Purpose: To evaluate the dosimetric differences between photon intensity-modulated radiation therapy (IMRT) plans, 3D conformal proton therapy (3DCPT), and intensity-modulated proton therapy (IMPT) plans and to investigate the dosimetric impact of different beam spot size and beam apertures in IMPT for pediatric Ewing sarcoma of the chest wall.
Methods and materials: Six proton pediatric patients with Ewing sarcoma in the upper, middle, and lower thoracic spine regions as well as upper lumbar spine region were treated with 3DCPT and retrospectively planned with photon IMRT and IMPT nozzles of different beam spot sizes with/without beam apertures. The plan dose distributions were compared both on target conformity and homogeneity, and on organs-at-risk (OARs) sparing using QUANTEC metrics of the lung, heart, liver, and kidney. The total integral doses of healthy tissue of all plans were also evaluated.
Results: Target conformity and homogeneity indices are generally better for the IMPT plans with beam aperture. Doses to the lung, heart, and liver for all patients are substantially lower with the 3DPT and IMPT plans than those of IMRT plans. In the IMPT plans with large spot without beam aperture, some OAR doses are higher than those of 3DCPT plans. The integral dose of each photon IMRT plan ranged from 2 to 4.3 times of proton plans.
Conclusion: Compared to IMRT, proton therapy delivers significant lower dose to almost all OARs and much lower healthy tissue integral dose. Compared to 3DCPT, IMPT with small beam spot size or using beam aperture has better dose conformity to the target.
Keywords: Ewing sarcoma; IMPT; IMRT; aperture; integral dose; spot size.
© 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.