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Feasibility of hybrid TomoHelical- and TomoDirect-based volumetric gradient matching technique for total body irradiation

 Chae-Seon Hong  ;  Min-Joo Kim  ;  Jihun Kim  ;  Kyung Hwan Chang  ;  Kwangwoo Park  ;  Dong Wook Kim  ;  Min Cheol Han  ;  Hong In Yoon  ;  Jin Sung Kim  ;  Ho Lee 
 RADIATION ONCOLOGY, Vol.14 : 233, 2019 
Journal Title
Issue Date
Total body irradiation ; Tomotherapy ; TomoHelical ; TomoDirect ; Field junction ; Dose gradient ; Setup error
Background: Tomotherapy-based total body irradiation (TBI) is performed using the head-first position (HFP) and
feet-first position (FFP) due to treatment length exceeding the 135 cm limit. To reduce the dosimetric variation at
the match lines, we propose and verify a volumetric gradient matching technique (VGMT) by combining
TomoHelical (TH) and TomoDirect (TD) modes.
Methods: Two planning CT image sets were acquired with HFP and FFP using 15 × 55 × 18 cm3 of solid water
phantom. Planning target volume (PTV) was divided into upper, lower, and gradient volumes. The junction
comprised 2-cm thick five and seven gradient volumes (5-GVs and 7-GVs) to create a dose distribution with a
gentle slope. TH-IMRT and TD-IMRT plans were generated with 5-GVs and 7-GVs. The setup error in the calculated
dose was assessed by shifting dose distribution of the FFP plan by 5, 10, 15, and 20 mm in the longitudinal
direction and comparing it with the original. Doses for 95% (D95) and 5% of the PTV (D5) were calculated for all
simulated setup error plans. Absolute dose measurements were performed using an ionization chamber in the
Results: The TH&TD plan produced a linear gradient in junction volume, comparable to that of the TH&TH plan. D5
of the PTV was 110% of the prescribed dose when the FFP plan was shifted 0.7 cm and 1.2 cm in the superior
direction for 5-GVs and 7-GVs. D95 of the PTV decreased to < 90% of the prescribed dose when the FF plan was
shifted 1.1 cm and 1.3 cm in the inferior direction for 5-GVs and 7-GVs. The absolute measured dose showed a
good correlation with the calculated dose in the gradient junction volume. The average percent difference (±SD) in
all measured points was − 0.7 ± 1.6%, and the average dose variations between depths was − 0.18 ± 1.07%.
Conclusion: VGMT can create a linear dose gradient across the junction area in both TH&TH and TH&TD and can
minimize the dose sensitivity to longitudinal setup errors in tomotherapy-based TBI.
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Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
Yonsei Authors
Kim, Dong Wook(김동욱) ORCID logo https://orcid.org/0000-0002-5819-9783
Kim, Jihun(김지훈) ORCID logo https://orcid.org/0000-0003-4856-6305
Kim, Jinsung(김진성) ORCID logo https://orcid.org/0000-0003-1415-6471
Park, Kwang Woo(박광우) ORCID logo https://orcid.org/0000-0002-9843-7985
Yoon, Hong In(윤홍인) ORCID logo https://orcid.org/0000-0002-2106-6856
Lee, Ho(이호) ORCID logo https://orcid.org/0000-0001-5773-6893
Chang, Kyung Hwan(장경환)
Han, Min Cheol(한민철)
Hong, Chae-Seon(홍채선) ORCID logo https://orcid.org/0000-0001-9120-6132
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