P05.25 Helical tomotherapy for whole- brain irradiation with integrated boost to multiple brain metastases: dosimetric analysisandclinical outcomes

Abstract

Background

A retrospective study was conducted to analyze the dose distribution characteristics, and to evaluate the feasibility and toxicities of whole brain radiation (WBRT) with simultaneously integrated boost (SIB) by helical tomotherapy (HT) in the treatment of multiple brain metastases (BMs).

Material and Methods

From 2014 to 2017, 43 patients with three or more BMs were analyzed. WBRT was delivered with 40 Gy in 20 fractions and SIB was 60 Gy in 20 fractions by HT. For some BMs larger than 6 cm3, gross tumor volume (GTV) was contracted by 2 mm to create Boost, which was given 66 to 70 Gy simultaneously. BMs located in brainstem were given 50 Gy in 20 fractions. Patients were reevaluated by magnetic resonance imaging (MRI) after 13 to 15 fractions. The radiation field would be shrunk if the gross target volume (GTV) was reduced. Target Coverage (TC), conformation index (CI), prescription isodose/ target volume ratio (PITV) and homogeneity index (HI) was accessed. Clinical endpoints included local recurrence- free survival (LRFS), intracranial progresstion- free survival (IPFS), progression- free survival (PFS), overall survival (OS) and toxicities.

Results

The median age was 61 (36- 81) years old. The median lesion number was 6 (3- 36) and median total volume of GTV was 8.74 cc (0.37- 120.3 cc). Median Dmean of GTV was 63.1 Gy (50.2- 72.6 Gy). There were 9 lesions located in brainstem, which received median dose of 52.5 Gy (51.3- 53.3 Gy). Seventeen large BMs received simultaneously boost, with median volume of 12.15 (6.79- 34.18) cm3. Mean ± standard deviation for GTV amounted to TC was 0.96 ± 0.028, CI 0.51 ± 0.164, PITV 2.09 ± 1.245, and HI 0.12 ± 0.066, respectively. TC and HI for whole brain were 0.95 ± 0.033 and 0.43 ± 0.161, respectively. 25.6% of patients got re-planned and the dose of normal tissue reduced. The median follow-up time was 14.4 months (2.0- 40.9 months). One-year LRFS, IPFS, PFS and OS were 95.7%,79.9%,39.4% and 85.6%, respectively. There were no grade 3- 5 toxicities.

Conclusion

Helical tomotherapy for WBRT and SIB shows excellent conformity and homogeneity, and it's efficient and safe for patients with multiple BMs. Lesions that get shrunk during treatment should be re-planned to reduce the dose of normal tissue.