Incorporation of the LETd-weighted biological dose in the evaluation of breast intensity-modulated proton therapy plans

Figures & data

Table 1. The OAR dose evaluation matrices.

OARs	DVH point	Limit	Minor deviation	Major deviation
Heart	Mean absolute dose	4 Gy	4 ≤ Dmean < 5 Gy	Dmean ≥ 5 Gy
Brachial plexus	Absolute dose at 0.1 cc	60 Gy	60 ≤ D0.1 cc < 66 Gy	D0.1 cc ≥ 66 Gy
Esophagus	Absolute dose at 0.1 cc	52.5 Gy	52.5 ≤ Dmax < 55 Gy	D0.1 cc ≥ 55 Gy
Ipsilateral lung	Relative volume at 5 Gy	65%	65 ≤ V5 < 70 %	V5 ≥ 70 %
Ipsilateral lung	Relative volume at 10 Gy	50%	50 ≤ V10 < 60 %	V10 ≥ 60 %
Ipsilateral lung	Relative volume at 20 Gy	30%	30 ≤ V20 < 35 %	V20 ≥ 35 %

DVH: dose-volume histogram; OARs: organs at risk.

Figure 1. The color-washed isodose distribution of a representative breast patient planned with (a) RayStation Dose(RBE = 1.1), (b) MCsquare Dose(RBE = 1.1), and (c) LETd-weighted dose. The beam angles of 355 and 325 degrees for this plan are indicated in panel (a). The color-washed LETd is displayed in panel (d). The red contour is the target volume. The dose profiles of the MCsquare Dose(REB = 1.1), the LETd-weighted dose, and the LETd are displayed in panel (e) and the profile line is indicated in panel (d). The DVH is shown in panel (f).

Figure 2. LETd volume histograms on OARs for all 20 patients. The blue and red line represent the population median and mean values, respectively. The shaded bands represent the range of the variation within the 20 patients.

Figure 3. Box plot of the ratio of the Dose(LETd) over the Dose(RBE = 1.1).

Table 2. The median (range) and mean (SD) of the OAR dose.

OAR	Patient Group	Dose (RBE = 1.1)		Dose (LETd)		Dose (LETd) / Dose (RBE = 1.1)
		Median (range)	Mean (SD)	Median (range)	Mean (SD)	Median (range)	Mean (SD)
Brachial Plexus D0.1cc (Gy)	All patients	50.2 (47.4–52.6)	49.8 (1.5)	54.0 (50.8–56.5)	53.8 (1.9)	1.08 (1.06–1.11)	1.08 (0.01)
	breast	49.9 (47.5–51.6)	49.5 (1.5)	53.8 (51.2–56.1)	53.5 (1.8)	1.08 (1.07–1.11)	1.08 (0.01)
	CW	50.5 (47.4–52.6)	50.2 (1.5)	54.0 (50.8–56.5)	54.0 (2.0)	1.08 (1.06–1.09)	1.08 (0.01)
Rib D0.5cc (Gy)	All patients	50.1 (48.1–51.4)	50.1 (0.8)	56.3 (54.0–58.5)	56.5 (1.2)	1.12 (1.10–1.15)	1.13 (0.01)
	breast	49.9 (48.1–50.9)	49.8 (0.7)	55.9 (54.0–56.9)	55.7 (0.8)	1.12 (1.10–1.14)	1.12 (0.01)
	CW	50.5 (49.6–51.4)	50.5 (0.6)	57.1 (55.7–58.5)	57.2 (1.0)	1.13 (1.12–1.15)	1.13 (0.01)
Ipsilateral Lung V5 (%)	All patients	50.9 (39.7–63.5)	50.5 (6.2)	51.3 (40.1–63.2)	50.7 (6.2)	1 (0.99–1.01)	1.00 (0.01)
	breast	50 (39.7–63.5)	50.1 (7.6)	50.2 (40.1–63.2)	50.2 (7.4)	1 (0.99–1.01)	1.00 (0.01)
	CW	51.9 (43.3–59.0)	51.0 (5.0)	52.2 (43.4–59.0)	51.2 (5.0)	1 (1.00–1.01)	1.00 (0.01)
Ipsilateral Lung V10 (%)	All patients	38.7 (27.8–46.3)	38.0 (5.6)	38.7 (28.1–45.5)	37.9 (5.5)	1 (0.98–1.01)	1.00 (0.01)
	breast	36.3 (27.8–46.3)	36.7 (6.4)	36.3 (28.1–45.5)	36.6 (6.3)	1 (0.98–1.01)	1.00 (0.01)
	CW	39.7 (30.7–45.6)	39.2 (4.6)	39.7 (30.6–45.3)	39.2 (4.6)	1 (0.99–1.01)	1.00 (0.01)
Ipsilateral Lung V20 (%)	All patients	21.5 (15.1–29.2)	21.0 (4.0)	21.3 (15.3–28.9)	20.9 (3.8)	1 (0.96–1.03)	1.00 (0.02)
	breast	19.3 (15.1–24.6)	19.4 (3.7)	19.6 (15.3–24.7)	19.3 (3.5)	1 (0.96–1.03)	1.00 (0.02)
	CW	22.6 (15.9–29.2)	22.6 (4.2)	22.4 (15.9–28.9)	22.4 (3.7)	0.99 (0.98–1.0)	0.99 (0.01)
Heart Dmean (Gy)	All patients	1.0 (0.4–2.4)	1.0 (0.5)	1.2 (0.5–2.9)	1.3 (0.6)	1.24 (1.20–1.29)	1.24 (0.02)
	breast	0.9 (0.4–1.4)	0.9 (0.3)	1.1 (0.5–1.7)	1.1 (0.4)	1.25 (1.22–1.29)	1.25 (0.02)
	CW	1.1 (0.6–2.4)	1.2 (0.6)	1.4 (0.7–2.9)	1.4 (0.8)	1.22 (1.20–1.28)	1.23 (0.03)
Heart Dmean (Gy)	Left-sided patients	1.3 (1.1−2.4)	1.5 (0.5)	1.7 (1.4−2.9)	1.8 (0.6)	1.23 (1.2−1.28)	1.23 (0.03)
Esophagus D0.1 cc (Gy)	All patients	46.8 (37.7−50.1)	45.7 (3.1)	51.1 (42.3−55.2)	50.1 (3.2)	1.1 (1.06−1.14)	1.10 (0.02)
	breast	46.1 (39.5−48.3)	45.4 (2.9)	50.4 (42.6−53.0)	49.5 (3.2)	1.09 (1.08−1.11)	1.09 (0.01)
	CW	46.9 (37.7−50.1)	45.9 (3.3)	51.1 (42.3−55.2)	50.6 (3.3)	1.1 (1.06−1.14)	1.10 (0.03)

The ratio of the Dose (LETd) and the Dose (RBE = 1.1) is also shown. CW: chest wall; OARs: organs at risk.