Does VMAT for treatment of NSCLC patients increase the risk of pneumonitis compared to IMRT ? – A planning study

Figures & data

Table I. Patient specifics.

Sex
Male	8
Female	7
Age [Years] median (min; max)	71 (56; 86)
Performance (WHO)
0	3
1	7
2	5
FEV1 [l/min] median (min; max)	1.6 (0.7; 3.1)
Stage*
1A	1
1B	2
2B	1
3A	6
3B	5
Affected lopes of lung**
Left (Lower/Upper)	7 (3/5)
Right (Lower/Middle/Upper)	8 (1/4/5)
Position
Central	8
Hilar	4
Periferial	2
Dorsal	1
Invading mediastinum	8
Histology
Squamous cell carcinoma	5
Adenocarcinoma	6
Large cell carcinoma	2
Undifferentiated	2
Taget Volume [cm^3] median (min; max)
GTV	13 (4; 109)
PTV	252 (77; 509)

If units are not given, values are number of patients out of the group of 15 patients.

^*Staging performed according to Goldstraw et al. [13]. ^**For one patient both lopes of the right lung were affected and for two patients both the middle and upper lope of the left lung were affected.

Figure 1. Field setups, dose distributions (a and b) and relevant Dose Volume Histograms (DVHs) (c) of the Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiation Therapy (IMRT) plans for one patient. The shaded area indicates the PTV. The arc of the VMAT plan is separated in two 90° arcs to avoid using anterior fields for treatment of a target volume with posterior location. The VMAT and IMRT plan provide similar target coverage, while the low dose region (< 20 Gy) is increased with VMAT compared to IMRT for this particular patient.

Figure 2. Population mean Dose Volume Histograms (DVHs) of residual lung (a) and PTV (b) for Volumetric Modulated Arc Therapy (VMAT) (solid line) and Intensity Modulated Radiation Therapy (IMRT) plans (dashed line). For each dose level p-value of Wilcoxon signed rank test is shown (dotted line) to indicate dose regions in which difference exists between IMRT and VMAT.

Table II. Dose metrices and toxicity calculations.

	Parameter	IMRT	VMAT	Difference: IMRT - VMAT	p-value
PTV	V105%; [%]	97.4 (91 – 100)	97.0 (92 – 100)	0.4 (−3.1 – 4.9)	0.3
	V95%; [%]	0.6 (0 – 3)	0.6 (0 – 3)	0 (−2.4 – 2.4)	0.6
	Std; [Gy]	1.4 (0.9 – 2.2)	1.6 (0.9 – 2.7)	−0.22 (−0.9–0.4)	0.1
Lung	V5; [%]	51.8 (34.1 – 70.0)	50.3 (27.6 – 71.5)	1.5 (−5.1–8.6)	0.3
	V20; [%]	21.6 (9 – 28)	20.4 (7 – 27)	1.3 (−0.6–2.6)	0.01
	MLD; [Gy]	13.1 (7 – 18)	12.8 (6 – 18)	0.3 (−0.8–1.2)	0.1
	*NTCP^‡LKB; [%]	10.2 (4 – 17)	9.8 (4 – 18)	0.4 (−1 – 1.4)	0.1
	*NTCP^‡LKS; [%]	7.6 (3 – 13)	7.3 (3 – 13)	0.3 (−0.6 – 0.9)	0.1
	**NTCP^†rdV; [%]	5.7 (3 – 8)	5.4 (2 – 8)	0.4 (−0.5 – 1.1)	0.01

Mean values and ranges for dose parameters of Planning Target Volume (PTV) and residual lung together with calculated Normal Tissue Complication Probability (NTCP) values. Differences are calculated as IMRT minus VMAT. The heterogeneity of the PTV is given as the standard deviation (SD) of the dose to the PTV. MLD is the Mean Lung Dose given in Gy. Doses used for NTCP calculations were *the physical doses or **doses corrected for fractionation (using an α/β ratio of 3 Gy); †NTCP calculated using a critical volume model with parameters published by Seppenwoolde et al. [6]; ^‡NTCP calculated using QUANTEC Lyman-Kutcher-Burman (LKB) parameters [3]. Statistically significant differences, according to Wilcoxon signed rank test, are shown in bold.

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