(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To calculate the individualized fraction regime (IFR) in stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) patients using the uncomplicated tumor control probability (UTCP, Pâ?º) function.
Methods: 33 patients with peripheral lung cancer or lung metastases who had undergone SBRT were analyzed. Treatment planning was performed using the dose regime of 48 Gy in 4 fractions. Dose volume histogram (DVH) data for the gross tumor volume (GTV), lung, chest wall (CW) and rib were exported and the dose was multiplied from 1% to 200% at a resolution of 1%. For each dose fraction, P+ values were calculated by considering the tumor control probability (TCP), radiation-induced pneumonitis (RIP), chest wall pain (CWP) and radiation-induced rib fracture (RIRF). UTCP values as a function of physical dose were plotted and the maximum P+ values corresponded to the optimal therapeutic gain. IFR in 3 fractions was also calculated with the same method by converted the dose using the linear quadratic (LQ) model.
Results: 33 patients attained an IFR using the introduced methods. All the patients achieved TCP value higher than 92.0%. The IFR ranged from 3×10.8 Gy to 3×12.5 Gy for 3 fraction regimes and from 4×9.2 Gy to 4×10.7 Gy for 4 fraction regimes, respectively. Four patients with typical tumor characteristics demonstrated the IFR was patient-specific and could maximize the therapeutic gain. Patients with large tumor were associated with lower TCP, UTCP and smaller fractional dose than patients with small tumor. Patients with tumor adjacent to the organ at risk (OAR) or at high risk of RIP showed lower UTCP and smaller fractional dose compared with patients with tumor away from the OAR.
Conclusion: The proposed method is capable of predicting the IFR for NSCLC patients undergoing SBRT. Further validation is required in clinical samples.
Funding Support, Disclosures, and Conflict of Interest: This work was sponsored by National Natural Science Foundation of China (81602667), Medical Scientific Research Foundation of Guangdong Province (A2015534, B2016048) and the Creative and Facilitating Program of Shantou University.
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