Orthovoltage Calibration Checklist
Equipment Needed:
Electrometer
Chamber A217 (this specific one needed, it has orthovoltage calibration factors)
Traix cable
Thermometer
Barometer
Rulers
Copper filters (to measure Half Value Layer)
Ring Stand with chamber holder
Tape (need a lot to hold filters for HVL measurement)
Stopwatch
Logbook
Measurement Procedure:
1. Take chamber cap off
2. Attach chamber to ring stand
3. Position chamber below the closed end plastic of applicator at about 50.3 cm (end of applicator
at 50 cm)
4. Do readings at 225 kVp & 250 kVp with appropriate filter in place-take 1 minute readings
5. Do readings for alpha timer* check – 4, 15 second readings
6. Do readings at 225 kVp & 250 kVp with appropriate filter in place-take 1 minute readings
7. Do HVL readings at 225 & 250 kVp at the 100 cm distance. Place the copper filters at the end of
the cone (about 50 cm).
8. Take flatness film for both 225 & 250 kVp. Place the film at the end of the cone.
* timer error () is based on the comparison of one reading of one minute (R1) versus 4 readings of
15 seconds (R2). It is assumed that there is one timer error associated with the one, one minute
reading and four timer errors associated with the four, 15 second readings. Solution of the following
equation yields the formula for the  timer error.
R1 / (t +  = R2 / (t + n
where n is 4 (for four readings) in this case and t is time of irradiation, one minute.
Thus  = (R1 - R2)t / (R2 – nR1)
How to run the Orthovoltage Unit:
1. Call Radiobiology (Rob Griffith) to schedule time on the unit.
2. Ask to have one of them warm up the unit.
3. Operation:
After completion of an irradaition,
-Hit TEST, RESET
-Then set time (one minute)
-Open door
-Take filter out (not all the way, just to open the microswitch)
-Close the door
-Turn unit on (hold down the “on” button, until a click is heard)
-For the inserted filter, the pin has to be in hole one for 250 kVp and hole two for 225 kVp