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SU‐FF‐T‐44: Dosimetric Analysis of the Effect of Edema in 131Cs Prostate Permanent Seed Implants
Author(s) -
Kehwar TS,
Jones HA,
Huq MS,
Beriwal S,
Benoit RM,
Smith RP
Publication year - 2009
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 - 10.1118/1.3181516
Subject(s) - medicine , implant , nuclear medicine , edema , prostate , ultrasound , radiology , surgery , cancer
Purpose: To investigate the effect of edema on different dosimetric parameters in131 Cs prostate permanent seed implants. Materials and Methods: Transrectal ultrasound (US) and computer tomography (CT) images were used to determine pre‐ and post‐needle implant volumes, and post‐implant prostate volumes in 31 patients who had received131 Cs implant. Dose volume histograms(DVH) were generated to determine the prostate volumes that received 100%, 150% and 200% of prescribed dose to calculate quality indices(QIs) and fractional D90(FD90) for each set of volumes for all patients. Results: No statistical differences were found between post‐needle and post‐implant(day 0) volumes obtained by US and CT images(p=0.56). The half life of the edema was found to be 9.72days. The change in mean values of coverage index(CI), dose non‐uniformity ratio(DNR), overdose index(ODI), relative dose‐homogeneity index(DHI) and FD90 can be described by CI ( t ) = CI ( 0 ) + [ 1 − CI ( 0 ) ] [ 1 − exp ( − λ CI t ) ] (1) DNR ( t ) = DNR ( 0 ) + [ 1 − DNR ( 0 ) ] [ 1 − exp ( − λ DNR t ) ] (2) ODI ( t ) = ODI ( 0 ) + [ 1 − ODI ( 0 ) ] [ 1 − exp ( − λ ODI t ) ] (3) DHI ( t ) = DHI ( 0 ) exp ( − λ DHI t ) (4) and D 90 ( t ) = ( R 0/ λ ) exp ( − λ t ) { FD 90 ( 0 ) + [ FD 90 ( 0 ) − a ] [ 1 − exp ( − λ FD t ) ] } (5) differential equations. The values of correlation coefficients and time constants obtained from least square fit of these equations were found to be 0.9867 & 0.0316 for CI, 0.9988 & 0.0148 for DNR, 0.9958 & 0.00148 for ODI, and 0.9983 & 0.0125 for DHI, respectively. Conclusions: CI, DHI and FD90 decreased, while DNR and ODI increased from pre‐implant plans to post‐implant plans at day 0 due to edema formation. CI, DNR, ODI and FD90 increased and DHI decreased with increasing post‐implant time and attained optimal values in 4 weeks. During this period 85% dose is delivered due to short half life of131 Cs seeds. Therefore, it is important to account for the effect of edema at the time of implant while defining seed positions. Implants performed based on pre‐implant volume study only result in poor dosimetric results in131 Cs implants.