The effect of MLC leaf width in single-isocenter multi-target radiosurgery with volumetric modulated arc therapy


© 2019 Old City Publishing, Inc. Purpose: Single-isocenter multi-target (SIMT) volumetric modulated arc therapy (VMAT) is primarily limited to linear accelerators utilizing 2.5 mm leaf width MLCs. We explore feasibility of applying this technique to linear accelerators utilizing MLCs with leaf width of 5 mm. Methods: Twenty patients with 3-10 intracranial brain metastases originally treated with 2.5 mm MLCs were re-planned using 5 mm MLCs and relevant dosimetric indices were compared. We also evaluated various strategies of adding VMAT arcs to mitigate degradations of dose quality values. Results: Wider MLCs caused small changes in total MUs (5827 ± 2334 vs 5572 ± 2220, p = 0.006), and conformity index (CI) (2.22% ± 0.05%, p = 0.045), but produced more substantial increases in brain V30%[%] and V50%[%] (27.75% ± 0.16% and 20.04% ± 0.13% respectively, p < 0.001 for both), and V12Gy[cc] (16.91% ± 0.12%, p < 0.001). Conclusion: SIMT radiosurgery delivered via VMAT using 5 mm wide MLCs can achieve similar CI compared to that using 2.5 mm leaf width MLCs but with moderately increased isodose spill, which can be only partially mitigated by increasing the number of VMAT arcs.








Scott Richard Floyd

Gary Hock and Lyn Proctor Associate Professor of Radiation Oncology

Diseases of the brain carry particular morbidity and mortality, given the fundamental function of the brain for human life and quality of life. Disease of the brain are also particularly difficult to study, given the complexity of the brain. Model systems that capture this complexity, but still allow for experiments to test therapies and mechanisms of disease are badly needed.  We have developed an experimental model system that uses slices made from rat and mouse brains to create a test platform to research new treatments for brain diseases such as stroke, Alzheimer's disease, Huntington's disease and brain tumors. This model system reduces the number of experimental animals used, and streamlines experiments so that final testing in laboratory animals is more efficient. We use this brainslice system and limited numbers of experimental animals to test drugs and genetic pathways to treat stroke, Alzheimer's disease, Huntington's disease and brain tumors. As many brain tumors are treated with radiation therapy, we have a particular interest in the cellular response to DNA damage caused by radiation. DNA damage signaling and repair are fundamental processes necessary for cells to maintain genomic integrity. Problems with these processes can lead to cancer. As many cancer cells have altered DNA damage and repair pathways, we can apply DNA damage as cancer therapy. Our knowledge of how normal and neoplastic cells handle DNA damage is still incomplete. A deeper understanding can lead to improved cancer treatment, and to better protection from the harmful effects of DNA damaging agents like radiation. To this end, we plan experiments that test the effects of radiation on normal animal tissues and animal models of cancer, as well as molecular pathways in brain diseases such as Alzheimer’s, Huntington’s and stroke.


Justus D Adamson

Associate Professor of Radiation Oncology

Radiosurgery and SBRT
Image Guided Radiation Therapy (IGRT)
Quality Assurance (QA) in Radiation Therapy
3D Dosimetry

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