Table 2 Summary of target volume coverage, heterogeneity index, and dose to organs at risk for proton plans calculated with pencil beam algorithm (PBA), recalculation of PBA plan using Monte Carlo (MC), re-optimized plan using MC and fixed RBE, and re-optimized plan using MC with variable RBE among 8 mediastinal lymphoma patients with free-breathing CT simulation scans (left 4 columns). Comparison plans on deep inspiration breath hold (DIBH) scans with optimized PBS plan using MC versus photon techniques. Median volume or dose with interquartile range (IQR) in parentheses. Pair-wise dose differences were compared using a Wilcoxon signed-rank test. Significant p-values (< 0.05) are bolded for emphasis

 V99*

100% (100–100%)

80.6% (66.2–91.4%)

99.9% (99.6–100%)

98.7% (69.8–99.4%)

99.7% (99.6–99.9%)

99.3% (99–99.8%)

 V95

100% (100–100%)

98.4% (96.7–99.3%)

100% (100–100%)

100% (99.8–100%)

100% (99.9–100%)

99.9% (99.8–100.0%)

 Global dose max

107.6% (106.1–108.1)

108.1% (105.5–109.1)

109.2% (107.9–109.5)

112.5% (110.5–114.4)

109.7% (109.4–109.9)

112.3% (111.2–112.7%)

 Homogeneity index (D95/D5)

0.97 (0.95–0.97)

0.94 (0.93–0.96)

0.97 (0.97–0.97)

0.95 (0.95–0.96)

0.96 (0.96–0.97)

0.96 (0.95–0.96)

 Mean lung (Gy)

6.6 (4.4–9.2)

6.6 (4.6–9.2)

7.1 (5.0–8.9)

7.5 (5.7–9.0)

5.9 (4.8–7.8)

8.9 (8.1–11.7)

 Lung V20

16.3% (9.7–21.4)

16.1% (9.6–21.3)

16.8% (10.7–20.1)

17.1% (13.8–20.5)

12.3% (9.8–16.5%)

17.6% (10.6–24.8)

 Lung V5

30.5% (22.3–45.4)

31.4% (23.3–47.2)

33.4% (25.4–43.9)

34.9% (26.4–44.5)

31.0% (24.2–38.4%)

53.3% (45.1–61.6)

 Mean heart (Gy)

9.3 (7.6–12.2)

9.1 (7.4–11.8)

9.9 (7.7–12.0)

10.2 (8.7–12.0)

8.6 (6.5–10.9)

10.4 (9.0–15.1)

 Mean left breast (Gy)

2.0 (0.5–4.2)

2.1 (0.6–4.3)

2.2 (0.6–4.8)

2.0 (0.6–4.5)

2.1 (0.6–4.0)

4.1 (1.2–7.5)

 Mean right breast (Gy)

1.2 (0.3–2.6)

1.3 (0.4–2.7)

1.4 (0.6–2.9)

1.7 (0.6–2.9)

1.4 (0.9–3.3)

2.9 (1.9–5.6)

 Max spinal cord (Gy)

13.8 (13.0–17.2)

16.5 (14.4–20.0)

17.9 (15.4–20.9)

19.0 (16.6–21.5)

19.7 (15.0–21.0)

30.4 (27.0–31.7)

 Max esophagus (Gy)

31.5 (31.3–32.3)

31.0 (30.7–31.3)

32.1 (31.1–32.5)

31.9 (31.3–32.8)

32.0 (31.7–32.3)

31.7 (31.6–32.5)

P-value

FB PBPB cRBE vs FB PBMC cRBE

FB PBPB cRBE vs FB MCMC cRBE

FB MCMC cRBE vs DIBH photon

DIBH MCMC cRBE vs DIBH photon

 V99*

0.012

0.093

0.12

0.16

 V95

0.012

0.20

0.075

0.36

 Global dose max

0.48

0.06

0.012

0.012

 Homogeneity index (D95/D5)

0.018

0.28

0.25

0.20

 Average lung (Gy)

0.08

0.16

0.012

0.012

 Lung V20

0.29

0.33

0.26

0.16

 Lung V5

0.012

0.05

0.012

0.012

 Average heart (Gy)

0.012

1.00

0.16

0.025

 Average left breast (Gy)

0.35

0.046

0.028

0.028

 Average right breast (Gy)

0.028

0.028

0.028

0.046

 Max spinal cord (Gy)

0.05

0.017

0.012

0.017

 Max esophagus (Gy)

0.012

0.58

0.78

1.00