Evaluation of ExacTrac® Imaging Device for Repositioning Quality of Patients Undergoing an External ENT Radiotherapy

Overview

Monocentric, category 2 study according to Jardé Law (minimal risks and constraints) of three prospective cohorts: Tumors located at the oropharynx, the oral cavity and the larynx-hypopharynx. The main objective is to evaluate the 3D vector of the absolute residual positioning error observed with the CBCT reference imaging, after repositioning performed with ExacTrac®. The secondary objectives are to evaluate: 1) the rate of residual errors ≥2mm (translations in all directions) and ≥2 ° (rotations in all directions) on CBCT imaging after repositionning with the ExacTrac® system; 2) the Evaluation of intrafraction movements amplitude by analyzing the ExacTrac® images taken during the irradiation; 3) the evolution of the relative position of the volume of the tumor at high risk of recurrence (CTVTHR) in relation to the spine over the entire duration of the treatment; 4) the impact of patient's weight loss, the advancement of RT and the realization of a chemotherapy / targeted therapy concomitant with RT, on the evolution of the relative position of the CTVTHR in relation to the column vertebral; 5) the dosimetric consequence of a strict bone registration on the CTVTHR coverage by calculating the post-treatment dose on the CBCT imaging.

The radiotherapy treatment preparation requires performing a dosimetric scanner (CT) of the patient in the treatment position, with the compression. The repositioning of the ENT sphere can be complex, especially in cases where there is irradiation of the supraclavicular lymph node areas. Indeed, the height of the irradiated area can easily exceed 20cm and it is necessary to ensure a good reproducibility of the repositioning of the spine relative to the skull. At the end of the dosimetric CT, the radiotherapist delineates the macroscopic tumor volume (GTV) as well as the clinical tumor target volumes (CTVT) and lymph nodes (CTVN), which take into account the infiltration risks of the tissue around the macroscopic tumor. Margins around the VCTs then make it possible to obtain the estimated PTV target volumes (T and N), defined so that the VCTs receive the prescribed dose despite the geometric uncertainties associated with the treatment. Contours of organs at risk (OAR) are also carried out on the dosimetric CT. Margins around the most critical OARs (eg: marrow, brainstem, chiasma and optic nerves) are then added to generate predictive target volumes of organs at risk (PRV), taking into account the geometric uncertainties. These uncertainties are separated into errors in the treatment execution (random) and errors in the treatment preparation (systematic). Execution errors include repositioning errors, organ movements (overnight), patient anatomical changes, intrafraction movements. Errors related to treatment preparation include repositioning errors related to patient's skin spotting of the treatment isocenter during the dosimetric CT (thanks to room lasers), errors related to the CT acquisition that sets the CTV in a given position, the CTV delineation errors. Dosimetry is then carried out taking into account the dose criteria to be respected on the PRVs and PTVs. Whatever the protocol used \[Shrinking Action Level (SAL), non-action-level (NAL) or e-NAL (extented NAL)\], it must at least make it possible to guarantee that the delivered dose complies with the planned dose. An optimization of the imaging protocol must then be able to reduce the margins without compromising the treatment quality, while reducing its toxicity for the patient. On the Centre Léon Bérard accelerators equipped with both CBCT and ExacTrac®, we would like to assess the possibility of replacing or reducing the frequency of CBCTs using ExacTrac®. The time-consuming and irradiating characteristics of CBCT encourage to propose this study, which will define the patients for whom the use of CBCT can be minimized. In addition, if the correlation between ExacTrac® and CBCT is good, the use of ExacTrac® will make it possible to control and correct intrafraction movements, and therefore reduce the random uncertainties associated with carrying out the treatment. The possibility of using ExacTrac® imaging for the repositioning of patients treated with RCMI ENT would allow a reduction in treatment time and therefore less discomfort for the patient, a reduction in the dose linked to repositioning imaging, follow-up and correction of patient movements during the irradiation period. Finally, this project will enable to propose new pre-treatment imaging strategies and personalized margins according to the position of the lesions to be treated at the ENT level in order to reduce the session time when possible, and to reduce the radiation doses. X due to imaging. The overall objective is to improve the care and quality of treatment for the patient.