open access

Vol 21, No 3 (2016)
Original research articles
Published online: 2016-05-01
Submitted: 2015-04-01
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Dosimetric intercomparison of permanent Ho-166 seed's implants and HDR Ir-192 brachytherapy in breast cancer

Tarcisio Passos de Campos, Luciana Batista Nogueira, Bruno Trindade, Ethel Mizrahy Cuperschmid
DOI: 10.1016/j.rpor.2015.11.007
·
Rep Pract Oncol Radiother 2016;21(3):240-249.

open access

Vol 21, No 3 (2016)
Original research articles
Published online: 2016-05-01
Submitted: 2015-04-01

Abstract

Aim

To provide a comparative dosimetric analysis of permanent implants of Ho166-seeds and temporary HDR Ir192-brachytherapy through computational simulation.

Background

Brachytherapy with Ir192-HDR or LDR based on temporary wires or permanent radioactive seed implants can be used as dose reinforcement for breast radiation therapy. Permanent breast implants have not been a practical clinical routine; although, I125 and Pd103-seeds have already been reported. Biodegradable Ho166-ceramic-seeds have been addressed recently.

Material and methods

Simulations of implants of nine Ho166-seeds and equivalent with HDR Ir192-brachytherapy were elaborated in MCNP5, shaped in a computational multivoxel simulator which reproduced a female thorax phantom. Spatial dose rate distributions and dose–volume histograms were generated. Protocol's analysis involving exposure time, seed's activities and dose were performed.

Results

Permanent Ho166-seed implants presented a maximum dose rate per unit of contained activity (MDR) of 1.1601[[ce:hsp sp="0.25"/]]μGy[[ce:hsp sp="0.25"/]]h−1[[ce:hsp sp="0.25"/]]Bq−1; and, a normalized MDR in standard points (8[[ce:hsp sp="0.25"/]]mm, equidistant to 03-seeds – SP1, 10[[ce:hsp sp="0.25"/]]mm – SP2) of 1.0% (SP1) and 0.5% (SP2), respectively. Ir192-brachytherapy presented MDR of 4.3945[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10−3[[ce:hsp sp="0.25"/]]μGy[[ce:hsp sp="0.25"/]]h−1[[ce:hsp sp="0.25"/]]Bq−1; and, 30% (SP1), and 20% (SP2). Therefore, seed's implant activities of 333[[ce:hsp sp="0.25"/]]MBq (Ho166) and 259[[ce:hsp sp="0.25"/]]GBq (Ir192) produced prescribed doses of 58[[ce:hsp sp="0.25"/]]Gy (SP1; 5d) and 56[[ce:hsp sp="0.25"/]]Gy (SP1, 5 fractions, 6[[ce:hsp sp="0.25"/]]min), respectively.

Conclusions

Breast Ho166-implants of 37–111[[ce:hsp sp="0.25"/]]MBq are attractive due to the high dose rate near 6–10[[ce:hsp sp="0.25"/]]mm from seeds, equivalent to Ir192-brachytherapy of 259[[ce:hsp sp="0.25"/]]GBq (3 fractions, 6[[ce:hsp sp="0.25"/]]min) providing similar dose in standard points at a week; however, with spatial dose distribution better confined. The seed positioning can be adjusted for controlling the breast tumor, in stages I and II, in flat and deep tumors, without any breast volumetric limitation.

Abstract

Aim

To provide a comparative dosimetric analysis of permanent implants of Ho166-seeds and temporary HDR Ir192-brachytherapy through computational simulation.

Background

Brachytherapy with Ir192-HDR or LDR based on temporary wires or permanent radioactive seed implants can be used as dose reinforcement for breast radiation therapy. Permanent breast implants have not been a practical clinical routine; although, I125 and Pd103-seeds have already been reported. Biodegradable Ho166-ceramic-seeds have been addressed recently.

Material and methods

Simulations of implants of nine Ho166-seeds and equivalent with HDR Ir192-brachytherapy were elaborated in MCNP5, shaped in a computational multivoxel simulator which reproduced a female thorax phantom. Spatial dose rate distributions and dose–volume histograms were generated. Protocol's analysis involving exposure time, seed's activities and dose were performed.

Results

Permanent Ho166-seed implants presented a maximum dose rate per unit of contained activity (MDR) of 1.1601[[ce:hsp sp="0.25"/]]μGy[[ce:hsp sp="0.25"/]]h−1[[ce:hsp sp="0.25"/]]Bq−1; and, a normalized MDR in standard points (8[[ce:hsp sp="0.25"/]]mm, equidistant to 03-seeds – SP1, 10[[ce:hsp sp="0.25"/]]mm – SP2) of 1.0% (SP1) and 0.5% (SP2), respectively. Ir192-brachytherapy presented MDR of 4.3945[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10−3[[ce:hsp sp="0.25"/]]μGy[[ce:hsp sp="0.25"/]]h−1[[ce:hsp sp="0.25"/]]Bq−1; and, 30% (SP1), and 20% (SP2). Therefore, seed's implant activities of 333[[ce:hsp sp="0.25"/]]MBq (Ho166) and 259[[ce:hsp sp="0.25"/]]GBq (Ir192) produced prescribed doses of 58[[ce:hsp sp="0.25"/]]Gy (SP1; 5d) and 56[[ce:hsp sp="0.25"/]]Gy (SP1, 5 fractions, 6[[ce:hsp sp="0.25"/]]min), respectively.

Conclusions

Breast Ho166-implants of 37–111[[ce:hsp sp="0.25"/]]MBq are attractive due to the high dose rate near 6–10[[ce:hsp sp="0.25"/]]mm from seeds, equivalent to Ir192-brachytherapy of 259[[ce:hsp sp="0.25"/]]GBq (3 fractions, 6[[ce:hsp sp="0.25"/]]min) providing similar dose in standard points at a week; however, with spatial dose distribution better confined. The seed positioning can be adjusted for controlling the breast tumor, in stages I and II, in flat and deep tumors, without any breast volumetric limitation.

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Keywords

Breast brachytherapy; HDR Ir-192; Permanent implants; Ho-166 seeds; MCNP

About this article
Title

Dosimetric intercomparison of permanent Ho-166 seed's implants and HDR Ir-192 brachytherapy in breast cancer

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 21, No 3 (2016)

Pages

240-249

Published online

2016-05-01

DOI

10.1016/j.rpor.2015.11.007

Bibliographic record

Rep Pract Oncol Radiother 2016;21(3):240-249.

Keywords

Breast brachytherapy
HDR Ir-192
Permanent implants
Ho-166 seeds
MCNP

Authors

Tarcisio Passos de Campos
Luciana Batista Nogueira
Bruno Trindade
Ethel Mizrahy Cuperschmid

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