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Dosimetry with LIF:Mg,Ti (TLD-100) for locating non-paubable breast cancer using Iodine-125 seeds
Hamona Novaes Santos1, Carla Daruich de Souza2, Lucas Verdi Angelocci2
1Nuclear and Energy Research Institute, IPEN, Av. Prof. Lineu Prestes, 2242 - Cidade Universitária - USP, ZIP: 05508-000 São Paulo, São Paulo State, Brazil; Sergipe Federal Institute, Rua Dom José Thomaz, 194 - São José, ZIP: 49015-090 Aracaju, Sergipe State, Brazil.
Purpose/Objective:
Radioguided Occult Lesion Localization using Iodine-125 seeds (ROLLIS) offers precise marking for non-palpable breast lesions, improving surgical margins. However, dosimetry for radiosensitive organs (heart, lungs, thyroid) is scarce. This study quantifies absorbed and effective doses from seeds at initial activities of 13.00 MBq, 6.00 MBq, and 1.10 MBq over 60 days, validating experimental TLD measurements against Monte Carlo simulations and assessing clinical safety.
Methods:
TLD-100 (LiF:Mg,Ti) dosimeters were selected per IPEN protocol (heat treatment at 400°C, Co-60 calibration with 1.409 energy correction factor for 29 keV I-125 vs. 1250 keV Co-60). Dosimeters were positioned at 14 sites on a male Alderson Rando phantom (ICRU 44/ICRP 89 compliant; 175 cm, 73.5 kg) with a custom paraffin-petroleum jelly breast attachment (0.91 g/cm3, 127 HU). High-activity seeds (132-158 MBq initial; three replicates at Israelita Albert Einstein Hospital) provided data extrapolated statistically to 60 days. Simulations used MCNP6 (10^8 histories, FMESH14 tally) via AMIGOBrachy (DICOM CT input, AAPM TG-186/TG-268 protocols). Effective doses applied ICRP 103 tissue weighting factors (wT sum = 0.32 for measured organs). Supporting Information details TLD selection/calibration curves, full effective/absorbed dose tables (per TLD position), relative errors vs. simulations, and uncertainty/error equations (Type A/B, propagation).
Results:
Absorbed doses obeyed inverse-square law, falling >50:1 from breast surface (86-193 mGy) to distal organs (0.02-4 mGy; thyroid lowest at 0.60 cGy max). Effective doses: 0.35 mSv (13 MBq), 0.16 mSv (6 MBq), 0.06 mSv (1.10 MBq); unmeasured organs <5% contribution (fluence <1% beyond 10 cm, μ ≈ 0.15 cm-1). Simulations matched experiments (<15% error near source; thyroid up to 459% due to low fluence). Combined uncertainties <10%. Doses below ICRP/BEIR thresholds (no deterministic effects; low stochastic risk).
Conclusions:
ROLLIS with low-activity I-125 seeds (recommend 1.10 MBq) is dosimetrically safe, providing first comprehensive organ-specific data. Supports ALARA optimization and Brazil-wide protocols. .
