Prevent one biochemical failure
7.25 NNT
13.8 percentage-point benefit
(95.0% whole-pelvic RT − 81.2% prostate-only RT = 13.8% absolute benefit)
Prostate only
81.2%
Whole pelvis
95.0%
Prostate cancer radiotherapy
Prophylactic Pelvic Nodal Irradiation – NNT Comparator
Compare absolute treatment effects from randomized evidence for prophylactic pelvic nodal irradiation, then test your own event-free outcome estimates.
POP-RT · 5-year outcomes
Whole-pelvic versus prostate-only radiotherapy
High- and very-high-risk, node-negative disease with estimated nodal risk ≥20%; all participants received long-term ADT.
Prevent one disease-free survival event
8.13 NNT
12.3 percentage-point benefit
(89.5% whole-pelvic RT − 77.2% prostate-only RT = 12.3% absolute benefit)
Prostate only
77.2%
Whole pelvis
89.5%
Prevent one distant metastasis/DMFS event
14.93 NNT
6.7 percentage-point benefit
(95.9% whole-pelvic RT − 89.2% prostate-only RT = 6.7% absolute benefit)
Prostate only
89.2%
Whole pelvis
95.9%
No demonstrated overall-survival benefit: 5-year OS was 90.8% versus 92.5% (HR 0.92; 95% CI 0.41–2.05; P=.83). These NNTs are trial-specific estimates derived from Kaplan–Meier rates.
Toxicity trade-off
17.7% vs 7.5% · NNH 9.80
(17.7% whole-pelvic RT − 7.5% prostate-only RT = 10.2% absolute increase; P=.03)
6.5% vs 3.8% · NNH 37.04
(2.7% numerical absolute increase; not statistically significant, P=.39)
No significant difference
The higher clinician-scored urinary toxicity was not reflected in a significant between-group QOL difference.
Original POP-RT toxicity analysis using RTOG scoring. The GI NNH is descriptive only because the comparison was not statistically significant.
The clinical trade-off in 100 comparable patients
Imagine 100 similar high-risk patients receiving whole-pelvic radiotherapy rather than prostate-only radiotherapy. At approximately 5 years, the POP-RT estimates suggest:
| Outcome | Approximate net effect per 100 treated |
|---|---|
| Biochemical failures prevented | 14 fewer |
| Disease-free-survival events prevented | 12 fewer |
| Distant-metastasis/DMFS events prevented | 7 fewer |
| Deaths prevented | No proven difference |
| Additional late grade ≥2 GU toxicity | About 10 more |
| Additional late grade ≥2 GI toxicity | No proven difference |
| Patient-reported QOL deterioration | No demonstrated between-group difference |
Rounded population illustration derived from the absolute differences in published 5-year estimates. Outcomes overlap and must not be added together. “No proven difference” does not establish equivalence.
NRG/RTOG 0534 SPPORT · 5-year FFP
Treatment intensification with ADT and pelvic nodal RT
Post-prostatectomy salvage setting: prostate-bed RT alone, with 4–6 months ADT, or with both ADT and pelvic nodal RT.
Add short-term ADT to prostate-bed RT
9.62 NNT
10.4 percentage-point benefit
(81.3% prostate-bed RT + short-term ADT − 70.9% prostate-bed RT = 10.4% absolute benefit)
PBRT
70.9%
PBRT + ADT
81.3%
Add pelvic nodes to PBRT + ADT
16.39 NNT
6.1 percentage-point benefit
(87.4% prostate-bed RT + ADT + pelvic-node RT − 81.3% prostate-bed RT + ADT = 6.1% absolute benefit)
PBRT + ADT
81.3%
+ pelvic nodes
87.4%
Add ADT + pelvic nodes to PBRT alone
6.06 NNT
16.5 percentage-point benefit
(87.4% prostate-bed RT + ADT + pelvic-node RT − 70.9% prostate-bed RT = 16.5% absolute benefit)
PBRT
70.9%
Full strategy
87.4%
Interpretation: these comparisons estimate prevention of one freedom-from-progression event by 5 years. The full strategy combines two interventions, so its NNT does not isolate the effect of pelvic irradiation alone.
Toxicity trade-off
19.7% → 37.7% → 44.6%
PBRT alone → PBRT + short-term ADT → PBRT + ADT + pelvic-node RT. NNH: 5.56 for adding ADT; 14.49 for adding pelvic-node RT; 4.02 for the full strategy versus PBRT.
4.4% → 8.8% → 12.2%
Acute grade ≥2 and ≥3 events increased significantly across the three arms (overall P<.001).
No significant difference
Late grade ≥2 GI: 10.3%, 10.2%, 9.1%; late grade ≥2 GU: 37.1%, 34.7%, 39.7% across Arms 1–3.
Late grade ≥2 blood/bone-marrow events were 1.8% with PBRT + ADT and 4.4% after adding pelvic-node RT (absolute increase 2.6%; descriptive NNH 38.46; one-sided P=.006), mainly leukopenia/lymphopenia. CTCAE v3.0; acute ≤3 months and late >3 months after RT.
2026 patient-reported quality-of-life analysis
644 participants
Bowel and urinary scores declined at 6 weeks, then improved at years 1 and 5, although they did not fully return to baseline.
Temporary ADT-related effect
Short-term ADT produced statistically poorer scores at 6 weeks and 1 year, but no between-arm difference remained at 5 years.
5.5 → 6.2 → 6.6 years
Mean quality-adjusted FFP for PBRT, PBRT + ADT, and PBRT + ADT + pelvic-node RT. Arms 2 and 3 were significantly better than PBRT alone.
There were no clinically significant QOL differences among treatment arms at 1 or 5 years. Overall-survival QALYs did not differ significantly. QOL was assessed with EPIC, Hopkins Symptom Checklist and EuroQol instruments.
The clinical trade-off in 100 comparable salvage patients
For 100 similar patients receiving salvage radiotherapy after prostatectomy, SPPORT suggests the following approximate changes at 5 years and during follow-up:
| Outcome | Add short-term ADT to PBRT | Add pelvic-node RT to PBRT + ADT | Full strategy vs PBRT alone |
|---|---|---|---|
| FFP events prevented by 5 years | About 10 fewer | About 6 fewer | About 17 fewer |
| Additional acute grade ≥2 adverse events | About 18 more | About 7 more | About 25 more |
| Additional acute grade ≥3 adverse events | About 4 more | About 3 more | About 8 more |
| Late grade ≥2 GI toxicity | No proven difference | No proven difference | No proven difference |
| Late grade ≥2 GU toxicity | No proven difference | No proven difference | No proven difference |
| Late grade ≥2 blood/bone-marrow events | No proven increase | About 3 more* | No proven difference |
| Clinically significant QOL difference at 1 or 5 years | None demonstrated | None demonstrated | None demonstrated |
| Overall-survival benefit | Not demonstrated | Not demonstrated | Not demonstrated |
Rounded absolute differences from the SPPORT trial: Arms 1, 2 and 3 had 5-year FFP of 70.9%, 81.3% and 87.4%; acute grade ≥2 adverse events of 19.7%, 37.7% and 44.6%; and acute grade ≥3 events of 4.4%, 8.8% and 12.2%. *The late blood/bone-marrow increase was significant for Arm 3 versus Arm 2, mainly leukopenia/lymphopenia, but the pattern was not significant for Arm 3 versus Arm 1. Outcome categories overlap and must not be summed.
Use your own parameters
Enter outcome-free survival or event rates at the same time point. The calculator uses the absolute difference between groups.
NNT 7.25(95.0% treatment − 81.2% comparator = 13.80% absolute benefit) · conventionally rounded NNT 8
This indicates benefit: the intervention improves the selected event-free outcome.
Method
How the calculation works
For an outcome where a higher percentage is desirable, the absolute benefit is treatment rate minus comparator rate. For an adverse event, the direction is reversed. The exact reciprocal is shown to two decimal places.
NNT = 1 ÷ absolute risk reduction
Primary references
Murthy V, et al. POP-RT efficacy outcomes.J Clin Oncol. 2021;39:1234–1242. DOI: 10.1200/JCO.20.03282 · PubMed
Pollack A, et al. NRG Oncology/RTOG 0534 SPPORT.Lancet. 2022;399:1886–1901. DOI: 10.1016/S0140-6736(21)01790-6 · Full text
Bruner DW, et al. SPPORT quality-of-life analysis.Int J Radiat Oncol Biol Phys. 2026. DOI: 10.1016/j.ijrobp.2026.06.3085 · Journal record
Murthy V, et al. POP-RT late toxicity and quality of life.Radiother Oncol. 2020;145:71–80. DOI: 10.1016/j.radonc.2019.12.006 · PubMed
Clinical-use notice. This educational calculator reproduces simple absolute-effect calculations from published trial estimates. It is not a validated decision-support device, does not adjust for confidence intervals or competing risks, and should not replace appraisal of eligibility, toxicity, imaging, comorbidity, patient preference, or current guidance.