Four-dimensional planning for motion synchronized dose delivery in lung stereotactic body radiation therapy

Background and purpose: To investigate a weighted four-dimensional (W-4D) treatment planning strategy based on the greater clinical advantage of the conformal over the intensity-moduIated technique in lung stereotactic body radiotherapy (SBRT). Material and methods: Two planning strategies (individual-phase 4D [IP-41D] and W-4D) were evaluated in eighteen lung SBRT patients. The IP-4D plan can deliver a constant fluence during whole respiratory phases. The W-4D plan's key concept was to escalate (or reduce) fluence using a 4D optimization algorithm when the tumour target was out-of-line (or in-line) with an organ-at-risk. The fluence was converted to a dynamic multi-leaf collimator leaf sequence for deliverable 4D irradiation. Results: In all patients, the W-4D plan enabled planning tumour volume conformity comparable to the IP-4D plan. The W-4D plan yielded a significantly lower maximum dose than the IP-4D plan for the spinal cord (-11%; p < 0.01), oesophagus (-14%; p < 0.01), heart (-22%; p = 0.01) and stomach (-23%; p = 0.07), and a lower mean dose to liver (-19%; p = 0.18) while maintaining the mean dose to lung (-1%; p = 0.23). Conclusions: W-4D is a robust, practical planning approach that achieves significant dose sparing relative to non-time-resolved tracking; it may be of greater clinical benefit in radiotherapy than the spatially intensity-modulated 4D approach. (C) 2016 Published by Elsevier Ireland Ltd.