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Comparison Between VMAT CT Planning and Segmented MRI Images with Assigned Bulk Density: A Dosimetric Study for Intact Prostate Patients

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A Sharif

A Sharif*, S Paloor, S Sheim, M McGarry, S Pienaar, G Perkins, R Hammoud, N Al Hammadi, Hamad Medical Corporation, Doha, Qatar

SU-E-J-177 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Variability in CT delineation and visualization of target volume has long been a problem in radiotherapy. USe of MR based radiotherapy(MR-RT) is currently being extensively investigated due to the superior soft tissue contrast which can be enhanced by using appropriate pulse sequences. Current MR Systems ensure that there is no loss of geometric accuracy and distortion however lack of electron density information remains a problem for MR-RT. This is a retrospective study using VMAT planning on segmented MR images with bulk density assigned for intact prostate patients.

Methods:
MR images for 10 patients were acquired on GE Optima MRI scanner and segmented, the bulk density was assigned as per ICRU 46 to the contours . VMAT plans were created and optimized on Varian Eclipse TPS using the AAA algorithm on the Pseudo CT/ MR study data. The resulting dose distributions were assessed for PTV coverage and OAR constraints to obtain clinically valid plans.
The resulting VMAT plan dose distributions were assessed by re calculating the MR optimized plans on the original CT data sets keeping the plan parameters the same. Using plan analysis features available in Eclipse the resulting differences in the dose distributions were analyzed using DVH data as well as slice by slice dose distribution. The TCP and NTCP were calculated for both sets of plans.
The optimized results for TCP and NTCP data will be presented for PTVs and OARs together with DVH comparisons. Quantitative analysis of the differences in dose distribution using Gamma Index Analysis will be performed using SunNuclear ArccheckTM and all results will be presented.

Results:
Detailed data analysis of the 10 Patients results will be presented.

Conclusion:
Initial assessment of the data indicates VMAT planning on MR only images with appropriately assigned bulk density information is clinically acceptable for intact prostate cases.

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