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MO23 - Radiotherapy II: Lung Toxicity, Target Definition and Quality Assurance (ID 107)
- Event: WCLC 2013
- Type: Mini Oral Abstract Session
- Track: Radiation Oncology + Radiotherapy
- Presentations: 1
MO23.08 - Inter-observer Variability in Gross Tumour Volume Delineation on Kilo-voltage Cone Beam Computed Tomography (CBCT) Scans for Lung Cancer Radiotherapy Treatment Verification (ID 3294)
10:30 - 12:00 | Author(s): M. Dimigen
The use of CBCT is essential for precise treatment delivery of radiotherapy for lung cancer. The current work practice at many centres is to use bony landmarks to match on-treatment CBCT to the radiotherapy planning CT to verify treatment. To take full advantage of this imaging modality for lung cancer, soft-tissue matching is preferred as it ensures that the actual lung cancer is within the radiotherapy fields regardless of bony anatomy. However Radiation Therapists (RTs) are trained in bony matching and not soft tissue matching. The purpose of this study was to determine the level of inter-observer variability in lung cancer gross tumour volume (GTV) delineation on CBCT and alignment of the CBCT with a planning GTV between Radiation Therapists (RTs), a Radiation Oncologist (RO) and a Radiologist (RD)
Ten RTs, one RO and one RD independently delineated the lung cancer GTV for fifteen lung cancer patients on Elekta Synergy CBCT image datasets taken on the first treatment fraction. The window and level settings used by each observer were recorded. Each observer then performed an alignment of the CBCT GVT to the radiotherapy planning GTV and translational errors were recorded. The difference in the isocentre corrections for the alignment shifts and Centre of Volume, Volume and Concordance Index (CI) for the contoured volumes were calculated to determine the level of agreement between the RT’s and the RD and between the RTs and the RO, in comparison to the variation between the RD and RO. In an ideal setting the difference between the RTs and the RO and the RTs and the RD would be at least equivalent to the difference between the RD and RO.
The difference between the RT’s and RO and RD was found to be not statistically equivalent to the difference between the RD and RO. The mean isocentre difference between the RO and RD was 0.40cm, compared with 0.42cm and 0.51cm between the RT’s and the RO and RD respectively. The mean CI between the RD and RO was 0.56 (0.44,0.69), which was smaller than the lower bound of the 95 % confidence intervals (95%) of the RT’s compared to the RD (0.5, 0.56) and RO (0.52,0.59). The mean log COV difference was -0.82cm between the RD and RO and -0.54 and -0.65cm between the RT’s and RO and RD respectively. The volume results showed that only 6 of thirty comparisons were equivalent. The mean volume difference between the RD and RO was 0.44cm and 4.73 cm and 5.7cm between the RT’s and RO and RD respectively.
The variation between the RTs and the RO and RD was greater than the variation between the RO and RD. Advanced training is necessary to educate the RTs on soft-tissue matching on CBCT for lung cancer radiotherapy.
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