Field Junction Technique for Total Body Irradiation Using Tomotherapy with TomoDirect Mode
Y Suetsugu1*, N Higashi2, Y Fukuyama3, K Inoue1, K Matsumoto4, H Terashima2, T Sasaki1, (1) Kyushu Univ. , Fukuoka-shi, Fukuoka-ken, JP, (2) Harasanshin Hosp. , Fukuoka-shi, Fukuoka-ken, JP, (3) Fukuoka Tokushukai Hosp. , Kasuga-shi, Fukuoka-ken, JP , (4) Kurume Univ. Hosp. , Kurume-shi, Fukuoka-ken, JP
Presentations
PO-GePV-T-318 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: The present study aims to verify the dose distribution of the field junction region using a volumetric gradient matching technique (VGMT) with TomoDirect (TD) mode.
Methods: Two planning CT image sets were acquired with the head first position (HFP) and feet first position (FFP) using two solid water phantoms mimicked the thighs. Planning target volume was divided into upper, lower and gradient volumes. The junction region was comprised of one 2.5 cm and four 2 cm thick gradient volumes to create descending slope dose distribution. TD plans were generated with 12 and 4 ports for HFP and FFP plans, respectively. Gafchromic film placed at the central coronal plane and measured dose profile was obtained. Dose verification, especially in the junction area, was performed by shifting deliberately the position of the FFP plan by 0.5, 1.0, and 1.5 cm in the superior and inferior direction. Absolute dose measurements were performed at 3 points for respectively HFP and FFP plans using ionization chamber at the matching plane.
Results: The TD plans produced a linear gradient in junction region. An optimum alignment of both HFP and FFP leads to a relatively constant dose profile. Relative dose deviations via film dosimetry of 6.5%, 11.1%, 17.2% and 11.7%, 15.1%, 16.9% were observed for 0.5, 1.0, and 1.5 cm setup errors in the superior and inferior direction, respectively. The absolute measured dose showed a good correlation with the calculated dose in the gradient junction except for 1 out of 6 measured points. The average percent difference (±SD) in five points was + 1.9 ± 2.1%.
Conclusion: VGMT with TD enables to create a linear dose gradient across the junction region and reduce the impact of longitudinal setup error on dose distribution.
Keywords
TBI, Tomotherapy, Treatment Techniques
Taxonomy
TH- External Beam- Photons: tomotherapy
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