Absorbed Dose Determination in External Beam Radiotherapy

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doi:10.61092/iaea.ve7q-y94k

Cited by 3 publications

(6 citation statements)

References 223 publications

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“…The mean energy expended in air per ion pair formed

can be considered similar in both qualities [ 28 ] (p. 40). Assuming that the Bragg–Gray principle is valid, the absorbed dose in water

is related to the mean absorbed dose in the air of the chamber cavity

And the same holds for any other quality Q :

Substituting both equations in Equation (3) yields the following:

Following IAEA TRS 398 formalism [ 26 ], the absorbed dose to water in the PMMA phantom using an Ir-192 source can be obtained from the following Equation (7):

where

is the Farmer chamber Co-60 calibration factor,

is the temperature and pressure corrected ionization measured in the PMMA phantom, and the

factor can be estimated by the Monte Carlo (Equation (6)) from the following:

To compare IVD measurements with treatment planning system (TPS)-calculated values following AAPM TG-43, the quantity of interest is not

, but

, because we want to measure ionization in the PMMA mini-phantom, but we want the absorbed dose in the full scatter geometry of AAPM TG-43. Using a new factor F :

F can be solved from Equations (7)–(9), as follows:

…”

Section: Resultsmentioning

confidence: 99%

“…In this work, the denominator ratio

has not been simulated; it was obtained directly from IAEA TRS 398 [ 26 ] for the PTW PMMA Farmer ionization chamber, as follows:

.…”

Section: Resultsmentioning

confidence: 99%

“…The computer code used for the Monte Carlo simulations is the PENELOPE/PenEasy [ 23 ]. Absorbed dose to water, polystyrene, and air (i.e., D w , D pol , and D air , respectively) were computed using an Ir-192 source model [ 24 ] in two geometries: the 10 cm × 10 cm cylindrical PMMA phantom and a water sphere with a radius of 40 cm [ 6 , 25 ] (full scatter conditions) to obtain the k QQ0 quality factor through International Atomic Energy Agency Technical Report Series (IAEA TRS)-398 formalism [ 26 ]. The obtained factor allows for absorbed dose to water determination in full scatter conditions from the ionization measured in the PMMA phantom.…”

Section: Methodsmentioning

confidence: 99%

“…Following IAEA TRS 398 formalism [26], the absorbed dose to water in the PMMA phantom using an Ir-192 source can be obtained from the following Equation ( 7): (7) where N D,w,Co-60 is the Farmer chamber Co-60 calibration factor, M PMMA phantom is the temperature and pressure corrected ionization measured in the PMMA phantom, and the k PMMMA phantom factor can be estimated by the Monte Carlo (Equation ( 6)) from the following:…”

Section: Monte Carlo Simulations and Experimental Validationmentioning

confidence: 99%

“…F can be solved from Equations ( 7)-( 9), as follows: (10) In this work, the denominator ratio (D w /D air ) I AEA TRS 398 geometry Co-60 has not been simulated; it was obtained directly from IAEA TRS 398 [26] for the PTW PMMA Farmer ionization chamber, as follows:…”

Section: Monte Carlo Simulations and Experimental Validationmentioning

confidence: 99%

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Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

Herreros,

Pérez-Calatayud,

Ballester

et al. 2024

JPM

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(1) Background: High dose gradients and manual steps in brachytherapy treatment procedures can lead to dose errors which make the use of in vivo dosimetry (IVD) highly recommended for verifying brachytherapy treatments. A new procedure was presented to obtain a calibration factor which allows fast and robust calibration of plastic scintillation detector (PSD) probes for the geometry of a compact phantom using Monte Carlo simulations. Additionally, characterization of PSD energy, angular, and temperature dependences was performed. (2) Methods: PENELOPE/PenEasy code was used to obtain the calibration factor. To characterize the energy dependence of the PSD, the signal was measured at different radial and transversal distances. The sensitivity to the angular position was characterized in axial and azimuthal planes. (3) Results: The calibration factor obtained allows for an absorbed dose to water determination in full scatter conditions from ionization measured in a mini polymethylmethacrylate (PMMA) phantom. The energy dependence of the PSD along the radial distances obtained was (2.3 ± 2.1)% (k = 1). The azimuthal angular dependence measured was (2.6 ± 3.4)% (k = 1). The PSD response decreased by (0.19 ± 0.02)%/°C with increasing detector probe temperature. (4) Conclusions: The energy, angular, and temperature dependence of a PSD is compatible with IVD.

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“…The mean energy expended in air per ion pair formed

can be considered similar in both qualities [ 28 ] (p. 40). Assuming that the Bragg–Gray principle is valid, the absorbed dose in water

is related to the mean absorbed dose in the air of the chamber cavity

And the same holds for any other quality Q :

Substituting both equations in Equation (3) yields the following:

Following IAEA TRS 398 formalism [ 26 ], the absorbed dose to water in the PMMA phantom using an Ir-192 source can be obtained from the following Equation (7):

where

is the Farmer chamber Co-60 calibration factor,

is the temperature and pressure corrected ionization measured in the PMMA phantom, and the

factor can be estimated by the Monte Carlo (Equation (6)) from the following:

To compare IVD measurements with treatment planning system (TPS)-calculated values following AAPM TG-43, the quantity of interest is not

, but

, because we want to measure ionization in the PMMA mini-phantom, but we want the absorbed dose in the full scatter geometry of AAPM TG-43. Using a new factor F :

F can be solved from Equations (7)–(9), as follows:

…”

Section: Resultsmentioning

confidence: 99%

“…In this work, the denominator ratio

has not been simulated; it was obtained directly from IAEA TRS 398 [ 26 ] for the PTW PMMA Farmer ionization chamber, as follows:

.…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Monte Carlo Simulations and Experimental Validationmentioning

confidence: 99%

Section: Monte Carlo Simulations and Experimental Validationmentioning

confidence: 99%

See 3 more Smart Citations

Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

Herreros,

Pérez-Calatayud,

Ballester

et al. 2024

JPM

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Organization and operation of multi particle therapy facilities: the Marburg Ion-Beam Therapy Center, Germany (MIT)

Zink,

Baumann,

Theiss

et al. 2024

Health Technol.

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Purpose The Marburg Ion-Beam Therapy Center (MIT) is one of two particle therapy centers in Germany that enables the treatment of patients with both protons and carbon ions. The facility was build by Siemens Healthineers and is one of only two centers worldwide built by Siemens (Marburg, Germany and Shanghai, China). The present report provides an overview of technical and clinical operations as well as research activities at MIT. Methods The MIT was completed in 2011 and uses a synchrotron for accelerating protons and carbon ions up to energies of 250 MeV/u and 430 MeV/u respectively. Three treatment rooms with a fixed horizontal beam-line and one room with a 45 degree beam angle are available. Results Since the start of clinical operations in 2015, around 2.500 patients have been treated at MIT, about 40% with carbon ions and 60% with protons. Currently around 400 patients are treated each year. The majority of the patients suffered from benign and malign CNS tumors (around 40%) followed by head and neck tumors (around 23%). MIT is actively involved in clinical studies with its patients. In addition to clinical operations, there is active research at MIT in the fields of radiation biology and medical physics. The focus is on translational research to improve the treatment of H & N carcinomas and lung cancer (NSCLC). Moreover, intensive work is being carried out on the technical implementation of FLASH irradiation for research purposes. Conclusion The MIT is one of two centers worldwide that were built by Siemens Healtineers and has been successfully in clinical operation since 2015. The service provided by Siemens is guaranteed until 2030, the future after 2030 is currently under discussion.

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Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

Perkins,

Healy,

Coldrey

2024

Phys Eng Sci Med

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The purpose of this work was to determine percentage depth dose (PDD) curves for kilovoltage x-rays from the WOmed-T105 unit, with open-ended steel applicators and beam qualities ranging from 0.5 to 4.2 mm Al. Measurements were made with parallel plate chambers in a water phantom, with extrapolation based on a fth order polynomial used to estimate the surface dose. Measurements were also made with parallel plate chambers in a plastic water phantom, with thin plastic sheets used to obtain detailed measurements at shallow depths (less than 1 mm). Monte Carlo simulations were performed using the EGSnrc package, with two different sources as input: a SpekPy simulation of the xray beam and a full simulation of the x-ray tube, treatment head and applicators. Results showed that all four methods (two measurements and two simulations) agreed within the measurement uncertainty at depths greater than 2 mm. At shallow depths, signi cant differences were noted. At depths less than 0.1 mm, the full Monte Carlo simulation and the solid water measurements showed a sharp spike in surface dose which is attributed to electron contamination, which was not seen in the SpekPy Monte Carlo simulation or the extrapolated water measurements. At depths between 0.1 mm and 2 mm, beyond the range of contaminant electrons, the extrapolated water measurements underestimate the dose by up to 13% compared to the full Monte Carlo simulation and the solid water measurements., attributed to uorescent photons generated in the applicators. This work demonstrates that for open-ended applicators, measurement of depth doses in water with extrapolation of surface dose has the potential to signi cantly underestimate the dose at shallow depths between the surface and 2 mm, even after eliminating electron contamination from the beam.

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Absorbed Dose Determination in External Beam Radiotherapy

Cited by 3 publications

References 223 publications

Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

Characterization of Plastic Scintillator Detector for In Vivo Dosimetry in Gynecologic Brachytherapy

Organization and operation of multi particle therapy facilities: the Marburg Ion-Beam Therapy Center, Germany (MIT)

Determination of kilovoltage x-ray therapy depth doses with open-ended applicators

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