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Dosimetric Evaluation of Permanent Brachytherapy Radioisotopes for Resected Metastatic Brain Tumors

R Badkul1*, (1) University of Kansas Medical Center, Kansas City, KS


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Permanent brachytherapy seeds are implanted to control local recurrence of resected brain metastases. Three commercially available radioisotopes:Cs131,I125 and Pd103 widely utilized for permanent-brachytherapy procedures.These isotopes offers rapid dose fall-off to minimize doses to normal-tissues due to their lower-energy(21-31KeV).Initial dose-rates of Cs131 is approximately 4 and 1.5 times higher than the I125 and Pd103 respectively.Aim of this study was to perform a dosimetric comparison of post-implant plans generated utilizing Cs131,I125, Pd103 seeds.

Methods: 11 patients who were implanted with Cs131 seeds after resecting the metastatic-brain lesions had CT and MRI within 1-3 days following surgery and post-implant plan was generated in Variseed.80Gy dose was prescribed 5mm from surface of tumor-cavity. Two more plans were generated for each patient using I125 and Pd103 using same number of seeds. Seed strength were adjusted to achieve same 80Gy volume coverage. Mean volume of prescription-dose(V80Gy) was 14.2cc(range 4.4-28.1cc),average number of seeds were 22(range 9-32).Average air-kerma-strength per seed were 2.4U,0.41U & 2.5U for Cs131,I125 and Pd103 respectively.Plans were evaluated for volumes of 80Gy (V80),160Gy(V160),120Gy(V120),60Gy(V60),40Gy(V40),20Gy(V20) and gradient indexes.

Results: Mean V160 & V120 were 4.6cc,7.5cc for Cs131; 4.3cc,7.7cc for I125; and 6.2cc, 9.2cc for Pd103. For Pd103 higher volumes of 200% and 150% were observed as compared to Cs131 and I125. V60 were 21.3cc, 21.2cc, 25.5cc; V40 were 35.6cc, 37.6cc, 32.5cc; V20 were 81.7cc, 79.5cc, 48.8cc for Cs131, I125 and Pd103 respectively. V60 was higher for Pd103 as compared to other two isotopes however lower dose volumes V40 and V50 were lower for Pd103 hence the sharper dose-fall-off.GI was lowest for Pd103.

Conclusion: From dosimetric point of view Cs131 and I125 brain implants yielded more homogeneous as compared to Pd103. However, Pd103 implants had sharper dose fall off, better dose gradient and smaller volume of brain tissue received lower doses as compared to I125 and Cs131.


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