Tomotherapy treatment plan quality assurance: The impact of applied criteria on passing rate in gamma index method

Bresciani, S.; Dia, A. Di; Maggio, A.; Cutaia, C.; Miranti, A.; Infusino, E.; Stasi, M.

doi:10.1118/1.4829515

Cited by 37 publications

(40 citation statements)

References 23 publications

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“…An automated phantom‐less protocol would lighten the workload. Second, the usual acceptance criteria may not be suitable for dose error detection, especially when incorrectly used . Another option would be to calculate the delivered dose on the patient planning images using the fluence measured inline by the treatment system.…”

Section: Introductionmentioning

confidence: 99%

In air and in vivo measurement of the leaf open time in tomotherapy using the on‐board detector pulse‐by‐pulse data

et al. 2019

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Purpose We developed an algorithm to measure the leaf open times (LOT) from the on‐board detector (OBD) pulse‐by‐pulse data in tomotherapy. We assessed the feasibility of measuring the LOTs in dynamic jaw mode and validated the algorithm on machine QA and clinical data. Knowledge of the actual LOTs is a basis toward calculating the delivered dose and performing efficient phantom‐less delivery quality assurance (DQA) controls of the multileaf collimator (MLC). In tomotherapy, the quality of the delivered dose depends on the correct performance of the MLC, hence on the accuracy of the LOTs. Materials and methods In the detector signal, the period of time during which a leaf is open corresponds to a high intensity region. The algorithm described here locally normalizes the detector signal and measures the FWHM of the high intensity regions. The Daily QA module of the TomoTherapy Quality Assurance (TQA) tool measures LOT errors. The Daily QA detector data were collected during 9 days on two tomotherapy units. The errors yielded by the method were compared to these reported by the Daily QA module. In addition, clinical data were acquired on the two units (25 plans in total), in air without attenuation material in the beam path and in vivo during a treatment fraction. The study included plans with fields of all existing sizes (1.05, 2.51, 5.05 cm). The collimator jaws were in dynamic mode (TomoEDGETM). The feasibility of measuring the LOTs was assessed with respect to the jaw aperture. Results The mean discrepancy between LOTs measured by the algorithm and those measured by TQA was of 0 ms, with a standard deviation of 0.3 ms. The LOT measured by the method had thus an uncertainty of 1 ms with a confidence level of 99%. In 5.05 cm dynamic jaw procedures, the detector is in the beam umbra at the beginning and at the end of the delivery. In such procedures, the algorithm could not measure the LOTs at jaw apertures between 7 and maximum 12.4 mm. Otherwise, no measurement error due to the jaw movement was observed. No LOT measurement difference between air and in vivo data was observed either. Conclusion The method we propose is reliable. It can equivalently measure the LOTs from data acquired in air or in vivo. It handles fully the static procedures and the 2.51 cm dynamic procedures. It handles partially the 5.05 cm dynamic procedures. The limitation was evaluated with respect to the jaw aperture.

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Section: Introductionmentioning

confidence: 99%

In air and in vivo measurement of the leaf open time in tomotherapy using the on‐board detector pulse‐by‐pulse data

et al. 2019

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“…32 Finally, another study reported no statistically significant differences between IMRT and VMAT deliveries when using ion chamber point doses, radiochromic film, or a 2D diode array. 33 A number of institutions have also reported differences in gamma passing rates for different treatment sites, 8,10,14,16,21,[34][35][36][37] while others have noted unremarkable differences between site-specific gamma passing rates. 13,38 Additionally, there has been little evidence suggesting an appropriate low dose threshold setting for gamma comparisons.…”

Section: Introductionmentioning

confidence: 99%

IMRT QA: Selecting gamma criteria based on error detection sensitivity

Steers

Fraass

2016

Medical Physics

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We have introduced the error curve method, an analysis technique which allows the quantitative determination of gamma criteria sensitivity to induced errors. The application of the error curve method using DMLC IMRT plans measured on the ArcCHECK® device demonstrated that large errors can potentially be missed in IMRT QA with commonly used gamma criteria (e.g., 3%/3 mm, threshold = 10%, 90% pixels passing). Additionally, increasing the dose threshold value can offer dramatic increases in error sensitivity. This approach may allow the selection of more meaningful gamma criteria for IMRT QA and is straightforward to apply to other combinations of devices and treatment techniques.

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“…Gamma analysis has been discussed extensively in many papers in terms of various criteria, the searching range, and a comparison between two‐dimensional (2D) and 3D gamma analysis. These studies compared various gamma analyses and suggested adequate levels of gamma parameters 2 , 3 , 12 , 13 …”

Section: Introductionmentioning

confidence: 99%

Gamma analysis dependence on specified low‐dose thresholds for VMAT QA

Song

Kim

Park

et al. 2015

J Applied Clin Med Phys

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The American Association of Physicists in Medicine Task Group 119 instructed institutions to use a low‐dose threshold of 10% or a region of interest determined by the jaw setting when they collected gamma analysis quality assurance (QA) data for the planar dose distribution. However, there are no clinical data to quantitatively demonstrate the impact of the low‐dose threshold on the gamma index. Therefore, we performed a gamma analysis with various low‐dose thresholds in the range of 0% to 15% according to both global and local normalization and different acceptance criteria (3%/3 mm, 2%/2 mm, and 1%/1 mm). A total of 30 treatment plans — 10 head and neck, 10 brain, and 10 prostate cancer cases — were randomly selected from the Varian Eclipse treatment planning system (TPS). For the gamma analysis, a calculated portal image was acquired through a portal dose calculation algorithm in the Eclipse TPS, and a measured portal image was obtained using an electronic portal‐imaging device. Then, the gamma analysis was performed using the Portal Dosimetry software (Varian Medical Systems, Palo Alto, CA). The gamma passing rate (%GP) for the global normalization decreased as the low‐dose threshold increased, and all low‐dose thresholds led to %GP values above 95% for both the 3%/3 mm and 2%/2 mm criteria. However, for the local normalization, %GP for a low‐dose threshold of 10% was 7.47%, 10.23%, and 6.71% greater than the low‐dose threshold of 0% for head and neck, brain, and prostate for the 3%/3 mm criteria, respectively. The results indicate that applying the low‐dose threshold to global normalization does not have a critical impact on patient‐specific QA results. However, in the local normalization, the low‐dose threshold level should be carefully selected because the excluded low‐dose points could cause the average %GP to increase rapidly.PACS number: 87.55.Qr

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Tomotherapy treatment plan quality assurance: The impact of applied criteria on passing rate in gamma index method

Cited by 37 publications

References 23 publications

In air and in vivo measurement of the leaf open time in tomotherapy using the on‐board detector pulse‐by‐pulse data

In air and in vivo measurement of the leaf open time in tomotherapy using the on‐board detector pulse‐by‐pulse data

IMRT QA: Selecting gamma criteria based on error detection sensitivity

Gamma analysis dependence on specified low‐dose thresholds for VMAT QA

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