Patients with IBD, and especially CD patients, undergo frequent diagnostic imaging and thus significant exposure to ionizing radiation. This radiation exposure reaches high levels in 7% of CD patients, mainly from CT scanning. Efforts should be made to minimize the radiation exposure from diagnostic imaging by reducing either the number of studies or radiation dose in modalities with ionizing radiation.
A new algorithm to determine collimator angles that favor delivery efficiency of intensity modulated radiotherapy plans was developed. It was found that the number of segments and monitor units (MUs) were largely reduced with the set of collimator angles determined with the new algorithm without compromising plan quality. The improvement of delivery efficiency using the new algorithm depends on the size and shape of the target(s), the number of modulation levels, and the type of leaf-sequencing algorithm. In a typical prostate case, when a sweeping leaf-sequencer is used for Varian 120 leaf (0.5 x 0.5 cm2 beamlet), 80 leaf (1 x 1 cm2 beamlet) and Elekta 40 leaf (1 x 1 cm2 beamlet), the number of segments was reduced by 42%, 29%, and 5%, respectively. The number of MUs was reduced by 41%, 35%, and 10%. For the Siemens MLC (IMFAST leaf sequencer, 1 x 1 cm2 beamlet) the segment reduction was 32% and the MU reduction was 14%. Comparison of the plans using the new and Brahme algorithms, in terms of target conformity index and dose volume histogram of the organs at risk, showed that the quality of the plans using the new algorithm was uncompromised. Similar results were obtained for a set of head and neck treatment plans.
Purpose: To verify the dosimetric characteristics of Flat and Surface applicators (two of each, 2cm and 4cm in diameters) for Zeiss Intrabeam systemMethods: Dose rate vs. distance from surface of the applicators were measured with the 1D water tank and PTW ion chamber provided by IntraBeam system. Gafchromic films and solid water were used to determine the 2D dose distribution and beam divergence of the applicators. Results: The highest dose rate is from 2cm Surface applicator (3.4Gy/min at 1.6mm from applicator surface, it drops to 0.52Gy/min at 10mm). The 2cm Flat applicator dose rate is 1.47Gy/min at 1.6mm; it drops to 0.36Gy/min at 10mm. The lowest dose rate is from the 4cm Flat applicator (0.49Gy/min at 1.6mm; it drops to 0.18Gy/min at 10mm). The 4cm Surface applicator dose rate is 1.36Gy/min at 1.6mm; it drops to 0.29Gy/min at 10mm. All the data were verified and confirmed with the manufacture factory measurements.Two dimensional dose profiles (parallel to applicator surface) at different depths were plotted from scanned Gafchromic films. Dose divergence of approximately 85 degree for 4cm applicators; and 65 degree for 2cm applicators; can also be seen from exposed films perpendicular to the applicator surface. Conclusion: Dosimetric characteristic were studied for both Flat and Surface applicators from Intrabeam system. Although all the applicators in this study are still pending FDA approval for clinical use, the data collected thus far can serve as a framework for both radiation oncologists and medical physicists to build the future clinical trials and treatment programs.
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