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

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• 作者：Tarcisio Passos Ribeiro de Campos^a ; ^{tprcampos@pq.cnpq.br" class="auth_mail" title="E-mail the corresponding author} ; Luciana Batista Nogueira^b ; ^{lucibn19@yahoo.com.br" class="auth_mail" title="E-mail the corresponding author} ; Bruno Trindade^c ; ^{brmtrindade@yahoo.com" class="auth_mail" title="E-mail the corresponding author} ; Ethel Mizrahy Cuperschmid^d ; ^{ethelmizrahy@yahoo.com.br" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Breast brachytherapy ; HDR Ir-192 ; Permanent implants ; Ho-166 seeds ; MCNP
• 刊名：Reports of Practical Oncology & Radiotherapy
• 出版年：2016
• 出版时间：May-June 2016
• 年：2016
• 卷：21
• 期：3
• 页码：240-249
• 全文大小：1670 K

文摘

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 μGy h⁻¹ Bq⁻¹; and, a normalized MDR in standard points (8 mm, equidistant to 03-seeds – SP₁, 10 mm – SP₂) of 1.0% (SP₁) and 0.5% (SP₂), respectively. Ir¹⁹²-brachytherapy presented MDR of 4.3945 × 10⁻³ μGy h⁻¹ Bq⁻¹; and, 30% (SP₁), and 20% (SP₂). Therefore, seed's implant activities of 333 MBq (Ho¹⁶⁶) and 259 GBq (Ir¹⁹²) produced prescribed doses of 58 Gy (SP₁; 5d) and 56 Gy (SP₁, 5 fractions, 6 min), respectively.

Conclusions

Breast Ho¹⁶⁶-implants of 37–111 MBq are attractive due to the high dose rate near 6–10 mm from seeds, equivalent to Ir¹⁹²-brachytherapy of 259 GBq (3 fractions, 6 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.