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The Effect of Dose Inhomogeneity On Sarcoma HDR Treatments

N Bassiri*, E Galvan , R Crownover , M Fakhreddine , N Papanikolaou , D Saenz , S Stathakis , N Kirby , K Rasmussen , Ut Health San Antonio, San Antonio, TX


(Tuesday, 7/31/2018) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 3

Purpose: The purpose of this study was to investigate the differences in dose distribution and deposition using a TG-43 based algorithm and a TG-186 based algorithm in sarcoma patients, treated with an Ir-192 source. The dose to the treatment volume, skin, and bone were under investigation.

Methods: Four patients that were clinically treated for post-surgical sarcoma radiation using sub-dermally implanted HDR catheters in a variety of locations were calculated using the Oncentra TPS version 4.5.3 using the standard 3D TG-43 based calculation and the TG-186 inhomogeneity-based calculation. Dwell weighting and times were kept constant from the clinically used plan. Dose inhomogeneity was based on the HU of the contoured structures (Skin/Bone/External). DVH files were exported to MATlab and plotted to determine difference between protocols for relevant organs of interest. Additionally, skin volumes were analyzed using both protocols to determine the skin volume receiving doses greater than 200cGy. Finally, the difference in average dose to each organ of interest was determined using the integral of the normalized DVH plot.

Results: The DVH curves for the selected patients vary between the TG-43 and TG-186 protocols for treatment volume, skin and bone contours. The average dose to the bone was calculated to be greater using TG-186 vs TG-43 for 3 out of 4 patients. Additionally, TG-43 calculated a greater dose to the skin for patients 2 out of 4 patients.

Conclusion: TG-43 and TG-186 dose calculations demonstrate quantifiable differences in sarcoma treatment planning. The significance of the role using TG-43 or TG-186 protocols have on the treatment planning and delivery process merits further investigation.


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