International Journal of Radiation Oncology � Biology � PhysicsS182

Results: In 140 patients treated with SABR, nervous system diseases

accounted for 44%, primary lung cancer for 24%, pulmonary metastases

for 11%, bone metastases for 15%, and others for 6%. In nervous system

diseases, benign diseases accounted for 23%, primary intracranial

meningiomas for 24%, brain metastases for 53%. Acoustic neuroma was

seen in patients with skull base and intracranial benign diseases (64%, 9 of

14). A total of 37 lesions were found in 32 patients with brain metastases.

There were 34 lesions in 33 primary lung cancer patients and there were 17

pulmonary metastases in 15 patients with primary extra-pulmonary tumor.

The median survival time for patients was not achieved. Treated diseases,

hypofractionated patterns, follow-up, selected adverse effects and effica-

cies are shown in the Table.

Conclusions: Stereotactic ablative radiation therapy (SABR) had a good

local control for relatively isolated lesions. The toxicities were low and

hypofractionated doses did not result in a loss in quality of life. SABR

ameliorated local tumor control and needed to be further study for long-

term outcomes in these entities.

Author Disclosure: J. Wang: None. T. Xia: None. L. Ma: None. B. Qu:

None. L. Pan: None. G. Zhou: None. Z. Ju: None. C. Xie: None. Y. Guo:

None.

1086WITHDRAWN

1087Understanding the Clinical Results From Contemporary StereotacticRadiation TherapyD.J. Brenner,1 I. Shuryak,1 D.J. Carlson,2 and J.M. Brown3; 1Center for

Radiological Research, Columbia University Medical Center, New York,

NY, 2Department of Therapeutic Radiology, Yale University School of

Medicine, New Haven, CT, 3Department of Radiation Oncology, Stanford

University, Stanford, CA

Purpose/Objective(s): Stereotactic radiation therapy (SRT, also referred

to as SRS, SBRT, or SABR) is rapidly becoming accepted practice for the

treatment of several common tumors. Typically SRT involves delivery of

one or a few large dose fractions in the range of 7 to 30 Gy per fraction.

Tumor control results to date are very encouraging. There are now suffi-

cient available SRT tumor-control (TCP) data to address two basic ques-

tions: First, is there clinical evidence of different radiotherapeutic

mechanisms at high SRT doses? Second, how do the clinical results with

single-fraction SRT compare with corresponding results from fractionated

SRT?

Materials/Methods: To date, the majority of published TCP data from

SRT are either for non small-cell lung cancer or for brain metastases. We

have analyzed all the amenable SRT data sets (totaling 40), including both

single- and multi-fraction studies, and fitted them separately and together

using the standard linear quadratic (LQ) model, as well as some semi-

empirical LQ model extensions.

Results: (1) The results show a monotonic increase in TCP as the bio-

logical effective dose (BED) increases (the reader is reminded that BED is

the physical dose modified to correct for the differing number of fractions

in different studies). (2) The data are consistent with the predictions of the

standard LQ model over the whole dose/BED range for which there are

data. The addition of extra high-dose terms to the standard LQ model does

not significantly improve agreement with the data in any dose range. (3)

The estimates of the LQ a/b parameter emerging from fitting the available

SRT TCP data are around 10 Gy, consistent with a/b values estimated from

conventional radiation therapy TCP data. (4) When all the single-fraction

data are analyzed together and compared with the combined multi-fraction

data, the single-fraction TCPs are significantly worse.

Conclusions: (1) The monotonic increase in TCP with BED implies that

there is little evidence from the clinical data for different radiotherapeutic

mechanisms at high SRT doses. We conclude that the success of SRT is

primarily due to the fact that the new SRT technologies allow the clinician

to prescribe very high tumor BEDs, which are simply not feasible with

conventional techniques. (2) Analyzed together, the multi-fraction TCP

data are statistically better than the single-fraction data. This is consistent

with expectations in the context of tumor hypoxia, in that fractionation

allows reoxygenation of hypoxic tumors, as analyzed in a recent study.

Author Disclosure: D.J. Brenner: None. I. Shuryak: None. D.J. Carlson:

None. J.M. Brown: None.

1088Stereotactic Ablative Body Radiation Therapy (SABR) to LymphNode Oligometastases: UK Experience and Clinical OutcomeC.S. Goldsmith, A. Gaya, and N. Plowman; Harley Street Clinic, London,

United Kingdom

Purpose/Objective(s): To report the toxicity and clinical outcome of

SABR delivered to lymph node oligometastases.

Materials/Methods: Between February 2009 and July 2012, 37 consecu-

tive patients with unresectable nodal metastases were treated with SABR

delivered by robotic radiosurgery. Median Disease-Free Interval Z 19

months. Median age Z 61. Of these patients, 29 (78%) had node-only

metastases, while 8 patients (22%) had dominant nodal lesions as part of

oligometastatic disease. A PET scan confirmed disease extent in 31

patients (84%). Fourteen (38%) had received prior conventional radiation

therapy to target nodal site. A total of 41 lymph node sites were treated:

Neck (nZ 3), Thorax (nZ 14), Abdomen (nZ 14), and Pelvis (nZ 10).

Histopathology of Primary: Colorectal (n Z 12), Breast (n Z 8),

Urological (n Z 6), Lung (n Z 4), Gynae (n Z 3), and Other/Unknown

primary (n Z 4). Median CTV-PTV margin Z 2 mm. The dose/frac-

tionation regimes used were 18 Gy single, 24-36 Gy in 3 fractions (BED

43-79 Gy10) and 35-47 Gy in 5 fractions (BED 60-91 Gy10). Dose was

prescribed to the median 66% isodose. 23 patients had fiducials inserted

(14 tracked with Synchrony), and 18 sites were tracked with spinal

tracking. Primary endpoint Z radiological progression at treatment site.

Secondary end-points included Progression Free Survival (PFS) and

Overall Survival (OS).

Results: Sixty-one percent of patients had no acute toxicity. Grade 1-2

toxicity was experienced by 34%, most commonly Grade 1 fatigue. There

was one case of grade 2 to grade 3 pain escalation in a disease progressor

following SABR to a pelvic lymph node metastasis. There were 2 cases of

Grade 3 late treatment-related toxicity. Both patients had received prior

conventional radiation therapy. Follow-up data was available at a median

follow-up 14 months. There was evidence of in-field disease progression in

5 sites giving a crude local control rate of 86%. Distant disease progression

was documented in 18 patients, translating to a Freedom from Distant

Disease Progression rate of 47%. Three patients have died, giving a crude

Overall Survival rate of 88%. Cause of death was disease progression in all

patients. Analysis by histopathology of primary showed a favorable

response in Colorectal Cancer patients with a Median progression-free

survival of 22 months.

Conclusions: SABR is a feasible and well-tolerated treatment for patients

with lymph node oligometastases. Local control rates in this series are very

good. Local Control rateZ 100% when SABR is prescribed to a threshold

BED of 72Gy10 (i.e., �36 Gy in 3 fractions, or �40 Gy in 5 fractions).

Colorectal histology is associated with a more favorable outcome (Median

Progression Free Survival Z 22 months).

Author Disclosure: C.S. Goldsmith: None. A. Gaya: None. N. Plowman:

None.

1089Initial Outcomes From a Single Institution Experience WithStereotactic Ablative Radiation Therapy (SABR) forOligometastasesR. Dagan, A.R. Yeung, R.A. Zlotecki, C.G. Morris, and P. Okunieff;

Department of Radiation Oncology, College of Medicine, University of

Florida, Gainesville, FL