Management of Independent Motion between Multiple Targets in Lung Cancer Radiotherapy

Publication date: Available online 2 September 2016
Source:Practical Radiation Oncology
Author(s): Feng Liu, An Tai, Ergun Ahunbay, Elizabeth Gore, Candice Johnstone, X. Allen Li
To quantify interfractional independent motions between multiple primary targets in radiotherapy (RT) of lung cancer and to study the dosimetric benefits of an online adaptive replanning method to account for these variations.MethodsNinety five on-treatment diagnostic-quality CTs acquired for nine lung cancer patients treated with image-guided radiation therapy (IGRT) using a CT-on rail (CTVision, Siemens) were analyzed. On each on-treatment CT set, contours of the targets (GTV, CTV, or involved nodes) and organs at risk were generated by populating the planning contours using an auto-segmentation tool (ABAS, Elekta) with manual editing. For each patient, an intensity modulated radiation therapy (IMRT) plan was generated based on the planning CT with a prescription dose of 60Gy in 2Gy per fraction. Three plans were generated and compared for each on-treatment CT set: an IGRT (repositioning) plan by copying the original plan with the required shifts, an online adaptive plan by rapidly modifying the aperture shapes and segment weights of the original plan to conform to the on-treatment anatomy and a new fully re-optimized plan based on the on-treatment CT.ResultsThe interfractional deviations of the distance between centers of masses of the targets from the planning CTs varied from −1.0 to 0.8cm with an average−0.09±0.41cm (one standard deviation). The average combined CTV V100 were 99.0±0.7%, 97.8±2.8%, 99.0±0.6%, and 99.1±0.6%, and the lung V20 Gy 928±332cm³, 944±315cm³, 917±300cm³, and 891±295cm³ for the original, repositioning, adaptive and re-optimized plans, respectively. Wilcoxon signed-rank tests showed that the adaptive plans were statistically significantly better than the repositioning plans and comparable with the re-optimized plans.ConclusionInterfractional, relative volume changes and independent motions between multiple primary targets during lung cancer RT which cannot be accounted for by the current IGRT repositioning exist, but can be corrected by the online adaptive replanning method.



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