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Table 5 Predicted late rectal toxicity rates using spatial NTCP models

From: Dosimetric feasibility of moderately hypofractionated/dose escalated radiation therapy for localised prostate cancer with intensity-modulated proton beam therapy using simultaneous integrated boost (SIB-IMPT) and impact of hydrogel prostate-rectum spacer

End point * Whole group
(23 patients)
Non-spacer group
(8 patients)
Spacer group
(15 patients)
P value
Necrosis/stenosis
Mean ± SD 3.9 ± 2.37% 5.87 ± 2.17% 2.87 ± 1.77% 0.005
Range (0–8%) (2–8%) (0–6%)
Late rectal bleeding ≥ 3
Mean ± SD 1.56 ± 1.24% 2.5 ± 1.51% 1.067 ± 0.7% 0.016
Range (0–5%) (0–5%) (0–2%)
Late toxicity ≥ 3
Mean ± SD 9.43 ± 4.15% 12.75 ± 2.87% 7.67 ± 3.66% 0.002
Range (1–15%) (7–15%) (1–13%)
  1. *Poisson-LQ model for Necrosis/stenosis [25], LKB model for late rectal bleeding ≥ 3 [26], and LKB model for late effects ≥ 3[27]