Table 3 Comparison of dose (mean and maximum) to cardiac substructures between proton plan with free breathing (FB), protons with deep inspiration breath hold (DIBH), and photons with DIBH. Proton plans were optimized with Monte Carlo dose algorithm and calculated with a variable relative biological effectiveness (RBE)

23.9 (16.8–27.7)

22.4 (17.1–27.3)

23.0 (19.3–29.0)

26.5 (16.9–28.6)

26.8 (22.6–29.7)

29.5 (26.4–31.1)

12.4 (4.9–22.3)

13.7 (4.8–20.8)

12.4 (6.3–22.5)

29.3 (19.7–31.0)

29.5 (21.9–31.3)

28.3 (23.9–32.1)

9.5 (4.3–16.3)

8.0 (3.1–11.8)

10.8 (6.8–17.0)

29.1 (18.4–30.0)

27.3 (18.1–30.0)

29.9 (18.7–31.3)

23.8 (14.6–26.1)

20.8 (10.3–26.5)

23.8 (8.5–29.0)

31.3 (30.8–31.8)

31.1 (30.3–31.9)

31.8 (30.5–32.1)

9.4 (4.5–18.3)

6.4 (3.4–12.0)

11.8 (7.7–16.8)

31.3 (23.6–32.2)

31.8 (25.9–32.2)

31.8 (30.5–32.2)

5.7 (0.2–9.0)

4.2 (0.3–7.0)

6.2 (4.1–10.8)

30.0 (8.7–32.3)

30.8 (10.7–32.3)

31.6 (22.2–32.4)

10.4 (8.1–19.0)

11.2 (5.5–18.1)

21.3 (6.1–26.1)

31.9 (31.1–32.3)

32.0 (31.6–32.4)

32.4 (32.1–32.6)

12.5 (6.6–14.1)

8.3 (6.0–15.7)

11.0 (8.0–15.7)

32.1 (31.6–32.7)

32.8 (32.4–33.3)

32.3 (31.9–33.2)

11.6 (5.8–18.6)

9.3 (3.3–13.1)

12.5 (9.1–21.1)

26.7 (21.8–29.5)

23.9 (20.2–25.9)

28.7 (25.7–30.4)

2.2 (0.1–5.8)

0.9 (0.1–2.1)

6.1 (3.5–9.7)

9.8 (0.5–23.1)

4.9 (0.4–19.8)

11.5 (6.3–24.3)

27.4 (26.5–29.9)

28.3 (26.8–30.0)

29.6 (23.6–30.7)

30.8 (30.5–31.5)

30.9 (30.5–31.7)

32.1 (31.9–32.3)

4.2 (1.9–6.9)

1.8 (0.4–8.1)

10.2 (2.4–20.9)

26.4 (19.5–28.8)

22.7 (3.2–30.1)

26.2 (5.7–32.1)