Inter-fractional Size Change of Lymph Node Metastases during MR-guided Stereotactic Body Radiotherapy in Oligometastatic Prostate Cancer

Motivation: MDT is promising for oligometastatic prostate cancer(omPC) and could have potential for better management of lymph node metastases(LNMs) through the use of MR-guided radiotherapy (MRgRT). Goal(s): The primary goal is to quantitatively assess inter-fractional size changes of irradiated LNMs during MRgRT and evaluate their clinical implications for treatment adaptation. Approach: We analyzed 42 LNMs across 14 patients, measuring size changes via daily MRI scans during a 5-fraction MRgSBRT treatment regimen. Results: Results showed a significant trend of size reduction in most LNMs, with 57.1% of patients exhibiting substantial changes that influenced online treatment adaptations, suggesting potential prognostic value for MRgSBRT outcomes. Impact: The study's findings could enhance clinical practices in managing LNMs in omPC, prompting further investigations into the prognostic value of inter-fractional size changes. This research may lead to improved treatment strategies and personalized approaches, ultimately benefiting patient outcomes.