Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements

Knill, Cory; Snyder, Michael; Rakowski, J; Zhuang, Lei; Matuszak, Martha M.; Burmeister, Jay

doi:10.1118/1.4946822

Cited by 7 publications

(4 citation statements)

References 21 publications

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“…11,15,[38][39][40][41] The diamond detector correction factors are unit specific, 42 and have dose-rate dependence 43,44 and preirradiation effect. 45 Liquid-filled ion chambers exhibit repetition rate, dose/pulse dependencies, [46][47][48] and angular dependence. 48 Electronic portal imaging devices (EPIDs) are not suitable for PSQA with couch rotations since the TPS dose object is tied to the rotating couch while the EPID remains stationary with respect to the gantry.…”

Section: Introductionmentioning

confidence: 99%

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

et al. 2020

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The SRS MapCHECK â , a recently developed patient-specific quality assurance (PSQA) tool for end-to-end testing of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT), was evaluated in a multi-institution study and compared with radiochromic film. Methods: The SRS MapCHECK was used to collect data on 84 SBRT or SRS PSQA plans/fields at nine institutions on treatment delivery devices (TDD) manufactured by Varian and Elekta. PSQA plans from five different treatment planning software (TPS) were selected and executed on TDDs operating at beam energies of 6 and 10 MV with and without a flattening filter. The patient plans were all VMAT except for ten conformal arc therapy fields. The plans were selected to encompass a range of size and tumor sites including brain, lung, spine, abdomen, ear, pancreas, and liver. Corresponding radiochromic film data was acquired in 50 plans/fields. Results were evaluated using gamma analysis with absolute dose criterion of 3% global dose-difference (DD) and 1 mm distanceto-agreement (DTA). Results: The mean 3% DD/1 mm DTA Gamma pass rate of SRS MapCHECK in comparison to film was 95.9%, whereas comparison of SRS MapCHECK to the treatment planning software was 94.7%. 80% of SRS MapCHECK comparisons against film exceed 95% pass rate, and about 30% of SRS MapCHECK comparisons against film exceed 99% pass rate. To maintain good agreement between SRS MapCHECK and film or TPS, authors recommend avoiding plans with a modified modulation complexity score (MMCS) <0.1 arbitrary units (a.u.). In the examples presented, this coincides with avoiding plans with a mu/dose limit of >3 µ/cGy. Conclusions: Stereotactic radiosurgery MapCHECK has been validated for PSQA for a variety of clinical SRS/SBRT plans in a wide range of treatment delivery conditions. The SRS MapCHECK comparison with film demonstrates near-equivalence for analysis of patient-specific QA deliveries comprised of small field measurements.

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Section: Introductionmentioning

confidence: 99%

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

et al. 2020

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“…We have found slightly lower passing rates for 6 MV-FFF than for 6 MV, which may be caused by recombination. In a recent report by Knill et al 39 they quantified the effect of recombination on the verification of treatment plans with the OCTAVIUS 1000 SRS by performing an offline recombination correction of raw data. They reported a slight improvement of passing rates for 6 MV and conventional tolerances when recombination was corrected for, which increased for tighter tolerances and FFF modalities.…”

Section: E Clinical Applicationmentioning

confidence: 99%

Development and clinical characterization of a novel 2041 liquid‐filled ionization chambers array for high‐resolution verification of radiotherapy treatments

et al. 2018

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The results show that the liquid filled ionization chamber prototype here presented is appropriate for the verification of radiotherapy treatments with high spatial resolution. Recombination effects do not affect very much the verification of relative dose distributions. However, verification of absolute dose distributions may require normalization to a radiation field which is representative of the dose rate of the treatment delivered.

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“…The same effect of general ion recombination can be observed in commonly used devices based on the use of a liquid ionization chamber, such as one- or two-dimensional chamber arrays. This can be a cause of disagreements in dose distribution analysis for stereotactic radiation therapy with a high dose rate [ 13 ].…”

Section: Discussionmentioning

confidence: 99%

General ion recombination effect in a liquid ionization chamber in high-dose-rate pulsed photon and electron beams

Takei

Isobe

Kitamura

et al. 2018

Journal of Radiation Research

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Liquid ionization chambers (LICs) are highly sensitive to dose irradiation and have small perturbations because of their liquid-filled sensitive volume. They require a sensitive volume much smaller than conventional air-filled chambers. However, it has been reported that the collection efficiency has dependencies on the dose per pulse and the pulse repetition frequency of a pulsed beam. The purpose of this study was to evaluate in detail the dependency of the ion collection efficiency on the pulse repetition frequency. A microLion (PTW, Freiburg, Germany) LIC was exposed to photon and electron beams from a TrueBeam (Varian Medical Systems, Palo Alto, USA) linear accelerator. The pulse repetition frequency was varied, but the dose per pulse was fixed. A theoretical evaluation of the collection efficiency was performed based on Boag’s theory. Linear correlations were observed between the frequency and the relative collection for all energies of the photon and electron beams. The decrease in the collected charge was within 1% for all the flattened photon and electron beams, and they were 1.1 and 1.8% for the 6 and 10 MV flattening filter-free photon beams, respectively. The theoretical ion collection efficiency was 0.990 for a 10 MV flattened photon beam with a dose rate of 3 Gy·min−1. It is suggested that the collected charge decreased because of the short time intervals of the beam pulse compared with the ion collection time. Thus, it is important to correctly choose the pulse repetition frequency, particularly when flattening filter-free mode is used for absolute dose measurements.

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Investigating ion recombination effects in a liquid-filled ionization chamber array used for IMRT QA measurements

Cited by 7 publications

References 21 publications

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

Development and clinical characterization of a novel 2041 liquid‐filled ionization chambers array for high‐resolution verification of radiotherapy treatments

General ion recombination effect in a liquid ionization chamber in high-dose-rate pulsed photon and electron beams

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