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. 2021 May;22(5):15-23.
doi: 10.1002/acm2.13217. Epub 2021 Apr 7.

Treatment planning of volumetric modulated arc therapy and positioning optimization for hippocampal-avoidance prophylactic cranial irradiation

Qi Fu  1 , Deqi Chen  1 , Hui Yan  1 , Jiayun Chen  1 , Ji Zhu  1 , Lingling Yan  1 , Yingjie Xu  1 , Lei Deng  1 , Kuo Men  1 , Jianrong Dai  1
Affiliations

Treatment planning of volumetric modulated arc therapy and positioning optimization for hippocampal-avoidance prophylactic cranial irradiation

Qi Fu et al. J Appl Clin Med Phys. 2021 May.

Abstract

Background: Hippocampal-avoidance prophylactic cranial irradiation (HA-PCI) offers potential neurocognitive benefits but raises technical challenges to treatment planning. This study aims to improve the conventional planning method using volumetric modulated arc therapy (VMAT) technique and investigate a better patient's head positioning to achieve a high quality of HA-PCI treatment plans.

Methods: The improved planning method set a wide expansion of hippocampus as a special region for dose decline. The whole brain target was divided into two parts according to whether the slice included hippocampus and their optimization objectives were set separately. Four coplanar full arcs with partial field sizes were employed to deliver radiation dose to different parts of the target. The collimator angle for all arcs was 90°. Tilting patient's head was achieved by rotating CT images. The improved planning method and tilted head positioning were verified using datasets from 16 patients previously treated with HA-PCI using helical tomotherapy (HT).

Results: For the improved VMAT plans, the max and mean doses to hippocampus were 7.88 Gy and 6.32 Gy, respectively, significantly lower than those for the conventional VMAT plans (P < 0.001). Meanwhile, the improved planning method significantly improved the plan quality. Compared to the HT plans, the improved VMAT plans result in similar mean dose to hippocampus (P > 0.1) but lower max dose (P < 0.02). Besides, the target coverage was the highest for the improved VMAT plans. The tilted head positioning further reduced the max and mean doses to hippocampus (P < 0.05), significantly decreased the max dose to lens (P < 0.001) and resulted in higher plan quality as compared to nontilted head positioning.

Conclusions: The improved planning method enables the VMAT plans to meet the clinical requirements of HA-PCI treatment with high plan quality and convenience. The tilted head positioning provides superior dosimetric advantages over the nontilted head positioning, which is recommended for clinical application.

Keywords: helical tomotherapy; hippocampus; prophylactic cranial irradiation; volumetric modulated arc therapy.

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Conflict of interest statement

No conflicts of interest.

Figures

Fig. 1
Fig. 1
Axial and sagittal CT images showing hippocampus (red), hippocampus PRV (cyan line), PTV_plan1 (green), PTV_plan2 (blue), dose decline region (yellow), ring PRV (pink), and ring PTV (orange).
Fig. 2
Fig. 2
Beam's eye view (BEV) at 270° showing field sizes of Arc 1 (yellow), Arc 2 and 3 (red), and Arc 4 (blue).
Fig. 3
Fig. 3
BEV at 270° for nontilted (a) and tilted (b) head positionings, with a collimator angle of 90°. PTV is shown in gray, hippocampus in red, eyeballs in blue.
Fig. 4
Fig. 4
Dose distributions of the conventional VMAT plans (a), the HT plans (b), and the improved VMAT plans with nontilted positioning (c) and tilted head positioning (d). Hippocampus is shown in red.
Fig. 5
Fig. 5
Dose–volume histogram of the conventional VMAT plans (a), the HT plans (b), and the improved VMAT plans with nontilted positioning (c) and tilted head positioning (d).
Fig. 6
Fig. 6
Examples of BEV with collimator angles of 0° (a) and 90° (b). PTV_plan1 is shown in green, PTV_plan2 in blue, hippocampus in red, eyeballs in purple.
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