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SU-E-T-07: Edema Induced Changes in Tumor Cell Survival Fraction and Tumor Control Probability in 131Cs Permanent Prostate Implant Patients.

Abstract：

PURPOSE:The purpose of this study is to estimate the effect of edema, developed during implant procedure, on tumor cell surviving fraction(SF) and tumor control probability(TCP) in the patients of prostate cancer who underwent 131 Cs permanent seed implants. METHODS:The impact of edema on SF and TCP, was calculated using LQ equation extended to account for exponential nature of edema decay, dose delivered to dematous prostate and inhomogeneous dose distribution. Where (1) S(D)=(1/V)Σi=1n [Vpi{1+M0 exp(-λe t)}Si (D)] Si (D)=exp[-αRi (0)∫0t [exp(- λt)/{1+M0 exp(-λe t)}τ/3]dt -βq(t){Ri (0)∫0t [exp(-λt)/{1+M0 exp(-λe t)}τ/3]dt }2 ] and (2) TCP=exp[-ρVpS(D)] Following parameters, α=0.15Gy-1 , β=0.05Gy-2 , α/β=3.0Gy, Tp=42days, μ=61.6d-1 and ρ=1×106 are used to calculate SF and TCP for 31 patients of 131 Cs permanent seed implants for edema half lives(EHL) ranging from 4 days to 34 days and for edemas of magnitudes(M0 ) varying from 5% to 60% of the actual prostate volume. RESULTS:The dose reductions in 131 Cs implants varied from 1.1% (for EHL=4 days and M0 =5%) to 32.3% (for EHL= 34 days and M0 = 60%). These are higher than the dose reduction in 125 I implants, which vary from 0.3% (for EHL= 4 days and M0 = 5%) to 17.5% (for EHL= 34 days and M0 = 60%). As edema half life increased from 4 days to 34 days and edema magnitude increased from 5% to 60% the SF increased by 4.57 log, and the TCP decreased by 0.80. CONCLUSIONS:Compensation of edema induced increase in the SF and decrease in the TCP in 131 Cs seed implants should be carefully done by redefining seed positions with the guidance of post needle plans. The presented model in this study can be used to estimate the SF or the TCP for pre plan or real time permanent prostate implants using day 0 post implant CT images.

journal_name

Med Phys

journal_title

Medical physics

authors

Kehwar TS,Huq MS,Smith RP

doi

10.1118/1.4735061

subject

Has Abstract

pub_date

2012-06-01 00:00:00

pages

3703

issue

6Part9

eissn

0094-2405

issn

2473-4209

journal_volume

pub_type

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SU-E-T-07: Edema Induced Changes in Tumor Cell Survival Fraction and Tumor Control Probability in 131Cs Permanent Prostate Implant Patients.