Professional Practice, QA/QC, Dose Calcs, Brachy

List the six principles of the CAMRT Code of Ethics.

Beneficence, Non-maleficence, Justice,

Autonomy, Veracity, Fidelity

Big Nurses Just Always Value Fidelity

What does “beneficence” mean in the context of RT ethics?

Acting in the best interest of the patient

— doing good, promoting their well-being.

What does “non-maleficence” mean?

“First, do no harm” — avoiding actions that cause unnecessary harm to the patient.

Define autonomy as an ethical principle.

Respecting the patient’s right to make their own informed decisions about treatment.

What does “veracity” require of an RTT?

Honesty and truthfulness in all patient communications and documentation.

What does “justice” mean in RT ethics?

Fair, equitable treatment for all patients regardless of

background, identity, or ability to pay.

List the five elements of informed consent.

Diagnosis
Proposed Tx
Alternatives
Risk/Benefit
Right to refuse

Who is responsible for obtaining informed consent for a radiation treatment plan?

Rad Onc

A patient says they want to stop treatment after 10 fractions due to side effects. What ethical principle

applies?

Autonomy. Patient has right to refuse whenever

What does TMR represent?

Tissue Maximum Ratio — the ratio of dose at a given depth to the dose at

dmax, for an isocentric (SAD) setup. It’s field-size and depth-dependent.

How does increasing field size affect PDD?

PDD increases with larger field size due to more scatter

reaching the central axis.

What is the effect of bolus on dmax?

Bolus brings dmax to the surface (eliminates skin-sparing),

increasing dose to superficial tumors or scar tissue.

An electron treatment uses bolus. What happens to the depth of coverage?

Bolus reduces the

depth of penetration — useful for limiting dose to deep structures

What is the ISL formula?

ISL = (reference SSD / actual SSD)²

What is the difference between Sc and Sp?

- Sc (collimator scatter factor): Scatter from the

collimator/head; depends on collimator field size

Sp (phantom scatter factor): Scatter within the

patient/phantom; depends on the equivalent square field size in tissue

What are 4 common isotopes used in bracy? Which are used for LDR and HDR

LDR = I-125, Pd-103, Cs-137

HDR = Ir-192

What are the two main categories of brachytherapy based on dose rate?

LDR (Low Dose Rate: < 2

Gy/hr) and HDR (High Dose Rate: > 12 Gy/hr)

Why is HDR brachytherapy safer for staff than LDR?

HDR uses remote afterloading — the

radioactive source travels through catheters via computer control, so no staff are in the room during delivery. LDR

sources remain in the patient for hours/days.

What isotope is typically used for prostate seed brachytherapy?

I-125 (most common) or Pd-103.

Permanent implant delivering 145 Gy total.

How many seeds are typically used in a prostate LDR implant?

Approximately 80–100 seeds.

Why is Pd-103 sometimes preferred over I-125 for prostate implants?

Pd-103 has a shorter half-life

(17 vs 60 days), so the dose is delivered faster — potentially better for faster-growing tumors.

Why is Cs-137 being phased out of clinical use?

Its 30-year half-life makes it a significant long-term

security and waste management concern. Being replaced by Ir-192 HDR.

What radiation protection measures apply to a patient with LDR prostate seeds?

- Stay 1 metre away from others as much as possible
- Avoid prolonged close contact with pregnant women and young children
- Sleep alone or in separate bed for ~2 months
- Use a filter (condom) during intercourse — seeds can rarely be expelled

What applicator system is used for cervical intracavitary brachytherapy?

Tandem and ring or tandem and ovoids applicator system (Fletcher-Suit style).

What type of brachytherapy is used for esophageal cancer?

Intraluminal brachytherapy — a

catheter is passed through the esophagus and the source travels through it.

What are the 5 types of brachy applications?

Interstitial = direct into tumor bed
Intracavity = in body cavity
Intraluminal = in body tubes
Intravascular = in vasculature
Surface = on top of skin