Guided radiotherapy by an in-vivo dosimetry for lung tumors

The paper reports a feasibility study to carry out the adaptive radiotherapy of the lung tumors, guided by an in-vivo dosimetry method. At the moment the image guided radiotherapy (IGRT) is used for this aim, but it requires many periodic radiological images during the treatment that increase the workload and patient dose. The in-vivo dosimetry method reported here can reduce the above efforts alerting the medical staff for the commissioning of new radiological images for an eventual adaptive plan. The reconstructed in-vivo dosimetry at the isocenter point, Diso, requires a convolution between the transit signal, St, obtained by an Electronic Portal Imaging Device and a dose reconstruction factor, C, obtained by processing the patient’s computed tomography scans and that depend on (i) tissue inhomogeneities along the beam central axis, (ii) the in-patient isocenter depth and (iii) the field dimension. In this work the dose reconstruction was carried out to check the Diso in the lung tumor during the 3D conformal radiotherapy technique (3D CRT), and the results have been used to detect the interfraction tumor anatomy variations that can require new CT image and an adaptive plan. One patient showed, at mid-treatment for all beams, Diso values outside the tolerance level of 6%, and the commissioned new CT scans were used for the elaboration of an hybrid plan. The dose volume histograms for a prescribed dose per fraction Diso,TPS = 2Gy suggested an adaptive plan to reduce the dose in lung tissue. The results of this research show that the dose guided radiotherapy (DGRT) by the Diso reconstruction is feasible for daily or periodic investigation about the morphological lung tumor changes. In other words, since during the 3D CRT treatments the lung tumor anatomical changes occur frequently, the DGRT can be well integrated with the IGRT.