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A Dosimetric Comparison Between Multiple Junction Shifts and Single Gradient Dose Junction for Craniospinal Irradiation (CSI)

A Hadley

A Hadley*, G Ding, Vanderbilt University, Nashville, TN

SU-E-T-599 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the impact of patient treatment setup errors on the dose distributions between multiple junction shifts and a single gradient dose junction for craniospinal irradiation (CSI).
Methods: Conventionally, two lateral brain fields and a posterior spine field are used for CSI. A weekly 1cm shift of the field junction is used to reduce the hot/cold spots due to patient positioning errors. This study retrospectively investigates the use of a single gradient dose falloff junction between two lateral brain fields and a posterior spine field. These fields were extended to allow for minimum 3cm overlap at the brain and spine junction. The dose gradient at the junction is achieved using IMRT and planned using Eclipse System (v10) . Optimization was set to create a gradient dose falloff from each contributing field throughout the overlapped area. The impact of patient positioning setup errors on the dose distributions for both techniques were simulated by applying shifts of +/- 3 and 5mm. The resulting dose profiles across the field junction for both techniques were calculated and compared. For the conventional plan, the dose profiles were calculated over the sum of the fractionation to include the effects from the weekly 1cm shift.
Results: Systematic positioning errors throughout the course of treatment resulted in comparable hot/cold spots for both the gradient (112.7%/85.7% 3mm; 116.2%/80.2% 5mm) and conventional (115.2%/84.1% 3mm; 119.2%/81.9% 5mm) techniques. In most cases, the gradient technique provided slightly better uniformity in dosimetry. A single fraction positioning error provided significantly larger hot/cold spots in the conventional technique compared to the gradient technique.
Conclusion: The advantages of the single gradient dose junction technique include improved single fraction dose uniformity and one plan for the entire treatment course, which reduces the possibility of human error compared to delivering the conventional four shifted plans.

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