The dosimetric impact of target volume delineation variation for cervical cancer radiotherapy

Abstract

BackgroundCervical cancer inter-observer delineation variation has been demonstrated. This article addresses its dosimetric impact. Methods21 centres outlined two INTERLACE trial quality assurance test cases. A gold standard clinical target volume (GSCTV) was created from a consensus and STAPLE outline. RapidArc plans were created for all centres’ planning target volumes (PTVs; PTV1+2). Gold standard PTVs (GSPTVs) were created for each plan by applying each centre’s CTV–PTV margins to GSCTV. DVH parameters including D95% and Dmean for each PTV1+2 and GSPTV were compared, representing planned versus GSPTV delivered dose. PTV1+2 and GSPTV V95% was also calculated. ResultsReviewing all parameters, no plans achieved acceptable GSPTV coverage. GSPTV V95%⩾95% was not achieved for any plan. GSPTV V95%<90% in 15/21 (case 1) and 14/22 (case 2) and <80% in 2 plans from both cases. GSPTV V95% is on average 10–15% lower than planned and GSPTV D95% is 10–20% lower than planned. Most common GSCTV anatomical areas not receiving 95% dose were vagina, obturator and external iliac nodes and, in case 1, the superior nodal aspect. ConclusionCervical cancer CTV delineation variation leads to significant reductions in dose delivered to GSPTV. This highlights the ongoing importance of standardising delineation in the IMRT era.