Optimal planning strategy among various arc arrangements for prostate stereotactic body radiotherapy with volumetric modulated arc therapy technique

Volume	Rectum	Bladder	Femoral heads
	V_42.7_{Gy (100%)} < 5%	V_42.7_Gy(100%) < 10%	V_29.9_{Gy (70%)} < 50%
	V_38.4_{Gy (90%)} < 15%	V_34.7_{Gy (81%)} < 25%	D_max <29.9 Gy
Constraints	V_32.0_{Gy (75%)} < 35%	V_{29.9 Gy(70%)} < 50%
	V_28.0_{Gy (65%)} < 45%
	V_24.8_{Gy (58%)} < 70%
	V_20.0_{Gy (47%)} < 80%

D_max = the maximum dose; V_xx_Gy = the volume receiving dose of xx Gy (x% of the prescription dose)

Table 2

Parameters used to calculated Niemierko’s EUD-based TCP and NTCP.

Tissue	100%dpf (Gy)	Fraction (#)	α	γ₅₀	TD₅₀ (Gy)	TCD₅₀ (Gy)	dpf (Gy)	α/β (Gy)
Prostate	6.1	7	-10	1.0		28.34	2	1.20
Rectum	6.1	7	8.33	4	80		2	3.90
Bladder	6.1	7	2	4	80		2	8.00
Femur	6.1	7	4	4	65		2	0.85

$\frac{α}{β}$ = Alpha-beta ratio; 100%dpf = 100% dose per fraction; dpf = Parameters’ source data’s dose per fraction

An example of the dose distributions achieved with **(A)** one full arc (1FA), **(B)** one partial arc (1PA), **(C)** two full arcs (2FA), and **(D)** two partial arcs (2PA) arrangement in prostate SBRT-VMAT for the same patient.

Average dose-volume histograms of the **(A)** PTV, **(B)** bladder, **(C)** rectum, **(D)** left femoral head, and **(E)** right femoral head from prostate SBRT-VMAT plans for four arc arrangements (1FA, 1PA, 2FA, and 2PA).

Table 3

Dosimetric results for target volumes in prostate SABR-VMAT plans using four arc arrangements.

	Avg ±SD (range)

	1FA	1PA	2FA	2PA
CTV coverage
D_50% (Gy)	44.9±0.4	44.6±0.5	44.5±0.5	44.4±0.3
D_50% (Gy)	(44.4-45.4)	(44.1-45.1)	(44.0-45.3)	(44.0-44.7)
D_5% (Gy)	46.0±0.1	45.9±0.1	45.9±0.1	45.8±0.2
D_5% (Gy)	(45.9-46.1)	(45.7-46.0)	(45.8-46.0)	(45.7-45.9)
D_95% (Gy)	43.5±0.5	43.1±0.4	43.1±0.6	42.8±0.2
D_95% (Gy)	(43.0-44.2)	(42.8-43.5)	(42.6-43.9)	(42.7-43.1)
V_100% (%)	98.4±1.8	97.9±0.0	97.8±3.8	97.6±2.0
V_100% (%)	(95.5-100.0)	(95.0-99.8)	(95.2-100.0)	(94.2-99.9)
PTV coverage
D_mean	44.3±0.2	44.2±0.1	44.1±0.3	44.3±0.1
D_mean	(44.2-44.6)	(44.0-44.4)	(44.0-44.6)	(44.2-44.5)
D_max	48.8±0.8	49.5±0.9	48.5±1.1	49.0±1.4
D_max	(47.8-49.8)	(48.4-50.5)	(47.2-50.0)	(47.4-50.5)
D_min	33.0±0.4	32.3±0.0	32.8±0.8	33.7±0.3
D_min	(32.4-33.2)	(31.9-33.7)	(32.1-33.9)	(33.4-34.1)
D_50% (Gy)	44.6±0.3	44.5±0.2	44.4±0.4	44.5±0.2
D_50% (Gy)	(44.2-45.0)	(44.3-44.8)	(44.1-45.0)	(44.3-44.8)
D_5% (Gy)	46.1±0.2	46.1±0.1	46.1±0.2	46.0±0.1
D_5% (Gy)	(45.9-46.3)	(45.9-46.2)	(45.9-46.3)	(45.9-46.2)
D_95% (Gy)	41.5±0.3	41.4±0.2	41.3±0.3	41.7±0.1
D_95% (Gy)	(41.1-41.8)	(41.2-41.8)	(41.0-41.7)	(41.6-41.9)
V_100% (%)	87.5±1.9	86.6±1.2	87.7±1.5	88.1±1.0
V_100% (%)	(85.1-90.2)	(85.0-87.8)	(85.8-89.3)	(87.1-89.9)
Conformity	1.05±0.00	1.04±0.01	1.03±0.01	1.05±0.01
index	(1.02-1.03)	(1.02-1.04)	(1.02-1.04)	(1.02-1.03)
Conformation	0.91±0.01	0.91±0.01	0.91±0.01	0.91±0.01
number	(0.90-0.92)	(0.09-0.92)	(0.91-0.92)	(0.90-0.93)
Homogeneity	0.10±0.01	0.11±0.00	0.11±0.01	0.10±0.00
index	(0.09-0.12)	(0.10-0.11)	(0.10-0.12)	(0.09-0.10)

Avg. = average; D_5% = the dose received at least 5% volume; D_mean = the mean dose; D_max = the maximum dose; D_min = the minimum dose; D_50% = the dose received at least 50% volume; D_95% = the dose received at least 95% volume; SD = the standard deviation; V_100% = the volume received 100% of prescription dose.

Table 4

Dosimetric results for organs at risk in prostate SABR-VMAT plans using four arc arrangements.

	Avg SD (range)

	IFA	1PA	2FA	2PA
Organs at risk
Rectum D_mean (Gy)	25.2±1.7	23.3±2.0	23.6±1.8	23.4±1.9
Rectum D_mean (Gy)	(23.1-27.2)	(21.4-25.8)	(21.3-26.0)	(21.3-26.4)
Rectum D_2% (Gy)	44.2±0.3	44.6±0.4	44.1±0.4	44.5±0.2
Rectum D_2% (Gy)	(43.7-44.5)	(44.0-45.1)	(43.8-44.7)	(44.3-44.9)
Rectum V_95% (%)	9.0±1.4	10.1±1.3	8.3±1.3	9.8±1.5
Rectum V_95% (%)	(6.6-10.3)	(8.1-11.5)	(7.0-10.2)	(7.6-11.6)
Rectum V_80% (%)	19.1±3.0	19.7±3.2	18.0±2.8	19.4±3.4
Rectum V_80% (%)	(15.1-23.2)	(15.2-23.8)	(15.2-21.9)	(14.8-24.3)
Rectum V_50% (%)	71.0±8.8	53.9±9.4	60.0±11.1	54.1±9.0
Rectum V_50% (%)	(61.1-80.1)	(41.9-63.7)	(46.9-77.4)	(42.5-66.7)
Rectum V_20% (%)	90.2±2.5	90.0±2.7	89.6±3.0	90.0±2.8
Rectum V_20% (%)	(87.7-93.4)	(87.1-94.1)	(85.6-93.5)	(87.3-94.0)
Bladder D_mean (Gy)	19.0±6.9	18.7±7.1	18.5±6.1	18.3±6.9
Bladder D_mean (Gy)	(13.4-31.1)	(13.2-31.0)	(15.7-29.0)	(12.9-30.4)
Bladder D_2% (Gy)	45.6±0.2	45.6±0.2	45.5±0.3	45.6±0.4
Bladder D_2% (Gy)	(45.5-45.8)	(45.3-45.9)	(45.0-45.8)	(45.3-46.4)
Bladder V_95% (%)	21.2±11.1	21.4±11.1	20.9±10.5	21.4±11.3
Bladder V_95% (%)	(10.5-39.3)	(10.6-39.4)	(10.3-37.7)	(10.7-39.9)
Bladder V_80% (%)	25.6±11.9	26.2±11.9	25.7±11.1	26.0±12.0
Bladder V_80% (%)	(16.6-46.4)	(16.5-46.3)	(16.6-44.6)	(16.3-46.2)
Bladder V_50% (%)	40.4±13.6	38.6±12.6	39.5±12.4	38.2±12.9
Bladder V_50% (%)	(29.4-64.1)	(28.5-60.5)	(29.2-60.7)	(27.5-60.6)
Bladder V_20% (%)	54.4±17.0	52.5±16.1	54.1±17.4	52.1±16.1
Bladder V_20% (%)	(37.2-79.1)	(36.4-76.5)	(37.0-79.4)	(36.2-76.1)
Left femoral head	12.8±1.8	18.7±2.3	12.7±2.4	13.9±1.4
D_mean (Gy)	(10.5-15.1)	(16.9-22.7)	(9.3-14.9)	(11.7-15.3)
Left femoral head	19.7±2.2	23.5±4.4	18.3±3.0	20.1±2.0
D_2% (Gy)	(16.9-21.8)	(15.6-26.1)	(13.4-20.7)	(16.7-21.8)
Right femoral	10.8±0.9	13.3±2.5	12.4±1.7	13.7±2.1
head D_mean (Gy)	(9.2-11.3)	(9.2-15.5)	(10.5-14.2)	(10.7-16.5)
Right femoral	16.4±1.3	20.6±3.7	18.1±1.9	19.7±2.3
head D_2% (Gy)	(14.3-18.0)	(14.3-23.6)	(15.8-20.1)	(16.2-22.5)

Table 5

Average monitor unit and delivery time for prostate SBRT-VMAT plans using four arc arrangements.

Beams	1FA (Mean ± SD)	1PA (Mean ± SD)	2FA (Mean ± SD)	2PA (Mean ± SD)
MU	1575±63	1627±56	1646±97	1660±98

Delivery time (min)	1.01±0.02	0.69±0.01	2.00±0.01	1.36±0.02

Table 6

TCP of prostate tumor and NTCP of OARs for four arc arrangement plans.

Beams	1FA (Mean±SD)	1PA (Mean±SD)	2FA (Mean±SD)	2PA (Mean±SD)
TCP (%)
Prostate	93.35±0.08	99.28±0.06	93.32±0.08	93.36±0.08
NTCP (%)
Rectum	0.44±0.23	0.61±0.21	0.40±0.23	0.56±0.22
Bladder	0.01±0.02	0.01±0.03	0.00±0.01	0.00±0.02
LT Femur	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00
RT Femur	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00

References

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Articles in this issue

DOI: https://doi.org/10.1515/raon-2017-0005 | Journal eISSN: 1581-3207 | Journal ISSN: 1318-2099

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Language: English

Page range: 112 - 120

Submitted on: Jul 19, 2016

Accepted on: Oct 25, 2016

Published on: Jan 15, 2017

Published by: Association of Radiology and Oncology

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

Keywords:

stereotactic body radiotherapy,

volumetric modulated arc therapy,

prostate cancer,

arc arrangement,

dosimetric and biological metrics

Related subjects:

Medicine,

Clinical medicine,

Radiology

© 2017 Sang Won Kang, Jin Beom Chung, Jae Sung Kim, In Ah Kim, Keun Yong Eom, Changhoon Song, Jeong Woo Lee, Jin Young Kim, Tae Suk Suh, published by Association of Radiology and Oncology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Volume 51 (2017): Issue 1 (March 2017)