Dosimetric study of CO-60 source step size in uterine cervix intracavitary HDR brachytherapy.

PURPOSE: The present work reports effects of source step sizes on dose distribution in patients treated with cobalt-60 (Co-60) high-dose-rate afterloading brachytherapy in carcinoma cervix (Ca-cx). METHODS AND MATERIALS: The retrospective study is based on data of 15 patients of Ca-cx treated with Co-60 high-dose-rate intracavitary brachytherapy with dose of 21 Gy in three fractions with source step size of 2.5 mm after external beam radiotherapy of 46 Gy. The effect of source step size on overall treatment procedure was evaluated from prescribed dose volume, dose to organ at risks, and treatment time for source step sizes of 1 mm, 2.5 mm, 5 mm, and 10 mm for each patient. RESULTS: The mean dose to bladder point for 1 mm, 2.5 mm, 5 mm, and 10 mm source step sizes was found to be 3.37 Gy (SD: 1.36), 3.44 Gy (SD: 1.38), 3.54 Gy (SD: 1.41), and 3.74 Gy (SD: 1.46), respectively. Similarly, the mean dose received by rectum point for these source step sizes were 2.86 Gy (SD: 0.64), 3.02 Gy (SD: 0.67), 3.25 Gy (SD: 0.71), and 3.63 Gy (SD: 0.73), respectively. The treatment time and prescribed dose coverage volume were both found to be gradually increasing with increase in step size. CONCLUSIONS: Our results on Ca-cx brachytherapy using Co-60 source indicate that the prescribed dose volume gradually increases from smaller source step to larger source step size. This results in increase of dose to the bladder and rectum and may lead to increase in toxicity and reduces quality of life. The study recommends that step size more than 5 mm should not be used for uterine cervix intracavitary application using Co-60 source.

ESTIMATION OF RADIATION EXPOSURE TO THE PATIENTS IN DIAGNOSTIC AND THERAPEUTIC INTERVENTIONAL PROCEDURES.

The present work reports data of the radiation exposure to the patient in various diagnostic and therapeutic interventional radiological (IR) procedures. The study includes 260 diagnostic and 195 therapeutic exposure data in 455 IR procedures. All the IR procedures were performed on a biplane angiographic machine in a tertiary care hospital. The radiation exposure was estimated from dose-area product (DAP), fluoroscopy time (FT), number of fluoroscopic runs, number of images and cumulative dose (CD) value recorded during the procedure. The data reported in the present study show significant variability in DAP values in diagnostic and therapeutic IR procedures. In diagnostic procedures, the minimum median DAP value is 8.93 Gy cm2 for upper limb angiography with mean FT of 2.7 min and maximum DAP value is 108.8 Gy cm2 for inferior vena cava angiography with mean FT of 12.55 min. For therapeutic procedures, the median value of DAP ranges from 2.43 Gy cm2 for sclerotherapy with mean FT 0.65 min to 267.23 Gy cm2 for coiling of cerebral aneurysm with mean FT of 60.52 min. The DAP value for each procedure was also correlated with FT, number of fluoroscopic runs, number of images and CD. The reported DAP values in this study are within the range of earlier published results which suggest that our finding provides at least approximate applicability to other hospitals. The third quartile DAP values of the procedures having significant number of patient data (n ≥ 10) serves as provisional reference values for the optimization of procedure protocols.