Brachy QA

Daily and SE QA for HDR

Daily QA1

Check the source strength on the consol and compare to decay chart 1% tolerance

Daily QA 2

Check console date and time accuracy Tolerance 1hr

Daily QA 3

Survey meter is present, battery check, and calibration check (calibration within the past yr)

Daily QA 4

Emergency response kit is complete and present

Daily QA 5

Audio and visual systems are working

Daily QA 6

Error when transfer tube/catheter is misconnected or missing

Daily QA 7

Error when an obstruction is present

Daily QA 8

Source out indicators are on

Daily QA 9

Radiation room monitor is working (prime alarms)

Daily QA 10

Treatment interrupt button works and source is retracted

Daily QA 11

Emergency source retraction button works

Daily QA 12

Source should retract when doors are opened

Daily QA 13

Source position accuracy tolerance 1 mm

Daily QA 14

Power failure: backup battery works and retracts source

Daily QA 15

Timer accuracy: making sure is out for the correct amount of time Tolerance 1s or 1% whichever is greater

Source exchange

1) Source strength measurement 3% tolerance

2) Timer linearity 1%

3) Position linearity

Draw a well chamber

What type of well chamber do we use and what is the active volume?

HDR 1000

Active volume 245 cm³

What is the bias voltage, leakage, stability, response, range, and sensitivity for our well chamber>

Bias: 300 V

Leakage: less than 50 fA

Stability: 0.2%

Response: 0.5% over 25 mm at center of axis

Range: 10 U to 80 MU 0.01 mCi to 20 ci

Sensitivity: depends on source ~2 pA/U

What is a well chamber measuring?

Get A (C/s) or C which gives dose rate or dose

How does a well chamber work?

Radiation interacts with the gas inside the chamber producing ion pairs. The ion pairs are collected by the central electrode and give out a current reading. The signal is proportional to air kerma strength

What is air kerma and what are the units?

Kerma = kinetic energy released per unit mass

Air kerma rate in free space multiplied by distance²

U or microGy*m²/hr or cGy*cm²/hr

What is the sweet spot and how is found?

The position in the well chamber where there is the highest signal reading

Source in 1 mm increments through the chamber

What corrections are needed to convert charge/current into source strength?

Temperature-pressure correction

Electrometer calibration factor

well chamber calibration factor

What is a tri ax cable?

Center conductor: carries the signal

Guard: same voltage as the center conductor and protects against leakage

Ground: Protects against electromagnetic interference

How is a well chamber calibrated for LDR and HDR?

LDR: calibrated by ADCL with a known source

HDR: Calibrated against another chamber that has direct traceability to NIST