Table 2.
Comparison of dosimetry between MRIdian-Linac PTV3mm and CT-Linac PTV3mm 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) | 35.9% (11.4) | .5 |
| V12.3 (cm3) | 219.4 (117) | 251.3 (133.8) | .1 |
| PTV metrics | |||
| Volume (cm3) | 84.3 (51.9) | 82.6 (55) | .5 |
| Ratio of PTV/ipsilateral breast volume | 13.0 (5.1) | 11.4 (5.0) | .03∗ |
| V23.4 ≥95% | 99% (0.9) | 99.5% (0.5) | .2 |
| D2cc<26.3Gy | 26.2 Gy (0.2) | 25.6 Gy (0.3) | .002∗ |
| V26.3Gy (cm3) | 1.9 (3.5) | 0.07 (0.1) | .01∗ |
| D2% (Gy) | 26.2 (0.2) | 25.7 (0.3) | .004∗ |
| D50% (Gy) | 25.5 (0.2) | 25.1 (0.1) | .002∗ |
| D98% (Gy) | 23.8 (0.4) | 24 (0.2) | .5 |
| Max point dose (Gy) | 26.8 (0.3) | 26.2 (0.6) | .03∗ |
| DHI ratio | 0 | 0 | >.99 |
| CI ratio | 1.0 | 1.0 | >.99 |
| R50 ratio | 4.6 (1.3) | 5.9 (1.7) | .09 |
| Skin metrics | |||
| Max point dose (Gy) | 23.46 (2.09) | 22.89 (1.47) | .38 |
| Contralateral breast | |||
| Point dose (Gy) | 0.62 (0.2) | 0.66 (0.12) | .4 |
| Ipsilateral lung | |||
| V7.7 <10% | 3.7% (2.6) | 4.5% (3.4) | .6 |
| V2.7 <20% | 16.75% (6.4) | 13.95% (6.0) | .1 |
| Mean dose (Gy) | 1.7 (0.54) | 1.5 (0.55) | .4 |
| Contralateral lung | |||
| V1.4 <15% | 1.94% (3.64) | 2.04% (4.35) | .7 |
| Mean dose (Gy) | 0.34 (0.16) | 0.29 (0.12) | .4 |
| Total lung | |||
| Mean dose (Gy) | 0.97 (0.33) | 0.88 (0.33) | .5 |
| Heart | |||
| Mean dose (Gy) | 0.44 (0.2) | 0.38 (0.23) | .6 |
| V4.0 (%) | 0.06% (0.2) | 0.44% (1.3) | .6 |
| V2.6 (%) | 0.5% (0.9) | 0.8% (1.3) | .6 |
| RTOG chest wall | |||
| V24 (cm3) | 8.5 (5.5) | 8.2 (6.0) | .8 |
| Max point dose <26 Gy | 24.1 Gy (6.2) | 23.6 Gy (6.2) | .009∗ |
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.