Leney M, Kim J, Liu C, Sevak P, Glide-Hurst C, Elshaikh M, Pantelic M, Movsas B, Chetty I, and Wen N. MR-only planning for simultaneous integrated boost of MRI-defined dominant intraprostatic lesions. Med Phys 2017; 44(6):3043.
Purpose: To assess the feasibility of using synthetic CT images for treatment planning of dominant intraprostatic lesions (DILs), a known high risk region of interest that may offer potential for increased local control.
Methods: A retrospective study was performed on three patients with biopsy-proven prostate cancer who underwent T2-weighted, mDixon, and diffusion-weighted imaging (DWI) 3T MRI. A radiologist interpreted MR examinations and the suspicious DIL was contoured based on the T2 and DWI MR images. Air, bone, fat, and soft tissue were segmented (assigned -1000, 285, -50, 40 HU respectively) to create a synthetic CT from the water and fat mDixon sequences. A 5 mm margin was added to the prostate and the DIL to compensate for setup uncertainty RapidArc treatment plans were created with the total dose being 79.2 Gy and a boost of 100 Gy to the DIL. All plans were evaluated using the dose volume histogram curves.
Results: The maximum dose and mean dose to the PTV were 87.0 ± 2.1 Gy and 79.6 ± 0.5 Gy. For the DIL, the maximum dose and mean dose were 108.1 ± 1.5 Gy and 104.4 ± 0.5 Gy. The total MU were 603, 574, and 634 for patients 1, 2, and 3. For each patient, the hotspot was located within the DIL. The femoral heads, rectum, bladder, and penial bulb all received a mean dose of 50 Gy or less with the highest mean dose being 50.3 Gy for the bladder of patient 2. The bladder and rectum received the highest doses for the organs at risk (OARs), but both were within the established clinical NRG guidelines.
Conclusion: We demonstrated the feasibility of implementing MR-only treatment planning for prostate cancer with a simultaneous integrated boost for DILs. The dose to the DIL can be escalated to 100 Gy on the synthetic CTs while maintaining the original prescription of 79.2 Gy and remaining in clinical criteria for the OARs.