Exhibit Hall | Forum 2
Purpose: In radiation therapy (RT) planning for thoracic or abdominal tumors, 4DCT is commonly used to assess the target motion and to generate the internal target volume (ITV) which is utilized for non-gated treatment delivery. With the availability of daily pre-treatment 4DMRI during MRI-guided adaptive RT (MRgART), it is feasible to assess respiratory motion daily. Our objective is to assess daily variations of liver target motion from 4DMRI and to investigate its impact on ITV during non-gated MRgART for liver cancer.
Methods: 4DCT was acquired for 6 liver cancer patients during simulation to generate the reference plan for patients undergoing liver stereotactic radiotherapy (SBRT) on a 1.5T MR-Linac. 4DMRI (T1- or fat-sat T2/T1 weighted) data was acquired during MRI simulation for 4 patients and daily respiratory-correlated 4DMRI was acquired pre-treatment using a 3D golden angle radial sequence for all treatment fractions (5 fraction treatments). In this study, 3 fractions and both the 4DCT and 4DMRI data acquired during simulation were analyzed (n=28). The maximum motion in the superior-inferior (SI), left-right (LR), and anterior-posterior (AP) directions were extracted using MIM software. ITV differences between the fractions were compared. T-test was utilized to determine statistical significance (p<0.05).
Results: The difference between the SI motion assessed from 4DCT and 4DMRI ranged from 0-11 mm. 37% of the treatments had statistically significant motion difference compared to the 4DCT. 13% of the treatments required an ITV adjustment to account for the daily respiratory motion changes in the SI direction. The difference between the LR and AP motion assessed from 4DCT and 4DMR ranged from 0-2mm and are statistically insignificant.
Conclusion: Daily variation of liver target motion can be assessed using daily 4DMRI and may be used to generate daily motion adapted ITV for non-gated MRgART of liver cancer, improving tumor targeting and/or normal tissue sparing.
MRI, Radiation Therapy, Treatment Planning
Not Applicable / None Entered.