International Journal of Radiation Oncology*Biology*Physics
Physics ContributionHelical Tomotherapy for Whole-Brain Irradiation With Integrated Boost to Multiple Brain Metastases: Evaluation of Dose Distribution Characteristics and Comparison With Alternative Techniques
Introduction
Population-based data reveal that symptomatic brain metastases develop in about 10% of cancer patients (1). Whole-brain radiation therapy (WBRT) is considered the standard treatment for patients with multiple (>3) brain metastases with a 1-year lesion control of 0% to 71% 2, 3. Stereotactic radiosurgery (RS) in addition to WBRT improves lesion control and enhances survival in patients with 1 metastasis (3). Also, for 1 to 4 metastases, WBRT combined with RS can increase intracranial lesion control (4). However, a survival benefit was not observed.
Multiple brain metastases still present a significant problem. Radiotherapeutic options include conventional fractionated WBRT, radiosurgery, or combinations of both 2, 3. Radiosurgery allows the delivery of a single high-dose fraction with highest precision, but it is restricted to few 1, 2, 3, 4 and small (<3-3.5 cm in diameter) metastases. Recently developed advanced radiation therapy techniques such as helical tomotherapy (HT) (5) enable a dose-escalated treatment compared with WBRT alone by combining WBRT with a highly conformal boost dose to the metastases in 1 treatment session 6, 7
Our group initiated a prospective phase 2 randomized clinical trial (Tomo-0701) to assess the therapeutic efficacy and safety of HT to deliver WBRT (10 × 3 Gy) with integrated boost (IB, 10 × 5 Gy) to 2 to 10 metastases as opposed to conventional WBRT. Patient recruitment started in April 2009. Here we report the treatment technique, focusing on the quantitative evaluation of the achieved dose distributions in terms of dose conformity, target coverage, and homogeneity. A systematic literature review was performed to compare the results with established RS techniques, considered the gold standard to treat single or oligo brain metastases, and with alternative approaches to deliver WBRT combined with either IB or sequential boost (SB).
Section snippets
Patient dataset
The analyzed dataset included 13 patients randomized into the HT arm of trial Tomo-0701 plus 10 additional patients who were treated with the same HT technique before the trial was opened. Included were patients with 4 to 10 metastases 3 to 40 mm in diameter and patients with 2 or 3 metastases not suited for RS.
Treatment planning
Treatment planning was based on kilovoltage computed tomography (CT) datasets with 1.5 to 2 mm slice thickness. Contouring was performed in the 3-dimensional treatment planning system
General plan characteristics
The total number of metastases in 23 patients was 81. The mean values ± standard deviation of Nmets, PTVmets, and PTVind met were 3.5 ± 1.6 (median, 3; range, 2-8), 8.7 ± 8.9 cm3 (median, 4.32 cm3; range, 1.3-35.5 cm3), and 2.5 ± 4.5 cm3 (median, 0.85 cm3; range, 0.19-24.7 cm3), respectively.
The standard parameter combination FW = 2.5 cm/pitch = 0.215/MF = 3 gave beam-on times of 10.1-14.5 minutes (mean, 12.5 ± 1 min; median, 12.7 min), which were well tolerated by all patients. The plan of the
Discussion
The quantitative evaluation of dose distribution characteristics in comparison with published values for alternative techniques has demonstrated that HT is well suited to deliver WBRT with IB to multiple brain metastases.
Conclusion
HT is a particularly suited technique to deliver WBRT with IB to patients with multiple brain metastases, yielding high-quality dose distributions that compare favorably with the majority of alternative techniques. The clinical benefit of the treatment concept is currently evaluated in a multi-institutional prospective randomized phase 2 clinical trial.
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Cited by (0)
Supported by Grant No. STU-151/9-1 from the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG).
Conflict of interest: none.