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Med Dosim. 2019 Feb 6. pii: S0958-3947(19)30010-X. doi: 10.1016/j.meddos.2019.01.001. [Epub ahead of print]

Monte Carlo dose verification for a single-isocenter VMAT plan in multiple brain metastases.

Author information

1
Graduate School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, 862-0976, Japan.
2
Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, 862-0976, Japan. Electronic address: f_araki@kumamoto-u.ac.jp.
3
Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, 862-0976, Japan.
4
Varian Medical Systems, K.K. Kabutocho Heiwa Bldg. No.1, 5-1 Nihonbashi-Kabutocho Chuo-ku, Tokyo, 103-0026, Japan.
5
Ion Beam Therapy Center, SAGA HIMAT Foundation, 1-802-3, Hondori-machi, Tosu, Saga 841-0033, Japan.

Abstract

The purpose of this study was to verify the accuracy of dose calculation algorithms of a treatment planning system for a single-isocenter volumetric modulated arc therapy (VMAT) plan in multiple brain metastases, by comparing the dose distributions of treatment planning system with those of Monte Carlo (MC) simulations. We used a multitarget phantom containing 9 acrylic balls with a diameter of 15.9 mm inside a Lucy phantom measuring 17 × 17 × 17 cm3. Seven VMAT plans were created using the multitarget phantom: 1 multitarget plan (MTP) and 6 single target plans (STP). Three of the STP plans had a large jaw field setting, almost equivalent to that of the MTP, while the other plans had a jaw field setting fitted to each planning target volume. The isocenter for all VMAT plans was set to the center of the phantom. The VMAT dose distributions were calculated using the analytical anisotropic algorithm (AAA) and were also recalculated through Acuros XB (AXB) and MC simulations under the same irradiation conditions. The AAA and AXB methods tended to overestimate dosage compared with the MC method in the MTP and in STPs with large jaw field settings. The dose distribution in single-isocenter VMAT plans for multiple brain metastases was influenced by jaw field settings. Finally, we concluded that MC-VMAT dose calculations are useful for 3D dose verification of single-isocenter VMAT plans for multiple brain metastases.

KEYWORDS:

Dose calculation algorithm; Monte Carlo method; Multiple brain metastases; Three-dimensional gamma analysis; Volumetric modulated arc therapy

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