Abstract

BackgroundThis study investigates the patterns of PET-positive lymph nodes (LNs) in anal cancer. The aim was to provide information that could inform future anal cancer radiotherapy contouring guidelines.MethodsThe baseline [18F]-FDG PET-CTs of 190 consecutive anal cancer patients were retrospectively assessed. LNs with a Deauville score (DS) of ≥3 were defined as PET-positive. Each PET-positive LN was allocated to a LN region and a LN sub-region; they were then mapped on a standard anatomy reference CT. The association between primary tumor localization and PET-positive LNs in different regions were analyzed.ResultsPET-positive LNs (n = 412) were identified in 103 of 190 patients (54%). Compared to anal canal tumors with extension into the rectum, anal canal tumors with perianal extension more often had inguinal (P < 0.001) and less often perirectal (P < 0.001) and internal iliac (P < 0.001) PET-positive LNs. Forty-two patients had PET-positive LNs confined to a solitary region, corresponding to first echelon nodes. The most common solitary LN region was inguinal (25 of 42; 60%) followed by perirectal (26%), internal iliac (10%), and external iliac (2%). No PET-positive LNs were identified in the ischiorectal fossa or in the inguinal area located posterolateral to deep vessels. Skip metastases above the bottom of the sacroiliac joint were quite rare. Most external iliac PET-positive LNs were located posterior to the external iliac vein; only one was located in the lateral external iliac sub-region.ConclusionsThe results support some specific modifications to the elective clinical target volume (CTV) in anal cancer. These changes would lead to reduced volumes of normal tissue being irradiated, which could contribute to a reduction in radiation side-effects.

Highlights

  • Anal cancer is a rare malignancy representing approximately 2–3% of all gastrointestinal cancers, but the incidence is increasing [1,2,3,4]

  • Distribution of Positron emission tomography (PET)-positive lymph nodes Most of the patients with PET-positive Lymph node (LN) had PETpositive LNs in the inguinal region (75 of 103; 73%)

  • The pattern of PET-positive LNs was dependent on the localization of the primary tumor (Fig. 1)

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Summary

Introduction

Anal cancer is a rare malignancy representing approximately 2–3% of all gastrointestinal cancers, but the incidence is increasing [1,2,3,4]. Standard treatment of anal cancer is radiotherapy with concurrent chemotherapy, which leads to a cure in 60–80% of the cases [5,6,7]. To further improve the treatment outcomes of anal cancer, optimization of the radiotherapy is important. This includes implementation of new techniques such as intensity-modulated radiotherapy (IMRT), which has been shown to reduce acute and chronic radiation-related toxicities [9]. Another line of development is to refine the target delineation, regarding lymph nodes (LNs) included in the elective clinical target volume (CTV). The aim was to provide information that could inform future anal cancer radiotherapy contouring guidelines

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