2495 - Toxicity Profile for Connective Tissue Disease Patients Treated with Lung Stereotactic Body Radiation Therapy (SBRT)

Purpose/Objective(s): Connective tissue diseases (CTDs) have historically been considered as presenting contraindications to radiotherapy (RT), in particular lung RT, due to concern for increased rates of severe toxicity. Lung stereotactic body radiation therapy (SBRT) used for inoperable early-stage lung cancer or oligometastases is associated with very low rates of high grade toxicity. The present study seeks to provide updated information on the toxicity profile of lung SBRT in CTD patients.

Materials/Methods: A single institution IRB-approved prospective lung SBRT registry was surveyed for all pts with a connective tissue disease treated for primary cancer, oligometastasis, or salvage from 2006 – 2024. Tumors were characterized as peripheral or central per RTOG criteria. Treatment-related toxicity was graded per CTCAE version 3.0. Medical management of CTDs was recorded at time of cancer consultation.

Results: A total of 118 CTD pts undergoing 144 courses of lung SBRT was available for analysis. Median age was 72 years (65 – 79, IQR) and 82 pts (69%) female. Median KPS was 80 (60 – 90, IQR). Median follow-up was 19 months (9 – 51, IQR). Median tumor size was 1.9 cm (1.5 – 3.2, IQR). Patient characteristics were 55 (47%) with rheumatoid arthritis (RA), 17 (14%) with systemic lupus, 28 (24%) with interstitial/idiopathic lung disease, 6 (5%) with scleroderma, and 42 (36%) with other CTDs. Twenty-six (22%) patients had multiple CTDs. At SBRT, 58 (49%) patients were on active medical treatment. Considering treatment characteristics, median SBRT BED₁₀ was 120 Gy (100 – 149, IQR, with the most common dose schedule being 50Gy/5fx. Twenty-eight tumors (24%) were central, of which 22 (19%) were considered ultracentral. Overall, 29 (26%) treatments resulted in grade 2 or higher toxicity, with 6 (5%) grade 3 and 1 grade 5 (0.1%). Lung toxicities included 13 (11%) chest wall pain, 11 (9%) pneumonitis, 2 (2%) cough, 1 (1%) pleural effusion, and 1 (1%) hemoptysis. Grade 3 pneumonitis rate was 11% for pts with interstitial/idiopathic lung disease, 2% for RA, and 0% for lupus and scleroderma. The case of grade 5 pneumonitis was associated with interstitial lung disease. No patient with a central tumor had = grade 2 toxicty. Three (14%) of the patients with ultracentral tumors had grade 2 chest wall toxicity, 2 (9%) had grade 2 pneumonitis, 1 (4.5%) had esophagitis and another had hemoptysis. Median time to first pulmonary function test was 2 months (1 – 4, IQR), with a median FEV1% change of -6 (1 – (-35), IQR) and a median DLCO change of -6 (0 – (-30), IQR).

Conclusion: Lung SBRT for CTD patients was not associated with increased rates of high-grade toxicity compared to historical results. Patients with interstitial/idiopathic lung disease were at increased risk for grade 3 or higher pneumonitis.