Stereotactic ablative radiation therapy in lung cancer: an emerging standard

Assessing the impact of intrafraction motion correction on PTV margins and target and OAR dosimetry for single-fraction free-breathing lung stereotactic body radiation therapy

The objective of this research is to investigate intrafraction motion correction on planning target volume (PTV) margin requirements and target and organ-at-risk (OAR) dosimetry in single-fraction lung stereotactic body radiation therapy (SBRT). Sixteen patients (15 with upper lobe lesions, 1 with a middle lobe lesion) were treated with single-fraction lung SBRT. Cone-beam computed tomography (CBCT) images were acquired before the treatment, between the arcs, and after the delivery of the treatment fraction. Shifts from the reference images were recorded in anterior-posterior (AP), superior-inferior (SI), and lateral (LAT) dimensions. The deviations from the reference image were calculated for 3 clinical scenarios: not applying intratreatment couch shifts and not correcting for pretreatment deviations < 3 mm ( scenario 1), not applying intratreatment couch shifts and correcting for pretreatment deviations < 3 mm ( scenario 2), and applying all pre- and intratreatment couch shifts (scenario 3). PTV margins were determined using the van Herk formalism for each scenario and maximum and average deviations were assessed. The clinical scenarios were modelled in the treatment planning system based on each patient dataset to assess target and OAR dosimetry. Calculated lower-bound PTV margins in the AP, SI, and LAT dimensions were [4.6, 3.5, 2.3] mm in scenario 1, [4.6, 2.4, 2.2] mm in scenario 2, and [1.7, 1.2, 1.0] mm in scenario 3. The margins are lower bounds because they do not include contributions from nonmotion related errors. Average and maximum intrafraction deviations were larger in the AP dimension compared to the SI and LAT dimensions for all scenarios. A unidimensional movement (several mm) in the negative AP dimension was observed in clinical scenarios 1 and 2 but not scenario 3. Average intrafraction deviation vectors were 1.2, 1.1, and 0.3 mm for scenarios 1, 2, and 3, respectively. Modelled clinical scenarios revealed that using scenario 3 yields significantly fewer treatment plan objective failures compared to scenarios 1 and 2 using a Wilcoxon signed-rank test. Intratreatment motion correction between each arc may enable reductions PTV margin requirements. It may also compensate for unidimensional negative AP movement, and improve target and OAR dosimetry.

Outcomes of stereotactic body radiotherapy versus lobectomy for stage I non-small cell lung cancer: a propensity score matching analysis

BACKGROUND

Lobectomy is the standard treatment for patients with stage I non-small cell lung cancer (NSCLC). Recent studies have shown promising results of stereotactic body radiation therapy (SBRT) in these patients. We retrospectively compared the outcomes of lobectomy and SBRT in these patients from our therapeutic center.

METHODS

Patients who underwent lobectomy or SBRT for clinical T1-2a (T size≤5 cm), N0 M0, NSCLC between December 2011 and August 2016 were reviewed. Patient characteristics, treatment-related outcomes and toxicities were analyzed. Propensity score matching (PSM) was performed to improve comparability between the two groups.

RESULTS

Median follow-up period in the lobectomy (n = 246) and SBRT (n = 70) group was 31.4 months and 24.9 months, respectively. Three-year local recurrence-free survival (LRFS) was comparable in the two groups (97% vs. 91.7%, respectively; P = 0.768). Recurrence-free survival (RFS) at 3-year in the lobectomy and SBRT groups was 85.4 and 69.5%, respectively (P = 0.014). Three-year overall survival (OS) after lobectomy and SBRT was 88.2 and 79.7%, respectively (P = 0.027), while 3-year cancer-specific survival (CSS) was 91.3 and 82.5% (P = 0.022). After PSM (45 matched patients in each group), there was no significant between-group difference with respect to 3-year LRFS (89.6% vs. 87.5%, P = 0.635), RFS (77.6% vs. 67.3%, P = 0.446), OS (78.5% vs. 79.5%, P = 0.915) or CSS (86.4 and 79.5%, P = 0.551). In matched subgroup, 30-day mortality after lobectomy was 2.2%, and no treatment-related death occurred after SBRT.

CONCLUSIONS

Treatment-related outcomes of SBRT and lobectomy were comparable. SBRT was well tolerated and had a very low toxicity profile in our study. SBRT is a promising alternative treatment option for stage I NSCLC patients. This study indicates that matching these disparate cohorts of patients is challenging. Clinical trials are essential to define the indications and relative efficacy of lobectomy and SBRT in a selected population.