Promising results have also been achieved using SBRT techniques, including the linear accelerator (Linac) and CyberKnife (CK) in the treatment of prostate cancer. It has been reported that various studies describe the advantages of the above mentioned techniques for various sites including head and neck, esophageal, brain, cervical cancers, ovarian cancers, etc.

Accurate measurement of transit time of the HDR brachytherapy source of a remote after-loading unit is necessary to calculate the total radiation dose given to the treatment volume. Presently, most of the HDR brachytherapy treatment planning systems neglect the transit time in the computation of dose. The aim of this investigation is to use a well type ionization chamber to measure the transit time during the source movement between two dwell positions. As well type ionization chamber and a precision electrometer (manufacturer CD instruments, Bangalore) were used to measure the charge generated during the movement of the Ir-192 source of a Gammamed HDR brachytherapy unit with an interstitial needle. Effective transit time and effective speed were determined on the basis of methodology described by Sahoo [2]. Corrections were done on the basis of relative sensitivity values for varaious dwell position in the ionization chamber. In the present study the variation of effective speed with interdwell distance was minimal as compared with that of Sahoo [2]. The effective transit times were 0.129, 0.182, 0.301, 0.402, 0.701, and 0.993 seconds for 1, 2, 4, 6, 8 and 10 cm interdwell separations respectively. The effective transit times in the present study were higher than those of Sahoo [2]. Software modification accounting for the dynamic dose should be incorporated into all HDR planning systems. Such an improvement would enhance the safety and accuracy of HDR brachytherapy.

No abstract

Objective:The study was conducted to quantitatively evaluate the dosimetric effects of high definition (2.5 mm) and standard definition (5.0 mm) MLC on the quality of SBRT plans using SIB-IMRT and SIB-VMAT technique for carcinoma prostate and also to evaluate the dosimetric advantage of one technique over the other. Materials and Methods: Seventeen annonymized planning CT data sets were used to generate plans for both VMAT and IMRT techniques using 2.5 mm and 5.0 mm MLC.The prescription to the nodule was 45Gy in 5 fractions and to the prostate was 35Gy in 5 fractions.CI, GI, D 2% , D 98% , D 50% and V 95% for target; D 2% , Dmean, V 80% , V 20% for OAR's; V 5% of the irradiated volume, and delivered MU's were analyzed.An independent t-test was used to compare the plans. Patient specific QA for all plans were also performed and analyzed. Results: Minor difference in dosimetric indices was observed between 2.5mm and 5mm MLC VMAT plans, except D 2% (PTV35) and D 98% (GTV45) were better in 2.5mm MLC plans (p<0.05).D 2% and D 50% to GTV45 with p<0.009 and <0.03 respectively, and D 2% of bladder (p<0.03) were significantly lesser for VMAT plans compared to IMRT plans. GI was significantly better for 2.5mm MLC plans in both techniques (p<0.05). 2.5mm MLC plans on an average had 9.9% and 7% more MU for VMAT and IMRT plans respectively. Conclusion: All the plans provided adequate dose coverage to target. Highly gradient plans with better conformity were achieved with 2.5mm MLC and VMAT combination with an increase in MU delivered, compared to 5mm MLC plans.