Comparison between prone and supine patient setup for spine stereotactic body radiosurgery

This paper investigates the dosimetric characteristics of stereotactic body radiotherapy (SBRT) treatment plans of spine patients in the prone position compared to the supine position. A feasibility study for treating spine patients in the prone position using a fiducial-less tracking method is presented. One patient with a multilevel spinal metastasis was simulated for SBRT treatment in both the supine and prone position. CT scans of the patient were acquired, and treatment plans were created using the CyberKnife® planning platform. The potential advantage of the prone setup as a function of lesion location and number of vertebral bodies involved was studied for targets extending over 1, 2 and 3 consecutive vertebral bodies in the thoracic and lumbar spine. The same process was repeated on an anthropomorphic phantom. A dose of 30 Gy in 5 fractions was prescribed to 95% of the tumor volume and the dose to the cord was limited to 25 Gy. To investigate the feasibility of a fiducial-less tracking method in the prone setup, the patient was positioned prone on the treatment table and the spine motion was monitored as a function of time. Patient movement with the respiratory cycle was reduced by means of a belly-board. Plans in the prone and supine position achieved similar tumor coverage and sparing of the critical structures immediately adjacent to the spine (such as cord and esophagus). However, the prone plans systematically resulted in a lower dose to the normal structures located in the anterior part of the body (such as heart for thoracic cases; stomach, lower gastrointestinal tract and liver for lumbar cases). In addition, prone plans resulted in a lower number of monitor units compared to supine plans.