Proton beam therapy and intensity-modulated radiation therapy (IMRT) were found to offer equivalent quality-of-life outcomes for patients with localized prostate cancer, according to data from the PARTIQoL trial. This phase III trial showed no measurable differences between the two approaches in terms of bowel function, urinary symptoms, or sexual function. These findings were presented at the 2024 American Society for Radiation Oncology (ASTRO) Annual Meeting.¹ The results may help inform the decision-making process for localized prostate cancer treatment.

“Our study demonstrates that IMRT and proton therapy provide patients with localized prostate cancer equally excellent quality-of-life outcomes and highly effective tumor control,” said principal investigator Jason Efstathiou, MD, DPhil, FASTRO, Professor at Harvard Medical School and Vice Chair of Faculty and Academic Affairs in the Department of Radiation Oncology at Massachusetts General Hospital. “The results show only small quality-of-life declines from baseline levels for each treatment arm, with no sustained differences between the two approaches.”

“Our study demonstrates that IMRT and proton therapy provide patients with localized prostate cancer equally excellent quality-of-life outcomes and highly effective tumor control.”

— JASON EFSTATHIOU, MD, DPhil, FASTRO

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Prostate cancer is the second most common cancer in men worldwide, with approximately 70% of new diagnoses being localized disease, noted Dr. Efstathiou. This accounts for more than 300,000 patients annually in the United States alone. Given the high survival rates for localized prostate cancer, he added, the long-term quality of life after treatment has become a crucial factor in treatment decision-making.

Study Design

The PARTIQoL trial is a multicenter, randomized study designed to compare patient-reported quality-of-life outcomes after external-beam radiation using either photons (IMRT) or proton beam therapy. IMRT uses high-dose x-rays, shaped to conform to the tumor’s three-dimensional shape, whereas proton therapy uses charged particles that release energy directly at the tumor site, potentially reducing damage to surrounding healthy tissue.

Between June 2012 and November 2021, a total of 450 patients with low- and intermediate-risk localized prostate cancers were randomly assigned to receive either proton beam therapy or IMRT, without hormonal therapy. The study involved 29 recruiting centers, and the median patient age was 68. Patients were followed for a median of 60.3 months after completing radiotherapy.

The primary endpoint was bowel function at 24 months, measured using the Expanded Prostate Cancer Index Composite (EPIC) score. Secondary outcomes included urinary and erectile functions, toxicity, disease control, and economic endpoints.

Key Results

Study results showed no significant difference between proton beam therapy and IMRT in any quality-of-life domains at any timepoint. Both arms demonstrated small, clinically nonmeaningful declines from baseline. For example, patients reported average bowel function scores of 93.7 (protons) and 93.5 (IMRT) out of 100 at baseline; after 2 years, the averages were 91.8 and 91.9, respectively, representing a decrease of roughly 2% for each arm (P = .836).

“The decline in bowel quality of life after 2 years was less than 2% on a 100-point scale for both treatment arms,” Dr. Efstathiou explained. “We also found no differences in other domains, including urinary incontinence, urinary irritation, or sexual function.”

In terms of disease control, the study revealed no significant difference between the arms in terms of progression-free survival. At 5 years after treatment, 93.7% of patients given IMRT and 93.4% of patients given proton therapy had not experienced tumor progression (P = .706).

Furthermore, subgroup analyses based on disease risk (low vs intermediate), age (older vs younger than 65), rectal spacer use, and fractionation schedule (shortened vs conventional) showed no sustained differences in quality-of-life domains or survival between the two treatments.

“We tested two contemporary, advanced forms of external-beam radiation for a very common cancer, and we demonstrated both are safe, effective treatments that give patients excellent outcomes in terms of quality of life and cancer control,” said Dr. Efstathiou.

However, Dr. Efstathiou noted some limitations of the study. The trial was restricted to patients with localized low- and intermediate-risk prostate cancers receiving either conventional or moderately hypofractionated therapy. It did not address higher-risk disease, nodal therapy, use of hormonal therapy or other systemic treatments, local recurrence, or retreatment scenarios. It is also not powered to assess the rare rates of potential radiation-associated second cancer risk.

What’s Next?

Dr. Efstathiou and colleagues continue to monitor participants for longer follow-up, secondary endpoints, and subgroup analyses. The research team is also analyzing results from a companion registry that enrolled an additional 400 patients who were either denied proton therapy or declined randomization in the main trial. Looking ahead, Dr. Efstathiou highlighted ongoing work to optimize radiation delivery techniques.

“Both protons and IMRT continue to evolve,” he concluded. “There’s a lot of ongoing work to improve delivery, including proton therapy with enhanced in-room imaging, arc therapy, adaptive therapy, and the trend toward ultrahypofractionation.” 

DISCLOSURE: Dr. Efstathiou reported financial relationships with AngioDynamics, Astellas Pharma, Bayer Healthcare, BioProtect, Blue Earth Diagnostics, Boston Scientific, Clarity Pharmaceuticals, Janssen, Johnson & Johnson, Lantheus, Pfizer, and UpToDate.

REFERENCE

1. Efstathiou JA, Yeap BY, Michalski JM, 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. 2024 ASTRO Annual Meeting. Abstract LBA01. Presented September 30, 2024.

EXPERT POINT OF VIEW

Invited discussant Sameer Keole, MD, FASTRO, Assistant Professor of Radiation Oncology, College of Medicine, Mayo Clinic, Arizona, said the “tremendous” findings of the PARTIQoL trial underscore the quality of options available to men with prostate cancer and their health-care providers.

“The results clearly demonstrate that we have two excellent options for external radiation therapy in the modern era,” said Dr. Keole. “Both proton therapy and IMRT [intensity-modulated radiation therapy] showed equal results across the board for tumor control and toxicity rates. What’s particularly striking is the phenomenal control rates achieved with very low complication rates,” he added.

According to Dr. Keole, the take-home message for men facing prostate cancer is clear: “When treatment is appropriate, they can confidently seek definitive treatment with a radiation oncologist. This study confirms that external-beam radiation therapy, whether it’s proton therapy or IMRT, is an excellent treatment option for localized prostate cancer.” 

DISCLOSURE: Dr. Keole reported no conflicts of interest.