open access

Vol 19, No 6 (2014)
Original research articles
Published online: 2014-11-01
Submitted: 2013-10-03
Get Citation

Dosimetric effect of tissue heterogeneity for I prostate implants

Susana Maria Oliveira, Nuno José Teixeira, Lisete Fernandes, Pedro Teles, Pedro Vaz
DOI: 10.1016/j.rpor.2014.03.004
·
Rep Pract Oncol Radiother 2014;19(6):392-398.

open access

Vol 19, No 6 (2014)
Original research articles
Published online: 2014-11-01
Submitted: 2013-10-03

Abstract

Aim

To use Monte Carlo (MC) together with voxel phantoms to analyze the tissue heterogeneity effect in the dose distributions and equivalent uniform dose (EUD) for 125I prostate implants.

Background

Dose distribution calculations in low dose-rate brachytherapy are based on the dose deposition around a single source in a water phantom. This formalism does not take into account tissue heterogeneities, interseed attenuation, or finite patient dimensions effects. Tissue composition is especially important due to the photoelectric effect.

Materials and methods

The computed tomographies (CT) of two patients with prostate cancer were used to create voxel phantoms for the MC simulations. An elemental composition and density were assigned to each structure. Densities of the prostate, vesicles, rectum and bladder were determined through the CT electronic densities of 100 patients. The same simulations were performed considering the same phantom as pure water. Results were compared via dose–volume histograms and EUD for the prostate and rectum.

Results

The mean absorbed doses presented deviations of 3.3–4.0% for the prostate and of 2.3–4.9% for the rectum, when comparing calculations in water with calculations in the heterogeneous phantom. In the calculations in water, the prostate D90 was overestimated by 2.8–3.9% and the rectum D0.1cc resulted in dose differences of 6–8%. The EUD resulted in an overestimation of 3.5–3.7% for the prostate and of 7.7–8.3% for the rectum.

Conclusions

The deposited dose was consistently overestimated for the simulation in water. In order to increase the accuracy in the determination of dose distributions, especially around the rectum, the introduction of the model-based algorithms is recommended.

Abstract

Aim

To use Monte Carlo (MC) together with voxel phantoms to analyze the tissue heterogeneity effect in the dose distributions and equivalent uniform dose (EUD) for 125I prostate implants.

Background

Dose distribution calculations in low dose-rate brachytherapy are based on the dose deposition around a single source in a water phantom. This formalism does not take into account tissue heterogeneities, interseed attenuation, or finite patient dimensions effects. Tissue composition is especially important due to the photoelectric effect.

Materials and methods

The computed tomographies (CT) of two patients with prostate cancer were used to create voxel phantoms for the MC simulations. An elemental composition and density were assigned to each structure. Densities of the prostate, vesicles, rectum and bladder were determined through the CT electronic densities of 100 patients. The same simulations were performed considering the same phantom as pure water. Results were compared via dose–volume histograms and EUD for the prostate and rectum.

Results

The mean absorbed doses presented deviations of 3.3–4.0% for the prostate and of 2.3–4.9% for the rectum, when comparing calculations in water with calculations in the heterogeneous phantom. In the calculations in water, the prostate D90 was overestimated by 2.8–3.9% and the rectum D0.1cc resulted in dose differences of 6–8%. The EUD resulted in an overestimation of 3.5–3.7% for the prostate and of 7.7–8.3% for the rectum.

Conclusions

The deposited dose was consistently overestimated for the simulation in water. In order to increase the accuracy in the determination of dose distributions, especially around the rectum, the introduction of the model-based algorithms is recommended.

Get Citation

Keywords

LDRBT; AAPM TG; PS; MC; CT; MBDCA; DVH; dDVH; EUD; TCP; NTCP; EBRT; OAR; HT; W; Brachytherapy; Prostate cancer; Monte Carlo; Tissue heterogeneity; Model-based calculation algorithms

About this article
Title

Dosimetric effect of tissue heterogeneity for I prostate implants

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 19, No 6 (2014)

Pages

392-398

Published online

2014-11-01

DOI

10.1016/j.rpor.2014.03.004

Bibliographic record

Rep Pract Oncol Radiother 2014;19(6):392-398.

Keywords

LDRBT
AAPM TG
PS
MC
CT
MBDCA
DVH
dDVH
EUD
TCP
NTCP
EBRT
OAR
HT
W
Brachytherapy
Prostate cancer
Monte Carlo
Tissue heterogeneity
Model-based calculation algorithms

Authors

Susana Maria Oliveira
Nuno José Teixeira
Lisete Fernandes
Pedro Teles
Pedro Vaz

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