Accuracy of dose planning for prostate radiotherapy in the presence of metallic implants evaluated by electron spin resonance dosimetry

Radiotherapy is one of the main approaches to cure prostate cancer, and its success depends on the accuracy of dose planning. A complicating factor is the presence of a metallic prosthesis in the femur and pelvis, which is becoming more common in elderly populations. The goal of this work was to perform dose measurements to check the accuracy of radiotherapy treatment planning under these complicated conditions. To accomplish this, a scale phantom of an adult pelvic region was used with alanine dosimeters inserted in the prostate region. This phantom was irradiated according to the planned treatment under the following three conditions: with two metallic prostheses in the region of the femur head, with only one prosthesis, and without any prostheses. The combined relative standard uncertainty of dose measurement by electron spin resonance (ESR)/alanine was 5.05%, whereas the combined relative standard uncertainty of the applied dose was 3.35%, resulting in a combined relative standard uncertainty of the whole process of 6.06%. The ESR dosimetry indicated that there was no difference (P>0.05, ANOVA) in dosage between the planned dose and treatments. The results are in the range of the planned dose, within the combined relative uncertainty, demonstrating that the treatment-planning system compensates for the effects caused by the presence of femur and hip metal prostheses.

Development of in-house software to calculate dose for intensity-modulated radiation therapy based on lung CT-patient data.

Background: In external radiotherapy, the delivered dose is calculated from the treatment planning system. Various types of software have been used to verify the patient dose distribution. Objective: Develop the in-house software (ISOFT) to calculate dose in intensity-modulated radiotherapy (IMRT) based on lung CT-patient data by combining the modified Clarkson integration with 3D-beam subtraction method. Materials and methods: An ISOFT was developed for 6MV X-rays Varian Clinac21EX linear accelerator and the CT-based patient data. The multileaf collimators (MLCs) file from the Varian Eclipse treatment planning was transferred to the ISOFT. The ISOFT was used to calculate the dose distribution with correction of tissue inhomogeneity. To test the accuracy of the ISOFT, the normal MLC-shaped fields and IMRT plans were measured in a water phantom and in a thorax phantom, respectively. Then, these measurements were compared with the doses calculated from the ISOFT and the Varian Eclipse treatment planning system. Results: The deviation between the measurements and calculations by the ISOFT for MLC-shaped fields in the water phantom fell within 0.5%. There were mostly higher calculated doses in lung compared with the measured result in the thorax phantom. The overestimated doses due to loss of scattering in the low-density materials were considered less in all methods of calculation. The measured lung dose difference from the ISOFT was within 5% criterion of acceptability. Conclusion: The ISOFT can be used conveniently to verify dose calculation in heterogeneous media.

Water-Fat Imaging with Automatic Field Inhomogeneity Correction Using Joint Phase Magnitude Density Function at Low Field MRI

PURPOSE: A new inhomogeneity correction method based on two-point Dixon sequence is proposed to obtain water and fat images at 0.35T, low field magnetic resonance imaging (MRI) system. MATERIALS AND METHODS: Joint phase-magnitude density function (JPMF) is obtained from the in-phase and out-of-phase images by the two-point Dixon method. The range of the water signal is adjusted from the JPMF, and 3D inhomogeneity map is obtained from the phase of corresponding water volume. The 3D inhomogeneity map is used to correct the inhomogeneity field iteratively. RESULTS: The proposed water-fat imaging method was successfully applied to various organs. The proposed 3D inhomogeneity correction algorithm provides good performances in overall multi-slice images. CONCLUSION: The proposed water-fat separation method using JPMF is robust to field inhomogeneity. Three dimensional inhomogeneity map and the iterative inhomogeneity correction algorithm improve water and fat imaging substantially.

Estimation of Inhomogeneity Correction Factor in Small Field Dosimetry / 의학물리

In this study, we estimated inhomogeneity correction factor in small field. And, we evaluated accuracy of treatment planning and measurement data which applied inhomogeneity correction factor or not. We developed the Inhomogeneity Correction Phantom (ICP) for insertion of inhomogeneity materials. The inhomogeneity materials were 12 types in each different electron density. This phantom is able to adapt the EBT film and 0.125 cc ion chamber for measurement of dose distribution and point dose. We evaluated comparison of planning and measurement data using ICP. When we applied to inhomogeneity correction factor or not, the average difference was 1.63% and 10.05% in each plan and film measurement data. And, the average difference of dose distribution was 10.09% in each measurement film. And the average difference of point dose was 0.43% and 2.09% in each plan and measurement data. In conclusion, if we did not apply the inhomogeneity correction factor in small field, it shows more great difference in measurement data. The planning system using this study shows good result for correction of inhomogeneity materials. In radiosurgery using small field, we should be correct the inhomogeneity correction factor, more exactly.