Evaluation of CTV-PTV margins for 3D-CRT of Head and Neck Cancers (HNC).

Purpose: Patients movement and Organs mobility during Three Dimensional Conformational Radiotherapy (3D-CRT) may introduce errors especially during the treatment delivery, random and systematic errors are one of the most accurate errors. In this work we implanted a method to determinate the Clinical Target Volume (CTV) to Planning Target Volume (PTV) margins. The aim of this study is to reduce these errors probability by the evaluation of the optimal for CTV-PTV margin by studying the corrected values of deviations for HNC at the Mohammed VI cancer treatment centre treated between 2019 and 2021. Material and Method: The study consists on creating a DATA base containing spatial movement of study group of 100 patients following the treatment machine axis Vrt, Lng, and Lat directions during the first four fractions. This study is done by Monaco (Version 5.11.02, Elekta, Stockholm Sweden) treatment planning system V 5.11.02 (TPS) and Mosaiq V 2.0 involving iViewGT R3.4.0 and XVI R5.0.3 on board imaging systems by Elekta Infinity Treatment Machine (Elekta Ltd, Crawley, UK). The patients were choosing randomly during the study and archived in a DATA base to collect the random and systematic errors, the root of the sum of the squares for the doubled value of method uncertainty based on the Van Herk and AL equation of PTV to CTV determination, Stroom's model of Tumour Control Probability (TCP) and ICRU-50 formalism. Included: The random choice was made to detect maximum of errors possible and to optimize the value of main function for errors margins obtained through the study. Each patient was controlled by Kv images (iViewGT R3.4.0 and XVI R5.0.3 on board imaging systems) to determinate the gap between the dosimetry-CT acquisition and the treatment session. The DATA analysis was made calculating about 400 parameters to obtain the main Function and standard deviation for every patient. Results: CTV-PTV margin collected DATA was obtained by the correction values obtained by imaging system before treatment gave us a Mean (M) deviation function, the systematic errors (S) value and random errors (s) respectively: 4.04 mm, 0.40 mm and 6.35 mm. the result obtained by the application of this values in the Van Herk equation for CTV-PTV margin was 5.7 mm. Conclusion: The value calculated allowed us to have a validation of our quality treatment for three dimensional radiotherapy HNC and make sure that at Mohammed VI cancer treatment centre the norms and recommendations of radiotherapy treatments delivery are respected. [ABSTRACT FROM AUTHOR]