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Effect of edema associated with 131 Cs prostate permanent seed implants on dosimetric quality indices Than S. Kehwar, Heather A. Jones, M. Saiful Huq, Sushil Beriwal, Ronald M. Benoit, and Ryan P. Smith Med. Phys. 36(8), August 2009, pp 3536-3542 Than S. Kehwar, Heather A. Jones, M. Saiful Huq, Sushil Beriwal, Ronald M. Benoit, and Ryan P. Smith Med. Phys. 36(8), August 2009, pp 3536-3542 Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Conclusion Edema adversely effects dose delivery Short half life of 131 Cs exacerbates effect w.r.t. other radionuclides Recommend: Use post-needle prostate volume to plan seed placement. Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Background American Brachytherapy Society (ABS) recommends: Dose plan based on pre- implant TRUS images Post-implant dosimetry based on CT at day 30 ( 0 ) after implant. Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Method 31 patients, Rx: 115 Gy Procedure: Pre-implant: Acquire TRUS images Pre-implant: Determine needle positions In OR: Acquire pre-needle-insertion TRUS images In OR: Insert needles In OR: Acquire post-needle-insertion TRUS images In OR: Use post-needle images for seed positioning Post-implant: Acquire CT images on day 0, 14, 28. Post-implant: Generate a plan based on pre-implant TRUS images. Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Functional forms: dose & edema V p = Pre-implant prostate vol. V 0 = Post-implant prosate vol. V t = Prostate volume at time, t. M 0 = (V 0 −V p )/V p Edema Dose Adam Cunha, UCSF Journal Club, 21 Aug. 2009 λ = ln( 2 )/t 1/2 R 0 = Initial source dose rate N.B. ln( 2 ) = 0.693 ∴ Total dose, TD = 1.44 ⋅ R 0 ⋅ t 1/2
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Pre-plan vs. post-needle plan This study none ( p = 0.87) What’s possibly wrong with this? ➛ Other studies: up to 30% difference in volumes contoured on CT vs US. N.B. The post-implant plant was that used for treatment, the pre- needle plan was generated a posteriori Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Δ Edema (cm 3 ) V 100 FD 90
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Conclusion Edema adversely effects dose delivery Short half life of 131 Cs exacerbates effect w.r.t. other radionuclides Recommend: Use post-needle prostate volume to plan seed placement. 61 Adam Cunha, UCSF Journal Club, 21 Aug. 2009
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Next Week YuanYuan: “Comparison of conventional inserts and an add-on electron MLC for chest wall irradiation of left-sided breast cancer” Tero Vatanen, Erik Traneus, and Tapani Lahtinen Acta Oncologica, 2009; 48: 446-451 Minghui: “Monte-Carlo-based adaptive EPID dose kernel accounting for different field size responses of imagers” Song Wang, Joseph K. Gardner, John J. Gordon, Weidon Li, Luke Clews, Peter B. Greer, and Jeffrey V. Siebers Med. Phys. 36(8), August 2009, pp 3582-3595 Andrew: “Stereotactic radiotherapy of intracranial tumors: A comparison of intensity- modulated radiotherapy and dynamic conformal arc” Ruud G. J. WiggenRaad, Anna L. Petoukhova, Lia Versluis, Jan P. C. van Santvoort Int. J. Radiation Oncology Biol. Phys., Vol. 74, No. 4, pp. 1018–1026, 2009
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