EPID-based dosimetry and its relation to other 2D and 3D dose measurement techniques in radiation therapy

Mijnheer, Ben J.

doi:10.1088/1742-6596/847/1/012024

Cited by 8 publications

(10 citation statements)

References 18 publications

(12 reference statements)

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“…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. Additionally, EPIDs over-respond to low-energy photons, 49 and have a dose rate dependence. 50 Studies with EPIDs have shown 16-23% errors in output factors for small field size (~8 mm 2 x 8 mm 2 ) in one study 51 and ~8% difference to film for measurements of small target plans (~3 mm 2 x 3 mm 2 ) in another.…”

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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“…In recent years, electronic portal imaging devices (EPIDs), previously used for pretreatment checks in radiotherapy, have gained popularity for in vivo verification measurements 1,2 . Electronic portal imaging device transmission measurements have shown utility in detecting patient‐related errors and also have been used clinically to identify meaningful errors that would otherwise go undetected by standard pretreatment quality assurance (QA) checks 3–5 . However, given the recent utilization of EPID images for in vivo treatment QA, there is currently no consensus regarding the ability of EPID images to detect deviations during treatment that could impact the intended dose distribution.…”

Section: Introductionmentioning

confidence: 99%

Using in vivo EPID images to detect and quantify patient anatomy changes with gradient dose segmented analysis

et al. 2020

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Purpose To investigate the utility of gradient dose segmented analysis (GDSA) in combination with in vivo electronic portal imaging device (EPID) images to predict changes in the PTV mean dose for patient cases. Also, we use the GDSA to retrospectively analyze patients treated in our clinic to assess deviations for different treatment sites and use time‐series data to observe any day‐to‐day changes. Methods In vivo EPID transit images acquired on the Varian Halcyon were analyzed for simulated errors in a phantom, including gas bubbles, weight loss, patient shifts, and an arm erroneously in the field. GDSA threshold parameters were tuned to maximize the coefficient of determination (R2) between GDSA metrics and the change in the PTV mean dose (Dmean) as estimated in a treatment planning system (TPS). Similarly for a gamma analysis, the gamma criteria were adjusted to maximize R2 between gamma pass rate and the change in the PTV Dmean from the TPS. The predictive accuracy of these models was tested on patient data measuring the mean and standard deviation of the difference in the predicted change in PTV Dmean and the change in PTV Dmean measured in the TPS. This analysis was extended retrospectively for every patient treated over a 23‐month period (n = 852 patients) to assess the range of expected deviations that occurred during routine clinical operation, as well as to assess any differences between treatment sites. Grouping patients treated on the same day, a time‐series analysis was performed to determine if GDSA metrics could add value in tracking machine behavior over time. Results For the phantom data, analyzing the errors, except for shifts, and comparing the change in PTV Dmean and GDSA mean, a maximal R2 = 0.90 was found for a dose threshold of 5% and gradient threshold of 3 mm. For the gamma approach a linear fit between the gamma pass rate for change in the PTV Dmean was assessed for different criteria, using the same image data. A maximal, R2 = 0.84 was found for a gamma criteria of 3%/3 mm, 45% lower dose threshold. For patient data, the predictive accuracy of the change in the PTV Dmean using the GDSA approach and the gamma approach was 0.09 ± 0.98 % and − 0.65 ± 2.21%, respectively. Comparing the two approaches the accuracy did not significantly differ (P = 0.38), whereas the precision of the GDSA prediction is significantly less (P < 0.001). The dosimetric impact of shifts was not detectable with either the GDSA or gamma approach. Analysis of all patients treated over 23 months showed that over 95% of fractions treated deviated from the first fraction by 2% or less. Deviations> 2% occurred most frequently for the later fractions of head‐and‐neck and lung treatments. Additionally, averaging the GDSA mean metric over all patients on a given treatment day showed that changes in the machine output on the order of 1% could be identified. Conclusions GDSA of in vivo EPID images is a useful technique for monitoring patient changes during the course of treatment, particularly weight loss and tumor shrinkage...

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“…6 In addition to the various modes of acquisition, the delivered dose can be estimated using several different approaches, including predicted forward-projected EPID comparisons and simple back-projection of measured data. 6,[8][9][10] It is becoming increasingly popular to use transmission EPID-based dosimetry to verify that the patient's received dose is correct and multiple commercial systems are now available for use. 6,8,11,12 One such approach is to use the 3D reconstructed EPID dose to calculate dose-volume histogram (DVH) statistics in the planning computed tomography (pCT) dataset.…”

Section: Introductionmentioning

confidence: 99%

“…Although these are useful metrics to quantify the repeatability of treatment fractions, these methods do not provide DVH-specific statistics that relate the delivered dose to the planning target volume (PTV). 6,8,9,[12][13][14] To address this issue, a new analysis technique was introduced as a pre-treatment verification method in a doctoral dissertation that did not require recalculation of EPID-based data to patient dose, or analysis by means of the pass/fail gamma criteria. 15 Recently, Steers et al 16 published their work on applying the gradient dose segmented analysis (GDSA) technique to in-vivo EPID images for dose verification.…”

Section: Introductionmentioning

confidence: 99%

“…Other commercial approaches allow users to compare first‐fraction EPID transmission images to those of all subsequent fractions by means of applying the usual gamma‐analysis metric. Although these are useful metrics to quantify the repeatability of treatment fractions, these methods do not provide DVH‐specific statistics that relate the delivered dose to the planning target volume (PTV) 6,8,9,12–14 …”

Section: Introductionmentioning

confidence: 99%

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The application of gradient dose segmented analysis of in‐vivo EPID images for patients undergoing VMAT in a resource‐constrained environment

Reenen

Trauernicht

Bojechko

2023

J Applied Clin Med Phys

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The gamma analysis metric is a commonly used metric for VMAT plan evaluation. The major drawback of this is the lack of correlation between gamma passing rates and DVH values. The novel GDSAmean metric was developed by Steers et al. to quantify changes in the PTV mean dose (Dmean) for VMAT patients. The aim of this work is to apply the GDSA retrospectively on head‐and‐neck cancer patients treated on the newly acquired Varian Halcyon, to assess changes in GDSAmean, and to evaluate the cause of day‐to‐day changes in the time‐plot series. In‐vivo EPID transmission images of head‐and‐neck cancer patients treated between August 2019 and July 2020 were analyzed retrospectively. The GDSAmean was determined for all patients treated. The changes in patient anatomy and rotational errors were quantified using the daily CBCT images and added to a time‐plot with the daily change in GDSAmean. Over 97% of the delivered treatment fractions had a GDSAmean < 3%. Thirteen of the patients received at least one treatment fraction where the GDSAmean > 3%. Most of these deviations occurred for the later fractions of radiotherapy treatment. Additionally, 92% of these patients were treated for malignancies involving the larynx and oropharynx. Notable deviations in the effective separation diameters were observed for 62% of the patients where the change in GDSAmean > 3%. For the other five cases with GDSAmean < 3%, the mean pitch, roll, and yaw rotational errors were 0.90°, 0.45°, and 0.43°, respectively. A GDSAmean > 3% was more likely due to a change in separation, whereas a GDSAmean < 3% was likely caused by rotational errors. Pitch errors were shown to be the most dominant. The GDSAmean is easily implementable and can aid in scheduling new CT scans for patients before significant deviations in dose delivery occur.

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EPID-based dosimetry and its relation to other 2D and 3D dose measurement techniques in radiation therapy

Cited by 8 publications

References 18 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

Using in vivo EPID images to detect and quantify patient anatomy changes with gradient dose segmented analysis

The application of gradient dose segmented analysis of in‐vivo EPID images for patients undergoing VMAT in a resource‐constrained environment

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