The goal of this prospective observational cohort study is to evaluate the long-term efficacy and safety of ultrahypofractionated proton beam therapy in patients with localized prostate cancer and to identify clinical and treatment-related factors associated with oncologic outcomes and treatment-related toxicity.
The main questions it aims to answer are:
What are the long-term biochemical recurrence-free survival, clinical progression-free survival, overall survival, and acute and late treatment-related toxicity outcomes following ultrahypofractionated proton beam therapy? Which clinical characteristics, treatment planning parameters, and patient-reported outcomes are predictive of long-term oncologic outcomes and treatment-related toxicity?
Participants will:
Receive protocol-based ultrahypofractionated proton beam therapy (35-40 Gy\[RBE\] in 5 fractions).
Undergo routine clinical evaluation, laboratory testing including prostate-specific antigen (PSA), and imaging studies according to the institutional follow-up schedule.
Complete patient-reported outcome questionnaires (EPIC-CP and Visual Analog Scale \[VAS\]) before treatment and during follow-up.
Be followed prospectively to assess biochemical recurrence, clinical progression, survival outcomes, and acute and late treatment-related toxicities.
Histologically confirmed localized adenocarcinoma of the prostate.
No evidence of distant metastasis (M0).
Eastern Cooperative Oncology Group (ECOG) performance status of 0-2.
Eligible to receive definitive image-guided ultrahypofractionated pencil beam scanning proton beam therapy according to the study protocol.
Residual or recurrent prostate cancer following prior radical prostatectomy.
Previous pelvic radiotherapy.
Evidence of distant metastatic disease.
Active malignancy within the previous 1 year, except adequately treated basal cell carcinoma or squamous cell carcinoma of the skin, carcinoma in situ of the cervix, or completely resected T1N0M0 malignancies.
Single group
Ultrahypofractionated Proton Beam Therapy
RadiationUltrahypofractionated proton beam therapy is delivered using pencil beam scanning (PBS) with image-guided proton therapy. Before treatment planning, all participants undergo placement of an absorbable rectal hydrogel spacer and two intraprostatic gold fiducial markers. Treatment planning is performed using CT simulation with MRI fusion after hydrogel stabilization. Daily cone-beam CT (CBCT) with fiducial marker matching is used for image guidance and patient positioning. A total dose of 36.25-40.0 Gy(RBE) is delivered in 5 fractions over approximately 1-2 weeks. Unlike conventional proton beam therapy using opposed right and left lateral beam arrangements, this protocol employs four oblique beam angles (right anterior oblique, right posterior oblique, left posterior oblique, and left anterior oblique) to optimize dose conformity while minimizing radiation exposure to adjacent normal tissues.
Biochemical recurrence-free survival
Biochemical recurrence is defined according to the Phoenix definition (PSA nadir + 2 ng/mL). Biochemical recurrence-free survival is measured from completion of proton beam therapy to biochemical recurrence or last follow-up.
Patient-reported quality of life
Patient-reported quality of life will be assessed using the Expanded Prostate Cancer Index Composite for Clinical Practice (EPIC-CP). Scores range from 0 to 100, with higher scores indicating better urinary quality of life.
Clinical recurrence-free survival
Time from radiotherapy completion to first occurrence of any clinical recurrence (local, regional, or distant) or death. Recurrence will be confirmed by imaging studies and/or histopathological findings when available.
Overall survival
Time from completion of ultrahypofractionated proton beam therapy to death from any cause. Participants who are alive at the time of analysis will be censored at the date of the last follow-up.
Treatment-related genitourinary toxicity
Treatment-related genitourinary (GU) toxicity will be assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4.03. Acute toxicity is defined as adverse events occurring within 90 days after completion of proton beam therapy, and late toxicity as events occurring more than 90 days after treatment completion.
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