Session Item

Inter-observer variation in target volume delineation (TVD) is the most significant source of uncertainty in radiotherapy (RT). Variation in TVD can have a negative impact on survival. For clinical trials, RTQA is an essential component of delivering safe and effective RT by ensuring adherence to trial protocols. In the UK there have been two recent major clinical trials involving neoadjuvant RT in oesophageal cancer; the NeoSCOPE and Neo-AEGIS trials. Both use markedly different delineation protocols to generate similiar target volumes. This study aims to see if one protocol introduces more variation in delineated volumes, identify common sources of error or variation and provide insights to inform future protocols.

Ten clinical oncologists with experience in upper GI cancers from across the UK were given two identical CT datasets (a mid and lower-third oesophagus case) with pre-delineated GTV. The clinicians were asked to generate target volumes (CTVA, CTVB, PTV) for each dataset using protocols from the NeoSCOPE and Neo-AEGIS studies. Submitted volumes were reviewed by an experienced RTQA clinician with protocol deviations identified. To evaluate the inter-observer concordance, the generalized conformity index (CI_gen), defined as the ratio of the sum of all overlapping volumes between pairs of observers and the sum of all overlapping and all non-overlapping volumes between the same pairs, was used. A CI_gen of 1 indicates 100% concordance and a CI_gen of 0 indicates no concordance in delineation.

Table 2: Generalised Conformity Index (CIgen) for CTVA, CTVB and PTV

Image 1: CTVB contours for lower third case below the gastro-oesophageal junction.

There was more TVD variation using the Neo-AEGIS protocol. For lower third cases, 6/10 cases had unacceptable variation from protocol. The most significant non-concordance was seen in the CTVB volume using the Neo-AEGIS protocol for lower third cases. Analysis of the protocols show that the NeoSCOPE uses systematic geometric expansion of GTV which is then edited back to generate CTVB. Neo-AEGIS uses anatomical landmarks to define the ’fat pad’ which forms the CTVB. Below the GOJ, both protocols use a ‘free-hand’ approach with anatomical landmarks to define CTVB. Both protocols included sample images, but in addition, NeoSCOPE included multiple worked examples.