J.G. Prévost, R.M.T. Pattynama, J.J. Nuyttens; Rotterdam/NL

Purpose
The administration of higher doses of radiotherapy is required to improve the poor treatment results of conventional radiotherapy (60-66 Gy) for early stage non-small cell lung cancer (NSCLC) and metastatic lung cancer in medically inoperable patients. The administration of large doses to tumors moving due to respiration, while limiting the toxicity, requires specific techniques such as gating and the Synchrony, the respiratory tumor tracking system of the CyberKnife. These techniques use an accurate definition of the location of the moving tumor to minimize the dose to the organs at risk and to maximize the dose delivered to the tumor. The use of markers, commonly inserted by transthoracic punction (TTP) or by bronchoscopy, is a method to accurately define the position of the tumor. However, the risk of 25-40% to develop a pneumothorax using the TTP is very high for these medically inoperable patients or the requirement of general anesthesia in 44% of the patients using the bronchoscopic insertion is often too risky. For that reason, we developed the use of vascularly inserted embolisation coils as markers for patients treated with the respiratory tumor tracking system of the CyberKnife.

Material and methods
A total number of 25 embolisation coils were inserted into the small subsegmental pulmonary endbranches adjacent to 8 tumors in 6 patients (NSCLC stage I =3, metastasis=3) using a transcatheter approach. The pulmonary artery catheter was inserted through the femoral vein in the groin under local anesthesia and by using ECG-monitoring. After the insertion of the markers, the patient was observed during a few hours to detect any post-punction bleeding. The Charlson comorbidity index was evaluated for the six patients. Three patients had a high score of 6, two other patients had a score of 3 and 4, and 1 patient had a low score of 1. The incidence of pulmonary infarction was evaluated based on the clinical symptoms. Due to the short follow up, clinical response was only evaluated in 3 patients, but will be reported at the meeting.

Results
Six patients were treated with the Synchrony using the embolisation coils as markers. The reason for prohibition of percutaneous placement of markers was: a major risk for pneumothorax (two patients with two lesions, one patient with a history of pneumothorax during the biopsy procedure), a possible dramatic consequence of a pneumothorax (one patient with a history of pneumonectomy, one oxygen dependent patient) and one patient because of the combination of an advanced age (81 years) and a previous lobectomy. Eight weeks after the treatment, the clinical response was evaluated in 3 patients with a CT thorax and showed one complete respons, one partial respons (reduction of the largest diameter with 44%) and one stable disease (a patient with two lesions, reduction of largest diameter with 24% and 11%). In one patient (16%), we noticed pleural pain and fever 8 hours after insertion that can be related to pulmonary infarction. The complaints were treated with analgesics. The other patients were free of any complaint. No patient suffered from an increase in shortness of breath in the weeks after the procedure. No migration of the coils was noticed between the position defined on the planning CT and the position defined by the CyberKnife at the start of each treatment session.

Conclusion
Even in a comorbid patient population, the use of embolisation coils as markers for high-dose radiotherapy in the treatment of primary or metastatic lung cancer is safe and effective.