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

Abstract

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.

Dosimetric evaluation in Helical TomoTherapy for lung SBRT using Monte Carlo‐based independent dose verification software

“…Several present studies have been reported that combining various QA tools improves the sensitivity of error detection 20,34,35 . O'Daniel et al.…”

“…Several present studies have been reported that combining various QA tools improves the sensitivity of error detection. 20,34,35 O'Daniel et al assessed the effective risk reduction of combinations of QA methods for IMRT/VMAT treatments. 34 They showed that the MC-based secondary dose calculation was available to reduce the overall risk.…”

“…19 Consequently, combining secondary dose verification software to measurement-based QA could improve the sensitivity to detect errors in TPS. 20 In practice, the software-based independent verification has been recommended as the dose verification for IMRT in AAPM TG-219 and previous studies. 21 Furthermore,numerous studies have investigated various factors such as tumor location, target volume, and heterogeneity of the density around the target can impact on target dose in lung SBRT.…”

“…Moreover, the independent verification software can provide comprehensive plan verifications through a comparison of dose‐volume histograms (DVH), three‐dimensional (3D) gamma analysis 19 . Consequently, combining secondary dose verification software to measurement‐based QA could improve the sensitivity to detect errors in TPS 20 . In practice, the software‐based independent verification has been recommended as the dose verification for IMRT in AAPM TG‐219 and previous studies 21 …”

“… 19 Consequently, combining secondary dose verification software to measurement‐based QA could improve the sensitivity to detect errors in TPS. 20 In practice, the software‐based independent verification has been recommended as the dose verification for IMRT in AAPM TG‐219 and previous studies. 21 …”