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- Title
Sacral-Nerve-Sparing Planning Strategy in Pelvic Sarcomas/Chordomas Treated with Carbon-Ion Radiotherapy.
- Authors
Nachankar, Ankita; Schafasand, Mansure; Hug, Eugen; Martino, Giovanna; Góra, Joanna; Carlino, Antonio; Stock, Markus; Fossati, Piero
- Abstract
Simple Summary: Late radiation-induced lumbosacral neuropathy (RILSN) is a rare, debilitating, but potentially avoidable morbidity associated with carbon-ion therapy (CIRT) for pelvic sarcomas/chordomas. This toxicity increases significantly if the long length of sacral nerves is exposed to CIRT doses > 70 Gy (RBE) [Japanese RBE model]. We propose a sacral-nerve-sparing optimized CIRT strategy (SNSo-CIRT) to minimize the risk of RILSN. This strategy is composed of (a) Contouring of individual sacral nerve roots between L5–S3 levels until sciatic nerve. (b) Restriction of doses to sacral nerves outside of high dose CTV (HD-CTV) (i.e., 'sacral nerves-to-spare') to doses to 5% of volume (DRBE|LEM-I|D5%) < 69 Gy (RBE). (c) Evaluation of robustness of SNSo-CIRT. With this strategy, doses to sacral nerves-to-spare were restricted to DRBE|LEM-I|D5% < 69 Gy (RBE) for 95% of patients. Patients who developed RILSN despite the application of the sacral-nerve-sparing strategy had significantly higher DRBE-filtered dose-averaged linear energy transfer (LETd) on sacral nerves-to-spare. DRBE-filtered-LETd can be optimized along with DRBE for SNSo-CIRT. To minimize radiation-induced lumbosacral neuropathy (RILSN), we employed sacral-nerve-sparing optimized carbon-ion therapy strategy (SNSo-CIRT) in treating 35 patients with pelvic sarcomas/chordomas. Plans were optimized using Local Effect Model-I (LEM-I), prescribed DRBE|LEM-I|D50% (median dose to HD-PTV) = 73.6 (70.4–76.8) Gy (RBE)/16 fractions. Sacral nerves were contoured between L5-S3 levels. DRBE|LEM-I to 5% of sacral nerves-to-spare (outside HD-CTV) (DRBE|LEM-I|D5%) were restricted to <69 Gy (RBE). The median follow-up was 25 months (range of 2–53). Three patients (9%) developed late RILSN (≥G3) after an average period of 8 months post-CIRT. The RILSN-free survival at 2 years was 91% (CI, 81–100). With SNSo-CIRT, DRBE|LEM-I|D5% for sacral nerves-to-spare = 66.9 ± 1.9 Gy (RBE), maintaining DRBE|LEM-I to 98% of HD-CTV (DRBE|LEM-I|D98%) = 70 ± 3.6 Gy (RBE). Two-year OS and LC were 100% and 93% (CI, 84–100), respectively. LETd and DRBE with modified-microdosimetric kinetic model (mMKM) were recomputed retrospectively. DRBE|LEM-I and DRBE|mMKM were similar, but DRBE-filtered-LETd was higher in sacral nerves-to-spare in patients with RILSN than those without. At DRBE|LEM-I cutoff = 64 Gy (RBE), 2-year RILSN-free survival was 100% in patients with <12% of sacral nerves-to-spare voxels receiving LETd > 55 keV/µm than 75% (CI, 54–100) in those with ≥12% of voxels (p < 0.05). DRBE-filtered-LETd holds promise for the SNSo-CIRT strategy but requires longer follow-up for validation.
- Subjects
DOSE-response relationship (Radiation); PELVIC tumors; SARCOMA; RESEARCH funding; DESCRIPTIVE statistics; SPINAL cord injuries; LUMBOSACRAL plexus; PROGRESSION-free survival; CONFIDENCE intervals; GERM cell tumors
- Publication
Cancers, 2024, Vol 16, Issue 7, p1284
- ISSN
2072-6694
- Publication type
Article
- DOI
10.3390/cancers16071284