Radiosurgery dose and target volume

As noted in the two studies below, using a high enough dose and adequate margin around the lesion should push the local control rate up to about 90%

Radiosurgery for brain metastasis: impact of CTV on local control.

Noel G, Simon JM, Valery CA, Cornu P, Boisserie G, Hasboun D, Ledu D, Tep B, Delattre JY, Marsault C, Baillet F, Mazeron JJ. Radiother Oncol. 2003 Jul;68(1):15-21.

Department of Radiation Oncology, Groupe Pitie-Salpetriere, Assistance Publique-Hopitaux de Paris,

PURPOSE: The purpose of the present analysis was to assess whether adding a 1 mm margin to the gross tumour volume (GTV) improves the control rate of brain metastasis treated with radiosurgery (RS).PATIENTS AND METHODS: All the patients had one or two brain metastases, 30 mm or less in diameter, and only one isocentre was used for RS. There were 23 females and 38 males. The median age was 54 years (34-76). The median Karnofsky performance status was 80 (60-100). At the time of RS, 23 patients had no evidence of extracranial disease and 38 had a progressive systemic disease. Thirty-eight patients were treated up-front with only RS. Twenty-three patients were treated for relapse or progression more than 2 months after whole brain radiotherapy. From January 1994 to July 1995, clinical target volume (CTV) was equal to GTV without any margin (33 metastases). From August 1995 to August 2000, CTV was defined as GTV plus a 1 mm margin (45 metastases). A dose of 20Gy was prescribed to the isocentre and 14Gy at the margin of CTV.RESULTS: The median follow-up was 10.5 months (1-45). The mean minimum dose delivered to GTV was 14.6Gy in the group without a margin and 16.8Gy in the group with a 1 mm margin (P<0.0001). The response of 11 metastases was never assessed because patients died before the first follow-up. Ten metastases recurred, eight in the group treated without a margin and two in the group treated with a 1 mm margin (P=0.01). Two-year local control rates were 50.7+/-12.7% and 89.7+/-7.4% (P=0.008), respectively. Univariate analysis showed that the treatment group (P=0.008) and the tumour volume (P=0.009) were prognostic factors for local control. In multivariate analysis, only the treatment group with a 1 mm margin was an independent prognostic factor for local control (P=0.04, RR: 5.8, 95% CI [1.08-31.13]). There were no significant differences, either in overall survival rate or in early and late side effects, between the two groups. CONCLUSION: Adding a 1 mm margin to the GTV in patients treated with RS significantly improves the probability of metastasis control without increasing the side effect

Dose-response relationships for radiotherapy of brain metastases: role of intermediate-dose stereotactic radiosurgery plus whole-brain radiotherapy.

Nieder C, Nestle U, Walter K, Niewald M, Schnabel K. Am J Clin Oncol. 2000 Dec;23(6):584-8.

Department of Radiotherapy, The Saarland University Hospital, Homburg/Saar, Germany.

The effects of intermediate-dose radiotherapy consisting of whole-brain radiotherapy (WBRT, 10 fractions of 3 Gy) plus stereotactic radiosurgery (SRS) were studied prospectively. Twenty-five adult patients with 31 brain metastases received WBRT plus linear accelerator (LINAC)-based single dose SRS with fixed treatment parameters (10 Gy at the isocenter, target volume enclosed by the 90% isodose). Median age was 63 years, median Karnofsky performance status 80%, and median diameter of brain metastases 2.4 cm. Fifteen patients had non-small-cell lung cancer. Because of some early deaths, only 26 lesions could be evaluated for response. We observed 1 complete and 15 partial remissions. Median time to progression inside or outside the SRS volume was 4.5 months. Actuarial local control of SRS-treated lesions was 61% at 1 year. At that time, only 37% of patients were free from new lesions outside the SRS volume. Median survival and cause-specific survival were 2.3 and 4.5 months, respectively (1-year survival rate 8% and 21%). Ten patients died of progressive brain metastases, 13 from extracranial disease progression (unknown cause of death in 2 cases). Comparable to SRS studies with higher doses, the majority of brain failures occurred outside the SRS volume and more patients died of extracranial progression than of uncontrolled brain metastases. Failure to improve survival can be explained by the high percentage of patients with extracranial metastases (52%). However, the present results appear less favorable than those of previous studies of SRS with 15 Gy to 16 Gy (1-year actuarial local control rates of 66-89%). Therefore, we recommend SRS with 15 Gy to 16 Gy for patients whose favorable prognostic factors justify a boost after WBRT.