Dose distribution to organs outside (laterally and depthwise) the treatment area following elongation co-efficient in case of radiotherapy treatment

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.