Assessment of the Sun Nuclear ArcCHECK to detect errors in 6MV FFF VMAT delivery of brain SABR using ROC analysis

With online adaptive radiotherapy (ART), patient-specific quality assurance (PSQA) testing cannot be performed prior to delivery of the adapted treatment plan. Consequently, the dose delivery accuracy of adapted plans (i.e., the ability of the system to interpret and deliver the treatment as planned) are not initially verified. We investigated the variation in dose delivery accuracy of ART on the MRIdian 0.35 T MR-linac (Viewray Inc., Oakwood, USA) between initial plans and their respective adapted plans, by analyzing PSQA results. Methods: We considered the two main digestive localizations treated with ART (liver and pancreas). A total of 124 PSQA results acquired with the ArcCHECK (Sun Nuclear Corporation, Melbourne, USA) multidetector system were analyzed. PSQA result variations between the initial plans and their respective adapted plans were statistically investigated and compared with the variation in MU number. Results: For the liver, limited deterioration in PSQA results was observed, and was within the limits of clinical tolerance (Initial = 98.2%, Adapted = 98.2%, p = 0.4503). For pancreas plans, only a few significant deteriorations extending beyond the limits of clinical tolerance were observed and were due to specific, complex anatomical configurations (Initial = 97.3%, Adapted = 96.5%, p = 0.0721). In parallel, we observed an influence of the increase in MU number on the PSQA results. Conclusion:We show that the dose delivery accuracy of adapted plans, in terms of PSQA results, is preserved in ART processes on the 0.35 T MR-linac. Respecting good practices, and minimizing the increase in MU number can help to preserve the accuracy of delivery of adapted plans as compared to their respective initial plans.

Section: Discussionmentioning

confidence: 99%

Online adaptive radiotherapy and dose delivery accuracy: A retrospective analysis

Bessiéres

Lorenzo

Bertaut

et al. 2023

“…Instead of the interior of a given structure, everything except the interior was overridden with the specified density. The structures complementary to the couch (three cases) with a density of 0.6 g/cm 3 or complementary to a metallic structure with the material specific density (four cases) was overridden incorrectly in such a way. Such inverted density overrides are a peculiarity of the TPS Pinnacle used in this study.…”

Section: Treatment Plansmentioning

confidence: 99%

“…Measurement‐based approaches range from point dose measurements to three‐dimensional dose measurements utilizing all sorts of detectors, including ion chambers, diodes, the electronic portal imager (EPID), and gel 1–6 . Typically, either fluences or dose distributions are compared.…”

Section: Introductionmentioning

confidence: 99%

“…as one systematic way to obtain those thresholds for IMRT plan‐specific QA 16 . It was since then applied to different QA systems 3,5,15,17 . Unlike other methods, ROC analysis is performed on a dataset of acceptable and unacceptable plans and derives decision thresholds by maximizing the sensitivity and specificity of a decision criterion.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Sensitivity and specificity of secondary dose calculation for head and neck treatment plans

Wegener,

Abu Rashed,

Sauer

et al. 2023

PurposeSecondary dose calculation (SDC) with an independent algorithm is one option to perform plan‐specific quality assurance (QA). While measurement‐based QA can potentially detect errors in plan delivery, the dose values are typically only compared to calculations on homogeneous phantom geometries instead of patient CT data. We analyzed the sensitivity and specificity of an SDC software by purposely introducing different errors and determined thresholds for optimal decisions.MethodsThirty head and neck VMAT plans and 30 modifications of those plans, including errors related to density and beam modelling, were recalculated using RadCalc with a Monte Carlo algorithm. Decision thresholds were obtained by receiver operating characteristics (ROC) analysis. For comparison, measurement‐based QA using the ArcCHECK phantom was carried out and evaluated in the same way.ResultsDespite optimized decision thresholds, none of the systems was able to reliably detect all errors. ArcCHECK analysis using a 2%/2 mm criterion with a threshold of 91.1% had an area under the curve (AUC) of 0.80. Evaluating differences in recalculated and planned DVH parameter of the target structures in RadCalc with a 2% threshold an AUC of 0.86 was achieved. Out‐of‐field deviations could be attributed to weaknesses in the beam model.ConclusionsSecondary dose calculation with RadCalc is an alternative to established measurement‐based phantom QA. Different tools catch different errors; therefore, a combination of approaches should be preferred.

“…Pre‐treatment patient‐specific quality assurance (PSQA) is an integral part of any radiotherapy workflow to ensure the actual dose received by the patients are similar to the planned dose. By doing so, it serves to detect errors arising from beam modeling deficiency, 1,2 LINAC output change, 3 or complex intensity modulated radiotherapy (IMRT) or volumetric arc radiotherapy (VMAT) treatment plans 4,5 . Unlike daily or monthly machine QA tolerances, which are laid out clearly in TG142, 6 the method of PSQA and its action limit varies between hospitals 7,8 .…”

Section: Introductionmentioning

confidence: 99%

Detecting outliers beyond tolerance limits derived from statistical process control in patient‐specific quality assurance

Tan,

Lew,

Wong

et al. 2023

BackgroundTolerance limit is defined on pre‐treatment patient specific quality assurance results to identify “out of the norm” dose discrepancy in plan. An out‐of‐tolerance plan during measurement can often cause treatment delays especially if replanning is required. In this study, we aim to develop an outlier detection model to identify out‐of‐tolerance plan early during treatment planning phase to mitigate the above‐mentioned risks.MethodsPatient‐specific quality assurance results with portal dosimetry for stereotactic body radiotherapy measured between January 2020 and December 2021 were used in this study. Data were divided into thorax and pelvis sites and gamma passing rates were recorded using 2%/2 mm, 2%/1 mm, and 1%/1 mm gamma criteria. Statistical process control method was used to determine six different site and criterion‐specific tolerance and action limits. Using only the inliers identified with our determined tolerance limits, we trained three different outlier detection models using the plan complexity metrics extracted from each treatment field—robust covariance, isolation forest, and one class support vector machine. The hyperparameters were optimized using the F1‐score calculated from both the inliers and validation outliers’ data.Results308 pelvis and 200 thorax fields were used in this study. The tolerance (action) limits for 2%/2 mm, 2%/1 mm, and 1%/1 mm gamma criteria in the pelvis site are 99.1% (98.1%), 95.8% (91.1%), and 91.7% (86.1%), respectively. The tolerance (action) limits in the thorax site are 99.0% (98.7%), 97.0% (96.2%), and 91.5% (87.2%). One class support vector machine performs the best among all the algorithms. The best performing model in the thorax (pelvis) site achieves a precision of 0.56 (0.54), recall of 1.0 (1.0), and F1‐score of 0.72 (0.70) when using the 2%/2 mm (2%/1 mm) criterion.ConclusionThe model will help the planner to identify an out‐of‐tolerance plan early so that they can refine the plan further during the planning stage without risking late discovery during measurement.