Local tumor control after retreatment of spinal metastasis using stereotactic body radiotherapy; comparison with initial treatment group

Figures & data

table I. Demographic characteristics and radiotherapeutic parameters (N = 185).

Group	Retreatment (N = 54)	Initial treatment (N = 131)	p-value
Number of lesions/patients	54/49	131/93
Age (years)
Mean	54.5 ± 11.8	50.1 ± 13.2	0.088
Median	55.5	51.0
Radiosensitivity of primary tumor			0.079
Sensitive; breast ca, prostate ca	7 (13.0%)	36 (27.5%)
Moderate	34 (63.0%)	63 (48.1%)
Resistant; RCC, HCC	13 (24.0%)	32 (24.4%)
Ratio of spinal cord level/cauda equina level	30 : 24	86 : 45	0.131
Proportion of cases with epidural mass (%)	25/54 (46.3%)	38/131 (29.0%)	0.024
Interval between RTx. and SBRT (months)	24.5 (range, 3–80)
Tumor volume (ml)
Mean	58.4 ± 61.0	36.4 ± 51.2	0.013
Median	34.3	20.5
Radiation dose to tumor during SBRT
Margin dose, single equivalent (Gy)	20.6 ± 5.9	19.9 ± 3.3	0.400
Margin dose, nBED (Gy2/10)	51.1 ± 15.9	50.7 ± 16.6	0.887
Maximal dose, single equivalent (Gy)	23.7	22.8
Minimal dose, single equivalent (Gy)	18.2	17.9
Total radiation dose to tumor (Gy2/10)	90.3 ± 19.9
Maximal spinal cord dose
SBRT nBED (Gy2/2)	46.19 ± 35.21	48.68 ± 29.97	0.547
Total nBED (Gy2/2)	83.37
Conformity index	1.24	1.29
Coverage (%)	95.8	96.1
Isodose line (%)	78.3	79.3

HCC, hepatocellular carcinoma; nBED, normalized biological effective dose; RCC, renal cell carcinoma; RTx, radiation therapy; SBRT, stereotactic body radiotherapy.

Figure 1. Survival curve in the retreatment and the initial treatment groups; mean value was 20.7 months and 32.4 months in each group, which showed statistical difference (p = 0.022).

Table II. Follow-up result in the retreatment SBRT and the initial treatment groups (N = 185).

Group	Retreatment (N = 54)	First-time treatment (N = 131)	p-value
Follow-up period (months)	17.3 ± 16.7	23.7 ± 20.8	0.047
Pain control rate
At 6 month	38/44 (86.4%)	105/113 (92.9%)	0.314
At 1 year	21/26 (80.8%)	74/83 (89.2%)	0.093
At 2 years	12/14 (85.7%)	46/51 (90.2%)	0.236
Radiologic control rate
At 6 month	42/44 (95.5%)	107/113 (94.7%)	0.699
At 1 year	21/26 (80.8%)	74/83 (89.2%)	0.093
At. 2 years	11/14 (78.6%)	46/51 (90.2%)	0.138
Progression free period (months)
Mean	18.0 ± 2.4	26.0 ± 2.2	0.029
Median	13.0	19.0
Survival time (months)
Mean	20.7 ± 3.2	32.4 ± 3.0	0.022
Median	11.0	19.0

Figure 2. Progression free probability curve of the retreatment and the initial treatment groups; mean value was 18.0 months and 26.0 months in each group, which was statistically different (p = 0.03).

Table III. Comparison between local control failure cases and controlled cases in retreatment group (N = 54).

Group	Local control failure (N = 13)	Controlled cases (N = 41)	p-value
Age
Mean	56.4 ± 7.5	53.9 ± 12.9	0.510
Median	55.0	57.0
Radio-sensitivity
Breast, prostate	1 (7.7%)	6 (14.6%)	0.708
Moderate	8 (61.5%)	26 (63.4%)
RCC, HCC	4 (30.8%)	9 (22.0%)
Ratio of spinal cord level/cauda equina level	7 : 6	23 : 18	0.887
Proportion of cases with epidural mass (%)	7/13 (53.8%)	18/41 (43.9%)	0.531
Interval between RTx. And SRS (months)
Mean	19.6 ± 13.4	26.1 ± 42.6	0.592
Median	15.0	12.3
Survival time (months)
Mean	17.4 ± 3.1	22.5 ± 4.2	0.835
Median	15.0	10.0
Tumor volume (ml)
Mean	67.2 ± 65.2	55.6 ± 60.2	0.555
Median	47.9	33.4
Radiation dose (SBRT dose)
Single equivalent (Gy)	20.2 ± 3.8	20.7 ± 6.5	0.767
Conventional 2 Gy	52.3 ± 15.2	50.7 ± 16.2	0.747
Total radiation dose
Single equivalent (Gy)
Conventional 2 Gy	91.4 ± 20.2	90.0 ± 20.1	0.829

HCC, hepatocellular carcinoma; nBED, normalized biological effective dose; RCC, renal cell carcinoma; RTx, radiation therapy; SBRT, stereotactic body radiotherapy.

Table IV. Current studies on spinal SBRT with reported local control rates for patients with image-based tumor progression and previous irradiation.

Authors/year	Number of retreated tumors	Follow-up period (months)	Local control rate (%)	Radiation dose/ fractionactions (Gy/fx.)	Previous irradiation dose (Gy)
Hamilton/1995	5	Median, 6 (range1–12)	100	10/1	Median, 45
Milker-Zaber/2003	19	Median, 12(range 4–33)	95	Median, 39.6/20	Median, 38
Mahan/2005	8	Mean, 15.2	100	Median, 30/15	Median, 30
Gerszten/2007	344	Median, 21 (range 3–53)	88	Mean, 20/1	NM
Sahgal/2009	37	Median, 7 (range 1/48)	92	Median, 24/3	Median, 36/14fx
Chang E/2007	35	12	84	30/5 or 27/3	NM
Tsai/2009	15	10	97	15.5/2	NM
Nelson/2008	22	NM	87.5	Median, 18/3	Median, 35
Amdur/2009	12	NM	96	15/1	NM
Yamada/2005	21	11	90.5	Median, 20/5	30
Choi/2010	51	12	75	Median, 20/2	Median, 40
Wright/2006	37	8	60	Median, 20/5	Median, 30
Gibbs/2007	50	9	NM	NM	NM
Chang*/2011	54	Median, 17.3	79	Median, 27/3	Median, 39.2
Garg/2011	63	Median, 17.7	76	30/5, 27/3	NM

Chang*, current authors' data; NM, not mentioned.