Chapter 3: Radiation Therapy Practices

BRAIN AND SPINAL CORD (CNS)

Anatomy of the Central Nervous System

• Cerebrum and Cerebellum: The brain consists of two hemispheres within the cerebrum and two hemispheres within the cerebellum.

• Protection: The brain is shielded by cranial bones, meninges, and cerebrospinal fluid (CSF).

• Cerebrospinal Fluid (CSF): The CNS contains approximately $3-5\,\text{ounces}$ of CSF.

• Ventricles: These are chambers or sinuses within the brain that facilitate communication with the spinal cord canal and subarachnoid space.     * There are four ventricles: two lateral ventricles, the third ventricle, and the fourth ventricle.     * The primary function of ventricles is the production of CSF.

• Matter Composition:     * Gray Matter: Composed of supportive nerve cells; it constitutes the outer portion of the cerebrum.     * White Matter: Composed of nerve fibers, axons, and dendrites.

• Circle of Willis: This is the primary blood source for the brain, comprised of the internal carotid and vertebral arteries.

• Spinal Cord: Extends from the medulla oblongata to the filum terminale at the level of $L1-L2$.

• Blood-Brain Barrier (BBB): Protects the brain from toxins.     * Permeability: Only lipid-soluble substances can pass without assistance (e.g., alcohol, nicotine, heroin).     * Water-Soluble Substances: Require a carrier molecule to cross (e.g., glucose, amino acids, sodium).

Histology and Common CNS Tumors

• Tumor Types: Includes gliomas (glioblastoma, astrocytoma, glioblastoma multiforme), medulloblastoma, oligodendroglioma, ependymoma, meningioma, lymphoma, and schwannoma.

• Prevalence by Group:     * Children: Astrocytoma is the most common primary brain tumor; medulloblastoma is the second most common.     * Adults: Glioblastoma multiforme is the most common primary brain tumor.

• Overall Statistics: Metastatic tumors are the most frequent brain tumors encountered overall.

Metastatic Patterns and Clinical Presentation

• Routes of Spread: CNS tumors primarily spread via local invasion and seeding through the CSF.     * Metastasis beyond the CNS is infrequent.     * There is no metastatic spread through the lymphatic system.     * The lumbosacral area is the most common site for CSF seeding.

• Lhermitte's Sign: A clinical sensation of electrical shock traveling down the neck followed by the extremities.

• Lobe-Specific Symptoms:     * Frontal Lobe: Personality changes, speech/thought/problem-solving difficulties, impaired motor skills, visual/olfactory disturbances, and seizures.     * Parietal Lobe: Sensory problems, impaired language comprehension, spatial orientation difficulty, and seizures.     * Temporal Lobe: Short- and long-term memory impairment, impaired sound/image comprehension, and seizures.     * Occipital Lobe: Visual disturbances, hallucinations, and seizures.     * Cerebellum: Hydrocephalus, ataxia, and coordination problems.     * Brainstem: Facial weakness, difficulty swallowing, hearing loss, facial sensation loss, muscle weakness/paralysis, and respiratory depression.     * Spinal Cord: Muscle weakness/paralysis, sensory problems, bowel/bladder incontinence, and pain.

CNS Staging

• System: Uses GTM (Grade, Tumor, Metastasis).

• Grades: Ranges from $G1$ (well-differentiated) to $G3$ (poorly differentiated).

HEAD AND NECK CANCERS

Oral Cavity

• Anatomy: Includes lips, buccal mucosa, gingiva, alveolar ridge, hard palate, floor of mouth, retromolar trigone, and the anterior two-thirds of the tongue.     * Extends from the lips to the posterior aspect of the hard palate.     * Circumvallate Papillae: Separates the anterior two-thirds (oral cavity) from the posterior tongue (oropharynx).

• Risk Factors and Signs:     * Associated with Plummer-Vinson syndrome (iron deficiency in females).     * HPV association: Tongue, floor of mouth, and tonsils.     * Most common site: Lips.     * Signs: Leukoplakia, erythroplasia, poor hygiene, non-healing ulcers.

• Pathology: Majority are Squamous Cell Carcinoma (SCC); variants include verrucous SCC or spindle cell SCC.

• Lymphatics and Spread:     * Upper lip: Submandibular and preauricular nodes.     * Lower lip/Anterior mouth: Submental nodes.     * Oral tongue: Anterior cervical chain.     * Buccal mucosa: Submandibular and subdigastric nodes.     * Spread: Blood-borne spread is rare; cervical lymph nodes are the most common site of spread.

Pharynx

• Anatomy: Three subdivisions ordered superior to inferior:     * Nasopharynx: Posterior to the nose, extends to the uvula (Level $C1$). Contains adenoids. Linked to Epstein-Barr Virus (EBV). High surgical risk due to brain base proximity.     * Oropharynx: Posterior to oral cavity, extending from soft palate to hyoid bone (Level $C2-C3$). Contains palatine tonsils (most common cancer site here).     * Laryngopharynx (Hypopharynx): Level $C3-C6$. Epiglottis is superior border. Contains pyriform sinuses (most common cancer site here), postcricoid, and posterior pharyngeal walls.

• Lymphatics:     * Nasopharynx: Cervical, Node of Rouvire (lateral retropharyngeal), and jugulodigastric nodes.     * Oropharynx: Subdigastric, upper cervical, submaxillary, and parapharyngeal nodes.     * Hypopharynx: Midcervical, superior deep, middle/low jugular, and Node of Rouvire.

• Spread Patterns:     * Nasopharynx: Cranial nerve involvement; metastasis to bone, lung, or liver.     * Hypopharynx: Invades nearby nerves and muscles.

Larynx

• Anatomy: Extends from epiglottis to cricoid cartilage (Level $C3-C6$). Sections: Glottis (true vocal cords), supraglottis, and subglottis.

• Factors: Strongly associated with cigarette smoking and HPV.

• Pathology: Majority are SCCs.

• Lymphatics: Glottic cancers rarely spread to nodes (treated with $5 \times 5\,\text{cm}$ or $6 \times 6\,\text{cm}$ fields). Supraglottic cancer spreads to spinal accessory chain nodes.

Salivary Glands and Thyroid

• Salivary Glands: Parotid (largest, wedge-pair technique), submandibular, sublingual.     * Parotid cancers are mostly adenocarcinoma presenting as rapidly growing masses.

• Thyroid: Right and left lobes connected by an isthmus. Near larynx, trachea, esophagus.     * Types: Papillary (most common), Follicular (spreads via blood to bone/lung), Medullary, Anaplastic (local tracheal invasion).     * Treatment: Papillary and follicular types may be treated with $\text{I-131}$.

BREAST CANCER

Anatomy and Physiology

• Structure: Comprised of $15-20\,\text{lobes}$, adipose tissue, connective tissue, nerves, and vessels.

• Positioning: Located between the 2nd and 6th ribs; extends from sternum to midaxillary line.

• Tail of Spence: Breast tissue extending toward the axilla.

• Musculature: Supported by pectoralis major, serratus anterior, pectoralis minor, and latissimus dorsi.

• Support: Cooper's suspensory ligaments provide structural support.

• Location: The upper outer quadrant (UOQ) is the most common site for malignancy.

Lymphatics and Spread

• Nodal Groups:     * Axillary Nodes: Primary drainage from ipsilateral breast ($10-38\,\text{nodes}$).         * Level I: Lowest/superficial.         * Level II: Under pectoralis minor.         * Level III: Superior to pectoralis minor.     * Internal Mammary (IM) Nodes: Lateral to sternum, 1st-3rd intercostal spaces (average $8\,\text{nodes}$, 4 per side).     * Supraclavicular Nodes: Above clavicle.

• Pathology: Infiltrating ductal carcinoma (most common), Infiltrating lobular carcinoma (2nd).

• Inflammatory Breast Cancer: Rare ($1\%$), presents with peau d'orange, erythema, and hardening. Survival < 2 years.

• Metastatic Patterns: Spreads via direct extension, regional nodes (can use skip metastasis), and blood through Batson venous plexus. Common distant sites: Bone (T-spine), lung, brain, or liver.

LUNG CANCER

Anatomy and Secondary Structures

• Lungs: Right lung (3 lobes, wider/shorter); Left lung (2 lobes).

• Pleura: Visceral (lines lung surface), Parietal (lines thoracic wall), Pleural cavity (space between).

• Carina: Bifurcation of the trachea at Level $T4-T5$.

• Hilum: Entry point for vessels and nerves.

• Specific Conditions:     * Pancoast Tumor: Apex tumor causing shoulder pain, atrophy, and Horner syndrome.     * Superior Vena Cava (SVC) Syndrome: Compression of SVC causing breathing difficulty.

Pathology and Lymphatics

• Small Cell Lung Cancer (SCLC): Aggressive, oat cell type, centrally located, linked to tobacco. Early brain metastasis (requires Prophylactic Cranial Irradiation [PCI]).

• Non-Small Cell Lung Cancer (NSCLC): Includes adenocarcinoma (periphery, common in women, not tobacco-linked), large cell, and squamous cell.

• Mesothelioma: Lining of the lung, linked to asbestos.

• Lymphatics: Main regional spread method. Includes paratracheal, subcarinal, and hilar nodes.

ABDOMINAL, PELVIC, AND GASTROINTESTINAL SYSTEMS

Esophagus and Stomach

• Esophagus: $25\,\text{cm}$ long, $C6$ to $T10$. Upper/middle sections (SCC common); Lower/GE junction (Adenocarcinoma common - most common overall). Skip lesions occur.

• Stomach: Four regions: cardiac, fundic, body, pyloric. Mostly adenocarcinoma. Lymphatics include celiac nodes and splenic hilum.

Small and Large Bowel

• Small Bowel: Duodenum, jejunum, ileum. Contains villi for nutrient absorption. Direct extension to liver is common.

• Large Bowel: Cecum, ascending/descending colon (retroperitoneal), transverse/sigmoid (intraperitoneal), rectum.     * Surgery: Anterior resection (removes colon, leaves rectum) vs. Abdominoperineal Resection (APR - removes anus/rectum).     * Condition: Familial Adenomatous Polyposis (FAP) is genetic.     * Pathology: Adenocarcinoma is most common.     * Staging: Dukes or Modified Astler-Coller (MAC)/.

Pancreas, Liver, and Adrenal

• Pancreas: $L1-L2$ level. Head (most common site for cancer) near duodenum, Tail near spleen. Whipple procedure (pancreaticoduodenectomy) for treatment.

• Adrenal: Cortex (outer, steroids), Medulla (inner, epinephrine). Spreads to paraaortic nodes.

• Liver: Largest gland, 4 lobes. Kupffer cells clean blood. Mostly Hepatocellular Carcinoma.

Genitourinary System

• Kidney: $T12$ to $L3$. Right lung is lower. Primarily Renal Cell Carcinoma.

• Bladder: Trigone (posterior wall, common cancer site). Spreads to iliac and paraaortic nodes.

• Urethra: Squamous cell. Females ($4\,\text{cm}$); Males (longer).

REPRODUCTIVE SYSTEMS

Prostate Cancer

• Anatomy: Surrounds male urethra, walnut-shaped, posterior to pubic symphysis.

• Screening: PSA ($PSA \leq 4\,ng/mL$ is normal).

• Grading: Gleason score $1-5$ (two locations added together).

• Pathology: Adenocarcinoma. Distant spread primarily to the spine (bone metastasis).

Testicular and Gynecologic Cancers

• Testes: Crytorchidism (undescended testes) increases risk. Germ cell tumors (Seminomas vs. Nonseminomatous like yolk sac or embryonal).

• Endometrium: Innermost uterus layer. Postmenopausal bleeding symptom. Associated with tamoxifen use.

• Cervix: Pap smear detection. Point A ($2\,cm$ superior/lateral to os); Point B ($3\,cm$ lateral to point A).

• Ovaries: Deadliest gynecologic cancer. Serum CA-125 is elevated. Contraceptives help decrease risk.

• Vagina/Vulva: Vagina (DES exposure linked to clear cell). Vulva (Cloquet's node involvement).

SKELETAL AND SOFT TISSUE SARCOMAS

Pathology and Location

• Origins: Mesoderm, primitive mesenchyme, or ectoderm cells.

• Growth Sites: Occur at growth plates (Distal femur, proximal tibia).

• Specific Sarcomas:     * Osteosarcoma: Most common bone tumor; involves distal femur/proximal tibia; occurs in ages 10-25.     * Ewing's Sarcoma: Diaphysis of bone; "onion-shaped" appearance on imaging; ages 10-20.     * Chondrosarcoma: Cartilage tumor; commonly in the pelvis; ages 35-60.

• Radiation Warning: When treating extremities, a strip of skin/tissue must be left unirradiated to allow lymphatic drainage and prevent edema.

LYMPHOMA AND HEMATOLOGIC DISORDERS

Lymphoma Classification

• Hodgkin Lymphoma (HL): Presence of Reed-Sternberg cells (giant binucleate cells). Bimodal age distribution ($25-30$ and $75-80$). Predictable, contiguous spread. Features "B symptoms" (fever, night sweats, $10\%$ weight loss).     * Subtypes: Nodular Sclerosing (NSHL) is most common.     * Treatment: Mantle field radiation; MOPP or ABVD chemotherapy.

• Non-Hodgkin Lymphoma (NHL): Random spread. Median age 67. Staging involves Waldeyer's ring, Peyer's patches, and spleen. Chemotherapy: CHOP.

Leukemia and Multiple Myeloma

• ALL: Most common in pediatric patients ($2-3\,\text{years}$ old).

• AML: Most common adult acute leukemia ($80\%$); features Auer rods.

• CML: Contains the Philadelphia chromosome.

• Multiple Myeloma: Plasma cell malignancy. $10\%$ bone marrow plasma cells required for diagnosis. Features multiple lytic bone lesions.

SKIN CANCERS AND BENIGN CONDITIONS

Skin Pathology

• Non-Melanoma: Basal Cell Carcinoma (BCC - most common, slow, stratum basale); Squamous Cell Carcinoma (SCC - faster, sun-exposed areas).

• Melanoma: Most aggressive. Uses ABCD Rule (Asymmetry, Border, Color, Diameter $> 6\,mm$).

• Mycosis Fungoides: Cutaneous T-cell lymphoma subgroup. Treated with Total-Skin Electron Beam (TSEB).

Benign Diseases

• Heterotopic Bone: Ossification in soft tissue post-hip surgery. Treated with $6-8\,Gy$ pre- or post-op.

• Keloid: Excess scar tissue. Radiation ($900-1,500\,cGy$) must occur within $24\,\text{hours}$ of surgery.

• Arteriovenous Malformations (AVM): Tangled vessels. Treated with $12-2,500\,cGy$.

ONCOLOGIC EMERGENCIES AND CLASSIFICATION

Emergencies

• Indications: SVC syndrome, skeletal metastasis, high intracranial pressure from brain mets, or heavy vaginal bleeding.

• Technique: High-dose fractions (1-2) using simple open fields for palliative relief.

Grading and Staging

• Histopathology: Benign (encapsulated, slow) vs. Malignant (rapid, life-threatening). Carcinomas (Epithelial/Lymphatic spread) vs. Sarcomas (Connective tissue/Blood-borne spread).

• Grade: Aggressiveness based on differentiation ($G1-G4$).

• Stage: Severity using TNM (Tumor size, Nodal involvement, Metastasis). Systems include AJCC, UICC, FIGO (gyn), Dukes (colorectal), and Ann Arbor (lymphoma).

TISSUE TOLERANCES (TD 5/5)

• Definition: The dose to healthy tissue with a $5\%$ chance of complication within five years.