PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): Precision Stereotactic Body Radiotherapy (SBRT) delivers ablative doses to a target, while minimising the dose to surrounding critical organs. While the use of SBRT has been well established in early stage non-small cell lung cancer (NSCLC), concerns about toxicity and tolerability have limited its use or led to a reduction in prescribed dose in the elderly population, particularly when larger lesions are treated. We hypothesize that SBRT given to the elderly (defined as ≥65 yo and above) patient with a larger T2 and above lesion is safe and offers effective disease control in a population who is otherwise not fit for surgical resection.
Materials/Methods: To investigate this, we performed a retrospective review of treatment outcomes for patients ≥65 yo with biopsy proven and PET staged T2 N0 and T3 N0 NSCLC who received lung SBRT in our centre from 2009 to 2017. 1 patient who had no follow-up imaging was excluded. To account for different dose fractionations, all doses were converted into biological equivalent doses (BED) using an α/ßTumour = 10. Response to treatment was assessed on serial CT imaging performed ever 3-4 mo, using RECIST criteria and toxicities were prospectively recorded using CTCAEv4. Kaplan-Meier was performed and survival outcomes compared using log-rank test.
Results: We identified a total of 25 patients with a median age of 76.8yo (IQR: 72.2 – 79.9yo). 18 (72%) were deemed medically inoperable while 7(28%) declined surgery. Median GTV-ITV was 24.9cc (19.2 – 38.6cc) and median PTV was 64cc (50.5 – 83.6cc). Median D95 BED10 was 94.5 (94.1 – 132.3) with a median D10 BED10 of 113.81 (102.7 – 146.9). 4 patients relapsed in-field, representing a 2y and 3y target control of 88.2% and 80.9% respectively; 2 target failures developed distant failures at the same time. 2y and 3y control rates were 91.3% and 84.8% [same lobe], 83.3% and 70.9% [Nodal], 83.3% and 70.9% [Ipsilateral lung] and 80.1% and 65.8% [distant] respectively. 2y and 3y survival rates were 74.6% and 49.7% [overall, OS] and 86.3% and 67.8% [cancer specific, CSS]. In our cohort, a D95 BED10≥100Gy was not associated with improved target control or OS. SBRT in this population was well tolerated with 1(4%) patient reporting grade 3 pneumonitis. Despite significant chest wall doses [median V30: 52.8cc, 26.1 – 70.7cc], only one patient had a rib fracture. Another patient died 1 week following SBRT but this was attributed to a flare of his pneumonia and COPD post RT. Interestingly, poorer OS was observed in patients with significant interstitial scarring post SBRT (46mo [scarring] vs 68.8mo [no scarring]; p = 0.165).
Conclusion: Herein, our data demonstrates excellent outcomes in elderly patients with bulky T2 N0 and above NSCLC treated with SBRT.
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