This study examined dosimetric parameters and local recurrence rates in 62 patients with single brain metastases treated with linear accelerator-based stereotactic radiosurgery (LB-SRS). The median prescribed dose was 14.5Gy to the 90% isodose line. Fifteen patients experienced local recurrence in the irradiated area. The study found no significant association between dosimetric parameters like minimum dose, and local recurrence rates. However, tumor coverage, homogeneity and conformity were acceptable. The study concluded that dosimetric factors may not be predictive of local control for LB-SRS of solitary brain metastases.

1. Dosimetric parameters in local
recurrence in patients with single brain
metastases treated with Linac-based
stereotactic radiosurgery (LB-SRS).
Sallabanda KF ,Sisamón IP , Cendales R., Bustos J.C., Gutierrez J.A., Marsiglia H., Samblas J.
Background Radiosurgery Unit. Sanatorio San Francisco de Asis.
Madrid, Spain.
Our series of single brain metastases patients
treated with LB-SRS showed an association between
minimum dose and overall survival. We aim to explore
the impact of dosimetric parameters in local control.
Material and Methods
All patients with newly-diagnosed, single-brain metastases
treated with collimator-framed, LB-SRS 200 Florida between
January 2005 and September 2009 were included. GTV was
defined based on CT/MRI fusion without margins. Planning was
performed using BrainScan 5.32 c2008. Clinical and MRI follow-
up was performed every three months. Local recurrence was
established when increase of treated lesion occurred, or when
persistent PET-CT positive lesions. Local intracranial relapse free
survival (LI-RFS) was analyzed. Dosimetric parameters were
explored as predictors of local control.
Tabla 1. General characteristics
Levels n %
Sex Male 38 61.29
Female 24 38.71
IK 90 16 25.81
80 20 32.26
Results
70 16 25.81 62 patients (38 males, 24 females) were eligible. Median age 58 years
60 10 16.13
Timing Sincronic 16 25.81 (30-85). 13% of patients had neurosurgery previously to LB-SRS.
Metacronic 46 74.19
Breast 15 24.19
WBRT was used as primary treatment in 29 patients (46.8%), 23
Colorectal 4 6.45 patients before, and 6 patients after LB-SRS. SIR classes were 1-
NSCLC 30 48.39
Primary tumor localization Kidney 2 3.23 3(30%), 4-7(68.4%), 8-10(1.6%). Median tumor volume was 4.1cc (0.4-
Melanoma 5 8.06
Others 6 9.68
26.3). Median tumor size was 23mm (6-40). Median prescribed dose
Complete response 22 35.48 was 14.5Gy (10-18) to 90% isodose-line. Median minimun dose(Dmin)
Parcial response 22 35.48
Primary tumor control Progression 16 25.81 was 11.9Gy (5.5-15.7). Median maximal dose was 16.6Gy (11.2-26.3).
No information 2 3.23 Median minimal dose administered to the 2% of the GTV (D2) was
Extracranial metastasis Without extracranial metastasis 33 53.23
Isolate bone metastasis 3 4.84 14Gy, median D4 14.3Gy, median D6 14.5Gy, median D8 14.8Gy.
Multiple bone metastasis 2 3.23
Isolate visceral metastasis 5 8.06
Median maximum dose administered to 0.01cc of GTV (D0.1cc) was
Multiple visceral metastasis 9 14.52 14.62Gy, median D0.5cc15.28Gy, median D1cc 15.4Gy. Median
Bone and visceral metastasis 6 9.68
No information 4 6.45 coverage index was 0.82, median homogeneity index 1.13, median
Isolate metastasis 8 12.90
Neurosurgery Without neurosurgery 54 87.10
tumoral conformity index 0.96. Twenty-seven patients had intracranial
Therapeutic WBRT 23 37.10 relapse: 15 patients had a recurrence on irradiated area. The 9,12,18-
WBRT pre-RS
WBRT post-RS
Without WBRT
WBRT in primary treatment
39
6
62.90
9.68
month LI-RFS probability was 94.3%, 84.2%, and 61.7% respectively.
WBRT rescue 4 6.45 Median LI-RFS was 38.4 months. Significant factors associated with LI-
Without WBRT 49 79.03
No information 3 4.84 RFS were RPA, neurosurgery previous to LB-SRS, and tumor size
Isolate metastasis 2 3.23 <30mm. D2, D4, D6, D8, D0.1cc, D0.5cc, D1cc and Dmin, were
Rescue RS for local Without rescue 56 90.32
recurrence No information 4 6.45 explored as potential prognostic factors for LI-RFS, but none of them
One lesion 6 9.68
Two lesions 1 1.61
were found to be relevant. Multivariate analyses did not evidence any
Rescue RS for distance Three or more lesions 1 1.61 relevant prognostic factors.
recurrence Without rescue 48 77.42
No information 6 9.68
SIR 1 18 29.03
2 41 66.13
3 1 1.61 Conclusion.
No information 2 3.23
RPA 1 18 29.03 We did not found any dosimetric factors associated to local control.
2 34 54.84 However, coverage, homogeneity, and tumoral conformity index were
3 10 16.13
GPA 1 9 14.52 acceptable, this reduce the possibility of finding significant associations.
2 13 20.97
3 33 53.23 It seems that on LB-SRS there is no place for analyzing the quality of
No information
4 3
4
4.84
6.45
the dose distribution within GTV area, and it seems this is not an
BSBMr 1 22 35.48 essential factor of few isocenters treatments.
2 17 27.42
3 12 19.35
4 6 9.68
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