A measure tool for evaluating dose falloff outside the target volume in high precision radiotherapy

Abstract

Introduction: A reliable and high resolution systemic with all aspects plan evaluation indices has been proposed in this study to measure the dose falloff outside the target volume. The essential goal of this study is to compensate the shortcomings for the judgment of planning target volume and dose-volume histogram by visual verification slice by slice in high precision modern radiotherapy techniques like stereotactic radiation surgery, volumetric arc therapy, and stereotactic body radiation therapy. Materials and methods: Dynamic Gradient Index has been proposed both geometric and dosimetric orientated in all aspects plan evaluation indices to measure the dose falloff outside the target volume. Organ at Risk Integral Dose, and Target Specific Gain Ratio are created for evaluating highly conformal plans and provide better sparing of normal tissue. Users can do the plan evaluation indices calculation proposed in this study just simply with a sequence of exported data including normal tissue volume covered by every isodose line, target volume covered by every isodose line, and organ at risk volume covered by every isodose line from the approved planning system. The results here were also compared with several indices usually used such as gradient index developed by various authors. Results: DGI avoids the mistaken judgment counted on a single gradient index on one referenced isodose line recommended by other published results for the evaluation of SRS, SBRT high precision needed plan. Dynamic Gradient Index is a measure of steep dose gradient outside the target volume; therefore; this index plays a significant role in SRS as a measure of plan quality, especially a judgment of complication cases. Furthermore, taking into consideration the Organ at Risk Integral Dose and normal tissue integral dose to evaluate the target therapeutic gain lets Target Specific Gain Ratio becomes a comprehensive evaluation tool for pros and cons tangled cases. Conclusions: The function of DGI successfully reflects the advantage of fast expanded isodose lines (low dose gradient) could be easily examined. The plan superiority is determined by how close the DGI and the other indices are to the line of the benchmark. The growing speed of DGI for the SRS curve is slower similar to VMAT than the other two treatment techniques. The DGI of SRS beyond 100% inside the target area shows the advantage of the plateau between 100% and 110%, which means the change of dose gradient is smaller and this phenomenon could not be checked in DVH as well in other plan evaluation indices.

Keywords

• Gradient index
• Plan evaluation tool
• Stereotactic radiation surgery
• Volumetric arc therapy
• Stereotactic body radiation therapy
• Organ at risk integral dose