Absolute measurement of LDR brachytherapy source emitted power: Instrument design and initial measurements

Malin, Martha; Palmer, B; DeWerd, Larry A.

doi:10.1118/1.4939666

Cited by 5 publications

(3 citation statements)

References 39 publications

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“…They successfully showed the feasibility of interferometry for absorbed dose measurement in HDR brachytherapy with 30 µm spatial resolution and a standard deviation on the measurements of around 2%. Building on the work by Stump et al (2005) and Malin et al (2014Malin et al ( , 2016 proposed a novel cryogenic calorimeter for measurement of emitted power from LDR brachytherapy sources. The measurements had an uncertainty ranging between 2.6% to 4.5% (k = 1).…”

Section: Other Calorimetric Techniquesmentioning

confidence: 99%

Absorbed dose calorimetry

2020

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This article reviews the development and summarizes the state-of-the-art in absorbed dose calorimetry for all the common clinical beam modalities covered in reference dosimetry codes of practice, as well as for small and nonstandard fields, and brachytherapy. It focuses primarily on work performed in the last ten years by national laboratories and research institutions and is not restricted to primary standard instruments. The most recent absorbed dose calorimetry review article was published over twenty years ago by Ross and Klassen ( Phys. Med. Biol. 41 1–29), and even then, its scope was limited to water calorimeters. Since the application of calorimetry to the measurement of radiation has a long and often overlooked history, a brief introduction into its origins is provided, along with a summary of some of the landmark research that have shaped the current landscape of absorbed dose calorimeters. Technical descriptions of water and graphite calorimetry are kept general, as these have been detailed extensively in relatively recent review articles (e.g. McEwen and DuSautoy ( Metrologia 46 S59–79) and Seuntjens and Duane ( Metrologia 46 S39–58). The review categorizes calorimeters by the radiation type for which they are applied; from the widely established standards for Co-60 and high-energy x-rays, to the prototype calorimeters used in high-energy electrons and hadron therapy. In each case, focus is placed on the issues and constraints affecting dose measurement in that beam type, and the innovations developed to meet these requirements. For photons, electrons, proton and carbon ion beams, a summary of the ionization chamber beam quality conversion factors (kQ) determined using said calorimeters is also provided. The article closes with a look forward to some of the most promising new techniques and areas of research and speculates about the future clinical role of absorbed dose calorimetry.

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Section: Other Calorimetric Techniquesmentioning

confidence: 99%

Absorbed dose calorimetry

2020

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“…In low-dose rate (LDR) treatments, the radioisotope 125 I is most commonly used, whereas 192 Ir is most common in high-dose rate (HDR) treatments. 75,76 There are several other radioisotopes that have also been explored in brachytherapy; these include 169 Yb, 75 Se,…”

Section: Introductionmentioning

confidence: 99%

Quantifying Radiobiological Variation in Cancer Radiotherapy Using Monte Carlo Simulation and Doped Plastic Scintillators

Nusrat¹

2021

Preprint

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This dissertation examines the extent to which radiobiological variations occur in photon radiotherapy, and then presents a novel methodology and detector prototype to measure this variation. In the first section, I examine the change in maximum RBE (RBEM) outside the primary field in open and composite 6 MV x-ray beams. This is done using Monte Carlo simulation and microdosimetric techniques. It was found that when comparing an open 10 10 cm2 6 MV beam to a composite 10 10 cm2 beam comprising one hundred 1x 1 cm2 beamlets, the out-of-field increase in RBE occurs much closer to the field edge in the composite case. This finding may have consequences for IMRT cases in which large amount of scattered radiation may be causing a higher than expected effective dose to organs at risk. In the second section, the maximum RBE variation is examined in the context of brachytherapy. The sources examined include 192Ir, 125I, and 169Yb. It was determined that maximum RBE of 125I relative to the source position did not vary significantly as distance from the source was increased, however, 192Ir and 169Yb were found to exhibit RBEM increases of 3.0% and 6.6% at a distance of 8 cm, respectively. Also, the impact of this variation on an HDR 192Ir prostate treatment plan was examined; it was found that RBEM hotspots of +3.6% occur at the treatment plan’s periphery. In the third part, the impact of lead doping on plastic scintillator response is quantified, a major step required for the development of the LET detector prototype. In this stage, 4 differently doped plastic scintillators were obtained, and measurements were conducted in low and medium LET beams. Using Geant4 Monte Carlo and the measured scintillator responses, the scintillator parameters: kB and L0 were determined as a function of dopant concentration and effective atomic number. Finally, the uniquely energy dependent scintillators were combined into a detector prototype used to measure the LET spectra produced by five low energy photon beams. These beams included four orthovoltage energies (100, 180, 250, and 300 kVp) along with an 192Ir HDR source. In this proof-of-principle work, the detector prototype and technique was found to accurately determine the LET spectra and the mean LET for all beams with the exception of the 100 kVp orthovoltage beam. Potential applications for the real-time LET detector prototype and technique described in this dissertation include LET measurement in radiotherapy, allowing for biologically optimized treatment plans improving patient care. This technique and prototype also has numerous applications in non-medical fields such as health physics, space travel dosimetry, and nuclear safety.

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“…Brachytherapy may be more susceptible to RBE variations given that the radioactive sources used are lower in energy. In low-dose rate (LDR) treatments, the radioisotope 125 I is most commonly used, whereas 192 Ir is most common in highdose rate (HDR) treatments [4,5]. There are several other radioisotopes that have also been explored in brachytherapy; these include 169 Yb 75 ,Se 153 ,Gd, and 1.1.…”

Section: Introductionmentioning

confidence: 99%

Maximum RBE change in ¹⁹²Ir, ¹²⁵I, and ¹⁶⁹Yb brachytherapy and the corresponding effect on treatment planning

Nusrat

Karim-Picco²,

Pang³

et al. 2020

Biomed. Phys. Eng. Express

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Purpose: The purpose of this study was to examine RBE variation as a function of distance from the radioactive source, and the potential impact of this variation on a realistic prostate brachytherapy treatment plan. Methods: Three brachytherapy sources ( 125 I, 192 Ir, and 169 Yb) were modelled in Geant4 Monte Carlo code, and the resulting electron energy spectrum in water in 3D space around these sources was scored (voxel size of 2 mm 3 ). With this energy spectrum, microdosimetric techniques were used to calculate the maximum RBE, RBE M , as a function of distance from the source. RBE M of 125 I relative to 192 Ir was calculated in order to validate simulations against literature; all other RBE M calculations were done by normalizing electron fluence at various distances to the source position. In order to examine the impact of RBE M variation in treatment planning, a realistic 192 Ir prostate plan was re-evaluated in terms of RBE instead of absorbed dose. Results: The RBE M of 125 I, 192 Ir, and 169 Yb at 8 cm away from the source was 0.994 (+/−0.002), 1.030 (+/−0.003), and 1.066 (+/−0.008), respectively. RBE M in the HDR prostate treatment plan exhibited several hot (+3.6% in RBE M ) spots. Conclusions: The large increase RBE M observed in 169 Yb has not yet been described in the literature. Despite the presence of radiobiological hotspots in the HDR treatment, these variations are likely nominal and clinically insignificant. 103Pd. These sources have different energy spectra and therefore have different mean energies (table 1).Since it is known that lower energy particles are more damaging, the question of whether RBE changes and if so by how much has been posed many times before [6][7][8][9][10]. In this section, the previous works on RECEIVED

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Absolute measurement of LDR brachytherapy source emitted power: Instrument design and initial measurements

Cited by 5 publications

References 39 publications

Absorbed dose calorimetry

Absorbed dose calorimetry

Quantifying Radiobiological Variation in Cancer Radiotherapy Using Monte Carlo Simulation and Doped Plastic Scintillators

Maximum RBE change in ¹⁹²Ir, ¹²⁵I, and ¹⁶⁹Yb brachytherapy and the corresponding effect on treatment planning

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Absolute measurement of LDR brachytherapy source emitted power: Instrument design and initial measurements

Cited by 5 publications

References 39 publications

Absorbed dose calorimetry

Absorbed dose calorimetry

Quantifying Radiobiological Variation in Cancer Radiotherapy Using Monte Carlo Simulation and Doped Plastic Scintillators

Maximum RBE change in 192Ir, 125I, and 169Yb brachytherapy and the corresponding effect on treatment planning

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Maximum RBE change in ¹⁹²Ir, ¹²⁵I, and ¹⁶⁹Yb brachytherapy and the corresponding effect on treatment planning