Table 3.
Association between hippocampal dosimetry and impairment in Wechsler Memory Scale-III Word Lists Delayed Recall at 18 months
| Dosimetry | Dosimetric cut point |
No impairment |
Impairment* |
p value |
|---|---|---|---|---|
| Bilateral hippocampi | ||||
| Maximum | ≤24.7 Gy | 66.7% | 33.3% | 0.500 |
| >24.7 Gy | 55.6% | 44.4% | ||
| D30% | ≤8.2 Gy | 77.8% | 22.2% | 0.167 |
| >8.2 Gy | 44.4% | 55.6% | ||
| D40% | ≤7.3 Gy | 88.9% | 11.1% | 0.025 |
| >7.3 Gy | 33.3% | 66.7% | ||
| D50% | ≤3.8 Gy | 66.7% | 33.3% | 0.500 |
| >3.8 Gy | 55.6% | 44.4% | ||
| D80% | ≤0.5 Gy | 55.6% | 44.4% | 0.500 |
| >0.5 Gy | 66.7% | 33.3% | ||
| D100% | ≤0.0 Gy | 76.9% | 23.1% | 0.047 |
| >0.0 Gy | 20.0% | 80.0% | ||
| Left hippocampus | ||||
| Maximum | ≤15.0 Gy | 55.6% | 44.4% | 0.500 |
| >15.0 Gy | 66.7% | 33.3% | ||
| D30% | ≤6.2 Gy | 66.7% | 33.3% | 0.500 |
| >6.2 Gy | 55.6% | 44.4% | ||
| D40% | ≤5.9 Gy | 77.8% | 22.2% | 0.167 |
| >5.9 Gy | 44.4% | 55.6% | ||
| D50% | ≤5.7 Gy | 77.8% | 22.2% | 0.167 |
| >5.7 Gy | 44.4% | 55.6% | ||
| D80% | ≤4.7 Gy | 77.8% | 22.2% | 0.167 |
| >4.7 Gy | 44.4% | 55.6% | ||
| D100% | ≤0.0 Gy | 44.4% | 55.6% | 0.167 |
| >0.0 Gy | 77.8% | 22.2% | ||
| Right hippocampus | ||||
| Maximum | ≤12.5 Gy | 55.6% | 44.4% | 0.500 |
| >12.5 Gy | 66.7% | 33.3% | ||
| D30% | ≤6.4 Gy | 66.7% | 33.3% | 0.500 |
| >6.4 Gy | 55.6% | 44.4% | ||
| D40% | ≤5.8 Gy | 66.7% | 33.3% | 0.500 |
| >5.8 Gy | 55.6% | 44.4% | ||
| D50% | ≤4.7 Gy | 66.7% | 33.3% | 0.500 |
| >4.7 Gy | 55.6% | 44.4% | ||
| D80% | ≤1.1 Gy | 77.8% | 22.2% | 0.167 |
| >1.1 Gy | 44.4% | 55.6% | ||
| D100% | ≤0.0 Gy | 57.1% | 42.9% | 0.485 |
| >0.0 Gy | 75.0% | 25.0% | ||
Abbreviations: D30% = equivalent dose in 2-Gy fractions (EQD2) assuming α/β=2 Gy to 30% of the structure volume; D40%=EQD2 to 40% of the structure volume; D50% = EQD2 to 50% of the structure volume; D80% = EQD2 to 80% of the structure volume; D100% = EQD2 to 100% of the structure volume; Dmax = maximum EQD2 to the structure volume.
*
Impairment defined by use of regression-based z scores standardized to similar healthy control individuals evaluated at the same test–retest interval. Impairment defined as z score ≤−1.5.