Purpose
Surgery is the treatment of choice for patients with early stage of non-small cell lung cancer or lung metastasis. Some patients however, never undergo surgery due to severe comorbidity, age or refusal. Such patients have traditionally been treated with external beam radiation therapy. The evolution in the management of these lesions has shown the necessity for the administration of a high radiation dose to achieve local tumor control. It had also been shown that stereotactic fractionated radiation therapy (SFRT) is an effective treatment approach because it combines the accurate focal dose delivery of stereotactic radiosurgery(SRS) with the biological advantages of fractionate RT. Geometric uncertainties due to set up variation and organ motion due to the breathing limit the precision of SFRT and lead to an increase volume of irradiated normal tissue. A reduction of geometric uncertainties should lead to reduced normal tissue irradiation, safer dose escalation and potentially improved local control and survival for patients with lung lesions. The aim of this study is to evaluate the feasibility of SFRT with Tomotherapy approaching the organ motion with a 4D-PET/TC study.
Material and methods
From May 2005 to April 2006, 8 patients affected by inoperable single or multiple lung metastasis were submitted to this procedure. The primitive neoplasms were: 3/8 lung; 1/8 kidney, 1/8 colo-rectal; 2/8 adenoid cystic. RT was given in 6 fractions every second day within a total treatment time of 12 days. The treatment was delivered with Helical Tomotherapy that has been designed for image guided (IG) intensity modulated radiation therapy. An on board megavoltage CT scanner enables verification CT scans to be acquired before treatment. The CT set can be automatically fused with a planning CT to determine the 3D shape and position of the target volume before radiotherapy. This information can be used to adjust the patient set up, if necessary. A CT scan at the time of treatment delivery can also be used as the basis for reconstructing the dose received by the patient. Dose reconstruction will allow the dose just delivered to be superimposed on the CT scan just acquired and compared with the planned dose distribution superimposed on a planning CT. Before treatment each patient underwent a standard Whole body(WB) 18F-FDG-PET/CT scan for staging, followed by a single field of view (FOV) 4D-PET/CT study on the region of interesting (the thorax). All patients were trained to regulary breath prior PET. 4D scans were performed during free breathing, monitored by the Real Time Position Management (RPM,Varian) system which allows the synchronizing of 4DPET and 4D CT scans to the respiratory cycle of the patient. 4D-PET and 4DCT studies allow a set of images (phases) to be generated, synchronized to the respiratory cycle and describing the tumor motion induced by patient respiration. The sets of 4DPET and4DCT image phases were then collapsed to single “integral” PET and CT images representing the full tumor motion. In these images Gross Tumor Volume (GTV) and Biological Target Volume(BTV) were defined by contouring the “standard” CT image (GTV), the “integral” 4DCT image (4DGTV) and the “integral” 4DPET image(4DBTV). Finally the “integral” GVT was expanded to a CTV “integral (plus 5mm.) and a PTV “integral” (plus 3 mm.) that could explicitly represent patient-specific target respiratory motion in order to ensure its correct dose coverage when free breathing is present during beam delivery.
Results
8/8 patients are valuable for the acute toxicity: according to RTOG lung scale 7pts presented G0, and 1pt G1 lung toxicity. 6/8 patients are valuable for response: with a medium follow up of 7 (4-11 ) months 5/6 are in PR and 1/6 is in SD. The response is evaluated with a PET/TC at 1 and 3 months after radiotherapy.
Conclusion
Our preliminary results allow us to confirm that tomotherapy can give a good level of control of the patient’s set up and tumor localization before every daily treatment. The internal margins required to account for the internal tumor motion in SFRT are substantial. Given the wide range of internal margins at different directions (x,y,z,) even for lesion in the same lobe of the lung, the use of an individualized internal margin for each patients would be desired to avoid geographic miss and spare the adjacent normal tissue. Our preliminary data suggest that PTV integral could explicitly represent patient-specific target respiratory motion in order to ensure its correct dose coverage when free breathing is present during beam delivery.