Proton Therapy and Intensity-Modulated Radiotherapy for Prostate Cancer: Which Is More Effective?

The Importance of Treatment Options in Prostate Cancer

Prostate cancer is one of the most common cancers in men, and treatment options are particularly varied for patients with localized (early-stage) disease. In treating early-stage prostate cancer, radiotherapy plays an important role. Advanced radiotherapy technologies such as proton therapy and intensity-modulated radiotherapy (IMRT = Intensity-Modulated Radiation Therapy) offer patients high success rates and favorable adverse-effect profiles. However, which of these two methods is more effective and how they affect long-term quality of life have long been debated. Addressing these questions, the phase 3 randomized controlled PARTIQoL study was presented on September 30, 2024, at the American Society for Radiation Oncology's annual meeting (ASTRO 2024). Its results may guide prostate cancer treatment. The study compares these two approaches and their effects on patients in detail to determine whether one is superior.

The PARTIQoL Study: Comparing IMRT and Proton Therapy

PARTIQoL is a large phase 3 randomized controlled study comparing the effectiveness and safety of proton therapy and IMRT in patients with localized low- and intermediate-risk prostate cancer. Its 450 patients were randomized to IMRT or proton therapy and followed. The study aimed to assess the effects of both approaches on aspects of quality of life such as bowel function, urinary incontinence, and sexual function. Treatment outcomes, such as disease-free survival rates, were also analyzed.

Proton Therapy and IMRT: What Do the Results Show?

• According to the findings, patients treated with either IMRT or proton therapy had disease control rates above 90% two years after treatment.
• There was no significant difference between the treatments in bowel function or other quality-of-life measures.
• These findings show that both approaches are equally effective and safe in treating low- and intermediate-risk prostate cancer.
• The principal investigator, Dr. Jason Efstathiou, stated that the findings showed “equivalent results in both disease control rates and toxicity rates”. In other words, there were no significant differences in quality-of-life domains such as bowel function, urinary incontinence, or sexual function.

Detailed Findings: Quality of Life and Survival Rates

At 24 months, both groups had a small, clinically insignificant decline of just 2% in bowel function. This shows that the effects of IMRT and proton therapy on bowel function were minimal, with no difference between them. Similar results were seen in other domains, including urinary incontinence and sexual function.

Disease-free survival also did not differ significantly. In the IMRT group, disease-free survival was 99% at 24 months and 93.7% at 60 months, compared with 98.1% and 93.4%, respectively, in the proton therapy group. These findings show similar effects on disease control and prevention of progression over the long term.

The Cost of Proton Therapy: Advantages and Challenges

Proton therapy offers dosimetric advantages and may reduce additional problems in some patients. However, compared with IMRT, it is more expensive and resource-intensive. Whether it is clinically superior when cost is considered remains unanswered. PARTIQoL found no clinical difference between IMRT and proton therapy. Nevertheless, proton therapy may remain a viable option in a setting without financial constraints.

Long-Term Follow-Up and Expectations: What Will We See?

Ongoing follow-up will provide more information on long-term outcomes. However, the study included only patients with localized low- and intermediate-risk prostate cancer. It provides no data on high-risk patients, those with cancer spread to lymph nodes requiring treatment in those regions, or patients receiving systemic treatment such as hormone therapy.

The anticipated COMPARE study may offer broader data by comparing the effects of proton therapy and IMRT on bowel, urinary, and sexual function.

Conclusion: Two Strong Treatment Options

PARTIQoL shows no substantial difference between IMRT and proton therapy for prostate cancer, with both being safe and effective options for low- and intermediate-risk patients. These findings allow patients to consider quality of life when making treatment decisions. Future studies will continue to assess broader outcomes of the two approaches.

Both stand out as strong options for prostate cancer treatment, helping patients make more informed decisions with their doctors.