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.

PATIENTS DOSE ESTIMATION IN CT EXAMINATIONS USING SIZE SPECIFIC DOSE ESTIMATES.

The present work reports data of radiation exposure to the patients during head, chest, pelvis and abdomen CT examinations performed on a third-generation 16-slice CT machine. Radiation exposure was estimated using size specific dose estimates (SSDE) method, which takes into account patient's physical dimensions in phantom measured computed tomography dose index (CTDI) value. The reported median CT dose volume index CTDIvol values in head, chest, pelvis and abdomen examinations were 26.76, 16.27, 29.81 and 14.74 mGy, respectively. The median doses evaluated using SSDE methodology for the above mentioned procedure were 54.1, 23.1, 42.8 and 20.1 mGy, respectively. Our results showed variation in dose values estimated using CTDI and SSDE methods in all examinations. The evaluated SSDE values were also compared to the values derived from data reported by the American Association of Physicist in Medicine (AAPM). SSDE values in present measurements are 4-8% lower than AAPM values. The present results show that CTDI parameters recorded on CT console should not be used to specify patient dose during CT procedures.

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.

DOSIMETRY OF ADULT AND PEDIATRIC PATIENTS FOR COMMON DIGITAL RADIOGRAPHY EXAMINATIONS.

The present work reports dosimetry data on adult and pediatric patients for some common radiographic examinations during the standard hospital routine. The measurements are the part of quality assurance program to determine radiation exposures to patients in these examinations. The entrance skin doses (ESDs) of the patients were measured from 2451 projection for 12 diagnostic examinations in digital radiography (DR). The ESDs in adult patient were measured using thermoluminescence dosemeters placed on the skin of the patient. In pediatric patients, ESDs were evaluated from the measured air kerma with ionization chamber, patient specific parameters and known values of machine exposure factors during examinations. The third quartile values of ESDs are proposed as local diagnostic reference levels (LDRLs) for radiographic examinations having statistical significant number of exposures (n ≥ 20). The proposed LDRL values are also compared with earlier published LDRL/DRL values.