Table 1.
Dosimetric comparison of original IMRT, optimized IMRT, and 4π optimized plans:
| Variable | IMRT original median (range) |
IMRT optimized median (range) |
4π optimized median (range) |
4π-IMRT orig % diff (p-value) |
4π-IMRT opt % diff (p-value) |
|
|---|---|---|---|---|---|---|
| Conformity index | 1.00(0.97–1.31) | 1.02(1.00–1.29) | 1.03(0.99–1.30) | 2%(0.001)* | 0%(0.414) | |
| Homogeneity index (%) | 7.95(4.35–9.29) | 9.78(5.45–12.38) | 7.11(4.90–10.13) | −11%(0.839) | −27%(0.005)* | |
| Gradient measure (cm) | 2.01(1.13–2.59) | 1.75(0.97–2.33) | 1.60(0.72–2.12) | −20%(<0.001)* | −8%(0.001)* | |
| Max point dose PTV (Gy) | 64.7(62.6–68.1) | 66.4(63.6–74.7) | 66.2(64.1–68.6) | 2%(0.017) | 0%(0.685) | |
| Min point dose PTV (Gy) | 55.1(24.1–57.2) | 52.6(20.6–57.1) | 55.7(46.5–57.6) | 1%(0.273) | 6%(0.010) | |
|
| ||||||
| Brainstem | Dmax (Gy)† | 32.8(1.8–58.9) | 35.3(1.7–59.8) | 21.7(8.3–59.6) | −34%(0.006) | −38%(0.005)* |
| Dmean (Gy) | 11.4(0.9–39.4) | 12.3(0.9–41.4) | 8.2(2.0–22.6) | −28%(0.017) | −33%(0.017) | |
| EUD (Gy) | 18.7(1.2–45.1) | 20.5(1.1–46.5) | 11.2(4.0–40.6) | −40%(0.001)* | −45%(0.001)* | |
|
| ||||||
| Optic chiasm | Dmax (Gy) | 21.3(1.3–52.1) | 21.8(1.2–54.3) | 13.0(5.2–54.3) | −39%(0.080) | −40%(0.022) |
| Dmean (Gy) | 14.0(1.1–33.2) | 12.0(1.1–31.6) | 8.2(2.2–22.4) | −41%(0.022) | −32%(0.008) | |
| EUD (Gy) | 18.4(1.2–44.2) | 18.3(1.1–45.4) | 11.0(4.3–43.9) | −40%(0.027) | −40%(0.010) | |
|
| ||||||
| Ipsilateral optic nerve | Dmax (Gy) | 9.9(1.0–52.0) | 10.1(0.9–53.4) | 7.6(1.0–45.8) | −23%(0.048) | −25%(0.048) |
| Dmean (Gy) | 7.6(0.8–34.1) | 7.3(0.7–33.2) | 5.2(0.7–19.8) | −32%(0.006) | −29%(0.013) | |
| EUD (Gy) | 8.4(0.9–44.2) | 8.4(0.8–44.9) | 6.5(0.9–36.8) | −23%(0.027) | −23%(0.009) | |
|
| ||||||
| Contralateral optic nerve | Dmax (Gy) | 6.5(1.0–23.5) | 6.6(0.9–24.6) | 4.9(1.0–13.5) | −25%(0.048) | −26%(0.040) |
| Dmean (Gy) | 2.6(0.8–11.4) | 2.4(0.7–11.8) | 2.6(0.7–4.3) | −1%(0.033) | 9%(0.040) | |
| EUD (Gy) | 5.5(0.9–19.9) | 5.5(0.8–21.1) | 4.0(0.9–10.6) | −27%(0.040) | −28%(0.007) | |
|
| ||||||
| Hippocampus | Dmax (Gy) | 60.1(19.9–61.8) | 61.4(17.0–62.8) | 58.3(22.1–63.3) | −3%(0.893) | −5%(0.048) |
| Dmean (Gy) | 20.1(1.9–28.2) | 20.1(1.7–29.2) | 12.4(6.1–16.2) | −38%(0.002)* | −39%(0.005)* | |
| EUD (Gy) | 35.0(5.9–39.9) | 35.5(5.3–39.7) | 30.3(8.1–35.5) | −14%(0.001)* | −15%(0.003)* | |
|
| ||||||
| Cortex minus PTV | Dmax (Gy) | 61.4(60.8–63.4) | 62.8(60.9–65.5) | 63.0(61.3–64.4) | 3%(<0.001)* | 0%(0.340) |
| Dmean (Gy) | 14.5(9.0–23.9) | 13.0(7.9–21.6) | 10.9(6.7–20.5) | −25%(<0.001)* | −16%(<0.001)* | |
| EUD (Gy) | 33.3(26.9–40.0) | 31.6(23.9–38.8) | 32.3(23.3–38.2) | −3%(<0.001)* | 2%(0.946) | |
| V60 | 0.09(0.02–0.63) | 0.06(0.01–0.26) | 0.16(0.01–0.53) | 76%(0.414) | 160%(0.080) | |
| V50 | 6.30(1.57–16.41) | 4.91(0.77–13.97) | 5.60(0.82–13.43) | −11%(<0.001)* | 14%(0.340) | |
| V40 | 8.63(3.40–22.81) | 6.72(1.99–19.39) | 7.55(1.74–17.73) | −13%(<0.001)* | 12%(0.340) | |
| V30 | 15.81(6.72–33.77) | 10.59(4.20–26.78) | 9.85(2.99–22.09) | −38%(<0.001)* | −7%(0.008) | |
|
| ||||||
| White matter minus PTV | Dmax (Gy) | 60.1(19.9–61.8) | 61.4(17.0–62.8) | 58.3(22.1–63.3) | −3%(0.893) | −5%(0.048) |
| Dmean (Gy) | 15.9(8.2–28.0) | 14.8(6.7–27.3) | 12.3(7.4–24.1) | −23%(<0.001)* | −17%(0.001)* | |
| EUD (Gy) | 33.6(27.7–41.9) | 32.9(24.9–41.6) | 31.2(25.0–40.7) | −7%(<0.001)* | −5%(0.001)* | |
| V60 | 0.08(0.01–0.88) | 0.17(0.02–0.83) | 0.14(0.02–0.85) | 77%(0.191) | −17%(0.305) | |
| V50 | 5.04(1.67–20.02) | 4.43(0.99–19.09) | 3.86(1.05–18.31) | −23%(<0.001)* | −13%(0.005) | |
| V40 | 8.74(4.00–28.77) | 7.77(2.12–26.44) | 6.55(2.23–21.94) | −25%(<0.001)* | −16%(<0.001)* | |
| V30 | 13.93(6.26–40.90) | 12.06(4.16–38.01) | 9.64(4.21–28.91) | −31%(<0.001)* | −20%(<0.001)* | |
|
| ||||||
| Cortical thinning | >2% | 0.44(0.37–0.58) | 0.42(0.35–0.55) | 0.39(0.33–0.53) | −12%(<0.001)* | −8%(<0.001)* |
| >3% | 0.26(0.18–0.40) | 0.24(0.16–0.36) | 0.20(0.14–0.34) | −21%(<0.001)* | −14%(<0.001)* | |
| >5% | 0.12(0.06–0.25) | 0.09(0.04–0.22) | 0.09(0.04–0.19) | −26%(<0.001)* | −3%(0.001)* | |
*
statistically significant p-values after Bonferroni correction (p<0.005)
†
Dose at volume of 0.03cc per RTOG 0825 [33]. All other max doses are maximum point dose to the respective structure.