Clinical thermoluminescence dosimetry: how do expectations results compare?* (original) (raw)
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Clinical thermoluminescence dosimetry: how do expectations and results compare?
Radiotherapy and Oncology, 1993
Thermoluminescence dosimetry (TLD) for radiotherapy treatment verification is performed in the Prince of Wales Hospital in Sydney for a wide range of applications: (A) to determine the dose in difficult treatment geometries, (B) to record the dose to critical organs, and (C) to monitor special treatments such as total body irradiation (TBI). TLD measurements were performed with the aim to investigate cases where dose prediction is difficult and not as part of a routine verification procedure. We reviewed 1058 reports of TLD performed during the treatment of 502 patients between 1986 and 1991 to evaluate how the TLD results compare with the dose determined by the treatment plan. Reasons for possible discrepancies should be identified. In 19% of all investigated cases a discrepancy of more than 10% was found between expected and measured doses. The discrepancies could be divided into three groups: (1) errors made in the TLD determination or evaluation, such as placement errors of the TLD chips (21% of all discrepancies); (2) mistakes made during the patient set-up, such as insufficient shielding or inadequate patient immobilisation (30~o); (3) inadequate treatment planning and dose calculation procedure, such as wrong inverse square law corrections or errors due to limitations of the two-dimensional treatment planning system used (41~0 of all). In 8% of all discrepancies the reason remained unclear. A number of changes to treatment plans and modalities (e.g. changed scrotal shield, modified bolus) were introduced due to TLD results. The increasing number of TLD requests per year attests to the value of TLD as a treatment verification method in clinical practice.
The IAEA/WHO TLD postal programme for radiotherapy hospitals
Radiotherapy and Oncology, 2000
Background and purpose: Since 1969 the International Atomic Energy Agency (IAEA), together with the World Health Organization (WHO), has performed postal TLD audits to verify the calibration of radiotherapy beams in developing countries. Materials and methods: A number of changes have recently been implemented to improve the ef®ciency of the IAEA/WHO TLD programme. The IAEA has increased the number of participants and reduced signi®cantly the total turnaround time to provide results to the hospitals within the shortest possible time following the TLD irradiations. The IAEA has established a regular follow-up programme for hospitals with results outside acceptance limits of^5%. Results: The IAEA has, over 30 years, veri®ed the calibration of more than 3300 clinical photon beams at approximately 1000 radiotherapy hospitals. Only 65% of those hospitals who receive TLDs for the ®rst time have results within the acceptance limits, while more than 80% of the users that have bene®ted from a previous TLD audit are successful. The experience of the IAEA in TLD audits has been transferred to the national level. The IAEA offers a standardized TLD methodology, provides guidelines and gives technical backup to the national TLD networks. Conclusion: The unsatisfactory status of the dosimetry for radiotherapy, as noted in the past, is gradually improving; however, the dosimetry practices in many hospitals in developing countries need to be revised in order to reach adequate conformity to hospitals that perform modern radiotherapy in Europe, USA and Australia.
A thermoluminescent dosimetry postal dose inter-comparison of radiation therapy centres in Malaysia
Australasian Physics & Engineering Sciences in Medicine, 2004
A thermoluminescent dosimetry (TLD) postal dose inter-comparison was carried out amongst radiotherapy centres in Malaysia. The aim of this TLD inter-comparison was to compare the uniformity involved in the measurement of absorbed dose among the participating centres. A set of 5 TLD chips placed within acrylic trays were mailed to all participating centres for irradiation to an absorbed dose to water of 2 Gy. Measurements were made for 6 MV and 60 Co photon beams. Results show an agreement of ±5% for all but three radiotherapy centres. The ratios of the TLD readings to that of the reference centre are comparable with other national/regional dose inter-comparisons. The importance of a proper ongoing quality assurance program is essential in maintaining the consistency and uniformity of doses delivered.
Trust, but verify – Accuracy of clinical commercial radiation Treatment Planning Systems
Journal of Physics: Conference Series, 2014
ABSTRACT Computer based Treatment Planning Systems (TPS) are used worldwide to design and calculate treatment plans for treating radiation therapy patients. TPS are generally well designed and thoroughly tested by their developers and local physicists prior to clinical use. However, the wide-reaching impact of their accuracy warrants ongoing vigilance. This work reviews the findings of the Australian national audit system and provides recommendations for checks of TPS. The Australian Clinical Dosimetry Service (ACDS) has designed and implemented a national system of audits, currently in a three year test phase. The Level III audits verify the accuracy of a beam model of a facility's TPS through a comparison of measurements with calculation at selected points in an anthropomorphic phantom. The plans are prescribed by the ACDS and all measurement equipment is brought in for independent onsite measurements. In this first version of audits, plans are comparatively simple, involving asymmetric fields, wedges and inhomogeneities. The ACDS has performed 14 Level III audits to-date. Six audits returned at least one measurement at Action Level, indicating that the measured dose differed more than 3.3% (but less than 5%) from the planned dose. Two audits failed (difference >5%). One fail was caused by a data transmission error coupled with quality assurance (QA) not being performed. The second fail was investigated and reduced to Action Level with the onsite audit team finding phantom setup at treatment a contributing factor. The Action Level results are attributed to small dose calculation deviations within the TPS, which are investigated and corrected by the facilities. Small deviations exist in clinical TPS which can add up and can combine with output variations to result in unacceptable variations. Ongoing checks and independent audits are recommended.
In present study, a special TLD holder inserted to a solid water phantom for TLD irradiation was designed and results were compared with the TLD results irradiated in a plastic bucked using International Atomic Energy Agency (IAEA), standard TLD holder as recommended by IAEA. Powder TLD-100 was used in the study and the capsules filling powder TLD were irradiated using Co-60 beams in RW3 type solid phantom with new holder. The absorbed dose measurements for TLD were performed by Harshaw 4500 model TLD reader and the results were confirmed using a 0.6 cc ionization chamber in RW3 plastic phantom. For different irradiation setup, the closest dose values to the prescribed dose of 2 Gy were only obtained with using the new TLD holder (2.022+ 0.017cGy) with lowest error value. The average and standard deviation for standard IAEA water phantom and plastic bucked set-up were 2.014+0.024 cGy and 1.948+0.062cGy respectively. While the maximum average absolute difference (%3.5) and the maximum % error (%3.16) were found in the hospital condition with bucket filled with water, the minimum average absolute difference and the minimum % error were %1.32 and %0.86 respectively, with our new TLD holder in the solid water phantom . In our opinion, the reason of this good consistency is the reproducibility of TLD position that created by means of our TLD holder. This study shows that non-standard conditions may cause important differences between SSDL (Secondary Standard Dosimetry Laboratory) and hospital dose results.
The British journal of radiology, 2015
Dosimetry audit plays an important role in the development and safety of radiotherapy. National and large scale audits are able to set, maintain and improve standards, as well as having the potential to identify issues which may cause harm to patients. They can support implementation of complex techniques and can facilitate awareness and understanding of any issues which may exist by benchmarking centres with similar equipment. This review examines the development of dosimetry audit in the UK over the last 30 years, including the involvement of the UK in international audits. A summary of audit results is given, with an overview of methodologies employed and lessons learnt. Recent and forthcoming more complex audits are considered, with a focus on future needs including the arrival of proton therapy in the UK and other advanced techniques such as 4D radiotherapy delivery and verification, stereotactic radiotherapy and MR linacs. The work of the main quality assurance and auditing bo...
Performance Evaluation of Thermolumniscence Dosimeters in Personnel in-Vivo Dosimetry
Thermolumniscence dosimeters (TLDs) are the most widely used dosimeters for personal dosimetry in radiodiagnosis and radiotherapy for in vivo measurements in most hospitals due to their availability, low cost, tissue equivalent and their ability to withstand high environmental conditions. To evaluate the dosimetric performance effectiveness of TLDs 100H, Calibrated and annealed LiF (Ti), Mg, Cu based TLD badges were officially obtained from Center for Energy Research and Training (CERT), Zaria and were serially irradiated using XR 6000 GE haulum x-ray machine with frequency of 50/60Hz under clinical settings. The TLDs readings were obtained for absorbed doses (personal dose equivalents); Hp(10) and Hp(0.07) through heating using Harshaw 4500 automatic TLD reader at CERT Zaria. The readings obtained ranged between 27.53 mSv and 24.67 mSv in homogeneity test with a factor of 0.12, representing 12% of percentage variation of readings. The mean of the evaluated doses and the standard deviation were 26.26 mSv and 0.02 mSv. The TLD badges homogeneity were 12%, 3.9% collectively and 2.1% separately for reproducibility performance test, 6% averaged for linearity, less than 2% in fading test and 0.11 mSv for self-irradiation performance test. TLDs performance tests conducted were found to satisfy the criteria of the international standard for TL dosimetry system for personal monitoring (IEC 1066 standard) except in the self-irradiation test which reveals slight increase in mSv values (of 0.01 mSv).
Radiotherapy and Oncology, 2003
Background and purpose: The IAEA/WHO TLD postal programme for external audits of the calibration of high-energy photon beams used in radiotherapy has been in operation since 1969. This work presents a survey of the 1317 TLD audits carried out during 1998-2001. The TLD results are discussed from the perspective of the dosimetry practices in hospitals in developing countries, based on the information provided by the participants in their TLD data sheets. Materials and methods: A detailed analysis of the TLD data sheets is systematically performed at the IAEA. It helps to trace the source of any discrepancy between the TLD measured dose and the user stated dose, and also provides information on equipment, dosimetry procedures and the use of codes of practice in the countries participating in the IAEA/WHO TLD audits. Result: The TLD results are within the 5% acceptance limit for 84% of the participants. The results for accelerator beams are typically better than for Co-60 units. Approximately 75% of participants reported dosimetry data, including details on their procedure for dose determination from ionisation chamber measurements. For the remaining 25% of hospitals, who did not submit these data, the results are poorer than the global TLD results. Most hospitals have Farmer type ionisation chambers calibrated in terms of air kerma by a standards laboratory. Less than 10% of the hospitals use new codes of practice based on standards of absorbed dose to water. Conclusion: Despite the differences in dosimetry equipment, traceability to different standards laboratories and uncertainties arising from the use of various dosimetry codes of practice, the determination of absorbed dose to water for photon beams typically agrees within 2% among hospitals. Correct implementation of any of the dosimetry protocols should ensure that significant errors in dosimetry are avoided.