Research Article

An Audit of Common Iliac Bifurcation in Patients with Rectal Cancer - do the Patterns of Failure from Published Literature Justify Vessel based Contouring of Nodal CTV?

Surekha Goyal*, Surya Prakash, Richa Tiwari and Geeta S Narayanan

Assistant Professor, Rajiv Gandhi University of Health Sciences, Bangalore

Submission: February 11, 2022; Published: February 23, 2022

*Corresponding Address: Surekha Goyal, Assistant Professor, Rajiv Gandhi University of Health Sciences, Bangalore

How to cite this article: Surekha G, Surya P, Richa T, Geeta S N. An Audit of Common Iliac Bifurcation in Patients with Rectal Cancer - do the Patterns of Failure from Published Literature Justify Vessel based Contouring of Nodal CTV?. Canc Therapy & Oncol Int J. 2022; 21(1): 556051. DOI:10.19080/CTOIJ.2022.21.556051

Abstract

Purpose: Assessment of the level of common iliac bifurcation in rectal cancer patients and compare it to the level of L5-S1 interspace, also to discuss the need for an optimal cranial border of radiation field based on patterns of failure from published literature.

Material and Methods: The bifurcation of common iliac artery to external and internal iliac arteries on right and left sides were marked on the scan for 236 biopsy proven rectal cancer patients. We defined L5-S1 interspace as the superior border of L5-S1 intervertebral space. The distance of the bifurcation on the left and right side from the superior border of L5-S1 intervertebral space was noted for all cases.

Result: In our study, 185 out of 236 (78.3%) patients had the bifurcation of right common iliac artery above L5-S1, by a mean distance of 2.02 ± 1.22cm. The bifurcation of left common iliac artery for 182 out of 236 (77.11%) patients was above the L5-S1 interspace, by a mean distance of 1.99 ± 1.16cm.

Conclusion: Based on the failures in rectal cancer patients seen in the published literature and our findings that the bifurcation of common iliac vessels is much higher than L5-S1 level, we conclude that the vessel-based contouring of the nodal CTV unnecessarily increases the treatment volume and thus will lead to increase in bowel toxicities in these patients. Thus, further studies should be done to re-evaluate the cranial border of radiation fields in rectal cancer patients.

Introduction

Colorectal cancer is one of the common cancers worldwide. According to Globocan 2018, the incidence of new colorectal cancer cases in both sexes was 10.2% worldwide and the mortality rate was 9.2% [1]. The present NCCN guidelines recommend multimodality treatment which includes pre-operative radiation therapy either as a short course regimen or fluropyrimidine based long course chemo radiation followed by surgery, this has reduced the local recurrence by about 50% when compared to surgery (TME) alone [2].

Radiation portals for rectum covers the primary tumor, mesorectum and draining lymph nodes. The lymphatic drainage of the rectal cancer depends on the location of the primary tumor. The tumors that arise above the anorectal ring drains along the middle rectal vessels to the internal iliac group of lymph nodes and the tumors that invades into the anal canal drains into the inferior rectal and external iliac pathways. The 2D borders uses L5-S1 interspace as the superior border and the inferior border was taken 3-5cm below the palpable gross tumor. The recent consensus contouring guidelines recommends the cranial limit of the lymph-nodal volume to be bifurcation of common iliac artery into external and internal iliac arteries [3].

Not many studies have been done to compare the discrepancies in the upper border of the radiation fields between the 2D and 3D planning in rectal cancer. We intend to assess the level of common iliac bifurcation in our patient population and compare it to the level of L5-S1 interspace. We also intend to discuss the need for an optimal cranial border of radiation field based on patterns of failure from published literature.

Material and Methods

We included 236 biopsy proven rectal cancer patients. All patients were planned for neoadjuvant chemo-radiation followed by surgery.

Simulation

All patients underwent bowel preparation overnight before the day of simulation. Patients were called empty stomach. Bladder protocol was followed for all cases before the CT simulation (500ml of water for half an hour). The patients were made to lie down in supine position using a leg separator, hands placed above the head. Fiducials were placed at the level of pubic symphysis. Intravenous contrast was given (1mg/kg body weight) during the scan. The CT scan was acquired with 5mm slice thickness.

Contouring

All patients were contoured based on the consensus recommendation for contouring of rectal cancer [4]. The CTV for primary was taken as entire mesorectum with 2cm margin superior to the gross disease and CTV for nodal stations was taken as mesorectal, presacral, obturator and internal iliac nodal region. The bifurcation of common iliac artery to external and internal iliac arteries on right and left sides were marked on the scan. We defined L5-S1 interspace as the superior border of L5- S1 intervertebral space. The distance of the bifurcation on the left and right side from the superior border of L5-S1 intervertebral space was noted for all cases.

Statistics

Mean and standard deviation of distance of the common iliac bifurcation from L5-S1 interspace was calculated. The percentage of patients in whom the common iliac bifurcation lies above L5- S1, at L5-S1 and below L5-S1 was be calculated.

Results

We analyzed 236 patients of rectal cancer, out of which 77 were females and 159 were males. In our study, 185 out of 236 (78.3%) patients had the bifurcation of right common iliac artery above L5-S1. The bifurcation was above the L5-S1 interspace by a mean distance of 2.02 ± 1.22cm. 25 patients (10.5%) had the bifurcation of right common iliac artery at the level of L5-S1 and 26 (11.01%) patients had bifurcation below L5-S1 at a mean distance of 0.94 ± 0.53cm. The bifurcation of left common iliac artery for 182 out of 236 (77.11%) patients was above the L5-S1 interspace. The mean distance above L5-S1 interspace for these patients was 1.99 ± 1.16cm. For 22 (9.32%) patients, the bifurcation was at L5-S1 interspace, and 32 (13.55%) patients had the bifurcation below L5-S1 interspace. The left common iliac artery bifurcation was below L5-S1 by a mean distance of 1 ± 0.66cm. For 37 patients, the level of bifurcation of right and left common iliac artery was not at same level (Figures 1 & 2).

Discussion

Historically, randomized clinical trials evaluating the benefit of radiotherapy have used bony landmarks for treatment planning. The cranial border is usually set at the level of L5-S1 interspace or sacral promontory to include internal iliac lymph nodes in the treatment field. RTOG atlas for elective clinical target volume delineation in anorectal cancers suggests the sacral promontory as an approximate bony landmark for common iliac bifurcation [4]. Consensus guidelines by Valentini et al. [3] recommend contouring the internal iliac vessels from the common iliac artery bifurcation for all node positive, T4 and MRF (mesorectal fascia) positive patients.

We aimed to analyze in our study if the use of bony landmarks with superior border as L5-S1 adequately covers radiation target volume in rectal cancer patients. We found that the internal iliac lymph nodes were missed in 78.3% patients on right side and 77.11% patients on left side, if L5-S1 is used as superior border. Similar study was done by Wier et al. [5], where they analyzed if L5-S1 as superior border of radiation therapy fields in rectal cancer will miss internal iliac lymph nodes in 60 patients and found out that internal iliac nodes were missed in 94% of patients. A study done by Chandana et al. [6], showed that 32 out of 86 patients had a geographical miss of internal iliac nodes if L5-S1 was taken as superior border.

We also reviewed the literature to see the site of failures after treatment in rectal cancer patients. Takahashi et al reviewed (n=764) routes of lymph node involvement and types of first cancer recurrence in patients who underwent total mesolectal excision and lateral lymph node dissection without radiotherapy. Extra pelvic lymph node recurrence is 1% (3/273) in patients with positive mesorectal (upward) nodes/negative lateral lymph nodes and 4% (2/50) in patients with positive mesorectal nodes/ positive lateral lymph nodes [7].

Sanfilippo NJ et al. studied (n=45) the patterns of failure in patients with T4 rectal cancer and found that only 1 patient had marginal recurrence in a common iliac node at the superior edge (L5-S1) of the treatment field [8]. Nijkamp J et al. [9] did a three-dimensional analysis of recurrence (n=114) patterns in rectal cancer patients (n=1417) treated in the DUTCH TME trial and found that majority of the recurrences are in the lower twothirds of pelvis below S2-S3 junction. The highest recurrence was at the level of mid S1. It was suggested that the cranial border of radiotherapy field be reduced to S2-S3 junction in node negative/ negative CRM (circumferential resection margin) patients [9].

Thus, a very few recurrences in rectal cancer patients occur above L5-S1. Contouring the internal iliac vessels from commoniliac bifurcation will result in a cranial border much higher than the bony landmark of L5-S1 interspace. This practice will result in increased small bowel toxicity and could be deemed appropriate only if it reduces recurrences above L5-S1.

Conclusion

Based on the failures in rectal cancer patients seen in the published literature and our findings that the bifurcation of common iliac vessels is much higher than L5-S1 level, we conclude that the vessel-based contouring of the nodal CTV unnecessarily increases the treatment volume and thus will lead to increase in bowel toxicities in these patients. Thus, further studies should be done to re-evaluate the cranial border of radiation fields in rectal cancer patients.

References

1. International agency for research on cancer. Globocan 2018
2. NCCN Guidelines Version 2.2020. Rectal cancer
3. Valentini V, Gambacorta MA, Barbaro B, Chiloiro G, Coco C, et al. (2016) International consensus guidelines on Clinical Target Volume delineation in rectal cancer. Radiother Oncol 120(2): 195-201.
4. Myerson RJ, Garofalo MC, El Naqa I, Ross A Abrams, Aditya Apte, et al. (2009) Elective clinical target volumes for conformal therapy in anorectal cancer: a radiation therapy oncology group consensus panel contouring atlas. Int J Radiat Oncol Biol Phys 74(3): 824-830.
5. RA Weir, AR Bhirud, NR Bennion, CA Enke, AO Wahl, et al. (2014) L5/S1 as the Superior Border of Radiation Therapy Fields in Rectal Cancer Misses Internal Iliac Lymph Nodes. International Journal of Radiation Oncology Biology Physics 90(1): S390-S391.
6. Chandana S, Prasanna K, Mayur M, MS Beliappa, B Krishnamoorthy R, et al. (2020) Is three-Dimensional CT based Conformal Radiotherapy Superior to Two-dimensional X ray-based Radiotherapy for Neoadjuvant Radiotherapy in Locally advanced Carcinoma Rectum?. Canc Therapy & Oncol Int J 15(3): 555915.
7. Takahashi T, Ueno M, Azekura K, H Ohta (2000) Lateral node dissection and total mesorectal excision for rectal cancer. Dis Colon Rectum 43: S59–S68.
8. Sanfilippo NJ, Crane CH, Skibber J, Feig B, Abbruzzese JL, et al. (2001) T4 rectal cancer treated with preoperative chemoradiation to the posterior pelvis followed by multivisceral resection: patterns of failure and limitations of treatment. Int J Radiat Oncol Biol Phys 51(1): 176-183.
9. Nijkamp J, Kusters M, Beets-Tan RG, Martijn H, Beets GL, et al. (2011) Three-dimensional analysis of recurrence patterns in rectal cancer: the cranial border in hypofractionated preoperative radiotherapy can be lowered. Int J Radiat Oncol Biol Phys 80(1): 103-110.