PBT, IMRT provide similar patient-reported outcomes for prostate cancer at 5 years

Jason Efstathiou, MD, PhD

Credit: OncLive

Proton beam therapy (PBT) and intensity modulated radiation therapy (IMRT) differ little in patient-reported function outcomes and progression-free survival (PFS) when used to treat localized prostate cancer, according to a late-breaking abstract presented at the American Society for Radiation Oncology (ASTRO) 2024 Annual Meeting in Washington, DC, this weekend.

Data from the phase 3 PARTIQoL trial show that both methods of contemporary radiotherapy were associated with “excellent” measures of patient quality of life as well as effective tumor control while not significantly differing from one another’s efficacy outcomes among patients with localized prostate cancer. Though the trial is ongoing for longterm analyses, the findings presented at ASTRO 2024 support the application of either IMRT or PBT for relevant patients.

Presented by Jason Efstathiou, MD, PhD, professor of radiation oncology at Harvard Medical School and a radiation oncologist at Massachusetts General Hospital, investigators sought to assess the previously held belief that PBT may result in improved patient-reported outcomes (PROs) in comparison to IMRT in men with localized prostate cancer.

“PBT has certain dosimetric advantages with the potential to reduce treatment-associated morbidity and improve oncologic outcomes, but it is generally more resource intensive than IMRT,” investigators noted.

The team randomized patients with intermediate or low-risk prostate cancer to either PBT or IMRT without hormonal therapy. Patients were stratified based on their age, rectal space user and fractionation of either 79.2 Gy/44 fractions or 70 Gy/28 fractions. Efstathiou and colleagues followed the patients to longitudinally assess PROs regarding bowel, sexual and urinary function 60 months post-radiotherapy completion; the primary endpoint was change from baseline in bowel quality of life via the 100-point health care software score at 24 months.

Investigators additionally sought secondary endpoints including comparison of sexual and urinary functions between IMRT and PBT, as well as toxicity and supplemental efficacy endpoints.

In total, 450 patients from 30 recruiting centers were randomized to either treatment methods between June 2012 and November 2021—226 to PBT, and 224 to IMRT. All but 5 and 8 patients in each respective treatment arm were eligible to initiate radiation for their prostate cancer, respectively.

At 60 months follow-up, 424 patients in the trial were still alive. Among them, median age was 68 years old; a majority had intermediate-risk disease (59%) and received hypofractionated care (51%). Approximately half additionally used a rectal spacer (48%), and 49% of patients administered PBT were treated via pencil beam scanning.

Efstathiou and colleagues observed no difference between the treatment arms for the primary outcome of health care software bowel score change at 24 months (P = .836), with both PBT and IMRT being associated with clinically insignificant reductions from baseline (-2.4 and -2.2, respectively). The team additionally reported no significant treatment-based differences in patient-reported bowel function at 3-month intervals through 18 months, as well as through 60 months overall.

Regarding secondary endpoints, there were no significant differences in hormonal, sexual or urinary domains at any observed timepoint in the 2 treatment arms. There was also virtually no difference in progression-free survival (PFS) between the PBT arm (93.4%) and IMRT arm (93.7%) at 60 months (hazard ratio [HR], 1.16; 95% CI, 0.53 – 2.57; P = .706).

Even when accounting for variables of patient stratification, investigators concluded that there were no significant differences in the levels of prostate cancer patient-reported improvement and treatment efficacy observed by investigators through 60 months post-care with either PBT or IMRT.

“This prospective randomized clinical trial shows that patients treated with contemporary radiotherapy for localized prostate cancer achieve excellent (quality of life) with highly effective tumor control, without measurable differences between PBT and IMRT,” investigators wrote. “We continue to monitor participants for longer follow-up and secondary endpoints.”

References

^{Efstathiou JA, Yeap BY, Michalski JM, Zietman AL, et al. Prostate Advanced Radiation Technologies Investigating Quality of Life (PARTIQoL): Phase III Randomized Clinical Trial of Proton Therapy vs. IMRT for Localized Prostate Cancer. Poster presented at: American Society for Radiation Oncology (ASTRO) 2024 Annual Meeting. Washington, DC. September 29 – October 2, 2024.}