Edema‐induced changes in tumor cell surviving fraction and tumor control probability in permanent prostate brachytherapy implant patients

Than S Kehwar,M Saiful Huq,Ryan P Smith,Heather A Jones

doi:10.1120/jacmp.v14i1.3862

Than S Kehwar, M Saiful Huq + Show 2 more

Open Access

https://doi.org/10.1120/jacmp.v14i1.3862

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Abstract

The study is designed to investigate the effect of edema on the delivered dose, tumor cell surviving fraction (SF), and tumor control probability (TCP) in the patients of prostate cancer who underwent 131Cs permanent seed implantation. The dose reduction, the SF, and the TCP for edematous prostate implants were calculated for 31 patients who underwent real‐time 131Cs permanent seed implantation for edema half‐lives (EHL), ranging from 4 days to 34 days and for edema magnitudes (M0) varying from 5% to 60% of the actual prostate volume. A dose reduction in 131Cs 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 125I implants, which vary from 0.3% (for EHL=4 days and M0=5%) to 17.5% (for EHL=34 days and M0=60%). As EHL increased from 4 days to 34 days and edema magnitude increased from 5% to 60%, the natural logarithmic value of SF increased by 4.57 and the TCP decreased by 0.80. Edema induced increase in the SF and decrease in the TCP in 131Cs seed implants, is significantly more pronounced in a combination of higher edema magnitude and larger edema half‐lives than for less edema magnitude and lower edema half‐lives, as compared for M0=60% and EHL=34, and M0=5% and EHL=4 days.PACS number: 87.53.Jw

Highlights

131Cs seeds have been implemented in many centers across USA, including our institution.[1,2,3] The design of 131Cs seed is similar to that of 125I and 103Pd, but has a shorter half-life of 9.7 days, and slightly higher average photon energy than 125I and 103Pd.[4,5,6] The shorter half-life of 131Cs can induce differences between planned and delivered doses due to prostatic edema, potentially impacting values of dosimetric and radiobiological quantities of interest
The present study investigates the effect of edema on dose reduction, tumor cell surviving fraction (SF), and tumor control probability (TCP), for 131Cs seed permanent prostate implants
The TCP values calculated for the dose delivered in time teff, using Eq [14] and individual postimplant CT volumes obtained at day 28, have no statistically significant differences (p > 0.05), and were found to ranged from 0.55 to 0.99 with a mean and SD of 0.76 ± 0.14

Summary

Introduction

Since 131Cs is a relatively new radioactive source used for prostate permanent seed implants, a number of studies have been done to investigate the effect on edema of 131Cs permanent seed implants.[2,3,7,8,9,10,11]. The present study investigates the effect of edema on dose reduction, tumor cell surviving fraction (SF), and tumor control probability (TCP), for 131Cs seed permanent prostate implants The exponential decay of prostatic edema induces a significant amount of change in dosimetric and radiobiological quantities in 131Cs implants due to its short half-life of 9.7 days.[2,3]

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