This work evaluates the possibility of creating an online patient dose verification
system through exit dose measurement on a Co-60 teletherapy machine which lacks an
electronic portal imaging device (EPID). Exit dose measurements were done by diode
and Barracuda and compared to those of an ionization chamber. The diode was first
calibrated and the necessary correction factors (depth and field size corrections)
determined using a PMMA phantom. The transmission factor of the couch was also
determined at gantry angles relevant to the study (0o
) and at various field sizes.
The estimated couch transmission factor was 0.96912. The exit dose measurements
were done both with PMMA phantom and an anthropomorphic phantom by calculating
a dose of 200 cGy to the various depths and corresponding field sizes. The detectors
were placed 30 cm underneath the treatment couch for all the measurements. Readings
from both detectors compared well with those of the ionization chamber. The
percentage deviations were generally lower with the PMMA phantom than for the
anthropomorphic phantom though they were all below 2%. The diode deviations range
between 0.098 to -1.322 for measurements with PMMA phantom at a depth of 15 cm
while those of the Barracuda were between 0.157 and -1.411 at the same conditions.
Diode in vivo dosimetry was found to be suitable for the verification of patient dose
through exit dose measurements. However the calibration and correction factors must
be determined carefully in order to generate more accurate results.
Eastern Network, L (2021). Exit Dose Measurement For Patient Treatment Dose Verification In Co-60 Teletherapy. Afribary.com: Retrieved April 17, 2021, from https://afribary.com/works/exit-dose-measurement-for-patient-treatment-dose-verification-in-co-60-teletherapy
Library, Eastern Network. "Exit Dose Measurement For Patient Treatment Dose Verification In Co-60 Teletherapy" Afribary.com. Afribary.com, 07 Apr. 2021, https://afribary.com/works/exit-dose-measurement-for-patient-treatment-dose-verification-in-co-60-teletherapy . Accessed 17 Apr. 2021.
Library, Eastern Network. "Exit Dose Measurement For Patient Treatment Dose Verification In Co-60 Teletherapy". Afribary.com, Afribary.com, 07 Apr. 2021. Web. 17 Apr. 2021. < https://afribary.com/works/exit-dose-measurement-for-patient-treatment-dose-verification-in-co-60-teletherapy >.
Library, Eastern Network. "Exit Dose Measurement For Patient Treatment Dose Verification In Co-60 Teletherapy" Afribary.com (2021). Accessed April 17, 2021. https://afribary.com/works/exit-dose-measurement-for-patient-treatment-dose-verification-in-co-60-teletherapy