EVALUATION OF ADDITIONAL SKIN MARK ON THE THORACIC REGION FOR HEAD AND NECK RADIOTHERAPY

Introduction: Misalignment between the face and the supraclavicular fossa is usual in head and neck radiotherapy when common thermoplastic masks are used. Since this sort of masks does not provide proper immobilization of the thoracic region, to reproduce the patient position acquired during the CT simulation is a challenging task. In this sense, in addition to the three conventional marks made on the mask, we introduced in the routine of radiotherapy of the University Hospital of Brasília a fourth mark made on the patient‘s chest with the aid of sagittal laser. Objective: The aim of this study was to analyze the effectiveness of additional skin mark on the thoracic region for head and neck radiotherapy on patients alignment. Methods: To see whether the skin mark on the thoracic region have improved day-to-day patient alignment, we carried out a retrospective analysis. Two groups of randomly chosen patients were compared: one group with 15 patients with the three conventional marks and other with 15 patients with the additional thoracic skin mark. During the treatment sessions, CR portal images were acquired to be registered with digitally reconstructed radiographs (DRRs), used as references, in a homemade software previously reported. Thirty portal images were evaluated. Initially, from these images, variations in the lateral-lateral and cranial-caudal coordinates were measured by matching corresponding bony landmarks of the face to the DRR. Then, a new image registration were performed taking into account only the thoracic bony landmarks. The coordinates difference obtained with these two images registration were used to quantify patient misalignment. We used Students t-test to compare the two groups of patients. Results: We observed statically significant difference between the two groups in both directions. The mean absolute variations (±1SD) in lateral-lateral direction were 0.56 (± 0.55) cm vs. 0.27 (± 0.22) cm [p= 0.034] for the group treated with 3 marks and the group with the additional thoracic mark, respectively. In cranial-caudal direction, the variations were 0.45 (± 0.31) cm vs. 0.11 (± 0.2) [p<0.001] for the group treated with 3 marks and the group with the additional thoracic mark, respectively. Conclusion: The patient alignment performed with the aid of the thoracic mark enables greater patient position reproducibility.