Local Tumor Control After Stereotactic Body Radiation Therapy for Early Lung Cancer is Not Impacted by the Use of Intensity Modulated Radiation Therapy or Respiratory Gating

Abstract

Though stereotactic body radiation therapy (SBRT) has become a standard treatment option for stage I NSCLC, the majority of published results relate to three-dimensional treatment planning (3D-CRT). Less data is available following treatment with IMRT, and there is also limited published experience using respiratory gating, where treatment is only delivered to a portion of the breathing cycle, during SBRT. Retrospective review of patients treated with SBRT for Stage I NSCLC between 2007 and 2015. All patients had a 4D simulation with the Varian RPMTM system and abdominal compression was used in the majority (81%). Respiratory gating was typically used if longitudinal tumor motion exceeded 1cm. Patient characteristics, treatment planning and delivery parameters, dosimetry information, and patient outcomes were collected and analyzed using SPSS statistical software (descriptive stats, bivariate procedures and survival analyses). A total of 297 patients (median age 71, range 43-89) with stage I NSCLC were included. Pathology was confirmed in 94.6% of patients. The majority of lesions were located in the upper lobes (60.9%) and clinical stage T1A (68%). The use of 3DCRT and IMRT planning was similar, 52% vs 48%, although an increased frequency of IMRT was noted in more recent years. Respiratory gating was employed in approximately 16% of cases (n=51). The gating cohort included 78% lower lobe tumors, while 26% of lesions treated without gating were in the lower lobes. The most common SBRT regimens were 48Gy in 4 fractions and 54-60Gy in 3 fractions. With a median follow up of 22.7 months, there were 17 local failures for a crude relapse rate of 5.7%. Local tumor relapse was similar in patients treated with 3DCRT and IMRT (6.5% vs 4.9%, p=0.962), and relapse likewise was similar with and without respiratory gating (7.8% vs 4.9%, p=0.560). In addition, T-stage, tumor size, pathology and SBRT regimen did not correlate with local tumor control. Overall survival for the entire population approximated 72% at 2 years. Treatment appeared tolerated well with 6 documented grade 3+ events, and thus there were too few events to compare toxicity amongst treatment cohorts. The utilization of respiratory gating or the use of IMRT does not appear to compromise the therapeutic ratio for patients treated with SBRT for stage I NSCLC.