UK audit of target volume and organ at risk delineation and dose optimisation for cervix radiotherapy treatments

Objective: Assessment of the extent of variation in delineations and dose optimisation performed at multiple UK centres as a result of interobserver variation and protocol differences. Methods: CT/MR images of 2 cervical cancer patients previously treated with external beam radiotherapy (EBRT) and Brachytherapy were distributed to 11 UK centres. Centres delineated structures and produced treatment plans following their local protocol. Organ at risk delineations were assessed dosimetrically through application of the original treatment plan and target volume delineations were assessed in terms of variation in absolute volume and length, width and height. Treatment plan variation was assessed across all centres and across centres that followed EMBRACE II. Treatment plans were assessed using total EQD(2) delivered and were compared to EMBRACE II dose aims. Variation in combined intracavitary/interstitial brachytherapy treatments was also assessed. Results: Brachytherapy target volume delineations contained variation due to differences in protocol used, window/level technique and differences in interpretations of grey zones. Planning target volume delineations were varied due to protocol differences and extended parametrial tissue inclusion. All centres met EMBRACE II plan aims for PTV V-95 and high-riskclinical target volume D-90 EQD(2), despite variation in prescription dose, fractionation and treatment technique. Conclusion: Brachytherapy target volume delineations are varied due to differences in contouring guidelines and protocols used. Planning target volume delineations are varied due to the uncertainties surrounding the extent of parametrial involvement. Dosimetric optimisation is sufficient across all centres to satisfy EMBRACE II planning aims despite significant variation in protocols used. Advances in knowledge: Previous multi-institutional audits of cervical cancer radiotherapy practices have been performed in Europe and the USA. This study is the first of its kind to be performed in the UK.