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SU‐GG‐T‐37: Dosimetric Comparison of Cs‐131 to I‐125 for Treatment of Occular Melenoma
Author(s) -
Maurizo A,
Watchman C
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2961787
Subject(s) - nuclear medicine , brachytherapy , dosimetry , kerma , medicine , pinnacle , radiation treatment planning , radiation therapy , effective dose (radiation) , radiology
Purpose: To determine the conditions where it is advantageous to use131 Cs as an alternative to125 I in the brachytherapy treatment of ocular melanoma. Method and Materials: The dosimetry of nine previously treated patient plans was evaluated comparing125 I seeds and131 Cs seeds in identical configurations of standard eye plaques. Calculations were performed following the TG43 protocol in ADAC Pinnacle Treatment planning software. The resulting doses to prescription point and other structures were compared for the same plan using the two different isotopes. In addition, comparisons using131 Cs were performed so that a prescribed dose of 85Gy was achieved, first by adjusting the source strength and second by adjusting the treatment time.131 Cs plans were also created for a dose range of 60–95 Gy to determine optimal conditions where131 Cs may provide dosimetric advantage compared to125 I . Results: 12% reduction in prescribed dose to the tumor is observed for the case where the125 I seed is replaced by a131 Cs seed with identical air kerma strengths. Other points of interest show a reduction in dose from 6 to 13 %. An average increase of 14 % for the131 Cs source strength results in a dose increase up to 10 % for other points of interest. An average increase of 15 % in treatment time results in a dose increase up to 10 % for some points of interest. Equivalent doses were found for risk structures when 70–75 Gy for131 Cs was used. Doses below 75 Gy demonstrated reduced dose to critical structures. Conclusion: For a given prescription dose at the tumor apex,131 Cs delivers greater doses to critical structures. Use of131 Cs as a source for ocular melanomas may provide a dosimetric advantage for at risk structures if the biological equivalent dose is found to be 75 Gy or less.