Abstract
Purposes: The purpose of this work is to retrospectively verify treatment dose delivered in patients treated with stereotactic radiotherapy (SRT) to the lung. Method and Materials: In this study, a stereotactic body localizer (SBL) system was used for lung cancer patient immobilization in the CT simulation and stereotactic treatment planning on a prospective dose escalation protocol for malignant lung tumors. Prior to each treatment, a localization CT san was obtained in the treatment room after the patient was immobilized in the SBL. The stereotactic coordinates of three pre‐selected bony landmarks were recorded from the pre‐treatment scan and compared with those of the planning scan. Couch shifts were made based on the bony‐landmark displacements. Image fusion was performed between the simulation CT scan to each pre‐treatment CT scan in order to obtain the same planning target volumes (PTVs) and critical structures. The same treatment plans were re‐loaded onto each pre‐treatment CT scan with their respective stereotactic coordinate system. The changes in dose distributions were assessed by dose‐volume histograms of the PTV and normal structures for the old and new isocenter coordinates using the bony‐landmark shifts. We compared D95, D99, and V95 for the PTV and GTV, and V20 and V30 for the ipsilateral lung. Results: Our preliminary study for 6 patients with 20 dose reconstructions showed that the average D95, D99, and V95 of the PTVs are 95.9%, 93.6%, and 98.4% of the planned values before bony‐landmark shifts. With the bony‐landmark shifts, these values are all improved to 100% of the planned values. The average V20 and V30 are 7–8% higher than the planned values without bony‐landmark shifts and recovered the planned values after the corrections. Conclusion: With near real‐time 3D image guidance for setup error correction, the delivered dose distribution can be ensured for SRT hypofractionated lung treatment.
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