Program Information
Dosimetric Effects of Latitudinal Source Distribution in Multi-Source Stereotactic Radiotherapy
Y Niu1*, O Krivosheev1 , B Kopchick2 , S Becker3 , C Yu1,3 , (1) Xcision Medical Systems, Columbia, MD, (2) The George Washington University, Washington DC, (3) Univ. of Maryland School Of Medicine, Baltimore, MD,
Presentations
WE-RAM3-GePD-IT-3 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Imaging ePoster Theater
Purpose: The principle of stereotactic radiosurgery (SRS) is geometric focusing. Multi-source SRS systems employ highly focused beams from a solid angle formed by 360 degrees in longitude and a varying range of latitudinal angles. The objective of this study was to study the dosimetric effects of latitudinal source distribution so that the optimal latitudinal angular range may be determined.
Methods: GammaPodᵀᴹ is a breast-specific stereotactic radiotherapy device which uses cobalt sources to create 36 non-overlapping conical beam arcs to achieve highly focused dose distribution. The 36 beam arcs span 36 degrees, i.e., from 18 to 53 degree off the horizontal plane with 1 degree latitude intervals. To assess the dosimetric effects of latitudinal source distribution, we performed dosimetric comparisons between the current design and the designs with reduced latitudinal ranges of 30 and 24 degrees. Plans with the same optimization engine and with the same plan objectives were created both in phantoms and in 4 patients treated on the GammaPod. Dose coverages to the target, as well as sparing for the normal breast and heart were compared.
Results: The rotational focusing of the current GammaPod design yielded rapid dose falloff from the edge of target, with excellent sparing of normal breast. Compared with 36 degrees of latitudinal angle range, reducing the range to 30 degrees and 24 degrees did not degrade target dose coverage. The DVHs for normal breasts also showed very small difference in the low to middle dose levels, increasing V50 by less than 2%, and V20 by less than 10%. The maximum dose to the proximal heart decreased rapidly (i.e., up to 40%) with the reduction of high-degree latitudinal beam range.
Conclusion: The dosimetric evaluation suggests substantial benefit in heart sparing with moderate reduction of the latitudinal ranges of source distribution for the GammaPod.
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