Radiation Oncology · Supplementary · from Radiation Oncology

Case 3: Stereotactic Body Radiation for Lung Cancer

Patient Presentation

Demographics: 76-year-old female retired librarian

Chief Complaint: "They found a spot on my lung on a screening CT scan."

History of Present Illness: A 76-year-old female presents to the radiation oncology department following diagnosis of an early-stage non-small cell lung cancer (NSCLC). She was enrolled in a low-dose CT lung cancer screening program due to her 45 pack-year smoking history (quit 8 years ago). Her annual screening LDCT revealed a new 2.2 cm solid, spiculated nodule in the right upper lobe that was not present on prior year's scan. PET/CT demonstrated the nodule to be intensely FDG-avid (SUVmax 8.4) with no mediastinal or hilar lymphadenopathy and no distant metastases. CT-guided percutaneous core needle biopsy confirmed adenocarcinoma (NSCLC), and staging was T1cN0M0, Stage IA3.

She was evaluated by thoracic surgery for consideration of lobectomy (standard of care for operable early-stage NSCLC). However, pulmonary function testing revealed severe COPD with an FEV1 of 0.82 L (38% predicted) and DLCO of 34% predicted. Her predicted post-operative FEV1 was calculated at 28% predicted, placing her at prohibitive surgical risk. The thoracic surgery team deemed her medically inoperable.

She was referred for stereotactic body radiation therapy (SBRT), which achieves local control rates of 90-95% for early-stage NSCLC and is the standard of care for medically inoperable patients.

Past Medical History:

• Severe COPD (GOLD Stage III, FEV1 38% predicted)
• Coronary artery disease (PCI with DES to RCA 4 years ago)
• Hypertension
• Osteoporosis
• Peripheral arterial disease
• Former smoker (45 pack-years, quit 8 years ago)

Medications:

• Tiotropium/olodaterol inhaler daily
• Albuterol inhaler PRN
• Aspirin 81 mg daily
• Clopidogrel 75 mg daily (continued post-PCI per cardiology)
• Atorvastatin 80 mg daily
• Metoprolol succinate 25 mg daily
• Alendronate 70 mg weekly
• Home oxygen 2L NC with exertion

Social History:

• Retired librarian
• Lives alone in single-story home
• Former smoker: 45 pack-years (1 pack/day for 45 years), quit 8 years ago
• No alcohol
• Uses home oxygen with exertion; walks with walker for longer distances
• ECOG Performance Status: 2

Family History:

• Mother: COPD, died at age 70
• Father: colon cancer at age 74
• Brother: lung cancer at age 68 (smoker)

Physical Examination

• Vital Signs: BP 132/78 mmHg, HR 72 bpm, RR 20/min, Temp 36.7°C, SpO2 92% on room air (96% on 2L NC), Weight 54 kg, BMI 21.2
• General: Thin, elderly female, mildly dyspneic at rest, barrel chest
• Lungs: Decreased breath sounds bilaterally, prolonged expiratory phase, scattered expiratory wheezes, no crackles; increased AP diameter
• Cardiovascular: Regular rate and rhythm, no murmurs
• Extremities: No clubbing, no edema, ABI 0.76 bilaterally
• Neurological: Alert, oriented, no focal deficits

Workup and Results

Laboratory Studies:

Pulmonary Function Tests:

Imaging/Additional Studies:

• Low-dose CT chest: 2.2 cm solid, spiculated nodule in right upper lobe (segment 1, apical); no other pulmonary nodules; severe emphysematous changes bilaterally
• PET/CT: FDG-avid RUL nodule, SUVmax 8.4; no FDG-avid mediastinal, hilar, or supraclavicular lymphadenopathy; no distant metastases
• CT-guided biopsy: Adenocarcinoma (NSCLC); TTF-1 positive; PD-L1 TPS 45%; EGFR/ALK/ROS1 negative (molecular testing for potential future systemic therapy)
• Brain MRI: No intracranial metastases
• EBUS (endobronchial ultrasound): Stations 4R and 7 sampled; no malignant cells (confirms N0 status)

SBRT Treatment Planning:

• CT simulation: 4D-CT acquired with abdominal compression to reduce respiratory motion; ITV (internal target volume) generated from all respiratory phases
• Tumor motion: 6 mm craniocaudal motion with free breathing, reduced to 3 mm with abdominal compression
• Target volumes:
• GTV: 2.2 cm visible tumor on CT
• ITV: GTV expanded to encompass tumor motion on 4D-CT
• PTV: ITV + 5 mm isotropic expansion
• Prescription: 54 Gy in 3 fractions (18 Gy/fraction), delivered every other day over 1 week
• OAR constraints (3-fraction regimen):
• Spinal cord: Max <18 Gy (single fraction equivalent)
• Chest wall: V30Gy <30 cc
• Esophagus: Max <27 Gy
• Heart: Max <30 Gy
• Proximal bronchial tree: Max <30 Gy (tumor is peripheral, >2 cm from proximal bronchial tree)
• Ipsilateral lung (minus GTV): V20Gy <10%
• Plan quality: PTV V100% = 95%; R50% (50% isodose volume/PTV volume) = 4.2 (within RTOG constraints); maximum dose 130% of prescription (within PTV)

Clinical Image

Diagram showing stereotactic body radiation therapy (SBRT) treatment plan for early-stage lung cancer with multiple non-coplanar beam arrangements, highly conformal dose distribution around the tumor, and steep dose falloff protecting surrounding normal lung tissue. Source: Educational illustration.

Diagnosis

Right Upper Lobe Adenocarcinoma (NSCLC), T1cN0M0, Stage IA3, Medically Inoperable Due to Severe COPD, Treated with Stereotactic Body Radiation Therapy (SBRT)

Key Diagnostic Criteria:

• Biopsy-confirmed adenocarcinoma of the lung
• Peripheral RUL location, 2.2 cm, spiculated, FDG-avid (SUVmax 8.4)
• Pathologic N0 status confirmed by EBUS
• No distant metastases on PET/CT and brain MRI
• Medically inoperable: FEV1 38% predicted, DLCO 34% predicted, predicted post-op FEV1 28% predicted (prohibitive risk per thoracic surgery)

Treatment Plan

1. SBRT delivery: 54 Gy in 3 fractions (18 Gy/fraction), BED₁₀ = 151.2 Gy (BED >100 Gy associated with >90% local control); treatments on Monday, Wednesday, Friday of a single week
2. Image guidance: Cone-beam CT (CBCT) before each fraction with online match to ITV; respiratory monitoring with abdominal compression device
3. Treatment delivery: VMAT with 6-10 MV photons, multiple non-coplanar arcs; total treatment time approximately 15-20 minutes per fraction
4. Monitoring during treatment: Pulse oximetry before and after each fraction; supplemental oxygen available
5. Acute toxicity management:

• Expected: mild fatigue, possible transient cough exacerbation
• Radiation pneumonitis risk: ~5-10% (Grade ≥2); prednisone taper if symptomatic (dyspnea, cough, fever at 2-6 months post-treatment)
• Chest wall pain: possible if tumor adjacent to ribs (this case: apical, low risk)

1. Follow-up imaging: CT chest at 3 months, then every 6 months for 2 years, then annually; expected post-SBRT changes include consolidation at treatment site (peak at 6-12 months, then slow regression)
2. Distinguish recurrence from fibrosis: If growing or newly FDG-avid mass at treatment site >12 months post-SBRT, consider PET/CT and possible biopsy; the "high-risk CT features" (bulging margins, loss of air bronchograms, enlargement after 12 months) suggest recurrence

Key Learning Points

• SBRT delivers ablative doses of radiation in 3-5 fractions using highly conformal treatment plans with steep dose gradients, achieving local control rates of 90-95% for early-stage peripheral NSCLC
• Biologically effective dose (BED) is the key metric for SBRT efficacy: BED₁₀ >100 Gy is associated with optimal local control (54 Gy in 3 fractions = BED₁₀ 151.2 Gy)
• 4D-CT simulation is essential for lung SBRT to account for respiratory tumor motion; the internal target volume (ITV) encompasses the tumor position throughout the breathing cycle
• SBRT is the standard of care for medically inoperable early-stage NSCLC; prospective data suggest outcomes comparable to surgery for operable patients, with the STARS and ROSEL trials and VALOR/SABRTooth trials ongoing
• Post-SBRT imaging interpretation requires expertise: benite consolidation and fibrotic changes at the treatment site are expected and can mimic recurrence on CT; PET/CT and serial imaging are needed to distinguish the two

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