Normal Tissue Complication Probability (NTCP) modeling of late rectal bleeding following external beam radiotherapy for prostate cancer: A Test of the QUANTEC-recommended NTCP model

Figures & data

Table I. Patient characteristics.

Patients	159
Mean age at RT (range), years	70.4 (34.4, 82.5)
Pelvic field (four-field box)
No	87 (55%)
Yes	72 (45%)
Hormone therapy	108 (68%)
Gleason score
6	51 (32%)
7	80 (50%)
8	14 (9%)
9	14 (9%)
Presenting PSA
≤ 10 ng/ml	85 (53%)
10 < and ≤ 20 ng/ml	44 (28%)
> 20 ng/ml	30 (19%)
Diabetes
Yes	29 (18%)
No	130 (82%)
Hypercholesterolemia
Yes	31 (19%)
No	128 (81%)
Hypertension
Yes	63 (40%)
No	96 (60%)
Haemorrhoids
Yes	12 (8%)
No	147 (92%)

Figure 1. Kaplan-Meier actuarial estimate of late rectal bleeding > = grade 2. Ninety percent of cases are observed within two years of the end of radiotherapy.

Figure 2. Freedom from > = grade 2 rectal bleeding in patients aged over (or under) 77 years when commencing RT (p=0.007; log-rank test).

Figure 3. Incidence of late rectal bleeding as a function of gEUD. Data was binned in 1 Gy intervals according to computed gEUD values with the best fit n parameter value of 0.068. Error bars are binomial 68% confidence intervals. Only three plans fell outside the gEUD range 62 to 68, and were not included. The estimated 95% confidence interval for the best-fit model is shown by thin solid lines. The QUANTEC-recommended LKB model is shown as the dashed line (ignoring a small error due to the slightly different n values). Observed rates are smaller than QUANTEC predicted rates at all gEUD levels.