MR Guided Stereotactic Body Radiation Therapy with Simultaneous Integrated Boost to Dominant Intraprostatic Lesions for Prostate Cancer: A Retrospective Dosimetric Study
Du D, Lee J, Pantelic M, Hurst N, Movsas B, Chetty I, and Wen N. MR Guided Stereotactic Body Radiation Therapy with Simultaneous Integrated Boost to Dominant Intraprostatic Lesions for Prostate Cancer: A Retrospective Dosimetric Study. J Med Phys 2019; 46(6):e268.
J Med Phys
Purpose: This study aims to test the feasibility to deliver simultaneous integrated boost to dominant intraprostatic lesions (DILs) for SBRT prostate treatment combining multiparametric MRI simulation with MR Linear Accelerator (MR-Linac) treatment. Methods: Three prostate patients were scanned on a 3T scanner using multiparametric MRI, including T2 weighted, Diffusion weighted images (DWI) and Dynamic contrast enhanced imaging (DCE) prior to treatment. An experienced radiologist annotated DIL on each MR modality as well as the urethra on T2W images. A combined DIL CTV was created by integrating the volume from each modality on the T2W image. T2W images were fused to the planning MRI with focus on the prostate gland, and the CTV of the DIL was then propagated to the planning MRI (bSSFP, TE/TR = 1.6 ms/3.8 ms). Prostate CTV and DIL CTV was expanded 3 mm, and cropped away from critical organs to generate a PTV. An SBRT plan was retrospectively created for each patient following the NRG-GU005 protocol (36.25 Gy in 5 fractions, DIL SIB dose >8 Gy). Total delivered dose was simulated using 5 daily MRI setup images and was compared with the initial SBRT plan dose. Results: Dose constraints were met for all the organ at risks following NRG-GU005 for all three patients. Planning boost dose to the DILs were 46.19, 48.56, and 44.74 Gy respectively for each patient. The prostate volume covered by the prescription dose was reduced by -8.91%, 0.34% and -0.25% in the accumulated dose compared to planning dose, while the dose covering 95% of DIL volume was reduced by -4.21%, -3.40% and -0.79% in accumulated dose. Conclusion: We demonstrated it is feasible to treat SBRT prostate with escalated dose to the DILs (with PTV cropped 1 mm away from rectum and bladder). Online daily adaptive planning is warranted to deliver prescription dose to both prostate gland and DIL.