Room: ePoster Forums
Purpose: Recent cytoreduction techniques such as immunotherapy in combination with RT demonstrated improved outcome in patients with limited metastatic disease. Treating all sites may cure more metastatic diseases. However, technical challenges including computationally intensive planning limit the wide-spread use of SBRT for metastatic disease. To meet these challenges, we have developed a novel autonomous SBRT treatment planning approach.
Methods: An oligometastases patient with six lesions(3 mediastinal, 1 right-upper-lobe, 1 anterior-hepatic and 1 T11-T12 paraspinal) previously treated with a 4 isocenter SBRT plan under an institutional IRB, was replanned using the autoplanning feature in Pinnacle 9.10. Targets within 5cm were treated by VMAT arcs at a single isocenter. OAR optimization goals included mean lung and liver dose, maximum dose to the spinal cord and the trachea/bronchial tree. The advanced autoplan parameters including 10% target-OAR tuning balance, 1.2cm dose fall-off margin and 120% hot-spot maximum were optimized to achieve the high conformality required in SBRT. Without further tuning, a dosimetric evaluation of PTV coverage and OARs was performed and compared with the clinical plan.
Results: For each of the 4 PTVs, the autoplanning method improved target coverage, ranging from 0.2 to 3.6% increase. The D0.03cc dose to the spinal cord, trachea and heart/pericardium OAR volumes saw modest increases, <3%, and all were well below clinically prescribed limits. The D0.03cc for the trachea & ipsilateral bronchus also saw a modest increase of 0.6 Gy but was the dose limiting structure. Liver mean dose and lung V10Gy and V20Gy all showed modest decreases. The planning process was reduced from 4 days to a short setup and overnight optimization.
Conclusion: With optimized parameter settings, the autoplan process efficiently produced a clinically viable plan, potentially increasing the availability of SBRT for metastatic disease. Future studies will increase the patient cohort to evaluate robustness and clinical feasibility.