Radiotherapy Approaches for High-Risk Prostate Cancer with Elective Lymph Node Fields: A Comparative Analysis

Purpose: Radiotherapy for high-risk prostate cancer patients with elective pelvic fields require large target margins to account for independent target motion. However, these margins increase the exposure of healthy tissue. This study compares standard, sequential, and robust treatment planning strategies to evaluate plan performance with varying target margins and motion. Our aim is to identify the most effective method that allows for a reduction in target margins while maintaining adequate dose coverage, thereby reducing healthy tissue exposure. Methods: Nine high-risk prostate cancer patients, each with a planning CT and five CBCTs, were included in the analysis. Nominal treatment plans were created based on the planning CT, while simulated plans integrated CBCTs to generate six dose fractions using deformable image registration and dose warping techniques. All treatment planning strategies employed VMAT, with prescribed doses of 77 Gy to the prostate and 56 Gy to lymph nodes and seminal vesicles over 35 fractions. Deformable image registration utilised either gold fiducial markers or bone anatomy as reference points. Results: The sequential treatment planning strategy achieved the highest overall performance, demonstrating the best adherence to clinical objectives and scoring metrics, while the standard treatment plan strategy performed the worst. The simulated plans reflected similar trends, with slightly reduced performance compared to the nominal plans. Conclusion: The sequential planning approach provides superior sparing of healthy tissue and target coverage but may require increased treatment time. Robust planning demonstrates consistent performance and adaptability, fulfilling clinical goals efficiently, although its higher computational demands warrant further investigation into optimising its practical implementation.