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. 2020 Apr 13;11(14):4166-4172.
doi: 10.7150/jca.41102. eCollection 2020.

Improving stereotactic radiotherapy (SRT) planning process for brain metastases by Cyberknife system: reducing dose distribution in healthy tissues

Yu Xuyao  1 , Yuan Zhiyong  1 , Wang Yuwen  1 , Yu Hui  2 , Song Yongchun  1 , Dong Yang  1 , Zhao LuJun  1 , Wang Ping  1
Affiliations

Improving stereotactic radiotherapy (SRT) planning process for brain metastases by Cyberknife system: reducing dose distribution in healthy tissues

Yu Xuyao et al. J Cancer. .

Abstract

Purpose: To pursue high precision dose in lesions and steeper dose fall-off in healthy tissues of brain metastases stereotactic radiotherapy (SRT), this study investigated an opitimized planning by comparison different prescription dose line in the treatment of brain metastases using Cyberknife (CK) Robotic Radiosurgery System. Methods: 77 patients (92 lesions) brain metastases patients CK SRT plans were replanned with 50%-80% (5% internal) prescription dose line to cover more than 95% of the planned target volume (PTV), under the same collimator by Multiplan System. Under the precondition of guaranteeing plans all meet the clinical requirements, the plan evaluation paraments (conformal index (CI) and homogeneity index (HI)), plan treatment time parameters (the total number of beams and monitor units (MU)) and dose distribution of organs at risk (OAR) and healthy brain tissues adjacent to the PTV were analyzed respectively. Resluts: Compared with 70% plans, 65% plans had: 1) average dose (Dmean ) and maximum dose (Dmax ) of healthy brain tissue outside of the PTV reduced 11.83% and 5.97% markedly; 2) Dmean and Dmax of brainstem decreased 11.43% and 2.86%; 3) the volumes of whole brain minus the tumors received a single dose equivalence of 12 Gy/14 Gy (V12Gy/V14Gy) had marked decline. The dose fall-off was considerably faster in the 60%-65% plans around the PTV and the maximum dose of healthy tissue was prominently lower. While the difference in CI and HI between different plans was not obvious, the plan treatment time was a little higher in 60%-65% plans than 70%-80% plans. Conclusions: Choosing a relatively lower isodose as the prescription dose line for brain metastases CK SRT planing could improve the dosimetry index of target and immensely reduce high dose in healthy brain tissue and OAR.

Keywords: CyberKnife; brain metastases; prescription dose line; stereotactic radiotherapy; treatment plan.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interest exists.

Figures

Figure 1
Figure 1
Different CK SRT plans for brain metastases patients. The representative patient had axial images taken, (A) and (D) were Patient 1 with metastases in the right lateral ventricle and Patient 2 with brainstem metastases. The red and purple lines area indicate the GTV and the PTV, respectively. Blue, orange and yellow lines represent Brainstem, Optic Nerves, and Eyes, respectively. (B) and (E) represent 50% prescription isodose covered more than 95% of the Patient 1 PTV and Patient 2 GTV (Plan_50%). (C) and (F) represent 80% prescription isodose covered more than 95% of the Patient 1 PTV or Patient 2 GTV (Plan_80%).Green line zones were covered 6-mm thick healthy brain tissue adjacent to the PTV or the GTV.
Figure 2
Figure 2
PTV+2, PTV+6 and brainstem dose volume histogram (DVH) of patient 2 with brainstem metastases. (A) and (B) were dosimetry distribution of 2-mm-thick and 6-mm-thick healthy brain tissue adjacent to the PTV. (C) was the dosimetry distribution of Brainstem.
Figure 3
Figure 3
The dosimetry distribution of the whole brain tissue in different plans for the same patients. (A) and (B) were the volume of healthy brain tissue received 12 Gy/14 Gy (V12Gy/V14Gy) in a single fraction.
See this image and copyright information in PMC

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