Assessment of multi-criteria optimization (MCO) for volumetric modulated arc therapy (VMAT) in hippocampal avoidance whole brain radiation therapy (HA-WBRT).

This study compared the dosimetric performance of (a) volumetric modulated arc therapy (VMAT) with standard optimization (STD) and (b) multi-criteria optimization (MCO) to (c) intensity modulated radiation therapy (IMRT) with MCO for hippocampal avoidance whole brain radiation therapy (HA-WBRT) in RayStation treatment planning system (TPS). Ten HA-WBRT patients previously treated with MCO-IMRT or MCO-VMAT on an Elekta Infinity accelerator with Agility multileaf collimators (5-mm leaves) were re-planned for the other two modalities. All patients received 30 Gy in 15 fractions to the planning target volume (PTV), namely, PTV30 expanded with a 2-mm margin from the whole brain excluding hippocampus with margin. The patients all had metastatic lesions (up to 12) of variable sizes and proximity to the hippocampus, treated with an additional 7.5 Gy from a simultaneous integrated boost (SIB) to PTV37.5. The IMRT plans used eight to eleven non-coplanar fields, whereas the VMAT plans used two coplanar full arcs and a vertex half arc. The averaged target coverage, dose to organs-at-risk (OARs) and monitor unit provided by the three modalities were compared, and a Wilcoxon signed-rank test was performed. MCO-VMAT provided statistically significant reduction of D100 of hippocampus compared to STD-VMAT, and Dmax of cochleas compared to MCO-IMRT. With statistical significance, MCO-VMAT improved V30 of PTV30 by 14.2% and 4.8%, respectively, compared to MCO-IMRT and STD-VMAT. It also raised D95 of PTV37.5 by 0.4 Gy compared to both MCO-IMRT and STD-VMAT. Improved plan quality parameters such as a decrease in overall plan Dmax and total monitor units (MU) were also observed for MCO-VMAT. MCO-VMAT is found to be the optimal modality for HA-WBRT in terms of PTV coverage, OAR sparing and delivery efficiency, compared to MCO-IMRT or STD-VMAT.

Zieminski S ，Khandekar M ，Wang Y 《Journal of Applied Clinical Medical Physics》

Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

Pokhrel D ，Sood S ，Lominska C ，Kumar P ，Badkul R ，Jiang H ，Wang F ... -  《Journal of Applied Clinical Medical Physics》

Volumetric modulated arc therapy (VMAT) for hippocampal-avoidance whole brain radiation therapy: planning comparison with Dual-arc and Split-arc partial-field techniques.

Yuen AHL ，Wu PM ，Li AKL ，Mak PCY ... -  《Radiation Oncology》

Treatment planning strategy for whole-brain radiotherapy with hippocampal sparing and simultaneous integrated boost for multiple brain metastases using intensity-modulated arc therapy.

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). 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 30Gy for WB-PTV and 45Gy 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. All 5 HS-WBRT with SIB plans met WB-PTV D2%, D98%, and V30Gy 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 (D100%) less than 16 and 9Gy, 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. 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.

Pokhrel D ，Sood S ，McClinton C ，Shen X ，Lominska C ，Saleh H ，Badkul R ，Jiang H ，Mitchell M ，Wang F ... -  《-》

Dosimetric evaluation of four whole brain radiation therapy approaches with hippocampus and inner ear avoidance and simultaneous integrated boost for limited brain metastases.

Jiang A ，Sun W ，Zhao F ，Wu Z ，Shang D ，Yu Q ，Wang S ，Zhu J ，Yang F ，Yuan S ... -  《Radiation Oncology》