A linear relationship for the LET-dependence of Gafchromic EBT3 film in spot-scanning proton therapy

Anderson, Sarah; Grams, Michael P.; Tseung, H. Wan Chan; Furutani, Keith M.; Beltran, Chris

doi:10.1088/1361-6560/ab0114

Cited by 32 publications

(48 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the simple

g_{Q, Q_{0}}

model, RE was approximated by a first,

R E false(L_{d} false) = a_{0} + a_{1} L_{d},

or fourth order polynomial of

L_{d}

similar to Ref. [17]. As mentioned earlier, the correction factor,

g_{Q, Q_{0}}

, is the reciprocal of RE.…”

Section: Methodsmentioning

confidence: 99%

“…An overall film positioning repeatability of ≤0.3 mm was found in other film experiments using the same measurement setup in‐house. For consistency with literature a value equal to 0.25 mm was propagated into the RE confidence interval (CI) calculation in addition to the standard deviation of the three film measurements.…”

Section: Methodsmentioning

confidence: 99%

“…The relative effectiveness (RE) was introduced to quantify the LET quenching effect . In literature RE is mostly defined either as the ratio of the absorbed dose to water,

D_{w}

, and the film dose,

D_{film}

, required to yield the same effect

R E = {(|, \frac{D_{film}}{D_{w, Q}})}_{iso - effect} = \frac{D (o_{Q_{0}} | p_{Q})}{D (o_{Q_{0}} | p_{Q_{0}})},

or as the ratio of

D_{w}

and the apparent film dose,

D_{w, normalapparent}

, applying the parameters obtained at

Q_{0}

R E = {(|, \frac{D_{w, normalapparent}}{D_{w, Q}})}_{iso - dose} = \frac{D (o_{Q} | p_{Q_{0}})}{D (o_{Q_{0}} | p_{Q_{0}})} .

Those two definitions are fundamentally different and cannot be mutually exchanged due to the nonlinear dependency of dose and net optical density [Eq. ].…”

Section: Introductionmentioning

confidence: 99%

“…A fourth order polynomial correction based on the fluence average LET was applied to correct the depth dose distribution of a single energy (161.6 MeV) proton beam . Another model suggests a correction following the reciprocal of a linear increase with dose‐averaged LET, which was validated for three single energy beams (71.3 MeV, 71.3 MeV plus filter and 159.9 MeV) and one spread‐out Bragg peak (SOBP) . In contrast to those two models based on the averaged LET, the model proposed by Fiorini et al averages the correction factor differential in energy, hence, taking into account the local energy distribution …”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Dose‐ rather than fluence‐averaged LET should be used as a single‐parameter descriptor of proton beam quality for radiochromic film dosimetry

et al. 2020

View full text Add to dashboard Cite

Purpose: The dose response of Gafchromic EBT3 films exposed to proton beams depends on the dose, and additionally on the beam quality, which is often quantified with the linear energy transfer (LET) and, hence, also referred to as LET quenching. Fundamentally different methods to determine correction factors for this LET quenching effect have been reported in literature and a new method using the local proton fluence distribution differential in LET is presented. This method was exploited to investigate whether a more practical correction based on the dose-or fluence-averaged LET is feasible in a variety of clinically possible beam arrangements. Methods: The relative effectiveness (RE) was characterized within a high LET spread-out Bragg peak (SOBP) in water made up by the six lowest available energies (62.4-67.5 MeV, configuration "b 1 ") resulting in one of the highest clinically feasible dose-averaged LET distributions. Additionally, two beams were measured where a low LET proton beam (252.7 MeV) was superimposed on "b 1 ", which contributed either 50% of the initial particle fluence or 50% of the dose in the SOBP, referred to as configuration "b 2 " and "b 3 ," respectively. The proton LET spectrum was simulated with GATE/ Geant4 at all measurement positions. The net optical density change differential in LET was integrated over the local proton spectrum to calculate the net optical density and therefrom the beam quality correction factor. The LET dependence of the film response was accounted for by an LET dependence of one of the three parameters in the calibration function and was determined from inverse optimization using measurement "b 1 ." This method was then validated on the measurements of "b 2 " and "b 3 " and subsequently used to calculate the RE at 900 positions in nine clinically relevant beams. The extrapolated RE set was used to derive a simple linear correction function based on dose-averaged LET (L d ) and verify the validity in all points of the comprehensive RE set. Results: The uncorrected film dose deviated up to 26% from the reference dose, whereas the corrected film dose agreed within 3% in all three beams in water ("b 1 ", "b 2 " and "b 3 "). The LET dependence of the calibration function started to strongly increase around 5 keV/lm and flatten out around 30 keV/lm. All REs calculated from the proton fluence in the nine simulated beams could be approximated with a linear function of dose-averaged LET (RE = 1.0258À0.0211 lm/keV L d ). However, no functional relationship of RE-and fluence-averaged LET could be found encompassing all beam energies and modulations. Conclusions: The film quenching was found to be nonlinear as a function of proton LET as well as of the dose-averaged LET. However, the linear relation of RE on dose-averaged LET was a good approximation in all cases. In contrast to dose-averaged LET, fluence-averaged LET could not describe the RE when multiple beams were applied.

show abstract

“…In the simple

g_{Q, Q_{0}}

model, RE was approximated by a first,

R E false(L_{d} false) = a_{0} + a_{1} L_{d},

or fourth order polynomial of

L_{d}

similar to Ref. [17]. As mentioned earlier, the correction factor,

g_{Q, Q_{0}}

, is the reciprocal of RE.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…The relative effectiveness (RE) was introduced to quantify the LET quenching effect . In literature RE is mostly defined either as the ratio of the absorbed dose to water,

D_{w}

, and the film dose,

D_{film}

, required to yield the same effect

R E = {(|, \frac{D_{film}}{D_{w, Q}})}_{iso - effect} = \frac{D (o_{Q_{0}} | p_{Q})}{D (o_{Q_{0}} | p_{Q_{0}})},

or as the ratio of

D_{w}

and the apparent film dose,

D_{w, normalapparent}

, applying the parameters obtained at

Q_{0}

R E = {(|, \frac{D_{w, normalapparent}}{D_{w, Q}})}_{iso - dose} = \frac{D (o_{Q} | p_{Q_{0}})}{D (o_{Q_{0}} | p_{Q_{0}})} .

Those two definitions are fundamentally different and cannot be mutually exchanged due to the nonlinear dependency of dose and net optical density [Eq. ].…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dose‐ rather than fluence‐averaged LET should be used as a single‐parameter descriptor of proton beam quality for radiochromic film dosimetry

et al. 2020

View full text Add to dashboard Cite

show abstract

“…A beam quality correction factor g Q;Q 0 was applied to correct the apparent dose D apparent from film measurements applying the calibration obtained at the reference beam quality Q 0 , that is, at 2 cm WET in a 179 MeV proton beam. 25 According to literature, 48 it can be derived from the dose-averaged LET:…”

Section: C3 Let Quenching Correctionmentioning

confidence: 99%

Benchmarking a GATE/Geant4 Monte Carlo model for proton beams in magnetic fields

et al. 2019

View full text Add to dashboard Cite

Purpose: Magnetic resonance guidance in proton therapy (MRPT) is expected to improve its current performance. The combination of magnetic fields with clinical proton beam lines poses several challenges for dosimetry, treatment planning and dose delivery. Proton beams are deflected by magnetic fields causing considerable changes in beam trajectories and also a retraction of the Bragg peak positions. A proper prediction and compensation of these effects is essential to ensure accurate dose calculations. This work aims to develop and benchmark a Monte Carlo (MC) beam model for dose calculation of MRPT for static magnetic fields up to 1 T. Methods: Proton beam interactions with magnetic fields were simulated using the GATE/Geant4 toolkit. The transport of charged particle in custom 3D magnetic field maps was implemented for the first time in GATE. Validation experiments were done using a horizontal proton pencil beam scanning system with energies between 62.4 and 252.7 MeV and a large gap dipole magnet (B = 0-1 T), positioned at the isocenter and creating magnetic fields transverse to the beam direction. Dose was measured with Gafchromic EBT3 films within a homogeneous PMMA phantom without and with bone and tissue equivalent material slab inserts. Linear energy transfer (LET) quenching of EBT3 films was corrected using a linear model on dose-averaged LET method to ensure a realistic dosimetric comparison between simulations and experiments. Planar dose distributions were measured with the films in two different configurations: parallel and transverse to the beam direction using single energy fields and spread-out Bragg peaks. The MC model was benchmarked against lateral deflections and spot sizes in air of single beams measured with a Lynx PT detector, as well as dose distributions using EBT3 films. Experimental and calculated dose distributions were compared to test the accuracy of the model. Results: Measured proton beam deflections in air at distances of 465, 665, and 1155 mm behind the isocenter after passing the magnetic field region agreed with MC-predicted values within 4 mm. Differences between calculated and measured beam full width at half maximum (FWHM) were lower than 2 mm. For the homogeneous phantom, measured and simulated in-depth dose profiles showed range and average dose differences below 0.2 mm and 1.2%, respectively. Simulated central beam positions and widths differed <1 mm to the measurements with films. For both heterogenous phantoms, differences within 1 mm between measured and simulated central beam positions and widths were obtained, confirming a good agreement of the MC model. Conclusions: A GATE/Geant4 beam model for protons interacting with magnetic fields up to 1 T was developed and benchmarked to experimental data. For the first time, the GATE/Geant4 model was successfully validated not only for single energy beams, but for SOBP, in homogeneous and heterogeneous phantoms. EBT3 film dosimetry demonstrated to be a powerful dosimetric tool, once the film response function is LET corrected,...

show abstract

Evaluation of radiophotoluminescent glass dosimeter response for therapeutic spot scanning proton beam: suggestion of linear energy transfer‐based correction

Nagata

Yasui

Omachi

et al. 2021

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

A linear relationship for the LET-dependence of Gafchromic EBT3 film in spot-scanning proton therapy

Cited by 32 publications

References 22 publications

Dose‐ rather than fluence‐averaged LET should be used as a single‐parameter descriptor of proton beam quality for radiochromic film dosimetry

Dose‐ rather than fluence‐averaged LET should be used as a single‐parameter descriptor of proton beam quality for radiochromic film dosimetry

Benchmarking a GATE/Geant4 Monte Carlo model for proton beams in magnetic fields

Evaluation of radiophotoluminescent glass dosimeter response for therapeutic spot scanning proton beam: suggestion of linear energy transfer‐based correction

Contact Info

Product

Resources

About