Table 3.
Comparison of dose metrics between MRIdian-Linac PTV3mm and CT-Linac PTV10mm plans
| Variables | MRIdian-Linac PTV3mm Average (SD) | CT-Linac PTV3mm Average (SD) | P-value |
|---|---|---|---|
| Whole breast metrics | |||
| Ipsilateral breast volume (cm3) | 671.8 (360.0) | 751.0 (414.7) | .04∗ |
| V12.3 <50% | 34.8% (12.7) | 44.4% (10.9) | .002∗ |
| V12.3 (cm3) | 219.4 (117) | 312.1 (147) | .002∗ |
| PTV metrics | |||
| Volume (cm3) | 84.3 (51.9) | 131.7 (74.4) | .002∗ |
| Ratio of PTV/ipsilateral breast volume | 13.0 (5.1) | 18.6 (6.4) | .002∗ |
| V23.4 ≥95% | 99% (0.9) | 97.6% (1.4) | .03∗ |
| D2cc <26.3 Gy | 26.1 Gy (0.19) | 25.7 Gy (0.33) | .01∗ |
| V26.3 Gy (cm3) | 0.9 (1.9) | 0.23 (0.67) | .06 |
| D2% (Gy) | 26.2 (0.17) | 25.6 (0.32) | .006∗ |
| D50% (Gy) | 25.5 (0.2) | 24.8 (0.17) | .002∗ |
| D98% (Gy) | 23.8 (0.4) | 23.5 (0.1) | .08 |
| Max point dose (Gy) | 26.8 (0.26) | 26.2 (0.36) | .01∗ |
| DHI ratio | 0.1 (0) | 0.08 (0.01) | .02∗ |
| CI ratio | 0.99 (0.03) | 0.95 (0.01) | .02∗ |
| R50 ratio | 4.6 (1.3) | 5.1 (1.4) | .5 |
| Skin metrics | |||
| Max point dose (Gy) | 23.46 (2.09) | 22.74 (1.58) | .43 |
| Contralateral breast | |||
| Point dose (Gy) | 0.6 (0.17) | 0.7 (0.2) | .2 |
| Ipsilateral lung | |||
| V7.7<10% | 3.7% (2.5) | 6.9% (3.2) | .02∗ |
| V2.7<20% | 16.7% (6.4) | 17.8% (5.3) | .99 |
| Mean dose (Gy) | 1.64 (0.55) | 2.0 (0.5) | .06 |
| Contralateral lung | |||
| V1.4 <15% | 1.9% (3.6) | 4.1% (6.1) | .64 |
| Mean dose (Gy) | 0.32 (0.16) | 0.4 (0.22) | .54 |
| Total lung | |||
| Mean dose (Gy) | 0.96 (0.36) | 1.2 (0.36) | .06 |
| Heart | |||
| Mean dose (Gy) | 0.4 (0.2) | 0.5 (0.2) | .6 |
| V4.0 (%) | 0.07% (0.2) | 0.34% (0.6) | .1 |
| V2.6 (%) | 0.5% (0.9) | 1.7% (2.0) | .1 |
| RTOG chest wall | |||
| V24 (cm3) | 8.5 (5.5) | 21.8 (14.9) | .004∗ |
| Max point dose <26 Gy | 24.1 Gy (6.2) | 23.8 Gy (5.8) | .2 |
Abbreviations: CI = conformality index; D2cm3 = dose to 2 cm3 of the target; DHI = dose homogeneity index; Dmax = maximum dose; Dx = dose to x% of the target; PTV = planning target volume; SD = standard deviation; Vx = dose to x% of the target volume.
∗
Statistically significant.