Table 2.
MRI-RT for spinal bone metastases in three fractions
| PTV | PTV Subsites |
Dose / PTV Coverage | S.Cord V22.5Gy (<0.03 cc) | S.Cord V13Gy (<1.2 cc) | C.Equina V25.5Gy (<0.03 cc) | C.Equina V21.9Gy (<5 cc) | Vol > 105% out of PTV (<3 cc) | Vol > 115% out Of PTV (0.0cc) |
Conformity index (<1.5) | Homogeneity Index (<2) |
|---|---|---|---|---|---|---|---|---|---|---|
| Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | Co-60 Linac | ||
| T4 (three fx) | 2 | 30 Gy 30 Gy 88–88% |
0.0cc 0.0cc | 0.43cc 0.43cc | N/A N/A | N/A N/A | 12.5cc 0.4cc | 6.9cc 0.0cc | 2.1 1.01 | 1.47 1.5 |
| L3 (three fx) | 1 | 24 Gy 24 Gy 99–99% |
N/A N/A | N/A N/A | 0.0cc 0.0cc | 0.0cc 0.0cc | 8.8cc 1.0cc | 0.6cc 0.0cc | 1.40 1.12 | 1.25 1.24 |
C.Equina, cauda equina.; Co-60, Cobalt-60; MRI-RT, magnetic resonance image-guided radiotherapy; OAR, organs-at-risk; SABR, stereotactic ablative radiotherapy; S.cord, spinal cord; VXGy, volume of OAR receiving at least X Gy; fx, fraction.
Both OAR objectives (spinal cord and cauda equina) and dose spillage were met per protocol objectives for three fraction linac plans as well. Objectives are given in parentheses (e.g. conformity index should be 1.5 or less).
Co-60 MRI-RT delivered plan vs linac-based MRI-RT replanning showing OAR constraints and dose spillages with objectives based on NRG BR001 protocol.