International Journal of Radiation Research
Volume:5 Issue: 4, Oct 2007

In the recent years, interstitial brachytherapy implantation has become the treatment of choice for early stage prostate cancer patients. Treatment of prostate cancer with radiation is traced back to 1909. Originally this treatment modality was very crude and could not gain much popularity till 1982. Advancements in radioactive source designs, introduction of new low energy radioactive sources, and new imaging modalities made this treatment modality a treatment of choice for early stage prostate cancer patients. Popularity of this modality is due to the fact that five-and ten-year disease control rates of brachytherapy are equal to those of the surgical, whereas, the toxicity and side-effects are perceived to be lower. This manuscript presents historical review of interstitial brachytherapy, innovations in radioactive source designs, dosimetry and dose calculations.

The dosimetric performance of Eclipse 6.5 three dimensional treatment planning system (3DTPS) is evaluated by comparing the calculated and measured dose in two dimensions following the guide lines of American Association for Physicists in Medicine Task Group 53. The calculations were performed by the 3DTPS for symmetric as well as asymmetric fields for standard source to surface distance (SSD) at dmax, 5, 10 and 20cm depths in water phantom using 45° and 60° enhanced dynamic wedges (EDWs) in a field of 15 cm×15 cm size for 6 MV photon beams. Measurements were carried out for 6 MV photon beams produced by a linear accelerator, Clinac EX - 2100, equipped with EDWs using 0.125cc volume PTW ionization chamber and PTW UNIDOS electrometer for beam axis and two off axis points. The deviations between the calculated dose (Dcalc) and the measured dose (Dmeas) at toe, centre and heel at different depths for symmetric as well as asymmetric fields for both the wedge angles is less than 2% at all the points and in all geometries. For 45° EDW the deviation was maximum at 20 cm depth and in asymmetric geometry. For 60° EDW the deviation was maximum at 20 cm depth but in symmetric geometry. The results indicate that the accuracy of Eclipse 6.5 (version 7.3.10) three dimensional treatment planning system used with the EDWs in symmetric as well asymmetric fields is adequate in clinical applications under the studied experimental conditio

The presence of small intestine in the radiation field during pelvic cancers treatment causes an interruption in radiotherapy. A non-invasive method was developed to exclude small intestine during conventional radiotherapy. The incidence of the radiation therapy interruption is highly dependent upon the area of the small intestine included in the portals and its absorbed dose. In order to investigate the radiation therapy interruption and the resulting elongation of the total treatment time, 35 patients suffering from pelvic cancers were selected and randomly assigned to control and study groups. All the patients were treated in prone position. In the 18 patients in the study group, a commercially available water bag was inserted between patient abdomen and treatment couch. Other 17 patients in the control group underwent similar therapy without water bag. The total treatment time was shown to be 1.52 days shorter in the study group with a statistically significant difference (p<0.003). Due to the lack of the early morbidities during radiotherapy, it is concluded that the current method helps to optimize total treatment time by preventing interruption of radiation therapy.

The Monte Carlo (MC) method is not only used for dose calculations around brachytherapy sources but also for benchmarking treatment planning systems (TPS) calculations. Three 60Co sources of GZP6 brachytherapy unit were simulated using MCNP4C MC Code. The radial dose functions were calculated by MC method and GZP6 TPS and were compared. There was a good agreement between MC and TPS calculations for all sources. Discrepancies up to 10% were observed for points close to the sources, but for those farther than 7mm from source center, differences were less than 2% for all sources. Our results showed that GZP6 TPS calculations can accurately be used for dose calculations in brachytherapy treatments for points farther than 7mm from the source center.

Currently available radioprotectors are poorly tolerated in man and the general use of aminothiols is compromised by their side effects. This study was carried out to test and compare the radioprotective potential of cimetidine and famotidine against lethally gamma irradiated NMRI mice. Adult male NMRI mice in groups of 10 were exposed to various doses of gamma rays at a dose rate of 93.3 cGy generated from a Co- 60 source. Mortality was examined daily for 30 days after irradiation. Various doses of gamma rays were used to calculate LD50/30. Different doses of cimetidine and famotidine were used in combination with 8 Gy gamma rays to find out the optimum protecting concentration of either drug. Finally the optimum protecting concentration of either drug was used in combination with various doses of gamma rays. Each experiment was repeated for three times. Results show that mean LD50/30 for radiation alone was found to be 723.7 cGy. When using different doses of cimetidine in combination with 801 cGy gamma rays, the dose of 15 mg/kg cimetidine produced optimum protection, while optimum dose of famotidine was found to be 10 mg/kg. However, LD50/30 obtained with optimum dose of either cimetidine or famotidine led to a DRF of 1.11 and 1.05 respectively. Cimetidine compared to famotidine was found to be more protective against mortality induced by radiation in mice. This effect of cimetidine might be due to its immunomodulatory role and thus protecting bone marrow and lymphoid tissue injuries following whole body gamma irradiation.

Investigation on the natural radionuclides 238U, 232Th, 40K and natural fallout radionuclide 210Po in the prominent plants species of Western Ghats tropical forest near Kotagiri have been carried out as a part of baseline background radiation studies in the forest environment. The prominent plants species of the region Evodia roxburghiana and Eleaocarpus oblangus were chosen and concentrations of 238U, 232Th, 40K and 210Po were measured by employing gamma ray spectrometer and alpha counter. The radioactivity concentrations in plants and soils reflect the impact of the existence of igneous nature of rock in the area of study. Concentration ratios (CR) of these radionuclides, between plants and underlying soil, have been studied and results shows that the concentration ratios (CR) seem to be depend on radionuclides in soil. From careful analysis of the results, these Plants could be used as an indicator to monitor these radionuclides.

The equivalent dose in the human body due to the natural gamma-emitting radionucides (238U, 232Th and 40K) in the surface soil surrounding the Consolidated Tin mine site in Bukuru-Jos, Nigeria has been determined in this study. Measurements of the soil natural radioactivity were made using a multi-channel pulseheight analyzer (Canberra Series 10 plus) coupled to a 76 mm×76 mm Nal (Tl) scintillation detector. The mean concentrations obtained for each of the radionuclides is 35.4±17.6 Bq/kg for 40K; 776.0± 158.0 Bq/kg for 238U and 2.72±0.58 kBq/kg for 232Th. The mean absorbed dose rate due to natural radioactivity calculated at a height of 1.0 m above the ground is 2.16 µGy/hr which converts to an equivalent dose of 3.0 mSv/y. The results obtained in this study are far above the world average equivalent dose of 0.41 mSv/y but lower than the annual limit of 20 mSv/y for radiation workers but still represents a health risk to workers on the site.

Iodine-123 (123I) is regarded as one of the best radionuclides for in vivo medical studies using single-photon emission computed tomography (SPECT) due to its suitable physical property. To design a new system in order to replace cryogenically solidified xenon target by the gas one, some necessary calculations are needed to be done such as finding the excitation functions variation of the production reactions, thick target yield of 123I production, etc. The computer codes Alice91 and SRIM have been used as a calculation tools. According to the suggested design, a conical shaped irradiation vessel made of copper with thickness of 1mm, outlet diameter of 1 cm, 5 cm length and 12° angle at summit can be fixed inside a liquid nitrogen housing chamber. The 124Xe gas was sent to the inside of this very cold conical trap and eventually deposited on its surface in solid form. Calculation showed that during bombardment with 17- 28 MeV proton energy, the thickness of solidified xenon layer remained about 0.28 mm. The production yield of 123I can be predicted to be around 150 mCi/µAh.