Stereotactic body radiotherapy for central lung tumors: Finding the balance between safety and efficacy in the "no fly" zone

STereotactic Ablative RadioTherapy in NEWly Diagnosed and Recurrent Locally Advanced Non-Small Cell Lung Cancer Patients Unfit for ConcurrEnt RAdio-Chemotherapy: Early Analysis of the START-NEW-ERA Non-Randomised Phase II Trial

PURPOSE

This is a single arm phase 2 trial (Clinical trials.gov NCT05291780) to assess local control (LC) and safety of SAbR in patients with unresectable locally advanced non-small cell lung cancer (LA-NSCLC) unfit for concurrent chemo-radiation therapy (ChT-RT).

METHODS

Neoadjuvant ChT was prescribed in fit patients. The tumor volume included primary tumor and any regionally positive node/s. The coprimary study endpoints were LC and safety.

RESULTS

Between December 31, 2015, and December 31, 2020, 50 patients with LA-NSCLC were enrolled. Histology was squamous cell carcinoma and adenocarcinoma (ADC) in 52% and 48%, respectively. Forty (80%) patients had ultracentral tumor. Twenty-seven (54%) received neoadjuvant ChT and 7 (14%) adjuvant durvalumab. Median prescribed dose was 45 Gy (range, 35-55) and 40 Gy (35-45) in 5 daily fractions to tumor and node/s, respectively. After a median follow-up of 38 months (range, 12-80), 19 (38%) patients had experienced local recurrence (LR) at a median time of 13 months (range, 7-34). The median LR-free survival (FS) was not reached (95% confidence interval [CI], 28 to not reached). The 1-, 2-, and 3-year LR-FS rates were 86% ± 5%, 66% ± 7%, and 56% ± 8%, respectively. At last follow-up, 33 (66%) patients were alive. Median overall survival (OS) was 55 months (95% CI, 43-55 months). The 1-, 2-, and 3-year OS rates were 94% ± 3%, 79% ± 6%, and 72% ± 7%, respectively. No patients developed ≥ grade (G) 3 toxicity. ADC (hazard ratio [HR], 3.61; 95% CI, 1.15-11.35) was a significant predictor of better LC, while OS was significantly conditioned by smaller planning target volumes (HR, 1.004; 95% CI, 1.001-1.010) and tumor, node, and metastasis stage (HR, 4.8; 95% CI, 1.34-17).

CONCLUSIONS

Patients with LA-NSCLC treated with SABR had optimal LC and promising OS in absence of ≥G3 toxicity. Our early outcomes would suggest the feasibility of using this approach in patients with LA-NSCLC unfit for concurrent ChT-RT.

Evidence-Based Planning Target Volume Margin Reduction for Modern Lung Stereotactic Ablative Radiation Therapy Using Deformable Registration

PURPOSE

Standard planning target volume (PTV) margins for lung stereotactic ablative radiation therapy (SABR) are 5 mm. High-dose-rate volumetric modulated arc therapy delivered using flattening filter-free (FFF) beams with modern immobilization systems may allow for PTV margin reduction. This study assesses whether PTV margins can be reduced from 5 to 3 mm.

METHODS

Target intrafractional motions derived from pretreatment and posttreatment cone beam computed tomography (CBCT) scans for 33 patients receiving lung SABR treated with 10XFFF energy and 5-mm PTV margins from 2016 to 2019 were used to calculate the required PTV margin. Deformable registration of the planning CT scan and internal gross tumor volume (IGTV) contour to posttreatment CBCT scans for 36 consecutive patients with 4 fraction schedules was completed to capture volume changes and intrafractional movement. Plans were replanned with 3-mm margins and recalculated on each deformed CT scan to assess deformed IGTV (d-IGTV) coverage and organ-at-risk doses.

RESULTS

Margin analysis showed PTV margins may be reduced to 3 mm. The mean d-IGTV coverage (percentage of the d-IGTV receiving ≥100% of the prescription dose [V100%] and the minimum dose covering 99.9% of the d-IGTV volume [D99.9%]) over 4 fractions for each patient was >95% with both margins. With 5-mm PTV margins, all 144 fractions had a d-IGTV V100% of >95% and a D99.9% >95%. With 3-mm PTV margins, the d-IGTV V100% was >95% in 99.3% of fractions (143 of 144) and the D99.9% was >95% in 98.6% of fractions (142 of 144). With 3-mm PTV margins, significant reductions in body V50%, body V80%, the volume of the lung receiving ≥20 Gy, and the mean lung dose and chest wall dose to 0.035 cm3 and 30 cm3 were observed (all P < .001). Using theoretical models, the normal tissue complication probability for radiation pneumonitis decreased by a mean of 0.8% (range, 0.1%-2.7%), and the mean 2-year tumor control probability was 96.1% and 95.2% with 5-mm and 3-mm PTV margins, respectively.

CONCLUSION

With modern treatment and immobilization techniques in lung SABR, 3-mm PTV margins maintain acceptable IGTV coverage, modestly reduce toxicity to organs at risk, and maintain a calculated 2-year local control rate of >95%.

Radiation Modalities Used in Lung Cancer: An Overview for Thoracic Surgeons

Radiation is a constantly evolving technology which plays a role in the management of lung cancer in a variety of settings: as an adjunct to surgery, definitively, and palliatively. Key aspects of radiation oncology-including acute and chronic toxicities of thoracic radiation and rationale for choosing one modality of radiation over another-may be obscure to those outside the field. We aim to provide a useful overview relevant for the thoracic surgeon of radiation technology and delivery. A review was performed of salient articles identifying radiation technologies used in lung cancer which were summarized and expounded upon with focus on integrating their history, evolution, and landmark trials establishing basis of their use. This article reviews the four fundamental means of external beam radiation employed in managing lung cancer and provides visual examples of comparison plans. We also touch on potential practice-changing developments in regards to proton therapy and radiation in the era of immunotherapy. Radiation oncology has evolved considerably over time to become a critical part of lung cancer management, particularly in early-stage inoperable disease and locally advanced disease. Maximizing tumor control while minimizing toxicity drives treatment strategies. Knowledge of these fundamentals will help the thoracic surgeon answer many questions patients pose regarding radiation.

Stereotactic body radiation therapy versus fractionated radiation therapy for early-stage bronchopulmonary carcinoid

Aim

To compare trends and outcomes in early stage bronchopulmonary carcinoid (BPC) tumors treated nonoperatively with conventionally fractionated radiotherapy (CFRT) and stereotactic body radiotherapy (SBRT).

Methods/materials

We queried the National Cancer Database for primary (typical) BPC staged cT1-2N0M0 and treated nonsurgically with lung-directed radiation and ≥1 month of follow-up. Odds ratios were used to predict likelihood of SBRT treatment and multivariable Cox regression determined predictors of survival.

Results

Out of 154 patients, 84 (55%) were treated with SBRT and the remainder were treated with CFRT. Although SBRT use was 0% from 2004 to 2007, it varied from 50 to 70% per year thereafter. Propensity-matched Kaplan-Meier analysis revealed improved survival with lung SBRT (median: 66 vs 58 months; p = 0.034).

Conclusion

SBRT for early stage, primary BPC has increased over time and was associated with higher survival than CFRT.

Stereotactic body radiation therapy in early-stage NSCLC: historical review, contemporary evidence and future implications

Clinical use of stereotactic body radiation therapy (SBRT) has increased dramatically over the last 2 decades and is the current standard-of-care in cases of inoperable early stage non-small-cell lung cancer. While surgical resection remains the standard-of-care for operable patients, several ongoing clinical trials are investigating the role of SBRT in these operative candidates as well. Taking into consideration the expanding role and utility of SBRT, this paper will: review the historical basis of SBRT; examine landmark trials establishing the framework for the current body of evidence; discuss areas of active and future research; and identify epidemiological trends that are likely to further increase the use of SBRT.