Knowledge Hub · Saxsons SPECT Lead-Lined Syringe Shield
Tc-99m at 140 keV sits just above the lead K-edge — exactly where lead's photoelectric absorption is at its strongest. 3 mm of lead is roughly 11 HVL, which attenuates the primary photopeak by more than three orders of magnitude. Going thicker adds chassis weight and operator fatigue with vanishing dose-rate benefit. This page is why 3 mm is the routine SPECT tier — and when the workflow calls for 6 mm or 9 mm instead.
Why this matters
Lead HVL at 140 keV
At 140 keV — the Tc-99m photopeak — the half-value layer (HVL) in pure lead is roughly 0.27 mm. A 3 mm wall is approximately 11 HVL of lead, which attenuates the primary photopeak by more than three orders of magnitude (> 99.95 %). Adding lead beyond this point produces vanishing dose-rate benefit while the shield gets heavier, the handle harder to manoeuvre and the operator more fatigued by mid-shift. 3 mm is the engineered match between attenuation and ergonomics for SPECT routine work.
Based on: NIST XCOM photon-attenuation cross-section database; NCRP Report 49 / Report 147 — Structural Shielding Design for Medical Imaging Facilities.
Read source ↗I-131 needs more lead
At 364 keV — the I-131 primary photopeak — the half-value layer in lead is roughly 3 mm. 3 mm of lead attenuates I-131 by only about 50 %; 9 mm gets to about 3 HVL (~87 % attenuation). A facility that handles I-131 capsule decant or oral-solution withdrawal needs the 9 mm tier on its dispensing shields, paired with bench-side shielding for high-activity work. The 6 mm tier sits between — for In-111, Ga-67 multi-peak and lower-activity I-131 flows.
Based on: NIST XCOM photon-attenuation database; IAEA Safety Reports 38 — Applying Radiation Safety Standards in Nuclear Medicine.
Read source ↗AERB extremity-dose budget
AERB caps the annual occupational extremity (skin / fingers / hands) dose for radiation workers at 500 mSv — five times the 100 mSv whole-body limit, but applied at a much smaller volume that absorbs much higher dose per dispense. A nuclear-medicine technologist dispensing 30+ Tc-99m doses per shift accumulates extremity dose at a rate that fills a measurable fraction of the annual budget if any handling is bare-syringe. The 3 mm lead shield is the engineered intervention that keeps the per-dispense extremity dose comfortably inside the annual budget.
Based on: AERB Safety Code for Nuclear Medicine Facility; ICRP Publication 103 occupational extremity-dose limit (500 mSv/year).
Read source ↗Lead-glass viewing window
A blind shield forces the operator to open it to verify the dose volume. Every open-close cycle adds finger exposure and risks droplet contamination of the shield interior. A lead-glass viewing window with an engraved calibration scale keeps the syringe volume readable through the shield — the operator reads the scale, confirms the volume against the prescription and dispenses without ever exposing fingers to the bare syringe. The window's lead-glass tier is matched to the surrounding lead so the weakest point still stays inside the dose-rate budget.
Based on: IAEA Operational Guidance on Hospital Radiopharmacy; manufacturer lead-glass equivalence certification.
Read source ↗Why lead, not tungsten, for SPECT
Tungsten outperforms lead per millimetre at high photon energies — at 511 keV its higher density gives it a clear edge for PET shielding. At 140 keV (Tc-99m) the cross-section ratio narrows: lead still attenuates well at this energy because of the lead K-edge at 88 keV which sits just below the Tc-99m photopeak, enhancing the photoelectric absorption. The added cost and machining complexity of tungsten gives no meaningful attenuation advantage at SPECT energies; lead is the right material choice.
Based on: NIST XCOM photon-attenuation cross-section database; NCRP Report 49 — Structural Shielding for Medical Use Facilities.
Read source ↗SS-202 vs SS-304 outer finish
A SPECT syringe shield sits on the dispensing bench inside the hot lab. The outer chassis sees daily wipe-down with the hot-lab decontaminant. SS-202 is the cost-optimised stainless tier — fully wipeable and corrosion-resistant for routine hot-lab work. SS-304 is the medical-grade tier — pharmaceutical-grade decontamination compliance, expected by pharmaceutical-licensed compounding radiopharmacies and by facilities certified to higher cleanroom-tier classifications. Pick the tier that matches the facility licence.
Based on: ISO 14644 cleanroom classification; EU GMP Annex 1 / Annex 3 for sterile-product manufacturing; AERB Safety Code expectations.
Read source ↗AERB, ICRP, NIST, NCRP and IAEA documents that anchor the SPECT syringe-shielding decision.
Indian regulatory framework for nuclear-medicine facility licensing including extremity-dose monitoring and shielded-dispensing expectations.
Current ICRP framework defining the 500 mSv/year occupational extremity-dose limit.
Authoritative reference for lead photon-attenuation coefficients at 140 keV (Tc-99m), 364 keV (I-131) and other SPECT energies.
NCRP shielding-design framework covering lead-attenuation half-value layers used to size shielding to SPECT isotope energy.
IAEA framework covering nuclear-medicine radiation protection including dispensing-line operator-protection equipment.
Where next
Product page →
SPECT lead-lined syringe shield specs + variant matrix
Sizes 1 / 2 / 3 / 5 / 10 cc, 3 / 6 / 9 mm lead tiers, SS-202 / SS-304 outer finish.
For the radiopharmacist →
Daily Tc-99m dispensing workflow
Per-kit dispense workflow (MDP, MIBI, ECD, MAG3, DMSA), ring-badge extremity-dose log, AERB record.