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Location: Marriott Marquis
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PQA 04 - PQA 04 Palliative Care and Central Nervous System Poster Q&A

2528 - Stereotactic Radiosurgery for Newly Diagnosed and Recurrent Chordomas of the Skull Base and Spine

Monday, September 30, 2024
10:45 AM – 12:00 PM ET
Location: Hall C

Screen: 21

J. Ho1, D. Klebaner1, M. Mendoza1, D. K. Fujimoto1, B. E. Turner1, E. Pollom1, I. C. Gibbs1, S. D. Chang2, R. L. Dodd2, D. Park2, A. Kattaa2, A. Persad2, Y. Hori2, and S. G. Soltys1; 1Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, 2Department of Neurosurgery, Stanford University School of Medicine, Stanford, CA

Purpose/Objective(s): In chordomas treated with conventionally fractionated radiotherapy, local progression historically occurs in over 40% of chordomas by 5 years. Given that the alpha/beta ratio for these slowly growing tumors is presumably low, we investigated if dose escalation through hypofractionated stereotactic radiosurgery (SRS) may improve tumor control. Materials/

Methods: We performed an IRB-approved retrospective review of patients treated with SRS (in 1 to 5 fractions) for chordoma. The cumulative incidences, with death as a competing risk, of local progression (LP) within the SRS field, regional progression (RP) in the surgical bed or regional soft tissue, and distant metastatic progression (DM) were estimated, as was the overall survival (OS), censored at last follow-up. Acute and late toxicity were assessed via CTCAE V4.0.
Results: We identified 47 consecutive patients with new or recurrent chordoma treated to 73 sites from 1997 to 2023. Median age at the time of first SRS was 51.9 years (interquartile range [IQR] 43.1-62.6 years) and 55% were male. SRS treated 31 newly diagnosed tumors (42%), 38 (52%) tumors recurrent after radiotherapy (n=27) or surgery alone (n=11) and 4 (5%) metastases. Tumors were in the skull base in 35 (48%) and the spine in 32 (44%) (13 cervical, 7 thoracic, 6 lumbar, 6 sacral). SRS treated gross disease in 51 (70%). The most common dose for newly diagnosed tumors was 40 Gy in 5 fractions (range, 20-45 Gy in 1-6 fractions) for a median EQD2 (equieffective dose in 2 Gy fractions, with an alpha/beta of 4) of 80 Gy4 (range, 39-134 Gy4). The median EQD2 for recurrent tumors was 58.5 Gy4 (range, 24-117 Gy4). Median PTV size was 11.4 cc (range, 0.2-289 cc). Newly diagnosed chordomas had a median follow-up of 100.7 months (IQR 65.6-146.7 months). OS at 5-years was 86.4% (IQR 74.9-99.8%). 5-year rates of progression were: LP 21% (95% confidence interval (CI), 8.3-38%), RP 8% (CI, 1.2-22%) and DM 8% (CI, 1.3-23%). No newly diagnosed patient had distant metastases as their first form of progression. Recurrent tumors had a median follow-up of 19.4 months (IQR 12.2-43.4 months) and median OS of 55.7 months (IQR 16.3-94.2 months); 5-year LP was 53% (CI, 32-71%), RP was 30% (CI, 12-51%) and DM was 22% (CI, 6.4-44%). Late toxicities occurred in 8 patients (11%): leg weakness (grade 2), cranial neuropathy (grade 2 in 5 and grade 3 in 1 patient), and sacral insufficiency fracture (grade 3).
Conclusion: With a 5-year local progression of 21% for newly diagnosed chordomas, these data suggest that dose escalation through hypofractionated SRS provides rates of local control comparable or higher than historical series of fractionated radiotherapy for selected, smaller tumors, and supports a low alpha/beta ratio for chordoma. Once recurrent, the risk of second recurrence is high; measures to improve outcomes for recurrent tumors are warranted.