In vivo dosimetry can be considered as a quality assurance tool that supplements port
films, computational double checks and phantom studies. It is a process of monitoring the
dose (skin, entrance, exit, mid plane and target) delivered to a patient during treatment
and plays a role in relating the degree to which the delivered dose matches the prescribed
dose. Dosimeters currently used for in vivo dosimetry are diodes, thermoluminescence
dosimeters (TLDs), electronic portal imaging detectors (EPID) and radiochromic films.
In this research, GafChromic EBT2 film (GAF2) from International Special Products
(ISP), USA, was used as the in vivo dosimeter due to its intrinsic characteristics such as
tissue equivalent nature (Z = 6.96), wide dose range (0.1cGy – 8Gy), ease of handling,
very small effective thickness( 0.29mm) and Two Dimensional (2D) dose distribution.
The behaviors of both bare film and a specially constructed encapsulated film were
considered in this research. The film was cut to 1cm×1 cm and exposed to known doses
of radiation determined by ion chamber reading under reference conditions. The optical
density (OD) was read with point densitometer and plotted against the corresponding
dose to obtain the calibration curve. The response of the film was also determined for
changes in field size, source to skin distance (SSD), gantry angle, trays and wedges.
Correction factors were then determined for SSD, field size, gantry angle, wedges and
tray since the clinical conditions may be different from the reference conditions. Also,
skin dose as well as entrance dose calibration factor were determined for both bare and
encapsulated GAF2. Knowledge of the surface film reading, calibration factor and
correction factors were used in the determination of entrance dose, skin dose as well as
percentage skin dose.
From a preliminary % skin dose assessment using both bare film and encapsulated film at
reference irradiation conditions, encapsulated film was observed to expose the skin to a
higher dose (68%) than bare film (23.7%) due to the bulkiness of the encapsulation
material and was subsequently eliminated from being used for entrance dose
measurements. Furthermore, percentage skin dose determination with bare film was
observed to be mainly affected by field size (45%). By varying one irradiation parameter
and keeping all others at reference conditions, the maximum percentage entrance dose
difference observed was 2.6% for a dose prescription of 200 cGy to dmax. This falls within
the tolerance level of 5% set by accredited regulatory bodies. However, by varying all the
irradiation parameters, the maximum percentage entrance dose difference was observed
to be higher than the tolerance level. It is therefore recommended to carry out further
studies on the use of GAF2 before being implemented as an in vivo dosimeter at KBTH
by minimizing and being cognizant of the various levels of errors and uncertainties
involved in the determination of the calibration curve, calibration factor and correction
Edu, F (2021). Implementation of Invivo Dosimetry For External Photo Beam Radiotherapy Using Gaftromic Ebt 2 Film. Afribary.com: Retrieved April 10, 2021, from https://afribary.com/works/implementation-of-invivo-dosimetry-for-external-photo-beam-radiotherapy-using-gaftromic-ebt-2-film
Frontiers, Edu. "Implementation of Invivo Dosimetry For External Photo Beam Radiotherapy Using Gaftromic Ebt 2 Film" Afribary.com. Afribary.com, 06 Apr. 2021, https://afribary.com/works/implementation-of-invivo-dosimetry-for-external-photo-beam-radiotherapy-using-gaftromic-ebt-2-film . Accessed 10 Apr. 2021.
Frontiers, Edu. "Implementation of Invivo Dosimetry For External Photo Beam Radiotherapy Using Gaftromic Ebt 2 Film". Afribary.com, Afribary.com, 06 Apr. 2021. Web. 10 Apr. 2021. < https://afribary.com/works/implementation-of-invivo-dosimetry-for-external-photo-beam-radiotherapy-using-gaftromic-ebt-2-film >.
Frontiers, Edu. "Implementation of Invivo Dosimetry For External Photo Beam Radiotherapy Using Gaftromic Ebt 2 Film" Afribary.com (2021). Accessed April 10, 2021. https://afribary.com/works/implementation-of-invivo-dosimetry-for-external-photo-beam-radiotherapy-using-gaftromic-ebt-2-film