Assessing Respiration-Induced Tumor Motion and Margin of Internal Target Volume for Image-Guided Radiotherapy of Lung Cancers

Can stereotactic ablative radiotherapy in early stage lung cancers produce comparable success as surgery?

Early stage non-small cell lung cancer is a potentially curable manifestation of a disease that is typically associated with a grim prognosis. Therapies directed at early stage disease can be challenging to deliver because patients tend to be elderly with multiple comorbidities. Surgery, the standard of care, has been validated with long-term follow-up. However, the risk of perioperative mortality and morbidity can limit the feasibility of an operation for many high-risk patients. Stereotactic ablative radiotherapy uses highly focused, ablative doses of radiation to treat tumors and has emerged as an alternative to surgery.

Scalpel or SABR for Treatment of Early-Stage Lung Cancer: Clinical Considerations for the Multidisciplinary Team

Treatment options for early-stage (T1-2 N0) non-small cell lung cancer are often limited by the patient's advanced age, poor performance status, and comorbidities. Despite these challenges, stereotactic ablative radiotherapy (SABR) provides a highly effective and safe therapy for intrathoracic tumors and has become the standard of care for delivering definitive treatment in medically inoperable patients. High-quality treatment, which includes reliable immobilization, accurate tumor targeting, and precise verification of dose delivery, is essential both to achieve successful cure and to avoid debilitating toxicities. Generally, SABR is well tolerated in patients with peripherally located tumors, but even centrally or superiorly located lesions can be treated if there is adequate conformal avoidance of normal structures and/or modified fractionation to meet dose constraints. While several preliminary studies suggest that SABR is as efficacious as surgery in operable patients, results of randomized data will illuminate whether the indications for SABR can be expanded to include patients who are candidates for surgical resection. Herein, we review the rationale for using SABR and its application in treating different patient populations with early-stage lung cancer.

Promising clinical outcome of stereotactic body radiation therapy for patients with inoperable Stage I/II non–small-cell lung cancer

PURPOSE

To evaluate the efficacy and toxicity of hypofractionated stereotactic body radiotherapy in patients with Stage I/II non-small-cell lung cancer.

METHODS AND MATERIALS

Forty-three patients with inoperable Stage I/II non-small-cell lung cancer underwent treatment prospectively using the stereotactic gamma-ray whole-body therapeutic system (body gamma-knife radiosurgery) with 30 rotary conical-surface Co(60) sources focused on the target volume. Low-speed computed tomography simulation was conducted, which was followed by three-dimensional conformal radiotherapy planning. A total dose of 50 Gy was delivered at 5 Gy/fraction to the 50% isodose line covering the planning target volume, whereas a total dose of 70 Gy was delivered at 7 Gy/fraction to the gross target volume. The median follow-up duration was 27 months.

RESULTS

Three to 6 months after treatment, the complete response rate for body-gamma knife radiosurgery was 63%, and the overall response rate was 95%. The 1-year, 2-year, and 3-year local control rates were all 95% in all patients. The 1-year, 2-year, and 3-year overall survival rates were 100%, 91%, and 91%, respectively, in patients with Stage I disease and 73%, 64%, and 64%, respectively, in those with Stage II disease. Only 2.3% (1/43) of the patients had Grade 3 pneumonitis.

CONCLUSION

Our highly focused stereotactic body radiotherapy method resulted in promising local control and survival with minimal toxicity.

Relation of external surface to internal tumor motion studied with cine CT

The accuracy of delivering gated-radiation therapy to lung tumors using an external respiratory surrogate relies on not only interfractional and intrafractional reproducibility, but also a strong correlation between external motion and internal tumor motion. The purpose of this work was to use the cine images acquired by four-dimensional computed tomography acquisition protocol to study the relation between external surface motion and internal tumor motion. The respiratory phase information of tumor motion and chest wall motion was measured on the cine images using a proposed region-of-interest (ROI) method and compared to measurement of an external respiratory monitoring device. On eight lung patient data sets, the phase shifts were measured between (1) the signal of a real-time positioning-management (RPM) respiratory monitoring device placed in the abdominal region and four surface locations on the chest wall, (2) the RPM signal in the abdominal region and tumor motions, and (3) chest wall surface motions and tumor motions. Respiratory waveforms measured at different surface locations during the same respiratory cycle often varied and had significant phase shifts. Seven of the 8 patients showed the abdominal motion leading chest wall motion. The best correlation (smallest phase shift) was found between the abdominal motion and the superior-inferior (S-I) tumor motion. A wide range of phase shifts was observed between external surface motion and tumor anterior-posterior (A-P)/lateral motion. The result supported the placement of the RPM block in the abdominal region and suggested that during a gated therapy utilizing the RPM system, it is necessary to place the RPM block at the same location as it is during treatment simulation in order to reduce potential errors introduced by the position of the RPM block. Correlations between external motions and lateral/A-P tumor motions were inconclusive due to a combination of patient selection and the limitation of the ROI method.

The clinical implementation of respiratory-gated intensity-modulated radiotherapy

The clinical use of respiratory-gated radiotherapy and the application of intensity-modulated radiotherapy (IMRT) are 2 relatively new innovations to the treatment of lung cancer. Respiratory gating can reduce the deleterious effects of intrafraction motion, and IMRT can concurrently increase tumor dose homogeneity and reduce dose to critical structures including the lungs, spinal cord, esophagus, and heart. The aim of this work is to describe the clinical implementation of respiratory-gated IMRT for the treatment of non-small cell lung cancer. Documented clinical procedures were developed to include a tumor motion study, gated CT imaging, IMRT treatment planning, and gated IMRT delivery. Treatment planning procedures for respiratory-gated IMRT including beam arrangements and dose-volume constraints were developed. Quality assurance procedures were designed to quantify both the dosimetric and positional accuracy of respiratory-gated IMRT, including film dosimetry dose measurements and Monte Carlo dose calculations for verification and validation of individual patient treatments. Respiratory-gated IMRT is accepted by both treatment staff and patients. The dosimetric and positional quality assurance test results indicate that respiratory-gated IMRT can be delivered accurately. If carefully implemented, respiratory-gated IMRT is a practical alternative to conventional thoracic radiotherapy. For mobile tumors, respiratory-gated radiotherapy is used as the standard of care at our institution. Due to the increased workload, the choice of IMRT is taken on a case-by-case basis, with approximately half of the non-small cell lung cancer patients receiving respiratory-gated IMRT. We are currently evaluating whether superior tumor coverage and limited normal tissue dosing will lead to improvements in local control and survival in non-small cell lung cancer.