Lung Cancer

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TU_28_3598 - Lung stereotactic body radiation therapy: Is there a difference in outcome based on respiratory gating?

Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3

Lung stereotactic body radiation therapy: Is there a difference in outcome based on respiratory gating?
M. Schub1, M. Dohopolski1, Z. D. Horne2, S. A. Burton1, N. Christie3, S. Jang1, and D. E. Heron4; 1Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 2Department of Radiation Oncology, UPMC Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA, 3Department of Thoracic Surgery, University of Pittsburgh Hillman Cancer Center, Pittsburgh, PA, 4UPMC Hillman Cancer Center, Pittsburgh, PA

Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) is being increasingly used for the treatment of both primary lung cancer and pulmonary oligometastases. Tumor motion during the breathing cycle can be accounted for with respiratory motion management with gating for example, which is employed in our institution if tumor excursion is greater than 5mm in any direction. There is evidence that there is a greater risk of target miss and loss of local control with gating as compared to contouring with the maximal intensity projection (MIP). Herein we compare lesion outcomes in groups of patients who required gating versus those who did not.

Materials/Methods: A retrospective case control study was carried out on 244 pulmonary lesions in both primary and metastatic lung disease in patients treated with SBRT from 2008-2014. Lesion motion was assessed on 4D-CT and motion limited in a gating window if >5mm in any direction. Target failure-free survival (TPFS) and progression-free survival (PFS) were calculated for lesions which were gated and lesions which were not and compared with Kaplan-Meier and log-rank methods. Univariate and multivariate Cox regression analyses were performed on factors predictive of outcomes. T-test and Chi-squared analysis with done on demographic data between groups.

Results: Median age at first SBRT was 70.1 years and median follow-up was 28.4 months (range: 0-74 months). Lobe distribution waas 139 upper lobe lesions, 16 in the middle lobe, and 98 in the lower lobes. Of lower lobe lesions, 77.6% were gated, 43.8% of middle lobe lesions, and 38.8% of upper lobe lesions were gated (p<0.001). Tumor size was not associated with likelihood of requiring gating. The median lesion excursion for gated lesions was 10mm vs 3mm for non-gated lesions p<0.001. The median maximum excursion in the treatment window was 4mm for gated lesions vs 3mm for non-gated lesions p=0.003. Two- and 3-year TPFS for the whole cohort were 89.1% and 86.2%, respectively. Target control was not statistically different at 2 and 3 years depending on gating use; non-gated 94.5% and 90.4% vs. 86.3% and 84.4%, p=0.136. Despite differential utilization of gating depending on lesion location, local control appeared to be similar, as can be seen in the table below. Middle lobe lesions were excluded from target control analysis because of small numbers. Maximum magnitude of lesion excursion in the treatment window did not impact TPFS (HR 1.393, 95%CI 0.153-12.681; p=0.769).
2/3-year TPFS
Upper Lobe Lower Lobe
Gated 90.4%/86.1% 86.7%/86.7%
Non-gated 95.6%/90.1% 94.7%/94.7%
p 0.602 0.439

Conclusion: The data suggest that the use of respiratory gating does not negatively impact local control and did not result in deterioration in expected outcomes. A gated approach may result in smaller amounts of normal tissue irradiated. Gating should be considered to reduce the potential toxicity of larger margins used in non-gated SBRT treatments verses the use of a maximum intensity projection.

Author Disclosure: M. Schub: None. M. Dohopolski: None. Z.D. Horne: None. S.A. Burton: None. S. Jang: None. D.E. Heron: No personal compensation; Accuray Exchange in Radiation Oncology. Partnership; Cancer Treatment Services International. Vice Chairman of Clinical Affairs; University of Pittsburgh School of Medicine. Director of Radiation Services; UPMC CancerCenter.

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