Brachytherapy

Sealed radioactive source placement inside or adjacent to tumor — prostate (LDR seeds or HDR), cervix / uterus (HDR tandem-and-ovoid, tandem-and-ring), breast (Mammosite, SAVI), skin, and eye plaques. Delivers very high dose to target with extremely rapid falloff. Distinct discipline from external beam — different workflow, different regulatory footprint (NRC byproduct license, Part 35.400 sealed-source provisions).

Clinical pathway

HDR gynecologic: applicator placement under ultrasound or CT guidance, CT or MRI planning scan, contouring and optimization (typically TG-43 or model-based dose calculation), treatment delivery via Ir-192 afterloader — 5–15 min delivery; applicator removal at console.

LDR prostate seeds: I-125 or Pd-103 seed implant under TRUS guidance in the OR, real-time or post-implant dosimetry, follow-up CT-based dose verification.

HDR prostate: catheter placement in OR under TRUS / MR guidance, CT / MRI planning, afterloader treatment over 1–3 fractions with catheters in place.

Skin / surface / breast: custom applicators (SAVI, contura, Mammosite) or surface molds; HDR Ir-192 afterloader delivery, often outpatient over 5 fractions.

Typical systems

Elekta Flexitron (HDR afterloader)
Varian BRAVOS (HDR afterloader)
Eckert & Ziegler MultiSource (HDR / PDR afterloader)
Sauerwein GammaMedplus (legacy HDR)
Brachytherapy planning suites — Oncentra Brachy (Elekta), BrachyVision (Varian)

Room + procedure characteristics

Suite requirements: shielded vault (lighter than linac vault), remote afterloader, emergency source-retraction procedures, manual emergency-retraction tools on-site, dedicated CT or MRI access for planning.
Team: radiation oncologist, medical physicist (required on-site during HDR treatment per NRC), nursing, anesthesia for gyne cases.
Regulatory: NRC or Agreement-State byproduct license, Part 35.400 sealed-source provisions, written directive, time-out, post-treatment survey.

Equipment considerations that bite

Source change cycle. Ir-192 has a 74-day half-life — HDR sources are physically replaced quarterly. Source-change service event is on the calendar; a missed cycle is a stopped program.
Afterloader emergency retraction — manual retraction tools, vault survey meter, and shielded source container must be on-site, tested, and inventoried. NRC inspection finding gateway.
Vault shielding survey — every relocation, modification, or major service event triggers a re-survey. Shielding margin is conservative for a reason; brachytherapy sources are point sources at very short standoff.
Applicator inventory — Tandem / ring / ovoid / cylinder / interstitial templates, MR-compatible vs CT-compatible, with documented sterilization workflow. A program without working applicators is theoretical.
Imaging integration — MR-guided brachy planning is the modern standard for cervical; programs without MR access run on CT planning at older standards-of-care.
Source-strength calibration — well chamber + electrometer, traceable to NIST. Non-negotiable for source acceptance testing.

Regulatory + safety reality

NRC license is a program-defining document. Authorized User physicists, ROs, and physicians are individually named; license amendments are required for staff changes. RSO accountability sits at the C-suite level.
Written-directive workflow — every HDR fraction requires written directive, time-out, and post-treatment survey. Misadministration reporting is rapid.
Source security and accountability — sealed-source inventory, leak testing on schedule, transport / disposal documentation. Old-source disposal is a non-trivial logistics event.

Operational reality

Brachytherapy programs are small-team and high-discipline. A center that runs HDR gyne plus prostate seeds typically does so with one or two physicists who own the program end-to-end.
Volume is concentrated — most U.S. brachytherapy is delivered at academic and tertiary cancer centers. Community programs commonly limit to gyne HDR or skin.
Refurb economics — Flexitron and BRAVOS dominate current installs; older afterloaders (microSelectron classic, Nucletron mHDR) appear on the refurb market but require source-change-vendor support.

IMRT
SBRT
Brain SRS
NRC regulation
AAPM TG-142 (sibling QA framework, external beam)
Rad Onc Physicist
RSO