Inhomogeneous dose escalation increases expected local control for NSCLC patients with lymph node involvement without increased mean lung dose

Figures & data

Table I. Patient characteristics and planning results for the lungs.

Study id	Age [y]	Tumour location	Clinical T N stage	Stage	Amplitude [mm]	GTV [cm^3]	Lung V20Gy [%]	Mean lung dose [Gy]
1	62	RLL	T2B N3	IIIB	11	23.9	31.4	16.5
2	65	LUL	T2A N0	IB	7	3.2	12.4	7.0
3	64	RUL	T3 N2	IIIA	0	46.0	33.3	20.1
4	78	RLL	T2B N2	IIIA	7	78.6	35.9	21.1
5	59	LUL	T2A N0	IB	0	31.2	24.0	14.6
6	73	RUL	T2B N2	IIIA	1	60.0	25.3	15.1
7	64	LUL	T1B N2	IIIA	5	9.9	22.3	12.9
8	85	RUL	T2B N2	IIIA	0	67.0	23.2	14.6
9	65	LUL	T4 N2	IIIB	1	66.4	19.6	12.3
10	61	LLL	T4 N2	IIIB	6	46.7	20.1	13.2
11	67	LUL	T4 N0	IIIA	1	399.2	25.0	16.8
12	66	LUL	T4 N2	IIIA	5	35.9	24.3	14.5
13	73	RUL	T4 N0	IIIA	4	8.6	20.5	11.5
14	69	LUL	T4 N3	IIIB	1	180.6	32.9	20.4
15	59	LUL	T4 N2	IIIB	0	105.6	27.4	16.2
16	77	RUL	T2B N2	IIIA	4	80.9	34.7	19.9
17	82	RLL	T3 N2	IIIA	2	33.6	34.3	19.9
18	76	RLL	T3 N3	IIIB	5	68.9	34.9	20.7
19	75	RUL	T4 N2	IIIB	0	53.4	26.2	14.8
20	63	RLL	T2B N3	IIIB	12	66.6	37.1	22.4

Tumour locations are: left upper lobe (LUL), left lower lobe (LLL), right upper lobe (RUL) and right lower lobe (RLL). The amplitude motion is the peak-to-peak motion in the cranio-caudal direction.

Figure 1. DVH for the homogeneous (black) and inhomogeneous (grey) dose distributions. Dashed lines: GTV, solid lines: CTV, dotted lines: PTV and dash-dotted lines: Lungs.

Table II. Planning results for the homogeneous and inhomogeneous plans.

	Units	Homogeneous	Inhomogeneous
GTV
D98%	[Gy]	64.8 ± 0.9	68.4 ± 2.9
Dmean	[Gy]	67.1 ± 0.8	75.7 ± 3.9
D2%	[Gy]	69.2 ± 1.3	81.8 ± 6.7
TCPM	[%]	19.9 ± 1.1	33.3 ± 6.0
TCPLQ	[%]	21.4 ± 8.3	34.1 ± 11.0
CTV
D98%	[Gy]	64.6 ± 0.9	66.3 ± 2.1
Dmean	[Gy]	67.0 ± 0.7	73.4 ± 2.0
D2%	[Gy]	69.5 ± 1.2	81.2 ± 6.3
TCPM	[%]	19.9 ± 1.1	29.4 ± 2.9
TCPLQ	[%]	21.2 ± 8.1	30.0 ± 9.7
PTV
D98%	[Gy]	63.4 ± 0.5	64.4 ± 1.0
Dmean	[Gy]	66.6 ± 0.5	71.0 ± 1.2
D2%	[Gy]	69.6 ± 0.9	80.0 ± 5.5
TCPM	[%]	19.2 ± 0.7	25.6 ± 1.7
TCPLQ	[%]	20.1 ± 7.8	25.8 ± 9.4

Values are listed as average and standard deviations of the patient population.

Figure 2. Histograms displays the difference in TCP for the inhomogeneous plan compared to the homogeneous plan for each patient. The left column shows the TCPM gain using the Martel model (Eq. 2), and in the righ column is shown the TCPLQ gain calculated using the LQ model (Eq. 4). The three rows represent calculations for clonogenic cells assumed to be homogeneous distributed over either PTV, CTV, or GTV.

Figure 3. Maximum doses (D_1cm³) to the organs at risk in the mediastinum area for the homogeneous versus inhomogeneous dose distributions. Each marker represents a patient. The diagonal lines are the identity lines (y = x).