Abstract:
Radiation dose to organs outside the radiotherapy treatment field can be significant
and therefore is of clinical interest. In the present work, (I) measurements have been
performed by using the teletherapy unit (Cobalt-60 gamma ray, 120 kY X-ray and 250
kY X-ray) in a polystyrene phantom (70 cm X 60 cm X 13 cm) using TLD chips (LiF-
100) to estimate the dose distribution at distances upto 40cm from the field edge
along the central axes of the field and these data have been fitted closely to an
exponential equation "y = a exp(-bx)", (2) measurements have been performed by
using the teletherapy unit (Cobalt-60) in a polystyrene phantom (70 cm X 60 cm X 13
cm) using TLD chips (LiF- I00) to estimate the dose distribution at distances upto 40
cm from the field edge along the central axes of the field following elongation
coefficients and these data have been fitted closely to an exponential equation "y = a
exp( -bx)" and using the data calculated from these fitted equation, elongation factor
(EF) have been calculated, (3) measurements have been performed by using the
teletherapy unit (Cobalt-60) in a polystyrene phantom (70 cm X 60 cm X 13 cm) using
TLD chips (LiF- 100) to estimate the dose distribution at distances upto 40 cm from
the field edge along the central axes of the field following depth I -cm, 5-cm, 10-cm
and the data of the dose distribution have been fitted closely to an exponential
equation "y = a exp( -bx)" and using the data calculated from these fitted equation,
depth factors (OF) have been calculated. The TL-responses were converted to dose in
mGy with the use of a calibration curve found by employing Cobalt-60 gamma ray,
superficial X-ray and deep X-ray (120 kY, 250 kY). The dose distribution outside the
treatment area is parametrized for each beam energy as a function of depth, distance
from field edge, and field size and shape. The results of the measurements so obtained
have been presented in the tables and figures.
The data so obtained would be useful to recommend measures for the protection of the
underlying healthy tissues of the whole body and other internal radiosensitive organs
of the patients undergoing radiotherapy.
