Dosimetry study in cancer treatment planning for radiotherapy and brachytherapy procedure

Abstract

Radiotherapy practices are being widely used for treatment of cancer patients in Bangladesh. For proper treatment of cancer patient with teletherapy, percentage depth dose and beam profile data are necessary. In the present study, central axis percentage depth doses were determined for 60Co beam for various field sizes and depths using a' locally fabricated solid acrylicphantom (40x50x15cm3). Dose measurements were made atthe surface of the acrylic phantom and atthe depths ofO. 7,2.0, 3.5, 5.0, 6.5, 8.0cmfor field si;es: 5x5 -lOxlO, l2x12, 15x15, 18 x18and 20x20cm2. An ionization chamber (Model 23323) of volume 0.lcm3 in conjunction with a PTW UNIDOS electrometer was used for dose measurement. The experimental data of percentage depth doses for each field size have been analyzed by least square method and found to fit to an empirical equation of the form y = mx+c}. The maximum deviation between the theoretical and experimental percentage depth dose value isfound to be within :1:2.10%. In addition, the. experimental percentage depth doses with the side of square field for particular depth have also been fitted to an equation of the form y=aLn(x) +C2.The deviation between the theoretical and experimental value of percentage depth dose is within :1: 0.84%. The dose variation across the field that is the beam profile of the wCo beam for 5.0cm depth at 80cm SSD was measured for field sizes lOxlOcm2 and l5x15cm2. The beam profile data for lOxlOcm2 field size was also performed by thermoluminecence dosimetry (TLD) technique and compared with the data measured by ionization chamber. Brachytherapy plays an important role in the treatment of carcinoma of the cervix at all stages of the disease. A 137Cs low dose rate manual afterloading system is being used at Delta Medical Center Ltd for the treatment of carcinoma of the cervix. The Manchester system was used to characterize the doses at four points, namely: point A, point B, bladder point and rectal point .. The dose rates at these points for different patients were calculated by Sievert integral method Using these dose rates, dosimetry planning was performed for the treatment of carcinoma of the cervix. From the dosimetry planning, it is found that the bladder dose/or three patients is much higher than that of the dose value at point A. Similarly, rectal dose is found to be higher than that of dose value at point A for one patient. It appears that the average value of the rectal dose is 56.09:t39.29 much lower than that of bladder dose lO6.16:t22.10 for these patients, with respect to dose value ofpoint A. The methods used in this study could be utilizedfor treatment of cancer patient in both teletherapy and brachytherapypractices in Bangladesh.