Treatment planning strategy for whole-brain radiotherapy with hippocampal sparing and simultaneous integrated boost for multiple brain metastases using intensity-modulated arc therapy
Purpose: To retrospectively evaluate the accuracy, plan quality and efficiency of intensity-modulated arc therapy (IMAT) for hippocampal sparing whole-brain radiotherapy (HS-WBRT) with simultaneous integrated boost (SIB) in patients with multiple brain metastases (m-BM). Materials and methods: A total of 5 patients with m-BM were retrospectively replanned for HS-WBRT with SIB using IMAT treatment planning. The hippocampus was contoured on diagnostic T1-weighted magnetic resonance imaging (MRI) which had been fused with the planning CT image set. The hippocampal avoidance zone (HAZ) was generated using a 5-mm uniform margin around the paired hippocampi. The m-BM planning target volumes (PTVs) were contoured on T1/T2-weighted MRI registered with the 3D planning computed tomography (CT). The whole-brain planning target volume (WB-PTV) was defined as the whole-brain tissue volume minus HAZ and m-BM PTVs. Highly conformal IMAT plans were generated in the Eclipse treatment planning system for Novalis-TX linear accelerator consisting of high-definition multileaf collimators (HD-MLCs: 2.5-mm leaf width at isocenter) and 6-MV beam. Prescription dose was 30 Gy for WB-PTV and 45 Gy for each m-BM in 10 fractions. Three full coplanar arcs with orbit avoidance sectors were used. Treatment plans were evaluated using homogeneity (HI) and conformity indices (CI) for target coverage and dose to organs at risk (OAR). Dose delivery efficiency and accuracy of each IMAT plan was assessed via quality assurance (QA) with a MapCHECK device. Actual beam-on time was recorded and a gamma index was used to compare dose agreement between the planned and measured doses. Results: All 5 HS-WBRT with SIB plans met WB-PTV D{sub 2%}, D{sub 98%}, and V{sub 30} {sub Gy} NRG-CC001 requirements. The plans demonstrated highly conformal and homogenous coverage of the WB-PTV with mean HI and CI values of 0.33 ± 0.04 (range: 0.27 to 0.36), and 0.96 ± 0.01 (range: 0.95 to 0.97), respectively. All 5 hippocampal sparing patients met protocol guidelines with maximum dose and dose to 100% of hippocampus (D{sub 100%}) less than 16 and 9 Gy, respectively. The dose to the optic apparatus was kept below protocol guidelines for all 5 patients. Highly conformal and homogenous radiosurgical dose distributions were achieved for all 5 patients with a total of 33 brain metastases. The m-BM PTVs had a mean HI = 0.09 ± 0.02 (range: 0.07 to 0.19) and a mean CI = 1.02 ± 0.06 (range: 0.93 to 1.2). The total number of monitor units (MU) was, on average, 1677 ± 166. The average beam-on time was 4.1 ± 0.4 minute . The IMAT plans demonstrated accurate dose delivery of 95.2 ± 0.6%, on average, for clinical gamma passing rate with 2%/2-mm criteria and 98.5 ± 0.9%, on average, with 3%/3-mm criteria. Conclusions: All hippocampal sparing plans were considered clinically acceptable per NRG-CC001 dosimetric compliance criteria. IMAT planning provided highly conformal and homogenous dose distributions for the WB-PTV and m-BM PTVs with lower doses to OAR such as the hippocampus. These results suggest that HS-WBRT with SIB is a clinically feasible, fast, and effective treatment option for patients with a relatively large numbers of m-BM lesions.
- OSTI ID:
- 22685167
- Journal Information:
- Medical Dosimetry, Vol. 41, Issue 4; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0958-3947
- Country of Publication:
- United States
- Language:
- English
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62 RADIOLOGY AND NUCLEAR MEDICINE
ANIMAL TISSUES
AVOIDANCE
BEAMS
COLLIMATORS
COMPARATIVE EVALUATIONS
COMPLIANCE
COMPUTERIZED TOMOGRAPHY
HEAT AFFECTED ZONE
HIPPOCAMPUS
LINEAR ACCELERATORS
METASTASES
NMR IMAGING
PATIENTS
PLANNING
QUALITY ASSURANCE
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIOTHERAPY
RECOMMENDATIONS
QUALITY MANAGEMENT