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Description
Introduction
Stereotactic body radiotherapy (SBRT) is a highly precise local treatment with high dose per fraction. Local
control rate in lung tumors treated with SBRT is high, 85-95%. Several studies showed the predictor for local control
of lung SBRT in patients with primary lung cancer and/or lung metastasis was the prescribed biological equivalent
dose with α/β = 10 (BED10) and common SBRT-related complications were radiation pneumonitis (RP), rib fracture,
and cardiotoxicity. For central/ultracentral lung tumors, the fatal complications, such as pulmonary hemorrhage, were
reported.
Despite increasing use of SBRT, there are still unclear predicting factors about its outcomes. Therefore,
patients with lung tumors treated with SBRT in Ramathibodi Hospital were reviewed.
Materials and methods
A retrospective cohort study was performed in therapeutic and prognostic type and received ethics approval
from the Institutional Review Board. Medical records and SBRT plans of all patients diagnosed early stage non-small cell lung cancer or lung metastases treated with SBRT from January 2009 to September 2018 in Ramathibodi Hospital
were reviewed. Inclusion criteria were histologically confirmed early stage NSCLC (T1-2N0M0), lung metastasis with
known primary malignancy and good performance status (ECOG ≤2). Exclusion criteria were missing data and reirradiation to in-field region.
We delineated additional interesting volumes such as a 3-cm shell outside the planning target volume (PTV),
left atrium, superior vena cava, and ribs. Dose prescription was prescribed at isodose line covering PTV at PTV
D95%. There was no clinical target volume (CTV) and gross target volume (GTV) was expanded 3- to 5-mm margin
to be PTV. Radiation was delivered by three linear accelerators as follows, with ray tracing, Acuros and Analytical
Anistropic Algorithm (AAA).
Imaging studies and SBRT plans were reviewed by either a thoracic radiation oncologist or a thoracic
radiologist in order to identify local recurrence or post-radiation change.
Results
59 patients with 98 lung lesions were eligible which primary NSCLC and lung metastasis were 15.3% and
84.7%, respectively. Median follow-up time was 16.8 months (0.1-71.7 months). There were variations in patient
demographics between two types of lung tumors. Primary NSCLC patients were older, more comorbidities and poorer
performance status compared to the other. Majority of tumor origin and histopathology were primary lung cancer, 49%
2
and adenocarcinoma, 82.7%. Median maximal diameter of the tumor was 2.3 cm (0.1-8 cm). Dose prescriptions were
various from 25-60 Gy in 1-10 fractions.
As competing risk analysis, overall 1-year local control rate was 90.8%, 93.4% found in primary lung cancer
and 90.1% in lung metastasis. The most common pattern of failure was distant failure, 46.9%. The follows were local
and regional failure patterns, 12.2% and 6.1% respectively. Of 9 (9.2%) lung tumors, pulmonary toxicities were
observed which radiation pneumonitis grade ≥2 found in 8 (8.2%) lesions and one of four patients with ultracentral
lesions experienced grade 5 pulmonary hemorrhage. The multivariate analysis of factors predicting local failure was
mean BED of the PTV. Mean BED of the PTV <100 Gy had more 1-year local failure compared to the dose ≥100 Gy,
15.5% versus 3%, adjusted SHR 5.41 (95% CI 1.14-25.69), p-value = 0.034. The maximal diameter of the tumor >5
cm had higher grade ≥2 pneumonitis, 18% versus 3.3%, adjusted SHR 5.34 (95% CI 1.52-18.69), p=0.009. 1-year
overall survival was 80% in primary NSCLC and 72% in lung metastasis. Median overall survival was 16.8 months
(0.1-71.7 months).
Conclusion
Local control rate of lung SBRT was high with acceptable toxicity. BED PTV mean was the predictive factor
for local tumor control. The tumor maximal diameter >5 cm might correlate with radiation pneumonitis grade ≥2.
Lung SBRT might not suitable for ultra-central lung tumors.
Figure1. Cumulative incidence curves of factors predicting
local failure and radiation pneumonitis grade ≥2
| Country or Int. Organization | Thailand |
|---|---|
| Affiliation | Ramathibodi Hospital, Mahidol University |
