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Improved simultaneous LET and dose measurements in proton therapy.

ABSTRACT: The objective of this study was to improve the precision of linear energy transfer (LET) measurements using [Formula: see text] optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4-6.5) [Formula: see text] range (in water). A commercial automated OSL reader with a built-in beta source was used for the readouts, which enabled a reference irradiation and readout of each OSLD to establish individual corrections. Pulsed OSL was used to separately measure the blue (F-center) and UV ([Formula: see text]-center) emission bands of [Formula: see text] and the ratio between them (UV/blue signal) was used for the LET measurements. The average deviation between the simulated and measured LET values along the central beam axis amounts to 5.5% if both the dose and LET are varied, but the average deviation is reduced to 3.5% if the OSLDs are irradiated with the same doses. With the measurement procedure and automated equipment used here, the variation in the signals used for LET estimates and quenching-corrections is reduced from 0.9 to 0.6%. The quenching-corrected OSLD doses are in agreement with ionization chamber measurements within the uncertainties. The automated OSLD corrections are demonstrated to improve the LET estimates and the ionization quenching-corrections in proton dosimetry for a clinically relevant energy range up to 230 MeV. It is also for the first time demonstrated how the LET can be estimated for different doses.

SUBMITTER: Christensen JB

PROVIDER: S-EPMC9117334 | biostudies-literature | 2022 May

REPOSITORIES: biostudies-literature

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Improved simultaneous LET and dose measurements in proton therapy.

Christensen Jeppe Brage JB Togno Michele M Bossin Lily L Pakari Oskari Ville OV Safai Sairos S Yukihara Eduardo Gardenali EG

Scientific reports 20220518 1

The objective of this study was to improve the precision of linear energy transfer (LET) measurements using [Formula: see text] optically stimulated luminescence detectors (OSLDs) in proton beams, and, with that, improve OSL dosimetry by correcting the readout for the LET-dependent ionization quenching. The OSLDs were irradiated in spot-scanning proton beams at different doses for fluence-averaged LET values in the (0.4-6.5) [Formula: see text] range (in water). A commercial automated OSL reader ...[more]

PMID: 35585205

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Project description:PurposeWhile intensity modulated proton therapy can deliver simultaneous integrated boost (SIB) to the dominant intraprostatic lesion (DIL) with high precision, it is sensitive to anatomic changes. We investigated the dosimetric effects from these changes based on pretreatment cone-beam computed tomographic (CBCT) images and identified the most important factors using a multilayer perceptron neural network (MLPNN).Methods and materialsDILs were contoured based on coregistered multiparametric magnetic resonance images for 25 previously treated prostate cancer patients. SIB plans were created with (1) prostate clinical target volume - V70 Gy = 98%; (2) DIL - V98 Gy > 95%; and (3) all organs at risk (OARs)"?> within clinical constraints. SIB plans were applied to daily CBCT-based deformed planning computed tomography (CT)"?>. DIL - V98 Gy, bladder/rectum maximum dose (Dmax) and volume changes, femur shifts, and the distance from DIL to organs at riskOARs"?> in both planning computed tomogramsCT"?> and CBCT were calculated. Wilcoxon signed-ranks tests were used to compare the changes. MLPNNs were used to model the change in ΔDIL - V98 Gy > 10% and bladder/rectum Dmax > 80 Gy, and the relative importance factors for the model were provided. The performances of the models were evaluated with receiver operating characteristic curves.ResultsComparing initial plan to the average from evaluation plans, respectively, DIL - V98 Gy was 89.3% ± 19.9% versus 86.2% ± 21.3% (P = .151); bladder Dmax 71.9 ± 0.6 Gy versus 74.5 ± 2.9 Gy (P < .001); and rectum Dmax 70.1 ± 2.4 Gy versus 74.9 ± 9.1Gy (P = .007). Bladder and rectal volumes were 99.6% ± 39.5% and 112.8% ± 27.2%, respectively, of their initial volume. The femur shift was 3.16 ± 2.52 mm. In the modeling of ΔDIL V98 Gy > 10%, DIL to rectum distance changes, DIL to bladder distance changes, and rectum volume changes ratio are the 3 most important factors. The areas under the receiver operating characteristic curves were 0.89, 1.00, and 0.99 for the modeling of ΔDIL - V98 Gy > 10%, and bladder and rectum Dmax > 80 Gy, respectively.ConclusionsDosimetric changes in DIL SIB with intensity modulated proton therapy can be modeled and classified based on anatomic changes on pretreatment images by an MLPNN.

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Improved simultaneous LET and dose measurements in proton therapy.

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Improved simultaneous LET and dose measurements in proton therapy.

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