Proton vs Photon Radiotherapy: A Multi-center Comparative Evaluation of Recurrence and Volumetric Progression Following Spinal Chordoma Resection.

Introduction: Few skull base, movable spine, and sacrum cancers probably develop from the embryonic notochord. Locally aggressive cancers often return after surgery and radiation. Precision over photon radiation may save tissue with proton treatment. Tree-based machine learning models evaluated recurrence and volumetric progression in chordoma patients receiving proton or photon therapy following surgery.

Methods: All Mayo Clinic patients in Minnesota, Florida, and Arizona who received surgical resection followed by adjuvant proton or photon radiation for chordoma were reviewed. The patient demographics, surgery and radiotherapy type, recurrence rate, volumetric progression, tumor histology, and other characteristics were extracted. Decision tree and random forest classifiers were trained and evaluated to predict long-term recurrence and progression utilizing 80/20 unseen data.

Results: Out of 53 chordoma patients who underwent surgery and adjuvant proton or photon treatment, the average age was 55.2 years (± 13.4). Male (n = 33, 62.3%) and White (n = 52, 98.1%) patients predominated. Gross resection happened 54.8% of the time (n = 29). Proton adjuvant radiation was most common (n = 45, 84.9%), followed by conventional or external beam radiotherapy (n = 5, 9.4%) and stereotactic radiosurgery (n = 3, 5.7%). Compared to non-proton therapy, proton therapy reduced recurrence and progression (OR = 10.5; CI = [1.19,92.75], p = 0.01). Decision-tree analysis showed that proton-treated tumors had a 40% recurrence rate compared to 88% for non-proton-treated tumors, with 64% accuracy. The approach predicted volumetric progression with 90% accuracy, with GTR plus adjuvant proton treatment having the lowest progression rate (23%). EMA and pancytokeratin predicted advancement, while S100 and EMA predicted recurrence, according to minimal depth analysis.

Conclusion : Following surgical resection, adjuvant proton therapy was associated with a lower risk of chordoma recurrence and progression compared to photon therapy. The described machine learning models were able to predict recurrence and progression based on the type of surgery and radiotherapy used.