A Biophysical and ALARA-Based Comparison of 3D-CRT and IMRT for Spinal Cord Compression

Metastatic spinal cord compression (MSCC) requires urgent radiotherapy. However, selecting the optimal technique that balances dosimetric precision with treatment efficiency remains clinically challenging. This study compares four radiotherapy modalities for MSCC—AP-PA with field-in-field, 3D-CRT, 5-field IMRT, and 7-field IMRT—evaluating their precision–efficiency trade-offs and proposing an ALARA-based clinical framework. In this observational dosimetry study, we analyzed treatment plans from 60 consecutive MSCC patients. Four plans were generated per patient (30 Gy/10 fractions). We assessed target coverage (D95%), conformity (Paddick CI), homogeneity (HI), organ-at-risk sparing, and treatment efficiency. The statistical analysis used a repeated-measures ANOVA with Bonferroni correction. IMRT-7 achieved superior dosimetric outcomes, with a target coverage of 95.8% ± 1.5% and a spinal cord dose of 7.4 ± 1.2 Gy—a 70.6% reduction versus AP-PA—but required prolonged sessions (16.9 ± 1.4 min). 3D-CRT provided acceptable coverage (91.2% ± 2.3%) and cord dose (22.8 ± 1.5 Gy) with significantly shorter delivery times (8.7 ± 1.3 min). IMRT-5 offered an intermediate option (cord dose: 8.2 ± 1.3 Gy; session time: 13.4 ± 0.8 min). IMRT benefits were most pronounced in lumbar lesions (68% cord dose reduction) and least in thoracic segments. IMRT offers superior dosimetry but distributes low-dose radiation to larger healthy tissue volumes. Although these doses remain within tolerance, they may conflict with the ALARA principle, whereas 3D-CRT with field-in-field achieves similar coverage and organ sparing in less time. Thus, 3D-CRT is preferred in most palliative settings. However, IMRT or arc therapy becomes essential for re-irradiation or when prior treatment to adjacent levels demands maximal cord sparing. Technique selection should integrate dosimetric goals with clinical context, patient status, and institutional resources.