12 Study of the anatomy position reproducibility during deep inspiration breath hold

Abstract

Introduction Mobile tumors radiotherapy (breast, lung, abdomen) is face to major discrepancies coming from respiratory movements. This is why innovative techniques have been developed with the objective of gating the beams. Deep Inspiration Breath Hold (DIBH) technique allows to control the respiratory movements with the help of a spirometer and visual feedback. The aim of this study is to estimate the anatomy position reproducibility during DIBH with images acquired during the treatment, for three sites: breast, lung, abdomen. Methods The files analyzed concerned patients benefiting from DIBH with the SDX/Dyn’R spirometer. The analyzes were performed on images acquired with the MV and kV imagers for the planar and CBCT modalities. Breast: Distance evaluations between the DRR and the weekly EPID image for 15 patients. Due to a lack of reliable bony marks in the breast EPID image, we used the sub-mammary fold position and some crossing between two ribs. Lung: Retrospective analysis of two thoracic CT acquired before the treatment and at 2/3 of the sessions for 30 patients. The measurements concerned: lung volume, diaphragm, heart, tracheal carina positions and patient thickness at the thoracic and abdominal levels. The daily kV images enabled to measure the diaphragm and the sternum positions with regard to the spine (10 patients). Abdomen: Estimation of the diaphragm and the sternum positions, with kV images for 15 patients. The CBCT acquisition allowed studying the reproducibility, between two apneas, of the soft tissues positions and specifically the displacement of the kidneys and biliary prosthesis (10 patients). Results Results are given in Fig. 1. The DIBH technique for a mammary tumor does not reveal important variation of the heart position with regard to the rib cage: mean 3.6 mm (±2.6 mm) perpendicularly to the internal tangential beam. Concerning the thorax, the biggest movements are situated at the diaphragmatic and abdominal levels in cranio-caudal direction, respectively mean 5.7 mm (±4.0 mm) and 7.3 mm (±5.9 mm). For the abdominal region (gastric, hepatic, pancreatic tumor), kidneys and diaphragm are subjected to the biggest gaps: mean 6.3 mm (±5.6 mm) and 5.8 mm (±4.0 mm) in cranio-caudal direction. Download : Download high-res image (141KB) Download : Download full-size image Conclusion The Deep Inspiration Breath Hold method offers anatomical immobilization. We have studied the reproducibility of the organs and tissues positions during several apneas. The results are on average infra-centimetric with more pronounced variations in the abdominal area affected by variations of the digestive filling. These evaluations establish the minimum margins to be taken into account to build a PTV volume.