Different dosimeters/detectors used in small-field dosimetry: Pros and cons

Parwaie, Wrya; Refahi, Soheila; Ardekani, Mahdieh Afkhami; Farhood, Bagher

doi:10.4103/jmss.jmss_3_18

Cited by 46 publications

(17 citation statements)

References 93 publications

(102 reference statements)

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“…Owing to their excellent tissue-equivalence and the ability to be miniaturized, multiple investigators have recommended the use of organic scintillators for small field dosimetry [21,45,92]. In particular, organic scintillators, such as the commercially available Exradin W1 (Standard Imaging) can be used as reference detectors for small fields against which correction factors for other detectors can be derived [45].…”

Section: Scintillatorsmentioning

confidence: 99%

“…These problems associated with small fields are well-documented [20]. This warranted a need for highresolution detectors which most vendors now typically provide for the measurement of cumulative dose distributions [21]. With the emergence of FLASH and other promising high dose-rate modalities, such as Microbeam Radiation Therapy (MRT) [22] and Synchrotron stereotactic radiotherapy [23], it is expected that new dosimetric challenges will arise.…”

Section: Introductionmentioning

confidence: 99%

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Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

et al. 2020

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While spatial dose conformity delivered to a target volume has been pushed to its practical limits with advanced treatment planning and delivery, investigations in novel temporal dose delivery are unfolding new mechanisms. Recent advances in ultra-high dose radiotherapy, abbreviated as FLASH, indicate the potential for reduction in healthy tissue damage while preserving tumor control. FLASH therapy relies on very high dose rate of > 40Gy/s with sub-second temporal beam modulation, taking a seemingly opposite direction from the conventional paradigm of fractionated therapy. FLASH brings unique challenges to dosimetry, beam control, and verification, as well as complexity of radiobiological effective dose through altered tissue response. In this review, we compare the dosimetric methods capable of operating under high dose rate environments. Due to excellent dose-rate independence, superior spatial (∼ <1 mm) and temporal (∼ns) resolution achievable with Cherenkov and scintillation-based detectors, we show that luminescent detectors have a key role to play in the development of FLASH, as the field rapidly progresses toward clinical adaptation. Additionally, we show that the unique ability of certain luminescence-based methods to provide tumor oxygenation maps in real-time with submillimeter resolution can elucidate the radiobiological mechanisms behind the FLASH effect. In particular, such techniques will be crucial for understanding the role of oxygen in mediating the FLASH effect.

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Section: Scintillatorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

et al. 2020

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“…The iris collimator creates fields of polygon with different sizes from 5 mm to 60 mm. Using such small field sizes, accurate and reliable dose measurements methods are required 7–13 …”

Section: Introductionmentioning

confidence: 99%

“…Using such small field sizes, accurate and reliable dose measurements methods are required. [7][8][9][10][11][12][13] Radiochromic films are the gold standard for 2D verification of dose distributions during radiation therapy and for many geometric quality assurance (QA) tests.…”

Section: Introductionmentioning

confidence: 99%

Radioluminescence imaging feasibility for robotic radiosurgery field size quality assurance

et al. 2022

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To investigate the feasibility of radioluminescence imaging (RLI) as a novel 2D quality assurance (QA) dosimetry system for CyberKnife®. Methods: We developed a field size measurement system based on a commercial complementary metal oxide semiconductor (CMOS) camera facing a radioluminescence screen located at the isocenter normal to the beam axis. The radioluminescence light collected by a lens was used to measure 2D dose distributions. An image transformation procedure, based on two reference phantoms, was developed to correct for projective distortion due to the angle (15 • ) between the optical and beam axis. Dose profiles were measured for field sizes ranging from 5 mm to 60 mm using fixed circular and iris collimators and compared against gafchromic (GC) film. The corresponding full width at half maximum (FWHM) was measured using RLI and benchmarked against GC film. A small shift in the source-to-surface distance (SSD) of the measurement plane was intentionally introduced to test the sensitivity of the RLI system to field size variations. To assess reproducibility, the entire RLI procedure was tested by acquiring the 60 mm circle field three times on two consecutive days. Results:The implemented procedure for perspective image distortion correction showed improvements of up to 1 mm using the star phantom against the square phantom. The FWHM measurements using the RLI system indicated a strong agreement with GC film with maximum absolute difference equal to 0.131 mm for fixed collimators and 0.056 mm for the iris. A 2D analysis of RLI with respect to GC film showed that the differences in the central region are negligible, while small discrepancies are in the penumbra region. Changes in field sizes of 0.2 mm were detectable by RLI. Repeatability measurements of the beam FWHM have shown a standard deviation equal to 0.11 mm. Conclusions:The first application of a RLI approach for CyberKnife® field size measurement was presented and tested. Results are in agreement with GC film measurements.Spatial resolution and immediate availability of the data indicate that RLI is a feasible technique for robotic radiosurgery QA.

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“…To manage these dosimetric issues, which represent new challenges for medical physicists, a new code of practice and formalism has been published [7,8]. Moreover, devices used with larger fields could not be assumed to perform optimally with small ones because different detectors have different dosimetric advantages [9]. Small beam fields characteristics like high dose gradients and energy spectrum space and time variations mean that the ionization chambers (the gold standard detector in radiotherapy dosimetry) are no longer suitable for dosimetric measurements.…”

Section: Introductionmentioning

confidence: 99%

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

et al. 2021

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Many new X-Ray treatment machines using small and/or non-standard radiation fields, e.g., Tomotherapy, Cyber-knife, and linear accelerators equipped with high-resolution multi-leaf collimators and on-board imaging system, have been introduced in the radiotherapy clinical routine within the last few years. The introduction of these new treatment modalities has led to the development of high conformal radiotherapy treatment techniques like Intensity Modulated photon Radiation Therapy, Volumetric Modulated Arc Therapy, and stereotactic radiotherapy. When using these treatment techniques, patients are exposed to non-uniform radiation fields, high dose gradients, time and space variation of dose rates, and beam energy spectrum. This makes reaching the required degree of accuracy in clinical dosimetry even more demanding. Continuing to use standard field procedures and detectors in fields smaller than 3 × 3 cm2, will generate a reduced accuracy of clinical dosimetry, running the risk to overshadowing the progress made so far in radiotherapy applications. These dosimetric issues represent a new challenge for medical physicists. To choose the most appropriate detector for small field dosimetry, different features must be considered. Short- and long-term stability, linear response to the absorbed dose and dose rate, no energy and angular dependence, are all needed but not sufficient. The two most sought-after attributes for small field dosimetry are water equivalence and small highly sensitive (high sensitivity) volumes. Both these requirements aim at minimizing perturbations of charged particle fluence approaching the Charged Particle Equilibrium condition as much as possible, while maintaining high spatial resolution by reducing the averaging effect for non-uniform radiation fields. A compromise between different features is necessary because no dosimeter currently fulfills all requirements, but diamond properties seem promising and could lead to a marked improvement. Diamonds have long been used as materials for dosimeters, but natural diamonds were only first used for medical applications in the 80 s. The availability of reproducible synthetic diamonds at a lower cost compared to natural ones made the diffusion of diamonds in dosimetry possible. This paper aims to review the use of synthetic poly and single-crystal diamond dosimeters in radiotherapy, focusing on their performance under MegaVoltage photon beams. Both commercial and prototype diamond dosimeters behaviour are described and analyzed. Moreover, this paper will report the main related results in literature, considering diamond development issues like growth modalities, electrical contacts, packaging, readout electronics, and how do they affect all the dosimetric parameters of interest such as signal linearity, energy dependence, dose-rate dependence, reproducibility, rise and decay times.

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Different dosimeters/detectors used in small-field dosimetry: Pros and cons

Cited by 46 publications

References 93 publications

Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

Radioluminescence imaging feasibility for robotic radiosurgery field size quality assurance

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

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