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Mathematical Formulation of Gantry Starting Angle for Right Medial Tangential Arc in Left Intact Partial Breast Irradiation Using Volumetric Modulated Arc Therapy (VMAT)

U Giri

U Giri*, B Sarkar , H Kaur , T Ganesh , A Munshi , B Mohanti , Fortis Memorial Research Institute, Gurgaon, Haryana


SU-F-T-414 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To choose appropriate gantry starting angle for partial left breast irradiation using volumetric modulated arc therapy (VMAT).

Methods: A random patient of left breast carcinoma was selected for this study. The slice which was selected for this mathematical formulation was having maximum breast thickness and maximum medial and lateral tangential distance. After this appropriate isocenter was chosen on that CT slice. The distances between various points were measured by the measuring tool in Monaco 5.00.04. Using the various trigonometric equations, a final equation was derived which shows the relationship between Gantry start angle, isocenter Location and tissue thickness.

Results: The final equation for gantry start for right medial tangential arc is given as
Starting angle = 270°+tan^(-1)(sin(θ)/(x_1/x_2 +cosθ ))
The above equation was tested for 10 cases and it was found to be appropriate for all the cases.

Conclusion: Gantry starting angle for partial arc irradiation depends upon Breast thickness, Distance between Medial and lateral tangent and isocenter location.

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