Stereotactic ablative radiotherapy (SABR) for early-stage central lung tumors: New insights and approaches

The use of stereotactic ablative radiotherapy (SABR) for central lung tumors is increasing. Centrally located lung tumors can be subdivided into two categories, namely the ‘moderately central’ tumors where the planning target volume is located within 2 cm of the proximal bronchial tree, and the ‘ultracentral’ tumors where a planning target volume (PTV) overlaps the trachea or main stem bronchi. The toxicity of SABR appears acceptable when ‘moderately central’ tumors are treated using techniques that comply with organs at risk tolerance doses used for prospective trials and in recent publications. A high toxicity is seen when ultracentral tumors are treated using SABR, and conventional radiotherapy appears more appropriate in such tumors as the true normal organ tolerance doses remain unknown. When ultracentral tumors are treated with non-SABR hypofractionated radiotherapy, a homogenous dose distribution in the planning target volume and limitation of both normal organ maximum point doses and volumes receiving high doses seems to be needed

Incidence of High-Risk Radiologic Features in Patients Without Local Recurrence After Stereotactic Ablative Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer

PURPOSE: To investigate, in the setting of stereotactic ablative radiation therapy (SABR) for early-stage non-small cell lung cancer, the incidence and patterns of change in high-risk radiologic features (HRFs) in patients known to have no local recurrence. METHODS AND MATERIALS: Computed tomography (CT) scans of patients treated using volumetric modulated arc therapy SABR between 2008 and 2013 were eligible if follow-up scans were available for 2 years and no local recurrences were diagnosed. All scans were reviewed at a workstation using an add-on tool for ClearCanvas (Synaptive Medical). Five clinicians who were blinded to clinical outcomes scored the presence of HRFs: enlarging opacity (EO), sequential enlarging opacity, enlarging opacity after 12 months (EO12), bulging margin, loss of linear margins, cranio-caudal growth, and loss of air bronchogram. After each review, clinicians recommended follow-up procedures based on published recommendations. RESULTS: A total of 88 patients (747 CT scans) were evaluated. The HRFs most frequently recorded by ≥3 observers on at least 1 follow-up scan were EO (64.8%), EO12 (50.0%), and sequential enlarging opacity (13.6%). Fifty-six patients developed EO within the first year after SABR, and of these, 46 also developed subsequent EO (EO12). In 76 patients who developed EO after 1 year of follow-up, 30 had not manifested EO previously. Three or more HRFs have been associated with recurrences, and this was observed on CT scan in 22.7% of patients. In their routine care, 6 patients had undergone a positron emission tomography scan because of a suspected local recurrence, and 4 underwent an attempt at biopsy. CONCLUSIONS: More than 50% of patients without a local recurrence after SABR develop HRFs. Because ≥3 HRFs were present in nearly 25% of patients, further refinement of follow-up recommendations are necessary