Tumour Volume (GTV) observed was 3 % for 70 mg NP / gram tissue of Bi.

Analysis of IAEA thermoluminiscent and radiophotoluminiscent postal dose audit of teleradiotherapy equipment performed in Russia over the past 20 years

The article addresses results of IAEA thermoluminescent (TL) and radio-photoluminescent (RPL) postal dose audit of the external beam radiotherapy (EBRT) equipment, linacs and cobalt units, performed in Russia over the past 20 years between 1999 and 2019. The aim of the work was to evaluate results of IAEA dose audit: to compare the dose determined at the IAEA Dosimetry La-boratory with the dose stated by the Russian participant. The acceptable deviation between the doses is ≤5%. In the first-time audit 817 dosimeter sets were used, 430 of them were irradiated with 60Co of EBRT machines and 387 sets were irradiated with bremsstrahlung radiation of vari-ous energies. To search factors that affected the clinical dosimetry quality 133 beams, mainly 60Co gamma-ray beams, were retested. Over the twenty-year period a total of 9% of bremsstrah-lung beams and 27% of gamma-ray beams exceeded the 5% tolerance interval. The observed deviation may be resulted from the use of outdated radiotherapy equipment, lack of trained workers with high-level experience and competence in medical radiology, medical physics, IT, as well as lack of appropriate dosimetry systems. The common reason of observed dosimetry audit outcomes may be the result of inconsistency between irradiation geometry calculated with the use of treatment planning system and the true irradiation geometry, as well as errors of calcula-tion. Having assessed the worksheets we have found many partially completed sheets, infor-mation on irradiation conditions and dose calculation process was unavailable or incorrect, all mentioned made it difficult to analyze causes of observed deviations. Nonetheless, we witness a positive trend in the dose audit outcomes, at the same time, the amount of errors in Russian worksheets is still larger than in other countries-participants of the IAEA/WHO audit. It is possible to improve the radiation therapy quality and to increase radiotherapy benefits and effectiveness due to expanding the practice of autonomous auditors at the Federal and regional levels, as well as organizing of specialists’ on-site visits to Radiotherapy Centers. Taking such actions makes it possible avoidance of communication problems and increase in the detection rate of true causes of observed shortcomings in clinical dosimetry quality.

CALCULATION OF BNCT DOSIMETRY FOR BRAIN CANCER BASED ON KARTINI RESEARCH REACTOR USING PHITS CODE

Cancer is a dangerous disease caused by the growth of a mass of cells that are unnatural and uncontrollable. Glioblastoma, also called as glioblastoma multiforme (GBM), is one of dangerous brain cancer. The dismal prognosis associated with glioblastoma is attributable not only to its aggressive and infiltrative behavior, but also to its location typically deep in the parenchyma of the brain. In resolving this chalenge, the BNCT method can be a solution. This study aims to calculate BNCT dosimetry in different of cancer positions and irradiation geometries using PHITS code. The results show that the deeper the cancers target at brain the slower the total absorbed dose rate of cancer target. It takes a longer treatment time. Based on the treatment time and total absorbed dose rate of cancer target, the TOP irradiation geometry is an appropriate choice in treating the cancer target in this case. To achieve the histopathological cure of GBM at the primary site, the absorbed dose of brain was calculated to be 1.07 Gy and 1.64 Gy for the LLAT and PA irradiation geometry, respectively. While, for cancer position of 3 cm, 5 cm, 7.15 cm, 9 cm, and 11 cm, the absorbed dose of brain is 0.25 Gy, 0.48 Gy, 0.85 Gy, 1.33 Gy, and 2.01 Gy, respectively. In addition to the stochastic effect, it was found also deterministic effects that may be produced such as cataracts.Keywords: BNCT dosimetry; GBM; brain cancer cases; PHITS; MIRD phantom PERHITUNGAN DOSIMETRI BNCT PADA KANKER OTAK BERBASIS REAKTOR RISET KARTINI MENGGUNAKAN PROGRAM PHITS. Kanker merupakansalahsatu penyakit berbahaya yang diakibatkan oleh tumbuhnya sekumpulan massa sel-sel yang tidak wajar dan tidak terkendali. Salah satu penyakit kanker otak yang berbahaya adalah Glioblastoma atau yang biasa disebut Glioblastoma Multiforme (GBM). Prognosis suram terkait dengan GBM tidak hanya untuk perilaku agresif dan infiltrasi, tetapi juga terhadaplokasi yang jauh di dalam parenkim otak. Untuk menjawab hal tersebut, Boron Neutron Capture Therapy (BNCT) dapat menjadi solusi. Penilitian ini bertujuan untuk menghitung dosimetri BNCT dalam berbagai posisikan kerdan geometri penyinaran dengan menggunakan program PHITS. Hasil perhitungan menunjukkan bahwa semakin dalam target kanker di otak maka semakin kecil total laju dosis serap dari target kanker. Semakin dalam target kanker di otak dibutuhkan waktu pengobatan yang semakin lama. Berdasarkan waktu pengobatan dan laju dosis serap dari target kanker, bidang penyinaran TOP merupakan pilihan yang tepat dalam mengobati target kanker dalam kasus ini. Untuk mencapai penyembuhan GBM secara histopatologis di lokasi utama, dosis serap dari otak dihitung berturut-turut sebesar 1,07 Gy dan 1,64 Gy untuk bidang penyinaran LLAT dan PA. Sedangkan, untuk posisi kanker 3 cm, 5 cm, 7,15 cm, 9 cm, dan 11 cm, berturut-turut dosis serap dari otak adalah 0,25 Gy, 0,48 Gy, 0,85 Gy, 1,33 Gy, and 2,01 Gy. Selain adanya efek stokastik, ditemukan juga efek deterministik yang mungkin dihasilkan seperti katarak.Kata kunci: Dosimetri BNCT, GBM, kasuskankerotak, geometripenyinaran, posisikanker, ORNLMIRD phantom.

Gamma irradiation effects in optical fibres, splitters, and connectors

The paper presents a brief overview of contemporary ELION techniques with stress on their use for material modification and dosimetry. In the attempt to avoid some common misjudges of irradiation effects, special attention is paid to exact definition of irradiation geometry and careful adjustment of dose rates, which enable a proper elaboration of experimental results. In particular, effects of g-rays irradiation on properties of commercial optical fibres, splitters, connectors, and fibre joints are examined, which enables monitoring of irradiation effects in complex configurations made of materials with different radiation hardness (resistance). It has been established that g-rays irradiation of the investigated elements influences, in different ways, the transmission of laser beam signals of various wavelengths, under different modulation regimes. After irradiation, the signal attenuation is noticeably larger, both in optical connectors and optical splitter, than before it, and the effect increases in time. The effects are more pronounced at the 99 % than at the 1 % Y-splitter output at both measured wavelengths, and are more pronounced at 1310 nm than at 1550 nm.