Résumé
Objective:To investigate the effects of off-target isocenter plans with different off-target distances on the plan quality and delivery accuracy of stereotactic body radiotherapy (SBRT) for lung cancer, aiming to provide a reference for the clinical plan design of SBRT for lung cancer.Methods:For 10 lung cancer patients treated with SBRT, isocenter reference plans were designed by setting the plan isocenters at the mass centers of tumors and 60 off-target isocenter plans by setting the isocenters at distances of 1, 3, 5, 8, and 10 cm from the mass centers of tumors. The dosimetric differences between the off-target isocenter plans and the reference plans. Subsequently was analyzed, under different positional errors (0-5 mm). The gamma pass rates (GPRs) of these plans were measured using the Octavius 4D high-resolution dose verification system, and 240 verifications of these plans were completed. The robustness of the delivery accuracy of the reference plans and off-target isocenter plans were analyzed under different positional errors.Results:The off-target isocenter plans yielded slightly worse dose gradient indices than the isocenter reference plans, but there was no statistically significant differences. With an increase in the off-target distance, the mean lung dose (MLD), V20 of normal lungs, as well as the Dmax of bronchi, showed slight upward trends. Compared with the isocenter reference plans, the MLD of the off-target isocenter plans increased by 0.8%, 0.8%, and 1.9% at off-target distances of 1, 3, and 10 cm, respectively, with statistically significant differences ( z = -2.34 to -1.99, P < 0.05), and the V20 of the off-target isocenter plans increased by 2.0%, 2.5%, and 3.7% at off-target distances of 1, 5, and 10 cm, respectively, with statistically significant differences ( z =-2.11 to -1.99, P < 0.05). In the case of a positional error of up to 5 mm, the GPRs of plans with off-target distances of 5 cm and above decreased by more than 1.0% on average and up to a maximum of 3.5%, showing statistically significant differences ( z = 2.13-2.75, P < 0.05). Conclusions:Compared to the reference plans, the off-target isocenter plans showed slightly lower dosimetric quality and less robust delivery accuracy under different positional errors. Therefore, it is necessary to avoid the plans and treatment with too large off-target distances (≥ 5 cm) as far as possible for SBRT of lung cancer.
Résumé
Objective:To establish a metaheuristics-based automatic radiotherapy treatment planning method (ATP-STAR) and verify its effectiveness.Methods:The main process of the ATP-STAR method was as follows. First, the optimization parameters were vectorized for encoding and corrected using Gaussian convolution. Then, the candidate optimization parameter vector set was selected through simulated annealing. Finally, the optimal combination of optimization parameters was determined by combining the field fluence optimization to achieve automatic trial-and-error. Twenty cases with large individual differences in tumors were selected for testing. Clinical physicists with more than five years of experience were invited to perform manual planning. Both the manual and ATP-STAR plans were made utilizing the matRad open source software for radiation treatment planning, with the fields and prescribed doses consistent with those of the clinical treatment plans. The dosimetric differences of target volumes and organs at risk between the ATP-STAR and manual plans for different diseases were analyzed.Results:For the target volumes, the ATP-STAR plans showed superior homogeneity compared with the manual plans (brain tumors: z = 2.28, P = 0.022; lung cancers: z = 2.29, P = 0.022; liver cancers: z = 2.11, P = 0.035). The conformability of the ATP-STAR plans was comparable to that of the manual plans for brain tumors and liver cancer and was slightly lower than that of the manual plans for lung cancer ( z = 2.29, P = 0.022). The comparison result of doses to organs at risk (OARs) between the manual plans and STAR plans were as follows. For OARs of brain tumors, the ATP-STAR plans decreased the mean left lens Dmean from 2.19 Gy to 1.76 Gy ( z = 2.28, P = 0.022), decreased left optic nerve Dmean from 11.36 Gy to 10.22 Gy ( z = 2.28, P = 0.022), decreased right optic nerve Dmax from 32.92 Gy to 29.97 Gy ( z = 2.10, P = 0.036), and decreased pituitary Dmax from 39.53 Gy to 35.21 Gy ( z = 2.29, P = 0.022). For OARs of lung cancer, the ATP-STAR plans decreased the mean spinal cord Dmax from 38.00 Gy to 31.17 Gy ( z = 2.12, P = 0.034), decreased the bilateral lungs Dmean from 8.51 Gy to 8.07 Gy ( z = 2.29, P = 0.022), and decreased cardiac Dmean from 3.21 Gy to 2.69 Gy ( z =2.29, P = 0.022). For OARs of liver cancer, the ATP-STAR plans decreased spinal cord Dmax from 18.19 Gy to 14.76 Gy ( z = 2.11, P = 0.035), decreased liver Dmean from 15.61 Gy to 14.45 Gy ( z = 2.11, P = 0.035), and decreased kidneys Dmean from 4.76 Gy to 4.04 Gy ( z = 2.10, P = 0.036). Conclusions:The proposed ATP-STAR method relies little on the experience of manual planning and thus is easy to be widely applied. This method is expected to improve the quality and consistency of IMRT plans and save clinical labor and time costs.