BackgroundRe-contouring of structures on consecutive planning computed tomography (CT) images for patients that exhibit anatomical changes is elaborate and may negatively impact the turn-around time if this is required for many patients. This study was therefore initiated to validate the accuracy and usefulness of automatic contour propagation for head and neck cancer patients using SmartAdapt® which is the deformable image registration (DIR) application in Varian’s Eclipse™ treatment planning system.MethodsCT images of eight head and neck cancer patients with multiple planning CTs were registered using SmartAdapt®. The contoured structures of target volumes and OARs of the primary planning CT were deformed accordingly and subsequently compared with a reference structure set being either: 1) a structure set independently contoured by the treating Radiation Oncologist (RO), or 2) the DIR-generated structure set after being reviewed and modified by the RO.ResultsApplication of DIR offered a considerable time saving for ROs in delineation of structures on CTs that were acquired mid-treatment. Quantitative analysis showed that 84% of the volume of the DIR-generated structures overlapped with the independently re-contoured structures, while 94% of the volume overlapped with the DIR-generated structures after review by the RO. This apparent intra-observer variation was further investigated resulting in the identification of several causes. Qualitative analysis showed that 92% of the DIR-generated structures either need no or only minor modification during RO reviews.ConclusionsSmartAdapt is a powerful tool with sufficient accuracy that saves considerable time in re-contouring structures on re-CTs. However, careful review of the DIR-generated structures is mandatory, in particular in areas where tumour regression plays a role.
This study showed that time-resolved dosimetry using an ionization chamber is feasible and can be largely automated which limits the required additional time compared to integrated dose measurements. It provides a unique QA method which enables identification and quantification of the contribution of various error sources during IMRT and VMAT delivery.
A difference of 12% has been observed in the output of an 80 kV, 2.2 mm A1 HVL x-ray beam when comparing measurements made according to the TRS 398 medium energy protocol with measurements made according to the TRS 277 low energy protocol. Absorbed dose to water chamber calibration factors used for the TRS 398 measurements were derived from standards of air kerma with the use of the TRS 277 medium energy protocol, and given this fact the discrepancy observed can be considered in terms of a difference between the TRS 277 low and medium energy protocols for this beam. Repeat measurements using the TRS 277 low and medium energy protocols have been made to confirm this. The most likely origins for the discrepancy observed are the chamber perturbation correction, p(u), obtained from TRS 277, and the value of the measured percentage depth dose at a depth of 2 g.cm(-2) for this beam. Given these findings, reference dosimetry for this beam will be performed according to the TRS 398 low energy protocol.
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