{"entity":{"id":"target-delineation-variability","kind":"term","name":"Variation between clinicians in drawing the radiotherapy target","aka":["delineation variability","contouring variability","inter-observer variability in contouring","target volume delineation"],"tldr":"Before a radiotherapy plan can be made, a doctor draws the tumour and the organs around it on the planning scan, and two doctors given the same scan do not draw the same outline. A 2016 review found 119 studies measuring this across every major cancer site, and only one in five checked what the differences did to the dose.","summary":"Every plan starts with outlines: the visible tumour, the region thought to hold microscopic spread, and the organs to protect. The outlines are drawn by hand or by software and approved by a clinician, and they are the one input every later step trusts. A margin added afterwards for set-up error and movement does not correct an outline that missed tumour or included healthy tissue: the same outline is used at every session, so its error is repeated each time.\n\nVinod and colleagues reviewed studies published from 2000 to 2014 that compared outlines drawn by more than two observers. They found 119, covering all major tumour sites, most often of the clinical and gross target volumes, with a median of seven participants. The studies used such varied measures that their results could not be pooled; 68 per cent reported a statistical analysis and 21 per cent reported what the variation did to the dose. The review proposed a common framework for future studies.\n\nApproaches to reducing it include contouring guidelines, peer review of outlines before treatment, imaging the target with MRI or PET alongside CT, and AI auto-contouring, which NICE allowed into NHS use in 2023 on condition that a professional reviews every outline and evidence continues to be collected.","asOf":"2026-10-20","links":[{"label":"Vinod et al., Uncertainties in volume delineation in radiation oncology: a systematic review (Radiotherapy and Oncology 2016)","url":"https://doi.org/10.1016/j.radonc.2016.09.009"},{"label":"NICE HTG695: AI technologies to aid contouring for radiotherapy treatment planning (2023)","url":"https://www.nice.org.uk/guidance/htg695/chapter/1-Recommendations"}],"tags":["precision","radiation"],"related":["radiation-roadmap"],"cancers":[],"sections":["radiation"],"technologies":["auto-contouring-ai","imrt-igrt","adaptive-radiotherapy","dose-painting"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["planning-target-volume","organs-at-risk"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":["paper-vinod-delineation-uncertainty-review-radiother-oncol-2016","paper-van-herk-ptv-margin-recipe-ijrobp-2000"],"journals":[],"dependsOn":[],"notes":[],"category":"Treatment jargon"},"route":"/terms/target-delineation-variability/","neighbours":{"roadmap":[{"id":"radiation-roadmap","kind":"roadmap","name":"Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH","route":"/roadmaps/radiation-roadmap/"}],"section":[{"id":"radiation","kind":"section","name":"Radiation Therapy","route":"/fronts/radiation/"}],"technology":[{"id":"adaptive-radiotherapy","kind":"technology","name":"Adaptive radiotherapy (online replanning)","route":"/technologies/adaptive-radiotherapy/"},{"id":"auto-contouring-ai","kind":"technology","name":"AI auto-contouring and adaptive planning","route":"/technologies/auto-contouring-ai/"},{"id":"dose-painting","kind":"technology","name":"Dose painting and biologically guided radiotherapy","route":"/technologies/dose-painting/"},{"id":"imrt-igrt","kind":"technology","name":"IMRT / IGRT (modern external beam)","route":"/technologies/imrt-igrt/"}],"term":[{"id":"planning-target-volume","kind":"term","name":"GTV, CTV and PTV (target volumes)","route":"/terms/planning-target-volume/"},{"id":"organs-at-risk","kind":"term","name":"Organs at risk and dose constraints","route":"/terms/organs-at-risk/"}],"paper":[{"id":"paper-flame-focal-boost-prostate-jco-2021","kind":"paper","name":"Focal boost to the intraprostatic tumor in external beam radiotherapy for patients with localized prostate cancer: results from the FLAME randomized phase III trial","route":"/key-papers/paper-flame-focal-boost-prostate-jco-2021/"},{"id":"paper-van-herk-ptv-margin-recipe-ijrobp-2000","kind":"paper","name":"The probability of correct target dosage: dose-population histograms for deriving treatment margins in radiotherapy","route":"/key-papers/paper-van-herk-ptv-margin-recipe-ijrobp-2000/"},{"id":"paper-vinod-delineation-uncertainty-review-radiother-oncol-2016","kind":"paper","name":"Uncertainties in volume delineation in radiation oncology: a systematic review and recommendations for future studies","route":"/key-papers/paper-vinod-delineation-uncertainty-review-radiother-oncol-2016/"}]}}