Spot-scanning-based proton therapy for extracranial chordoma

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Extracranial chordomas (ECC) are rare bone tumors requiring advanced treatment strategies.
• Proton radiotherapy (PT) offers precise dose delivery, potentially improving outcomes for challenging tumor sites.
• Evaluating novel PT techniques like spot-scanning is crucial for optimizing cancer care.

Purpose of the Study:

• To assess the efficacy and safety of spot-scanning proton therapy for extracranial chordomas.
• To determine the impact of prior surgical stabilization on treatment outcomes.
• To identify factors influencing local control and survival in ECC patients treated with PT.

Main Methods:

• A cohort of 40 patients with chordomas of the spine and sacrum were treated with spot-scanning PT.
• Patients received a median total dose of 72.5 Gy(RBE) at 1.8-2.0 Gy(RBE) per fraction.
• Data on prior surgical stabilization, residual disease, and follow-up were analyzed.

Main Results:

• Five-year local control was 100% in patients without surgical stabilization, compared to 30% in those with it (p=0.0003).
• Overall, the cohort achieved 5-year local control of 62%, disease-free survival of 57%, and overall survival of 80%.
• No dosimetric parameters predicted tumor control on univariate analysis, highlighting the importance of surgical factors.

Conclusions:

• Spot-scanning PT is a safe and highly effective treatment for ECC, particularly when not combined with extensive surgical instrumentation.
• Function-preserving surgery followed by PT shows promising results for unresectable ECC.
• Treatment outcomes are significantly influenced by the extent of prior surgical stabilization.