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Individual lymph nodes: "See it and Zap it"
Dennis Winkel1, Anita M Werensteijn-Honingh1, Petra S Kroon1
1Department of Radiotherapy, University Medical Center, Utrecht, The Netherlands.
Clinical and Translational Radiation Oncology
|July 26, 2019
Summary
Online MRI-guided radiotherapy using adaptive treatment planning effectively covers metastatic lymph nodes. This approach ensures adequate planning target volume and gross tumor volume coverage for stereotactic body radiotherapy, making "seeing and zapping" feasible.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Cancer Therapy
Background:
- Magnetic resonance imaging (MRI)-guided radiotherapy systems, such as the 1.5T MR-linac, enable real-time visualization of patient anatomy during treatment.
- These advanced systems facilitate the precise targeting of metastatic lymph nodes using stereotactic body radiotherapy (SBRT).
Purpose of the Study:
- To investigate various online treatment planning strategies for MR-linac radiotherapy.
- To determine the necessary planning target volume (PTV) margin for effective target coverage in lymph node oligometastases treated with SBRT.
Main Methods:
- Ten patients with single pelvic or para-aortic lymph node metastases were treated with 5x7Gy SBRT on a 1.5T MR-linac.
- New treatment plans were generated daily based on actual contours (adapt to shape, ATS), compared to plans adapted for online target position (adapt to position, ATP).
- Post-treatment MRIs evaluated gross tumor volume (GTV) coverage and PTV margins.
Main Results:
- ATS plans achieved a median PTV V35Gy of 99.9%, compared to 93.6% for ATP plans.
- Median GTV V35Gy during delivery was 100% for ATS and 100% for ATP.
- The 3 mm isotropic PTV margin was found to be adequate for coverage.
Conclusions:
- Online MRI-guided adaptive treatment planning (ATS) provides adequate PTV and GTV coverage for metastatic lymph nodes by accounting for daily anatomical changes.
- Both adaptive strategies generally maintained adequate GTV coverage throughout treatment.
- MRI-guided SBRT on MR-linacs makes precise "seeing and zapping" of metastatic lymph nodes achievable.