Simulation of the Upper Esophagus

Overview

Structural Anatomy

Fig. 8.8 - The pharynx, upper esophageal sphincter, and upper third of the esophagus are composed of striated muscle. The lower two-thirds are smooth muscle. (Costanzo Physiology, 7th ed.)

Wall Layers (proximal to deep)

1. Mucosa - stratified squamous epithelium, lamina propria, muscularis mucosae
2. Submucosa - connective tissue, blood/lymphatics, Meissner (submucosal) plexus
3. Muscularis propria - inner circular + Auerbach (myenteric) plexus + outer longitudinal muscle
4. No serosa - unlike most of the GI tract (clinically important: perforations spread freely)

Musculature Transition

Upper Esophageal Sphincter (UES)

• Formed by the lowermost fibers of the inferior constrictor muscle (cricopharyngeus)
• Tonically contracted at rest - creates a high-pressure zone (~50 mmHg) that prevents inspired air from entering the esophagus and prevents esophageal reflux into the pharynx
• Relaxes during swallowing, actively dilated by laryngeal elevation during deglutition
• Composed of striated muscle (4th, 5th, and 6th branchial arches)
• Innervated by the vagus nerve and recurrent laryngeal nerve

Innervation of the Upper Esophagus

• Parasympathetics (vagus nerve) regulate peristalsis in the esophagus
• Cell bodies in the medulla split into two functional populations:
  • Nucleus ambiguus → controls striated muscle (upper esophagus)
  • Dorsal motor nucleus of vagus → controls smooth muscle (lower esophagus)
• Medullary vagal postganglionic efferent fibers terminate directly at motor endplates of skeletal muscle in the upper esophagus (no intermediate ganglion)
• In contrast, fibers to smooth muscle are preganglionic and synapse on Auerbach plexus neurons

Blood Supply

Physiology: Swallowing and Peristalsis

1. Oral Phase (voluntary)

• Tongue pushes bolus posteriorly into pharynx
• Activates somatosensory receptors in pharynx
• Triggers involuntary swallowing reflex in medullary swallowing center

2. Pharyngeal Phase (reflex)

1. Soft palate elevates - seals nasopharynx
2. Epiglottis covers laryngeal inlet; larynx elevates
3. UES relaxes - opens passage from pharynx to esophagus
4. Peristaltic wave initiated in pharynx propels bolus through open UES
5. Respiration is briefly inhibited

3. Esophageal Phase

• The upper third (striated muscle) has the most rapid peristalsis - transit time less than 1 second
• The lower two-thirds (smooth muscle) transit takes approximately 3 seconds
• Gravity plays only a minor role; swallowing works normally regardless of body position

Pressure Profile During Swallowing

Fig. 8.9 - At rest, the UES is at ~50 mmHg and the LES at ~20 mmHg. With swallowing (dotted line), the UES shows a transient pressure drop (relaxation) followed by a contraction wave; the LES relaxes to allow bolus entry. (Costanzo Physiology, 7th ed.)

Clinical Correlates of the Upper Esophagus

• Costanzo Physiology, 7th Edition - Swallowing section, p. 355
• K.J. Lee's Essential Otolaryngology - Anatomy and Physiology of the Esophagus, p. 671
• Sleisenger & Fordtran's GI and Liver Disease - Esophageal anatomy and innervation
• Yamada's Textbook of Gastroenterology, 7th ed. - The Esophagus, p. 283
• Goldman-Cecil Medicine - Normal Anatomy and Physiology

CT Simulation for Upper Esophageal Cancer - Radiation Therapy Planning

1. Anatomic Segmentation of the Esophagus (Relevant Context)

2. Pre-Simulation Workup

• Endoscopy - defines proximal/distal mucosal extent; endoscopic clips can be placed at tumor margins (especially for superficial tumors not visible on CT) - clip placement should be followed immediately by CT sim
• Endoscopic ultrasound (EUS) - depth of invasion (T stage)
• Contrast-enhanced CT chest/abdomen/pelvis - defines nodal involvement, invasion of adjacent structures
• FDG-PET/CT - strongly recommended; improves positive predictive value for lymph node metastasis vs. CT alone. PET improves detection of nodal disease and occult metastases. If FDG-PET/CT is obtained in the treatment position, the CT from this scan can serve as the planning CT
• Chromoendoscopy - essential for SCC; look for synchronous lesions

3. Patient Preparation for CT Simulation

4. Patient Positioning and Immobilization

For Cervical and Upper 1/3 Esophageal Tumors:

• Position: Supine
• Arms: Arms DOWN by the side (not raised above head)
  • Rationale: Proximity to the neck/thoracic inlet; arms-down allows thermoplastic shell/mask immobilization of the head and neck region
• Knee support: Yes
• Immobilization device: 5-point thermoplastic shell (head, neck, shoulders) or equivalent - this provides rigid immobilization of the cervical region and prevents rotational errors
• A vacuum cushion/alpha cradle can supplement

For Middle/Lower 1/3 and GOJ Tumors (contrast):

• Arms above head (to maximize beam entry angles and spare lung)
• Vacuum cushion or thermoplastic device

Key clinical point: The arms-down + 5-point shell combination is specific to cervical/upper esophageal lesions because these tumors are treated with head-and-neck style field arrangements, and the thermoplastic mask provides the reproducibility needed for precise daily setup. - West Midlands Cancer Alliance Radiotherapy Protocol

5. CT Simulation Imaging Parameters

6. Motion Assessment

• For upper esophageal tumors: respiratory motion is small; 3DCT free-breathing is adequate
• Established ITV margins from 4DCT data (primarily from lower esophagus studies): ~0.8 cm A-P and lateral, ~1.8 cm cranio-caudal for 95% coverage - apply conservatively to upper lesions

7. Target Volume Delineation

GTV (Gross Tumor Volume)

• Delineated on the planning CT using multimodality correlation (endoscopy, CT, PET, EUS, fluoroscopy)
• Reference landmarks used: tracheal carina and aortic arch
• Superficial tumors invisible on CT: use endoscopically placed metallic clips at proximal and distal tumor margins
• GTV encompasses all disease visible on any single imaging modality (CT, PET, or EUS)

• Any pathologically involved regional lymph node by imaging criteria

CTV (Clinical Target Volume)

• Pathological studies show a 30 mm margin covers 94% of microscopic invasion
• Standard: GTV-primary + 2-4 cm cranio-caudal margin along the esophageal axis
• Radial expansion: 1.0-1.5 cm circumferential
• The entire circumference of the esophageal wall is included throughout the CTV length

• Crop off: vertebral bone, trachea/bronchi, aorta, lung (structures where direct invasion is unlikely)
• For posterior margin: sculpt to the anterior border of the vertebral body (5 mm posterior growth)
• For upper tumors: include peri-esophageal nodal regions in the superior mediastinum

ITV (Internal Target Volume)

• CTV-primary + CTV-lymph node ± elective nodal CTV is adjusted for respiratory motion
• For upper esophagus: motion is small; ITV-CTV margin is minimal on standard free-breathing CT

PTV (Planning Target Volume)

• PTV initial phase: 45-50.4 Gy in 1.8 Gy/fraction (25-28 fx)
• Boost PTV: GTVp + GTVn with 0.5-1.0 cm expansion → 50.4-66 Gy
• West Midlands protocol (SCOPE): 66 Gy in 33 fractions (simultaneous integrated boost to PTV66 primary and PTV66 node)

8. Organs at Risk (OAR) - Upper Esophagus Specific

9. Treatment Technique

• IMRT/VMAT: Preferred for upper esophageal tumors - superior OAR sparing vs. 3DCRT given proximity to spinal cord, lungs, larynx
• Coplanar or non-coplanar beams: Non-coplanar encouraged for complex geometries to improve conformity
• Beam angles: Avoid tangential approach to moving organs (chest wall, heart)
• Image guidance: Daily CBCT for position verification is standard
• Concurrent chemotherapy: Carboplatin/paclitaxel (CROSS regimen) or cisplatin/5-FU; given concurrently during radiation

10. Summary Workflow

Pre-sim workup (endoscopy + EUS + CT + PET)
        ↓
Patient NPO 2 hrs → 200 mL liquid 30 min before
        ↓
Supine, arms DOWN, knee support, 5-point thermoplastic shell
        ↓
3DCT free-breathing, ≤3 mm slices, skull base to liver
± IV contrast; PET/CT in treatment position if available
        ↓
GTV-p delineation (CT + PET + endoscopy clips)
        ↓
CTV: GTV + 2-4 cm sup/inf + 1-1.5 cm radial + elective nodes
        ↓
PTV: CTV + 0.5-1.0 cm margins (CBCT-verified daily)
        ↓
IMRT/VMAT planning with OAR constraints
        ↓
Concurrent chemotherapy + radiation

• JASTRO 2024 Radiotherapy Planning Guidelines for Esophageal Cancer (PMC12283517)
• West Midlands Cancer Alliance Radiotherapy Upper GI Protocol
• NRG Oncology Esophageal Cancer Protocol Template
• ASTRO ARRO Case: Esophageal Cancer (RTOG 1010 target volume definitions)
• Sleisenger & Fordtran's GI and Liver Disease - Esophageal anatomy and innervation