ESTRO 2022

Session Item

Saturday

May 07

16:55 - 17:55

Room D3

Lower GI

Co-Chair: , France;

Chair: , Italy

Session Code: 1500

Session Type: Proffered Papers

Track: Clinical

16:45 - 16:55

Comprising a consensus-based delineation guideline for locally recurrent rectal cancer

Floor Piqeur, The Netherlands

Presentation Number: OC-0267

Abstract

Abstract Title:

Comprising a consensus-based delineation guideline for locally recurrent rectal cancer

Authors:

Floor Piqeur¹, B.J.P. Hupkens², P. Meijnen³, H.M. Ceha⁴, M. Berbee⁵, M. Dieters⁶, J.W.A. Burger⁷, H.J.T. Rutten⁷, J. Nederend⁸, C.A.M. Marijnen^9,10, H.M.U. Peulen², M.G. Witte¹¹

¹Catharina Hospital , Radiation Oncology, Eindhoven, The Netherlands; ²Catharina Hospital, Radiation Oncology, Eindhoven, The Netherlands; ³Amsterdam University Medical Centre, Radiation Oncology, Amsterdam, The Netherlands; ⁴Haaglanden Medical Centre, Radiation Oncology, Leidschendam, The Netherlands; ⁵Maastro Clinic, Radiation Oncology, Maastricht, The Netherlands; ⁶University Medical Centre Groningen, Radiation Oncology, Groningen, The Netherlands; ⁷Catharina Hospital, Surgery, Eindhoven, The Netherlands; ⁸Catharina Hospital, Radiology, Eindhoven, The Netherlands; ⁹Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands; ¹⁰Leiden University Medical Centre, Radiation Oncology, Leiden, The Netherlands; ¹¹The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands

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Purpose or Objective

Locally recurrent rectal cancer (LRRC) requires multidisciplinary management. The PelvEx-II trial evaluates the benefit of induction chemotherapy (IC) preceding chemoradiotherapy (CRT) for LRRC. CRT is used to downstage the tumour volume and facilitate a radical resection. However, delineation in LRRC is hampered by factors such as previous surgery, multifocality and presence of fibrosis. Additionally, radiation oncologists (ROs) often have limited experience with LRRC and evidence-based resources to aid in delineation are lacking. Therefore, target volumes may vary, potentially causing tumour miss or unnecessary re-irradiation of OAR. Through 2 workshops we developed a delineation guideline to optimize consistency within the trial.

Material and Methods

7 ROs from 7 Dutch centres treating > 10 yearly cases of LRRC participated in 2 meetings. ROs delineated 3 cases per meeting. During meeting 1, 3 surgeons and a radiologist identified regions at risk for re-recurrence or involved resection margins, leading to guidelines for RT naive patients and patients undergoing re-irradiation. These were validated and adjusted during meeting 2. Case 1.2 was repeated in case 2.1 to test guideline adherence. A median delineation was calculated per case. Dice similarity coefficient (DSC) was calculated for each GTV and CTV, in reference to the median delineation.

Results

The following consensus guideline was developed, specifically targeting identified at-risk regions.

GTV should encompass all macroscopic visible tumour, including involved areas of any organ. If no distinction can be made between fibrosis and GTV, the fibrotic area should be included in the GTV. Otherwise, the fibrotic area can be included in the CTV. After IC, GTV may be adjusted for regression (towards other structures). CTV includes GTV with a 1 cm margin and all pre-treatment GTV. CTV should not be adjusted towards other organs, except towards the pelvic bones if bony invasion is clearly absent. Multifocal recurrences should be encompassed in one CTV, with the upper and lower limit 1 cm beyond the most cranial and caudal GTV respectively.

For RT naïve patients, elective CTV is advised, conform treatment of LARC, i.e. lymph nodes, remaining mesorectal fat and, depending on recurrence location, the anal sphincter. For previously irradiated patients, no elective fields should be irradiated.

Average DSC of GTV and CTV increased from 0.60 to 0.66 and 0.71 to 0.81 between case 1.2 and 2.1 respectively.

Institution Case	1	2	3	4	5	Mean
1.1	0.84	0.86	0.72	0.28	0.75	0.69
1.2	0.82	0.85	0.80	0.27	0.82	0.71
1.3	0.83	0.94		0.64	0.86	0.81
2.1	0.82	0.87	0.80	0.81	0.73	0.81
2.2	0.66	0.75	0.76	0.71		0.72
2.3	0.85	0.35	0.89	0.89		0.74

Table 1: DSC of CTV in reference to median delineation.

Conclusion

Currently, there is limited evidence for delineation guidelines in LRRC. This study provides a first multidisciplinary, consensus-based guideline. Verification in re-recurrences is needed to understand disease behaviour and recurrence patterns and to optimize delineation guidelines accordingly.