Prostate Radiotherapy
Proton Therapy vs IMRT for Prostate Cancer: What PARTIQoL Found
The randomized PARTIQoL trial found similar quality of life and five-year cancer control with proton therapy and IMRT for localized prostate cancer.
Short answer: In the randomized phase 3 PARTIQoL trial, proton therapy and intensity-modulated radiation therapy (IMRT) produced similarly high quality of life and cancer control for low- or intermediate-risk localized prostate cancer. The study did not show that proton therapy was clinically superior.
What did PARTIQoL compare?
PARTIQoL randomly assigned 450 people to proton beam therapy or photon-based IMRT. All had localized low- or intermediate-risk prostate cancer. Hormone therapy and pelvic lymph-node radiation were not part of the study.
Participants received either a conventional schedule of 44 treatments or a moderately shortened schedule of 28 treatments. About half used a rectal spacer. These details matter because the trial compared contemporary treatment approaches rather than a single rigid technique.
What did patients report?
The primary endpoint was change in bowel quality of life at two years. Both groups began with high average bowel-function scores and experienced small declines:
- the proton group declined by about 2.4 points;
- the IMRT group declined by about 2.2 points; and
- the difference was not statistically or clinically meaningful.
There were also no sustained differences in urinary, sexual, or hormonal quality-of-life scores at measured timepoints through five years.
Was cancer control different?
No difference was detected. At five years, progression-free survival was:
- 93.4% with proton therapy; and
- 93.7% with IMRT.
The hazard ratio was 1.16 with a wide confidence interval, and the comparison was not statistically significant. Longer follow-up remains useful, but the available randomized data do not support claiming better prostate cancer control from one of these beam types.
Why can proton plans still look different?
Protons deposit radiation differently from photons and may reduce the amount of low-dose radiation that continues beyond a target. A treatment plan can therefore show dosimetric advantages without guaranteeing that a patient will feel better or have better cancer control.
PARTIQoL tested whether those physical differences translated into outcomes patients could report. In this population, they did not create a measurable advantage in the studied quality-of-life domains.
What does the trial not answer?
The results should not be generalized automatically to:
- high-risk prostate cancer;
- pelvic lymph-node radiation;
- treatment combined with hormone therapy;
- reirradiation or unusual anatomy; or
- every newer proton-delivery technique.
PARTIQoL was reported as a late-breaking randomized trial abstract. Continued follow-up and a full peer-reviewed outcomes report can add detail, but the randomized comparison is more reliable than assuming one technology is better from dose maps alone.
Has this finding been confirmed since?
Yes. In 2026, early results from COMPPARE — a prospective comparison of 2,343 analyzed patients treated with protons or IMRT at 51 centers — reached the same conclusion: no significant difference in patient-reported bowel symptoms, gastrointestinal toxicity, or early cancer control. Two complementary study designs, one randomized and one pragmatic and real-world, now point the same direction.
How should someone choose?
When both options are available, ask about the team's prostate-specific experience, image guidance, motion management, normal-tissue doses, treatment schedule, travel, insurance coverage, and out-of-pocket cost.
The practical message is not that technology is irrelevant. It is that high-quality planning and delivery matter more than the label “proton” or “photon” for the low- and intermediate-risk population studied.
Questions patients often ask
Is proton therapy better than IMRT for localized prostate cancer?
PARTIQoL did not find better patient-reported quality of life or progression-free survival with proton therapy. Either can be an effective choice when planned and delivered well.
Does proton therapy cause fewer bowel side effects?
Not in this trial. Average bowel scores declined only slightly in both groups, with no meaningful difference at two years or through five years.
Does PARTIQoL apply to high-risk or metastatic prostate cancer?
No. Participants had low- or intermediate-risk localized disease, did not receive hormone therapy, and did not receive pelvic lymph-node radiation.
Sources and further reading
- PARTIQoL: Phase III Randomized Clinical Trial of Proton Therapy vs IMRT. International Journal of Radiation Oncology, Biology, Physics (2024).
- IMRT and Proton Therapy Offer Equally High Quality of Life and Tumor Control. American Society for Radiation Oncology (2024).
- PARTIQoL Clinical Trial Record. ClinicalTrials.gov (2026).
