Susu Yan1, Nicolas Depauw1, Judith Adams1, Bram L Gorissen1, Helen A Shih2, Jay Flanz1, Thomas Bortfeld1, Hsiao-Ming Lu3. 1. Division of Radiation Biophysics, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA. 2. Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA. 3. Hefei Ion Medical Center and Ion Medical Research Institute, University of Science and Technology of China, Hefei, China.
Abstract
PURPOSE: Proton therapy systems without a gantry can be more compact and less expensive in terms of capital cost and therefore more available to a larger patient population. Would the advances in pencil beam scanning (PBS) and robotics make gantry-less treatment possible? In this study, we explore if the high-quality treatment plans can be obtained without a gantry. METHODS AND MATERIALS: We recently showed that proton treatments with the patient in an upright position may be feasible with a new soft robotic immobilization device and imaging which enables multiple possible patient orientations during a treatment. In this study, we evaluate if this new treatment geometry could enable high quality treatment plans without a gantry. We created PBS treatment plans for seven patients with head-and-neck or brain tumors. Each patient was planned with two scenarios: one with a gantry with the patient in supine position and the other with a gantry-less fixed horizontal beam-line with the patient sitting upright. For the treatment plans, dose-volume-histograms (DVHs), target homogeneity index (HI), mean dose, D 2 ${D_2}$ , and D 98 ${D_{98}}$ are reported. A robustness analysis of one plan was performed with ± $ \pm $ 2.5-mm setup errors and ± $ \pm $ 3.5% range uncertainties with nine scenarios. RESULTS: Most of the PBS-gantry-less plans had similar target HI and organs-at-risk mean dose as compared to PBS-gantry plans and similar robustness with respect to range uncertainties and setup errors. CONCLUSIONS: PBS provides sufficient power to deliver high quality treatment plans without requiring a gantry for head-and-neck or brain tumors. In combination with the development of the new positioning and immobilization methods required to support this treatment geometry, this work suggests the feasibility of further development of a compact proton therapy system with a fixed horizontal beam-line to treat patients in sitting and reclined positions.
PURPOSE: Proton therapy systems without a gantry can be more compact and less expensive in terms of capital cost and therefore more available to a larger patient population. Would the advances in pencil beam scanning (PBS) and robotics make gantry-less treatment possible? In this study, we explore if the high-quality treatment plans can be obtained without a gantry. METHODS AND MATERIALS: We recently showed that proton treatments with the patient in an upright position may be feasible with a new soft robotic immobilization device and imaging which enables multiple possible patient orientations during a treatment. In this study, we evaluate if this new treatment geometry could enable high quality treatment plans without a gantry. We created PBS treatment plans for seven patients with head-and-neck or brain tumors. Each patient was planned with two scenarios: one with a gantry with the patient in supine position and the other with a gantry-less fixed horizontal beam-line with the patient sitting upright. For the treatment plans, dose-volume-histograms (DVHs), target homogeneity index (HI), mean dose, D 2 ${D_2}$ , and D 98 ${D_{98}}$ are reported. A robustness analysis of one plan was performed with ± $ \pm $ 2.5-mm setup errors and ± $ \pm $ 3.5% range uncertainties with nine scenarios. RESULTS: Most of the PBS-gantry-less plans had similar target HI and organs-at-risk mean dose as compared to PBS-gantry plans and similar robustness with respect to range uncertainties and setup errors. CONCLUSIONS: PBS provides sufficient power to deliver high quality treatment plans without requiring a gantry for head-and-neck or brain tumors. In combination with the development of the new positioning and immobilization methods required to support this treatment geometry, this work suggests the feasibility of further development of a compact proton therapy system with a fixed horizontal beam-line to treat patients in sitting and reclined positions.