ART for head and neck patients: On the difference between VMAT and IMPT

Figures & data

Figure 1. Magnitude of GTV and CTV shrinkage.

Figure 2. Dose distribution for the initial plan, non-adapted plan, adapted plan, a) VMAT technique for patient with large volume shrinkage, b) IMPT technique for patient with large volume shrinkage, c) VMAT technique for patient with small volume shrinkage, d) IMPT technique for patient with small volume shrinkage, blue lines – PTV volumes, black lines – OARs, i.e. spinal cord, parotid glands.

Figure 3. Dose volume histograms for patient with large volume changes a) and small volume changes b).

Table I. Variation of dosimetric treatment plan parameters for OARs and PTV structures for the various treatment scenarios. Volumes are specified as median and range (min, max) for 6 patients.

		VMAT			IMPT
		Week 1–2	Week 3–4	Week 5–6	Week 1–2	Week 3–4	Week 5–6
Brainstem	D2%(biweekly) [Gy]	11.2 (9.7–13.7)	14.9 (12.0–19.7)	14.9 (11.9–19.7)	7.7 (4.8–9.6)	9.1 (4.3–14.8)	8.3 (4.3–13.7)
Spinal cord	D2%(biweekly) [Gy]	13.9 (12.3–14.4)	14.9 (11.0–20.7)	14.9 (11.5–17.2)	6.7 (2.9–7.1)	10.0 (3.6–17.8)	9.6 (7.2–13.7)
Contr. Parotid	Dmean (biweekly) [Gy]	8.7 (6.9–19.2)	10.7 (6.1–19.9)	9.9 (6.3–18.4)	6.5 (2.8–11.9)	8.6 (4.5–17.6)	8.0 (4.8–15.0)
Larynx	Dmean (biweekly) [Gy]	15.9 (15.5–19.5)	16.8 (15.0–19.7)	17.0 (16.4–20.8)	13.8 (10.0–18.2)	15.8 (9.3–17.7)	16.8 (12.4–19.5)
PTV70Gy	D2%(biweekly) [Gy]	26.0 (25.01–26.3)	25.7 (25.4–26.8)	25.9 (25.1–26.5)	24.5 (24.1–24.7)	27.4 (25.8–29.1)	27.1 (24.4–31.0)
PTV70Gy	D98%(biweekly) [Gy]	22.5 (22.3–23.0)	21.7 (20.7–25.9)	22.3 (20.7–25.9)	22.6 (22.5–24.5)	20.8 (17.5–27.5)	20.1 (14.0–27.1)

In brackets range for 6 patients, D_{2% (biweekly)}, dose delivered to 2% of the volume; D_{98% (biweekly)}, dose delivered to 98% of the volume; Week 1–2, biweekly doses of the initial plan calculated on the planning CT; Week 3–4, biweekly doses of the initial plan recalculated on the CT₁ ; Week 5–6, biweekly doses of the initial plan recalculated on the CT₂.

Table II. Variation of dosimetric treatment plan parameters for OARs and PTV structures in biweekly intervals. Volumes are specified as median and range (min and max) for 6 patients.

		VMAT			IMPT
		Initial plan	Non-adapted plan	Adapted plan	Initial plan	Non-adapted plan	Adapted plan
Brainstem	D2% [Gy]	32.5 (28.2–40.0)	44.8 (34.6–53.8)	38.1 (37.4–45.6)	22.5 (14.0–28.0)	24.7 (12.4–35.6)	21.1 (8.0–27.8)
Spinal cord	D2% [Gy]	40.5 (36.0–42.0)	42.9 (33.6–50.6)	41.1 (37.0–41.6)	19.5 (8.6 –20.6)	25.3 (11.4–39.4)	20.8 (7.0–24.2)
Contr. Parotid	Dmean [Gy]	25.3 (20.2–56.0)	27.7 (12.1–52.2)	23.8 (14.5–50.6)	18.8 (15.7–36.4)	20.7 (8.7–40.4)	22.8 (8.2–30.6)
Larynx	Dmean [Gy]	46.5 (45.2–56.9)	48.5 (46.6–56.8)	49.7 (44.8–54.9)	40.1 (29.6–53.2)	39.4 (33.5–49.5)	45.9 (34.0–50.6)
PTV70Gy	D2% [Gy]	75.9 (73.2–76.6)	74.1 (72.6–76.4)	72.6 (71.4–73.6)	71.4 (70.4–72.0)	75.0 (71.2–78.4)	70.6 (70.2–70.6)
PTV70Gy	D98% [Gy]	65.7 (65.0–67.0)	64.4 (54.8–66.2)	61.4 (60.0–64.4)	66.1 (65.6–66.4)	58.8 (57.8–63.6)	59.3 (53.8–64.0)

Initial plan, Treatment plan created on the initial, planning CT (CT0); Adapted plan, result of deformation and accumulation on CT0 of the initial plan, plan created on CT1 and plan created on CT2, Non-adapted plan, result of deformation and accumulation initial plan calculated on CT0 and recalculated on the CT1 and CT2, in brackets range within 6 patients; D2%, dose delivered to 2% of the volume, D98%, dose delivered to 98% of the volume. In bold, differences between non-adapted and adapted plan which are statistically significant.