Anal Carcinoma

Abstract

The primary aim of treatment with chemoradiation (CRT) in anal cancer is to achieve locoregional control and preserve anal function without a colostomy. However, acute toxicity with CRT and reported late effects in terms of bowel, urinary and sexual late function are significant. Radiotherapy techniques which rely on anterior-posterior/posterior-anterior (APPA) fields may be associated with severe acute toxicity causing excessive breaks in treatment leading to treatment failure and also late radiation morbidity. More conformal treatment strategies such as intensity-modulated radiotherapy (IMRT) spare organs at risk, reduce toxicity and may allow full or even escalated doses to be achieved within a shorter overall treatment time (OTT). This chapter aims to provide a clear practical guide to target delineation in anal cancer – based on historical surgical series, the probability of lymph node metastases within the pelvis and groins and patterns of local recurrence after CRT. We have modified current available tumour and normal tissue atlases and adapted the results of small pioneering IMRT studies. We offer recommendations for imaging and planning guidelines for radiation oncologists and physicists to treat anal cancer with external beam irradiation.

Appendices

Appendices

11.1.1 Appendix 11.1

11.1.2 Appendix 11.2

TNM staging for anal canal cancer

Primary tumour (T)
Tx	Primary tumour cannot be assessed
Tis	Carcinoma in situ [Bowen’s disease, high-grade intraepithelial lesion (HSIL), anal intraepithelial neoplasia (AIN) II–III]
T1	Tumour less than 2 cm in greatest dimension
T2	Tumour between 2 and 5 cm in greatest dimension
T3	Tumour more than 5 cm in greatest dimension
T4	Tumour invading adjacent organs [vagina, urethra, bladder, sacrum]
Regional lymph nodes (N)
NX	Regional nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastasis in perirectal nodes
N2	Metastasis in unilateral internal iliac and/or inguinal nodes
N3	Metastasis in perirectal and/or bilateral internal iliac or inguinal nodes
Distant metastasis (M)
M0	No distant metastasis
M1	Distant metastasis

11.1.3 Appendix 11.3: MRI Protocol for ANAL CANCER – Acquisition and Reporting

High-resolution MRI is an accurate tool for locoregional staging and response assessment. MRI provides an accurate depiction of tumour site and tumour size, defines the relationship of the tumour to adjacent structures and enables locoregional lymph nodes to be assessed.

The aim in anal cancer is to:

• Identify patients with T3- or T4- and/or node-positive disease who have a poorer prognosis

• Define the locoregional extent of disease to assist radiotherapy planning

• Define the locoregional extent and degree of disease regression post therapy in order to tailor further treatment

11.1.3.1 Patient Preparation

In terms of patient preparation, we do not advocate the routine use of bowel cleansing (purgative or enema) or luminal distension. The use of an antiperistaltic (Buscopan or glucagon IM) may be helpful.

11.1.3.2 Sequences

Imaging may be performed on 1.5- or 3-T systems. Following localisation sequences, pelvic and tumour sequences are acquired. Pelvic sequences provide an overview of the entire pelvis and locoregional nodes reflecting the lymphatic drainage of the tumour. The axial sequences are from the level of L5/S1 to below the symphysis pubis. Tumour sequences are taken axial and coronal to the anal tumour and canal.

Table 11.1 summarises the sequences applied. These include T1-weighted, T2-weighted and diffusion-weighted sequences.

Table 11.1 MRI acquisition

11.1.3.3 MRI Reporting

MRI reporting should reflect the site and locoregional extent of the tumour and the presence and site of nodal disease and provide the maximal tumour dimension (RECIST 1.1.) and an overall stage (TNM).

At baseline, reports should include:.

• Involvement of the anterior urogenital triangle

• Lymph node disease including the location and size of nodes

• TNM stage

• RECIST

Posttreatment reports should include:

• Site of tumour (low, mid- or upper anal canal)

• Size (maximal transaxial dimension) of the primary tumour

• Maximal length of the primary tumour

• Height of tumour from the anal verge

• Morphologic appearance of tumour including any necrotic component

• Extent of extramural spread, which should be reflected by descriptors of locoregional extent:

  • Involvement of the rectum

  • Involvement of the levator ani

  • Involvement of the ischiorectal fossa

  • Involvement of the anterior urogenital triangle

  • Lymph node disease including the location and size of nodes

  • TNM: tumour downstaging, lymph node downstaging

  • RECIST response

  • Presence of post-CRT changes: fibrosis, desmoplasia, inflammatory change, submucosal oedema and necrosis

11.1.3.4 RECIST Response

This is as per RECIST 1.1 and the maximal tumour length is used.

11.1.4 Appendix 11.4

Lymph node volumes should follow vessels as defined by contrast CT using asymmetric manual expansions to nodes along tissue planes as defined in the table below from Taylor et al. Clinical Oncology. 2007;19:542–550

Lymph node group	Recommended margins
Common iliac	7-mm margin around vessels; extend posterior and lateral borders to psoas and vertebral body
External iliac	7-mm margin around vessels; extend anterior border by additional 10 mm anterolaterally along iliopsoas muscle to include lateral external iliac nodes
Obturator	Join external and internal iliac regions with 18-mm-wide strip along pelvic sidewall
Internal iliac	7-mm margin around vessels; extend lateral borders to pelvic sidewall
Presacral	10-mm strip over anterior sacrum
Inguinal	Not described

11.1.5 Appendix 11.5: Algorithm for Planning According to Site and Stage

1. Anal canal – T1/T2
Site: anal canal	Recommended GTV/CTV/PTV	Imaging	Additional
Stage T1,T2 N0 a IMRT or VMAT or 3D conformal IMRT or VMAT	(i) GTV primary + 10 mm ant/post/laterally + 15 mm sup and inf = CTVp CTVp + 10 mm = PTVp (ii) CTVm mesorectal nodes to 5 cm CTVn = vessels + 7 mm External iliac, internal iliac obturator nodes from the level of S2 inferiorly (ACT II – 2 cm above the most inferior aspect of SI joints) Inguinal nodes as compartment (CTVm + CTVn) + 5 mm = PTVn	TRUS and/or MRI and CT scanning	Patient supine Fiducial markers only if involved field only for small T1 Anal canal (see Table 11.1) Nodes (see Table 11.2)
B
Stage T1,T2, N1 b (metastasis in lower perirectal nodes) IMRT or VMAT or 3D conformal	(i) GTV primary + 10 mm ant/post/laterally + 15 mm sup and inf = CTVp CTVp + 10 mm = PTVp (ii) CTVm mesorectal nodes to superior rectal artery + presacral nodes CTVn = vessels + 7 mm Pelvic nodes below bifurcation of common iliac vessels, i.e. external iliac, internal iliac, obturator nodes Inguinal nodes as compartment (CTVm + CTVn) + 5 mm = PTVn	TRUS and/or MRI and CT scanning PET/CT recommended	Patient supine Anal canal (see Table 11.1) Nodes (see Table 11.2)
C
Stage T1,T2, N2–N3 c (N2-metastasis in unilateral internal iliac and/or inguinal nodes or N3) IMRT or VMAT or 3D conformal	(i) GTV primary + 10 mm ant/post/laterally + 15 mm sup and inf = CTVp CTVp + 10 mm = PTVp (ii) GTV nodes + 10 mm = CTVn (iii) CTVm mesorectal nodes + presacral nodes CTVn = vessels + 7 mm Pelvic nodes below bifurcation of common iliac vessels, i.e. external iliac, internal iliac, obturator nodes Inguinal nodes as compartment extending inferiorly if involved superficial inguinal nodes (CTVm + CTVn) + 5 mm = PTVn	TRUS and/or MRI and CT scanning PET/CT highly recommended	Patient supine Anal canal (see Table 11.1) Nodes (see Table 11.2)
2. Anal canal – T3/T4
Anal canal/anal margin/rectum
C
Stage T3,T4, N0–N3 (N2-metastasis in unilateral internal iliac and/or inguinal nodes or N3) IMRT or VMAT or 3D conformal	(i) GTV primary + 10 mm ant/post/laterally + 15 mm sup and inf = CTVp CTVp + 10 mm = PTVp (ii) GTV nodes + 10 mm = CTVn (iii) CTVm mesorectal nodes + presacral nodes CTVn = vessels + 7 mm Pelvic nodes below bifurcation of common iliac vessels, i.e. external iliac, internal iliac, obturator nodes Inguinal nodes as compartment extending more inferiorly if involved superficial inguinal nodes (CTVm + CTVn) + 5 mm = PTVn	TRUS and/or MRI and CT scanning PET/CT highly recommended	Patient supine Anal canal (see Table 11.1) Nodes (see Tables 11.2 and 11.3)

1. ^aT1/T2N0 and T1/T2N1 (inguinal nodes) anal margin treat as above A, except ensuring adequate coverage inferiorly
2. ^bAnal canal/rectum, i.e. anal canal extending >1 cm above dentate line, treat whole mesorectum/presacral area as for rectal cancer, but also the whole anal canal to the anal margin as CTV, i.e. treat as C above
3. ^cFor T3/T4 cancers at any site – use algorithm C above even if cNO

Table 11.2 Node size criteria. The following maximal size criteria are used to define the upper limit of normal nodes

Table 11.3 Various guidelines for pelvic node CTV drawing

11.1.6 Appendix 11.6: Anal IMRT Planning Sheet