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Comparison of the Dosimetric Efficacy of Helical Dynamic Jaw Vs. Fixed Jaw of TomoTherapy HDA

E Han

E Han1*, D Kim2 , X Zhang1 , X Liang1 , A Wurtz1 , M Hardee1 , J Penagaricano1 , R Vaneerat1 , S Morrill1 , (1) University of Arkansas Medical Science, Little Rock, AR, (2) Kyung Hee University International Med. Serv., Seoul


SU-E-T-83 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:One of the advanced features of Tomotherapy HDA is that the jaws move dynamically at the cephalocaudal ends of the target to make shaper dose fall-off. The purpose of this project is to determine the dosimetric efficacy of volumetric dose shaping using dynamic jaw vs. fixed jaw.
Methods:To evaluate the improvement offered by dynamic jaw collimation, five different cases were planned using both dynamic and fixed jaw collimation. Dose profiles and statistics for PTV and OARs were compared for each treatment site. The treatment plans were then delivered to a PTW 2D array and to a SunNuclear ArcCheck for volumetric dose comparison. The total delivered dose of one patient plan using dynamic jaw was reconstructed based on MVCTs of Tomotherapy and compared with the original plan by Tomotherapy Plan Adaptive. Plans using different jaw sizes and total treatment time from dynamic jaw vs. fixed jaw were dosimetrically evaluated.
Results:Cephalocaudal dose profiles using dynamic jaw vs. fixed jaw show large differences but the lateral dose profiles are similar. A plan using dynamic jaw reduced mean doses to spinal cord(42.6%), kidney(42.7%), liver(60.4%) and bowel(51%) comparing to a plan with fixed jaw while the PTV dose coverage is similar. The largest dose discrepancy occurs when comparing plans with 5cm dynamic jaws vs. 5cm fixed jaws. The 2.5cm dynamic jaw produced the sharpest dose fall off. Plans using the 5cm dynamic Jaw can produce better yet similar results compared to the plan using 2.5cm fixed jaw. There were no significant differences between the reconstructed delivered doses vs. dose from the original plan.
Conclusion:The use of dynamic jaws in Tomotherapy planning largely spare doses to OARs adjacent to the PTV. When this planning option is not available, planners should use < 2.5cm fixed jaw when critical OARs are located cephalocaudally to the PTV.

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