Plan quality and delivery accuracy of flattening filter free beam for SBRT lung treatments

Figures & data

Table I. Mean target and OAR doses and conformity indexes for the GTV and PTV. Mean dose and D_V are given as percent of the dose prescribed to the specific target. The dose to targets are in Gy and V_D are in % volume. Uncertainties of all values are reported as one standard deviation, except for the target median volume where ranges are reported. All p-values are obtained from a paired two-sided Wilcoxon-signed rank test. Statistically significant differences are shown in bold.

Parameter	dFF	dFFF	sFFF	dFF vs. dFFF	dFF vs. sFFF	dFFF vs. sFFF
GTV (66 Gy)				p	p	p
Median volume	7.6 (1.0–28.2)
Mean dose (Gy)	66.6 ± 1.0	66.7 ± 1.0	66.9 ± 1.1	0.74	0.01	0.01
Std of dose (Gy)	2.6 ± 0.7	2.7 ± 0.7	2.8 ± 0.7	0.13	0.01	0.07
D2% (Gy)	71.1 ± 1.9	71.3 ± 2.0	71.6 ± 1.9	0.19	0.04	0.48
D98% (Gy)	61.1 ± 1.1	61.1 ± 1.1	60.9 ± 1.2	0.69	0.04	0.02
V62.7 Gy (%)	91.7 ± 5.1	91.8 ± 5.2	91.1 ± 5.8	0.93	0.23	0.05
V70.6 Gy (%)	7.9 ± 11.0	8.2 ± 7.9	11.5 ± 13.4	0.80	0.01	0.06
PTV (45 Gy)
Median volume	39.4 (10.8–87.5)
Mean dose (Gy)	56.9 ± 1.5	56.9 ± 1.5	57.0 ± 1.5	0.43	0.43	0.09
Std of dose (Gy)	6.9 ± 0.8	6.9 ± 0.8	6.9 ± 0.9	0.74	0.74	0.07
D2% (Gy)	69.9 ± 1.9	70.0 ± 1.9	70.4 ± 2.1	0.22	0.22	0.09
D98% (Gy)	45.7 ± 1.0	45.7 ± 1.0	45.7 ± 0.9	0.99	0.99	0.79
V45.0 Gy (%)	98.8 ± 1.2	98.8 ± 1.1	98.8 ± 1.0	0.43	0.43	0.79
V48.2 Gy (%)	89.4 ± 4.0	89.6 ± 4.0	89.9 ± 4.1	0.23	0.23	0.61
CI
V62.7 Gy/VGTV	1.03 ± 0.16	1.03 ± 0.16	1.05 ± 0.19	0.82	0.39	0.39
V45.0 Gy/VPTV	1.18 ± 0.09	1.18 ± 0.09	1.20 ± 0.10	0.50	0.02	0.02
V22.5 Gy/VPTV	7.01 ± 1.7	6.68 ± 1.5	6.9 ± 1.8	0.0002	0.04	0.002
Spinal cord
Mean (Gy)	2.10 ± 1.0	1.98 ± 1.0	2.00 ± 1.0	0.002	0.12	0.79
D2 (Gy)	9.5 ± 4.2	9.2 ± 4.2	9.3 ± 4.1	0.15	0.61	0.57
Heart
Mean (Gy)	1.4 ± 1.9	1.3 ± 1.8	1.4 ± 2.0	0.002	0.06	0.01
D2 (Gy)	5.2 ± 5.6	4.9 ± 5.2	5.4 ± 5.8	0.002	0.59	0.02
V12 Gy (%)	1.1 ± 2.3	0.8 ± 1.7	1.4 ± 3.1	0.02	0.74	0.05
Ipsilateral lung
Mean (Gy)	5.6 ± 1.7	5.4 ± 1.7	5.4 ± 1.7	0.0001	0.001	0.64
V22.5 Gy (%)	7.3 ± 2.6	7.1 ± 2.6	7.2 ± 2.7	0.002	0.50	0.02
V12 Gy (%)	14.8 ± 4.4	14.7 ± 4.5	14.7 ± 4.5	0.09	0.64	0.19
Contralateral lung
Mean (Gy)	1.24 ± 0.4	1.19 ± 0.5	1.17 ± 0.4	0.0001	0.001	0.34
V12 Gy (%)	0.02 ± 0.1	0.02 ± 0.1	0.02 ± 0.1	0.88	0.13	1.00
V6 Gy (%)	1.6 ± 1.9	1.5 ± 1.9	1.3 ± 1.5	0.09	0.02	0.21
External – Target
Mean (Gy)	1.84 ± 0.5	1.77 ± 0.5	1.77 ± 0.5	0.0001	0.0001	0.52
V22.5 Gy (%)	1.16 ± 0.5	1.10 ± 0.5	1.14 ± 0.5	0.001	0.05	0.003
V12 Gy (%)	4.04 ± 1.4	3.86 ± 1.4	3.92 ± 1.4	0.0001	0.003	0.04

Figure 1. Mean difference in DVH between dFF and dFFF plans in absolute volumes (solid black) for the external – PTV ROI. p-Values are obtained from a paired two-sided Wilcoxon-signed rank test. The grey dotted line indicates the level of 5% statistical significance. Between 0.2 Gy and 38.4 Gy the volume is statistically significant lower for dFFF compared to dFF.

Table II. Results for the delivery efficiency and accuracy. The accuracy is given by the mean dosimetric result of the ArcCheck measurements. The numbers are percentages of measuring points passing the gamma deviation criteria of 3 mm and 3%. Uncertainties of all values are reported as one standard deviation. p-Values are obtained from a paired two-sided Wilcoxon-signed rank test. Statistically significant differences are shown in bold.

	dFF	dFFF	sFFF	dFF vs. dFFF	dFF vs. sFFF	dFFF vs. sFFF
Delivery accuracy				p	p	p
Gamma pass rate	99.3 ± 1.0	98.0 ± 1.1	98.0 ± 1.7	0.0004	0.001	0.64
Delivery efficiency
MU	2877 ± 231	2841 ± 237	2743 ± 223	0.01	0.0001	0.0003
Beam-on time (s)	382 ± 30	148 ± 12	146 ± 12	0.0001	0.0001	0.01
Dose rate (%)	97.3 ± 0.8	89.2 ± 1.2	87.6 ± 0.9	0.0001	0.0001	0.01