ESTRO 2024 - Abstract Book

S3799

Physics - Image acquisition and processing

ESTRO 2024

To verify this technique, provide confidence that our clinical approach was consistent with independent estimates, and to quantify the total dose to the cord and brainstem, the method was retrospectively and independently audited. For this, we used the registration and voxel-wise EQD2 conversion tools in the independent TPS RayStation v2023B (Stockholm, Sweden). The previous and reirradiation CT scans, dose and structure sets were imported to RayStation and the dose converted to EQD2 using an α/β of 2 Gy for cord and brainstem and 3 Gy for other normal tissues (CTVs were neglected as unnecessary). The previous and re-irradiation planning CT scans were deformably registered using default settings. The dose was accumulated on the reirradiation scan, and the D0.1cm 3 extracted for the cord, brainstem, and their PRVs. A retrospective review of the notes was undertaken to extract reported neurological side effects of treatment.

Results:

All prescriptions, first treatment and reirradiation, were equivalent to 58.4-66 Gy in 2 Gy fractions, ranging from 55 Gy in 20 fractions to 65 Gy in 30 fractions. The combined EQD2 D0.1cm 3 audited doses for the cord and brainstem (and PRVs) are presented in figure 1, demonstrating that the D0.1cc EQD2 did not exceed our maximum safe permitted dose for the spinal cord or brainstem and only one case was close to this threshold. We can therefore conclude that our technique is robust. Neurological side effects were reported for three out of the ten patients included, with no conclusive results linking their occurrence to their re-irradiation. One patient reported non-specific brain deterioration, believed to linked to disease progression. A second patient reported memory loss, but only reported this side effect after a third course of electron therapy to the scalp. A third patient reported facial palsy, but it is not clear from the notes if this is related to radiation or not.