IBS-GEC ESTRO-ABS recommendations for CT based contouring in image guided adaptive brachytherapy for cervical cancer

Abstract

MR Imaging is regarded asthe gold standardfor Image Gudied Adaptive Brachytherapy (IGABT) for cervical cancer. However, its wide applicability is limited by its availability, logistics and financial implications. Use of alternative imaging like CTand Ultrasound (US) for IGABT has been attempted. In order to arrive at a systematic, uniform and international approach for CT based definition and contouring of target structures, GEC ESTRO, IBS and ABS agreed to jointly develop such recommendations based on the concepts and terms as published in the ICRU Report 89. The minimum requirements are clinical examination & documentation, CT or MR imaging at diagnosis and at a minimum, CT imaging with the applicator in place. The recommendations are based on (i) assessment of the GTV at diagnosis and at brachytherapy, (ii) categorizing the response to external radiation into different clinical remission patterns, (iii) defining various clinico-radiological environments and (iv) definition & delineation of a target on CT imaging at the time of brachytherapy with the applicator in situ. CT based target contouring recommendations based on 4 remission categories within 8 defined environments, aim at improving the contouring accuracy for IGABT using CT, US and MRI as available. For each clinico-radiological environment, there is an attempt to minimize the specific uncertainties in order to arrive at the best possible contouring accuracy. Evaluating feasibility & reproducibility, to achieve a benchmark towards a gold standard MR IGABT and further clinical research including outcomes with CT Based IGABT will become the next steps.

Keywords: CT based contouring; CT environments; Cervical cancer; Cervical cancer brachytherapy recommendations; IGABT.

Fig. 1.

Revised clinical drawing with tumor GTV-T_init, GTV-T_res/CTV-T_HR dimensions to be documented in terms of height, thickness and width including parametrial disease, near maximum distance (NMD), FIGO/TNM staging.

Fig. 2.

Schematic diagram showing definition of CTV- T_HR-CT for CT_DG – CT_BT Environment based on the disease at diagnosis (cervix and parametrium in blue fill & vaginal disease in green lines), residual disease at BT (blue oblique lines), CTV-T_HR (in red continuous lines) and safety margins (red dotted lines).

Fig. 3.

Schematic diagram showing definition of CTV- T_HR-CT for MR_DG – CT_BT Environment based on the disease at diagnosis (cervix and parametrium in blue fill & vaginal disease in green lines), residual disease at BT (blue oblique lines), CTV-T_HR (in red continuous lines) and safety margins (red dotted lines).

Fig. 4.

Schematic diagram showing definition of CTV- T_HR-CT for CT_DG – Pre BT MRI and CT_BT Environment. Based on the disease at diagnosis (cervix and parametrium in blue fill & vaginal disease in green lines), residual disease at BT (blue oblique lines), CTV-T_HR (in red continuous lines) and safety margins (red dotted lines).

Fig. 5.

Schematic diagram showing definition of CTV- T_HR-CT for MR_DG – Pre BT MRI and CT_BT Environment based on the disease at diagnosis (cervix and parametrium in blue fill & vaginal disease in green lines), residual disease at BT (blue oblique lines), CTV-T_HR (in red continuous lines) and safety margins (red dotted lines).