Radiation Therapy: Treatment & Spread Routes

• RTT 1251 - Treatment Procedures I
• Week 6 - Treatments of the Thorax

Topographic Anatomy Review

• Surface anatomy includes the jugular notch, clavicle, anterior axillary fold, manubrium, sternal angle and manubriosternal joint, rib, intermammary cleft, body of sternum, xiphisternal joint, epigastric fossa, infrasternal (subcostal) angle, costal margin, and midclavicular line.
• On a chest X-ray, key anatomical structures can be identified, including the manubrium, superior vena cava, aortic arch, right main bronchus, horizontal fissure, right atrium, oblique fissure, inferior vena cava, diaphragm over the liver, gastric bubble, pulmonary trunk, left main bronchus, left atrium, left ventricle, oblique fissure, left costophrenic angle.
• Additional structures visible on a chest X-ray are the ribs (1-12), clavicle, scapula, manubrium sternum, azygoesophageal line, descending aorta, breast shadow, and stomach, and the right costophrenic angle.

Vertebral Levels

• Apex of Right and Left Lung corresponds with T1.
• Suprasternal Notch corresponds with T2.
• Superior vena cava (formation) corresponds with T3.
• Aortic arch corresponds with T4.
• Bifurcation of trachea (Carina) corresponds with T4.
• Angle of Louis (Junction of manubrium and body) corresponds with T5.
• Base of the heart (highest point) corresponds with T6.
• The carina is the area in the body where the trachea bifurcates (T4).
• Other vertebral levels of interest include:
• Jugular notch at T2.
• Base of scapular spine at T3.
• Top of aortic arch at to T4.
• Sternal angle, second costal cartilage and Trachea bifurcation at T4.
• Upper end of ascending aorta and beginning of descending aorta at T4.
• Arch of azygos vein and its entrance into superior vena cava at T4.
• Inferior angle of scapula at T7.
• Inferior vena cava hiatus at T8.
• Xiphoid process at T9.
• Esophageal hiatus is located at T10.
• Aortic hiatus is located at T12.

Anatomy of the Thorax

• The thoracic cavity contains all organs enclosed by the rib cage.
• Extends superiorly from T1 posteriorly to the clavicles and sternum anteriorly, and inferiorly to the diaphragm
• Organs within the thorax include the heart and large vessels (SVC, Aorta), trachea, bronchus, esophagus, and lungs.

Lung Anatomy

• The right lung has three lobes
• The left lung has two lobes
• The superior compartment sits above the bifurcation
• The inferior compartment sits below the bifurcation
• Lymphatics include paratracheal, hilar, mediastinal nodes

Alimentary System (Esophagus)

• In the thoracic cavity, the alimentary system (digestive tract) runs the length of the esophagus.
• Extends from the pharynx (8-10") through the diaphragm into the stomach.
• It runs posterior to both the trachea and heart and is anterior to the spine.

Esophageal Anatomy

• Cervical esophagus extends from cricoid cartilage to the thoracic inlet at T1
• The upper portion runs from the inlet to the bifurcation of the trachea
• Middle thoracic runs superior half between bifurcation and gastroesophageal (GE) junction
• The lower portion runs inferior half between bifurcation and GE junction

Cancers of Thorax

• Small cell lung tumors make up only 10-15% of lung tumors.
• Oat cell and small cell undifferentiated carcinoma are considered small cell lung cancers
• Non-small cell lung tumors makeup 85% of lung tumors.
• Squamous cell carcinoma, adenocarcinoma and large cell carcinoma are types of non-small cell carcinomas
• Metastatic cancers can spread to the lung, for example from the breast via the lymphatic system.
• Lung dose is dependent on the size of the lesion and the intent of treatment
• Ranges for treatment can be 45 Gy (4500 cGy) to 70 Gy (7000 cGy) for smaller lesions that are treated with 3D CRT/Boost
• Typical treatment amounts average around 5000 cGy, delivered in 180-200 cGy fx's
• Esophageal cancers spread through lymphatics and blood.
• Treatment margins typically require 5cm above (caudal) and the 5cm below (cephalad) the tumor, plus a 1.5-2cm margin radially around PTV.
• May use surgery and/or chemo with RT.
• Radiation therapy (RT) is the typically preferred over surgery for inferior portions of the esophagus because of location.

Esophageal Doses

• Esophageal tumors are typically treated to 4500 cGy-5040 cGy in 180-200 cGy Fx's
• Fields can be treated AP/PA with a boost using obliques to get off of the cord or more often IMRT.

Circulatory System Cancers

• Tumors rarely develop on the heart and are typically metastatic from elsewhere included breast and lungs.
• The following will not be discussed: primary or metastatic tumors that are almost never evaluated for radiation treatment.
• SVC syndrome is a medical and radiation therapy (RT) emergency.
• A tumor that is lying near or invading the Superior Vena Cava (SVC) presses on it, which backs up blood flow.
• Typically lung tumor of lymphoma.

SVC Syndrome

• SVC syndrome symptoms include: shortness of breath, facial swelling, distension of veins in neck and thorax, chest pain, coughing, dysphagia (difficulty swallowing).
• The onset of treatment should be immediate

Treatment

• The patient is typically in supine position, with arms raised above the head on a wing board and foam headrest.
• The head may also need to be hyperextended to prevent beams from entering or exiting through the mouth or face (superior portions)
• Compression or respiratory gating may also need to be done because of breathing.

Parallel Opposed Fields Protocol

• A basic treatment approach for lung fields
• AP/PA protocols include tumor, margin & mediastinal lymphatics, including 2–2.5 cm margin beyond demonstrable disease
• Treat to 4000 cGy, and then must change technique to come off the cord.
• Upper lobe tumors or tumors near bronchus may include ipsilateral (same side) s'clav nodes
• Lower lobe disease should be treated toward the bottom of T10.

3D & IMRT

• Computed tomography (CT) provides for planning to create 3D volume based treatments
• Image Guided Radiation Therapy (IGRT) and Intensity Modulated Radiation Therapy (IMRT) are standard of care
• Minimal amounts of non-cancerous lung tissue is to be included in field
• Smaller margins equal better immobilization required
• Various compression devices may aid in the process
• Heterogeneity correction included in planning accounts for density reduction in lung compared to aqueous tissue
• Volumetric Modulated Arc Therapy (VMAT).

Tumor Motion & Respiratory Gating (4D)

• Tumor motion with respiratory gating (4D)

Treatments: Side Effects

• Acute side effects include dermatitis, erythema, esophagitis
• Occasionally side effects include coughing, dry throat, excessive mucus
• Chronic side effects include dry, non-productive cough, fibrosis of lung and skin

Complications For Exceeding Tolerance Dose To Organ

• Complications for exceeding tolerance dose to organ may include pneumonitis or myelopathy
• Complications can be serious and may be fatal

Tolerance Doses

• Spinal cord TD 5/5 is 5000cGy and TD 50/5 is 6000cGy.
• Normal lung TD 5/5 is 2000cGy and TD 50/5 is 3000cGy
• Heart TD 5/5 is 4300cGy and TD 50/5 is 5000cGy.
• Esophagus TD 5/5 is 5000cGy and TD 50/5 is 5500cGy.
• Bone marrow TD 5/5 is 2500cGy and TD 50/5 is 3500cGy.
• Skin TD 5/5 is 5500cGy and TD 50/5 is 7000cGy.
• Liver TD 5/5 is 3500cGy and TD 50/5 is 4000cGy.
• Bone TD 5/5 is 6500cGy and TD 50/5 is 7000cGy.

Exploration of cancer spread routes and treatment planning strategies. Covers radiation therapy preferences, treatment margins, and positioning for lung cancer. Addresses tumor location at the carina and surgical access to the superior vena cava.