Abstract
PurposeTo provide additional clinical data about the re-irradiation tolerance of the spinal cord.MethodsThis was a retrospective bi-institutional study of patients re-irradiated to the cervical or thoracic spinal cord with minimum follow-up of 6 months. The maximum dose (Dmax) and dose to 0.1cc (D0.1cc) were determined (magnetic resonance imaging [MRI]-defined cord) and expressed as equivalent dose in 2‑Gy fractions (EQD2) with an α/β value of 2 Gy.ResultsAll 32 patients remained free from radiation myelopathy after a median follow-up of 12 months. Re-irradiation was performed after 6–97 months (median 15). In 22 cases (69%) the re-irradiation spinal cord EQD2 Dmax was higher than that of the first treatment course. Forty-eight of 64 treatment courses employed fraction sizes of 2.5 to 4 Gy to the target volume. The median cumulative spinal cord EQD2 Dmax was 80.7 Gy, minimum 61.12 Gy, maximum 114.79 Gy. The median cumulative spinal cord D0.1cc EQD2 was 76.1 Gy, minimum 61.12 Gy, maximum 95.62 Gy. Besides cumulative dose, other risk factors for myelopathy were present (single-course Dmax EQD2 ≥51 Gy in 9 patients, single-course D0.1cc EQD2 ≥51 Gy in 5 patients).ConclusionEven patients treated to higher cumulative doses than previously recommended, or at a considerable risk of myelopathy according to a published risk score, remained free from this complication, although one must acknowledge the potential for manifestation of damage in patients currently alive, i.e., still at risk. Individualized decisions to re-irradiate after appropriate informed consent are an acceptable strategy, including scenarios where low re-irradiation doses to the spinal cord would compromise target coverage and tumor control probability to an unacceptable degree.
Highlights
Experimental animal data have suggested that spinal cord re-irradiation is a feasible approach [1, 2]
Spinal cord equivalent dose in 2-Gy fractions (EQD2) was calculated according to the linear-quadratic model with an α/β value of 2 Gy [15, 16], based on the dose–volume histograms of the three-dimensional treatment plans where the true spinal cord had been contoured, as opposed to surrogate structures such as the spinal canal
In case of two-dimensional treatment techniques, spinal cord doses were reconstructed on fused computed tomography (CT) and magnetic resonance imaging (MRI) scans
Summary
Experimental animal data have suggested that spinal cord re-irradiation is a feasible approach [1, 2]. Several treatment planning and delivery techniques allow for sparing of the spinal cord [3,4,5,6,7,8]. A simple method for calculating re-irradiation tolerance is to assume time-dependent recovery (25% after 6 months, 50% after 12 months), resulting in tolerance doses of 125% and 150%, respectively [10]. An initial treatment course that resulted in an equivalent K. Strahlenther Onkol (2021) 197:463–473 Risk factor Characteristic Points Time interval
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