IMRT QA: Selecting gamma criteria based on error detection sensitivity

Steers, Jennifer M.; Fraass, Benedick A.

doi:10.1118/1.4943953

Cited by 49 publications

(55 citation statements)

References 53 publications

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“…Although γ analysis is widely used in clinical practice, recent publications have raised concerns on whether it is capable of catching planning or machine errors [14, 19, 20]. It was demonstrated that even with intentional errors, the pass rate may still be higher than 90 % [14, 19].…”

Section: Discussionmentioning

confidence: 99%

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Comparisons of volumetric modulated arc therapy (VMAT) quality assurance (QA) systems: sensitivity analysis to machine errors

et al. 2016

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BackgroundIn volumetric modulated arc therapy (VMAT), gantry angles, dose rate and the MLC positions vary with the radiation delivery. The quality assurance (QA) system should be able to catch the planning and machine errors. The aim of this study was to investigate the sensitivity of three VMAT QA systems to machine errors.MethodsSeveral types of potential linac machine errors unique to VMAT delivery were simulated in sinusoidal function of gantry angle, including gantry angle itself, MLC position and linac output. Two commercial QA systems, ArcCheck and Delta4, and an in-house developed EPID technique were compared in this study. Fifteen full arcs from head and neck plans were selected and modified to include five magnitudes of each type of error, resulting in measurements and γ analyses of 240 arcs on each system. Both qualitative and quantitative comparisons were performed using receiver operating characteristic (ROC), γ pass rate gradient, and overlap histogram methods.ResultsIn ROC analysis, the area under curve (AUC) represents the sensitivity and increases with the error magnitude. Using the criteria of 2 %/2 mm/2° (angle to agreement, ATA, only for EPID) and keeping AUC > 0.95, the minimum error detectable of ArcCheck, Delta4 and EPID are (2, 3, 3)° in gantry angle and (4, 2, 3) mm in MLC positions for the head and neck plans. No system is sensitive to the simulated output error, the AUC values were all below 0.70 even with 5 % output error. The γ gradient for gantry angle, MLC position and output errors are (−5.1, −2.6, −3.6)%/°, (−2.6, −7.1, −3.3)%/mm and (−0.2, −0.2, −0.3)%/% for ArcCheck, Delta4 and EPID, respectively. Therefore, these two analyses are consistent and support the same conclusion. The ATA parameter in EPID technique can be adjusted to tune its sensitivity.ConclusionsWe found that ArcCheck is more sensitive to gantry angle error and Delta4 is more sensitive to MLC position error. All three systems are not sensitive to the simulated output error. With additional analysis parameter, the EPID technique can be tuned to have optimal sensitivity and is able to perform QA for full field size with highest resolution. In addition, ROC analysis avoids the choice of γ pass rate threshold and is more robust compared with other analysis methods.

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Section: Discussionmentioning

confidence: 99%

“…It was demonstrated that even with intentional errors, the pass rate may still be higher than 90 % [14, 19]. In this study, we simulated machine errors with varying magnitudes, and the sensitivity was investigated with γ gradient and ROC analysis.…”

Section: Discussionmentioning

confidence: 99%

Comparisons of volumetric modulated arc therapy (VMAT) quality assurance (QA) systems: sensitivity analysis to machine errors

et al. 2016

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“…Gamma‐index analysis 20 was used to compare the measurements and calculations, by applying a criterion of 3% local pixel dose difference (LPDD)/2 mm distance‐to‐agreement (DTA) and a threshold of 30% of the maximum dose. This criterion was determined based on previous studies,21, 22, 23 and the threshold was set according to the dose constraints of the critical organs.…”

Section: Methodsmentioning

confidence: 99%

Clinical usefulness of MLCs in robotic radiosurgery systems for prostate SBRT

Tomida

Kamomae

Suzuki

et al. 2017

J Applied Clin Med Phys

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Stereotactic body radiation therapy (SBRT) using recently introduced multileaf collimators (MLC) is preferred over circular collimators in the treatment of localized prostate cancer. The objective of this study was to assess the clinical usefulness of MLCs in prostate SBRT by comparing the effectiveness of treatment plans using fixed collimators, variable collimators, and MLCs and by ensuring delivery quality assurance (DQA) for each. For each patient who underwent conventional radiation therapy for localized prostate cancer, mock SBRT plans were created using a fixed collimator, a variable collimator, and an MLC. The total MUs, treatment times, and dose–volume histograms of the planning target volumes and organs at risk for each treatment plan were compared. For DQA, a phantom with a radiochromic film or an ionization chamber was irradiated in each plan. We performed gamma‐index analysis to evaluate the consistency between the measured and calculated doses. The MLC‐based plans had an ~27% lower average total MU than the plans involving other collimators. Moreover, the average estimated treatment time for the MLC plan was 31% and 20% shorter than that for the fixed and variable collimator plans respectively. The gamma‐index passing rate in the DQA using film measurements was slightly lower for the MLC than for the other collimators. The DQA results acquired using the ionization chamber showed that the discrepancies between the measured and calculated doses were within 3% in all cases. The results reinforce the usefulness of MLCs in robotic radiosurgery for prostrate SBRT treatment planning; most notably, the total MU and treatment time were both reduced compared to the cases using other types of collimators. Moreover, although the DQA results based on film dosimetry yielded a slightly lower gamma‐index passing rate for the MLC than for the other collimators, the MLC accuracy was determined to be sufficient for clinical use.

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“…The plan is verified by comparing the “in air” recorded cumulative EPID image with a predicted one. Additional tools based upon diode arrays can be employed, but concerns surround the lack of tissue equivalence and sparse data sampling [1]. Recently, an EPID-based computational method for online 3D dose verification has been developed [2].…”

Section: Introductionmentioning

confidence: 99%

“…Gel dosimetry has become a tool for moderately accurate dosimetry in a tissue equivalent or anthropomorphic geometry, however the material-specific and readout errors [4] as well as long readout times [5] prevail. Diode array based systems are perhaps the industry standard for verification of individual plans but these have distinct limits on spatial resolution [1][6]. Transit dosimetry based upon reconstructing the dose inside a phantom portal can achieve images [7][8], but still require a simulation-based scatter correction for accuracy and/or other assumptions about the beam depth dose curve in the media.…”

Section: Introductionmentioning

confidence: 99%

Online Combination of EPID & Cherenkov Imaging for 3-D Dosimetry in a Liquid Phantom

Brůža

Andreozzi

Gladstone

et al. 2017

IEEE Trans. Med. Imaging

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Online acquisition of Cherenkov and portal imaging data was combined with a reconstruction scheme called EC3D, providing a full 3D dosimetry of megavoltage X-ray beams in a water tank. The methodology was demonstrated and quantified in a single static beam. Furthermore, the dynamics and visualization of the 3D dose reconstruction were demonstrated with a volumetric modulated arc therapy (VMAT) plan for TG-119 C-Shape geometry. The developed algorithm combines depth dose information, provided by Cherenkov images, with the lateral dose distribution, provided by the electronic portal imaging device (EPID). The strength of our approach lies in the acquisition of both imaging data-streams with sub-millimeter theoretical resolution at 5 Hz frame-rate, which can be concurrently processed by Fast Fourier Transform-based analysis, thus providing means for an efficient real-time 3D dosimetry.

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IMRT QA: Selecting gamma criteria based on error detection sensitivity

Cited by 49 publications

References 53 publications

Comparisons of volumetric modulated arc therapy (VMAT) quality assurance (QA) systems: sensitivity analysis to machine errors

Comparisons of volumetric modulated arc therapy (VMAT) quality assurance (QA) systems: sensitivity analysis to machine errors

Clinical usefulness of MLCs in robotic radiosurgery systems for prostate SBRT

Online Combination of EPID & Cherenkov Imaging for 3-D Dosimetry in a Liquid Phantom

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