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Background
The aim of this study was to investigate if the flattening filter free mode (FFF) of a linear accelerator reduces the excess absolute risk (EAR) for second cancer as compared to the flat beam mode (FF) in simultaneous integrated boost (SIB) radiation therapy of right-sided breast cancer.
Patients and methods
Six plans were generated treating the whole breast to 50.4 Gy and a SIB volume to 63 Gy on CT data of 10 patients: intensity-modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), and a tangential arc VMAT (tVMAT), each with flattening filter and without. The EAR was calculated for the contralateral breast and the lungs from dose-volume histograms (DVH) based on the linear-exponential, the plateau, and the full mechanistic dose-response model. Peripheral low-dose measurements were performed to compare the EAR in more distant regions as the thyroids and the uterus.
Results
FFF reduces the EAR significantly in the contralateral and peripheral organs for tVMAT and in the peripheral organs for VMAT. No reduction was found for IMRT. The lowest EAR for the contralateral breast and lung was achieved with tVMAT FFF, reducing the EAR by 25 % and 29 % as compared to tVMAT FF, and by 44 % to 58 % as compared to VMAT and IMRT in both irradiation modes. tVMAT FFF showed also the lowest peripheral dose corresponding to the lowest EAR in the thyroids and the uterus.
Conclusion
The use of FFF mode allows reducing the EAR significantly when tVMAT is used as the treatment technique. When second cancer risk is a major concern, tVMAT FFF is considered the preferred treatment option in SIB irradiation of right-sided breast cancer.
Purpose
The complexity of the treatment techniques IMRT (Intensity Modulated Radiation Therapy) and VMAT (Volumetric Modulated Arc Therapy) introduced the requirement of an individual plan verification. The latest development is 3D verification which allows evaluation in terms of 3D gamma values but also a judgment based on differences in dose distributions on individual patient CT data and in dose volume histograms. For a verification tool the error detection sensitivity is important. The purpose of this work is to evaluate the accuracy and the sensitivity of the gamma evaluation of the 3D verification software MobiusFx when a systematic error in one parameter is applied. The results are compared to an established 2D-measurement based method.
Methods
11 IMRT and 11 VMAT plans were selected as reference plans. For every reference plan a systematic offset of 1 mm, 2 mm and 3 mm in the same direction was applied to the Multi-Leaf-Collimator (MLC) positions. All plans were irradiated and verified simultaneously with MobiusFx and MatriXX Evolution 2D array measurement. For both verification systems the applied dose distributions were evaluated using the gamma method based on the reference plans. In MobiusFx additionally the MLC position errors were evaluated.
Results
Regarding the gamma evaluation results, MobiusFx and MatriXX Evolution 2D measurements have almost the same sensitivity: The gamma evaluation of both systems detected shifts of 1 mm in VMAT plans and shifts of 2 mm and larger in IMRT plans. The information of the MLC position error provided by MobiusFx allows further to detect errors down to a shift of 1 mm in IMRT plans, giving an advantage over the MatriXX measurement.
Conclusions
MobiusFx shows a high error detection sensitivity, comparable to MatriXX Evolution. Through the gamma calculation and the MLC position error it is possible to detect errors down to a shift in MLC positions of 1 mm. It is recommended to inspect all the above parameters during plan verification.
Purpose:
Total body irradiation (TBI) in extended source surface distance (SSD) is a common treatment technique before hematopoietic stem cell transplant. The lungs are organs at risk, which often are treated with a lower dose than the whole body.
Methods:
This can be achieved by the application of blocks. Three-dimensional (3D) printers are a modern tool to be used in the production process of these blocks.
Results:
We demonstrate the applicability of a specific printer and printing material, describe the process, and evaluate the accuracy of the product.
Conclusion:
The blocks and apertures were found to be applicable in clinical routine.