Program Information
Clinical Applications of Spatially Fractionated Radiation Therapy (GRID) Using Helical Tomotherapy
X Zhang1*, j Penagaricano2 , X Liang3 , S Morrill4 , Y Yan5 , P Corry6 , R Griffin7 , N Paudel8 , V Ratanatharathorn, Vaneerat9 , (1) University of Arkansas Medical Science, Little Rock, AR, (2) University of Arkansas for Medical Science, Little Rock, Arkansas, (3) University of Arkansas Medical Science, Little Rock, AR, (4) University of Arkansas for Medical Sciences, Little Rock, AR, (5) UT Southwestern Medical Center, Dallas, TX, (6) University of Arkansas for Medical Sciences, Little Rock, AR, (7) University of Arkansas for Medical Sciences, Little Rock, Arkansas, (8) University of Arkansas for Medical Sciences, Little Rock, AR, (9) University of Arkansas for Medical Sciences, Little Rock, AR
Presentations
SU-E-P-30 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To present the first clinical applications of Helical Tomotherapy-based spatially fractionated radiotherapy (HT-GRID) for deep seated tumors and associated dosimetric study.
Methods:Ten previously treated GRID patients were selected (5 HT-GRID and 5 LINAC-GRID using a commercially available GRID block). Each case was re-planned either in HT-GRID or LINAC-GRID for a total of 10 plans for both techniques using same prescribed dose of 20 Gy to maximum point dose of GRID GTV. For TOMO-GRID, a programmable virtual TOMOGRID template mimicking a GRID pattern was generated. Dosimetric parameters compared included: GRID GTV mean dose (Dmean) and equivalent uniform dose (EUD), GRID GTV dose inhomogeneity (Ratio(valley/peak)), normal tissue Dmean and EUD, and other organs-at-risk(OARs) doses.
Results:The median tumor volume was 634 cc, ranging from 182 to 4646 cc. Median distance from skin to the deepest part of tumor was 22cm, ranging from 8.9 to 38cm. The median GRID GTV Dmean and EUD was 10.65Gy (9.8-12.5Gy) and 7.62Gy (4.31-11.06Gy) for HT-GRID and was 6.73Gy (4.44-8.44Gy) and 3.95Gy (0.14-4.2Gy) for LINAC-GRID. The median Ratio(valley/peak) was 0.144(0.05-0.29) for HT-GRID and was 0.055(0.0001-0.14) for LINAC-GRID. For normal tissue in HT-GRID, the median Dmean and EUD was 1.24Gy (0.34-2.54Gy) and 5.45 Gy(3.45-6.89Gy) and was 0.61 Gy(0.11-1.52Gy) and 6Gy(4.45-6.82Gy) for LINAC-GRID. The OAR doses were comparable between the HT-GRID and LINAC-GRID. However, in some cases it was not possible to avoid a critical structure in LINAC-GRID; while HT-GRID can spare more tissue doses for certain critical structures.
Conclusion:HT-GRID delivers higher GRID GTV Dmean, EUD and Ratio(valley/peak) compared to LINAC-GRID. HT-GRID delivers higher Dmean and lower EUD for normal tissue compared to LINAC-GRID. TOMOGRID template can be highly patient-specific and allows adjustment of the GRID pattern to different tumor sizes and shapes when they are deeply-seated and cannot be safely treated with LINAC-GRID.
Contact Email: