An interventional study of Low-Dose Radiotherapy (LDRT) in Knee Osteoarthritis, sponsored by Universidad Rey Juan Carlos. Not yet recruiting at 4 sites in Spain. Open to participants aged 60 Years and older. Per ClinicalTrials.gov, last updated 2026-10-21.
Sponsored by Universidad Rey Juan Carlos · Not applicable, Interventional, and Treatment
Knee osteoarthritis is a common cause of chronic pain and difficulty with everyday activities, particularly in older adults. Some patients continue to experience clinically relevant knee pain despite medication, therapeutic exercise, physiotherapy, or other conservative treatments.
This prospective, multicenter study will evaluate changes in pain, physical function, health-related quality of life, and safety after low-dose radiotherapy (LDRT) in adults aged 60 years or older with painful primary knee osteoarthritis. All participants will receive the same treatment, and there will be no control or sham-treatment group.
Participants will receive one course of low-dose radiotherapy to the study knee, consisting of six fractions of 0.5 Gy, for a total dose of 3.0 Gy, administered twice weekly on nonconsecutive days over approximately 3 weeks.
Clinical assessments will be performed before treatment and approximately 45 and 90 days after the last radiotherapy fraction. The main outcome is the change from baseline to Day 90 in average knee pain during the previous 7 days, measured on a 0-to-10 Numerical Rating Scale. The study hypothesis is that average knee pain will be lower at Day 90 than before treatment. Other outcomes include physical function, health-related quality of life, the participant's overall assessment of the affected knee, pain response, analgesic use, treatment completion, additional knee treatments, and adverse events.
Low-dose radiotherapy (LDRT) has been used in several European countries for painful degenerative musculoskeletal disorders, including knee osteoarthritis. Clinical studies have reported improvements in pain and function after LDRT, although findings from controlled trials have been heterogeneous and uncertainty remains regarding the magnitude of the treatment-specific effect. This study is designed to prospectively characterize clinical changes following a standardized LDRT regimen in patients with painful primary knee osteoarthritis treated across multiple centers.
This is a prospective, multicenter, interdisciplinary, open-label, non-randomized, single-group interventional study. A total of 283 participants aged 60 years or older with symptomatic primary knee osteoarthritis will be enrolled. Each participant will contribute one index knee; in participants with bilateral knee osteoarthritis, the more painful knee will be designated as the index knee.
All participants will receive one continuous course of LDRT consisting of six fractions of 0.5 Gy, for a total dose of 3.0 Gy. Fractions will be administered twice weekly on nonconsecutive days over approximately 3 weeks. Treatment will be planned using computed tomography and delivered using a standardized technique across participating centers. No second protocol-scheduled radiotherapy course will be administered before completion of the Day 90 assessment.
Participants will be evaluated before treatment and at approximately 45 and 90 days after the last radiotherapy fraction. The primary analysis will assess the change from baseline to Day 90 in average pain intensity in the index knee during the previous 7 days, measured using an 11-point Numerical Rating Scale. Additional assessments will evaluate pain, stiffness, physical function, health-related quality of life, global patient assessment, clinically relevant pain response, analgesic treatment, co-interventions, treatment adherence, and adverse events.
Because the study has no concurrent control or sham-treatment group, observed changes after treatment cannot be attributed exclusively to radiotherapy. The study is intended to estimate within-participant longitudinal changes after a standardized LDRT intervention and to describe clinical response and safety in routine multicenter practice. Potential contributions from the natural course of osteoarthritis, regression to the mean, participant expectations, and concomitant treatments will be considered when interpreting the results.
3,391 studies on the registry are indexed under Osteoarthritis, Knee; 628 are open to participants now.
This study's planned enrollment of 283 is above the median of 69 across 2,808 interventional studies indexed under Osteoarthritis, Knee.
Browse Osteoarthritis, Knee studies →Universidad Rey Juan Carlos is the lead sponsor of 113 studies on the registry; 23 are open to participants now.
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Exclusion Criteria:
Participants will receive a single course of low-dose radiotherapy to the index knee consisting of six fractions of 0.5 Gy, for a total dose of 3.0 Gy, administered twice weekly on nonconsecutive days over approximately 3 weeks.
Radiation: Low-Dose Radiotherapy (LDRT)
Low-dose radiotherapy will be delivered to the index knee as six fractions of 0.5 Gy each, for a total prescribed dose of 3.0 Gy. Fractions will be administered twice weekly on nonconsecutive days over approximately 3 weeks. Treatment will be planned using computed tomography simulation. The clinical target volume will include the relevant femoral and tibial articular and subchondral surfaces, joint capsule, synovium, and periarticular tissues. A nominal 5-mm planning target volume margin will be applied. Treatment will be delivered using opposed anteroposterior and posteroanterior fields with 6-MV photons.
Change From Baseline in Average Index-Knee Pain Intensity at Day 90
Average pain intensity in the index knee during the previous 7 days will be assessed using an 11-point Numerical Rating Scale (NRS) ranging from 0 (no pain) to 10 (worst imaginable pain). Change will be calculated as baseline NRS minus Day 90 NRS. Positive values indicate improvement, zero indicates no change, and negative values indicate worsening.
Time frame: Baseline and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in Average Index-Knee Pain Intensity at Day 45
Average pain intensity in the index knee during the previous 7 days will be assessed using an 11-point Numerical Rating Scale (NRS) ranging from 0 (no pain) to 10 (worst imaginable pain). Change will be calculated as baseline NRS minus Day 45 NRS. Positive values indicate improvement, zero indicates no change, and negative values indicate worsening.
Time frame: Baseline and Day 45 (45 ± 7 days after the last radiotherapy fraction)
Change From Baseline in WOMAC Pain Subscale Score
The WOMAC pain subscale consists of 5 items, each scored from 0 to 4, yielding a total score from 0 to 20. Higher scores indicate greater pain. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in WOMAC Stiffness Subscale Score
The WOMAC stiffness subscale consists of 2 items, each scored from 0 to 4, yielding a total score from 0 to 8. Higher scores indicate greater stiffness. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in WOMAC Physical Function Subscale Score
The WOMAC physical function subscale consists of 17 items, each scored from 0 to 4, yielding a total score from 0 to 68. Higher scores indicate greater functional limitation. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in KOOS-PS Score
The 7-item Knee injury and Osteoarthritis Outcome Score-Physical Function Shortform (KOOS-PS) will be used to assess physical function. The raw score will be transformed to a 0-to-100 Rasch-based score, where 0 indicates no difficulty and 100 indicates extreme difficulty. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in EQ-5D-3L Health Utility Index
Health-related quality of life will be assessed using the Spanish EQ-5D-3L. The health utility index will be calculated from the five dimensions using the Spanish value set. Higher index values indicate better health status. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in EQ VAS Score
Overall health status will be assessed using the EQ Visual Analogue Scale (EQ VAS), ranging from 0 to 100, where 0 represents the worst imaginable health state and 100 represents the best imaginable health state. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Change From Baseline in Patient Global Assessment of the Index Knee
Patient Global Assessment (PGA) will evaluate the overall impact of index-knee osteoarthritis during the previous 7 days using a 0-to-100 scale. Participants will answer: "Considering all the ways in which the osteoarthritis of your index knee affects you, how would you rate your knee during the past 7 days?" A score of 0 indicates very well/no impact and 100 indicates very poorly/maximum impact. Change from baseline will be assessed at Day 45 and Day 90.
Time frame: Baseline, Day 45 (45 ± 7 days after the last radiotherapy fraction), and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Proportion of Participants With at Least a 30% Reduction in NRS Pain Intensity
A pain responder will be defined as a participant with at least a 30% reduction from baseline in average index-knee pain intensity measured using the 0-to-10 Numerical Rating Scale (NRS). Percentage reduction will be calculated as \[(baseline NRS - follow-up NRS) / baseline NRS\] × 100. The proportion of participants meeting this criterion will be assessed at Day 45 and Day 90.
Time frame: Day 45 (45 ± 7 days after the last radiotherapy fraction) and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Proportion of Participants With at Least a 50% Reduction in NRS Pain Intensity
A pain responder will be defined as a participant with at least a 50% reduction from baseline in average index-knee pain intensity measured using the 0-to-10 Numerical Rating Scale (NRS). Percentage reduction will be calculated as \[(baseline NRS - follow-up NRS) / baseline NRS\] × 100. The proportion of participants meeting this criterion will be assessed at Day 45 and Day 90.
Time frame: Day 45 (45 ± 7 days after the last radiotherapy fraction) and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Proportion of Participants Meeting OMERACT-OARSI Responder Criteria
Participants will be classified as OMERACT-OARSI responders if they meet either of the following criteria: (1) high improvement in pain or physical function, defined as an improvement of at least 50% and an absolute improvement of at least 20 points on a 0-to-100 scale; or (2) improvement in at least 2 of 3 domains-pain, physical function, and Patient Global Assessment-defined as an improvement of at least 20% and an absolute improvement of at least 10 points on a 0-to-100 scale. The proportion of responders will be assessed at Day 45 and Day 90.
Time frame: Day 45 (45 ± 7 days after the last radiotherapy fraction) and Day 90 (90 ± 14 days after the last radiotherapy fraction)
Participants With Changes in Analgesic Treatment or Rescue Medication Use
Changes in analgesic treatment for index-knee osteoarthritis will be recorded throughout follow-up, including initiation, discontinuation, or dose modification of analgesic medication and use of rescue medication. The proportion of participants with at least one change in analgesic treatment or rescue medication use will be summarized through Day 90.
Time frame: From baseline through Day 90 (90 ± 14 days after the last radiotherapy fraction)
Participants Receiving an Index-Knee Co-intervention During Follow-up
Index-knee co-interventions during follow-up will be recorded, including intra-articular corticosteroid or hyaluronic acid injections, radiofrequency procedures, other interventional procedures, or surgery. The proportion of participants receiving at least one such co-intervention will be summarized through Day 90.
Time frame: From baseline through Day 90 (90 ± 14 days after the last radiotherapy fraction)
Proportion of Participants Completing the Planned Radiotherapy Course
Treatment completion will be defined as receipt of all six planned radiotherapy fractions of 0.5 Gy each, corresponding to a total prescribed dose of 3.0 Gy to the index knee. The proportion of participants completing the planned radiotherapy course will be summarized.
Time frame: From the first radiotherapy fraction through completion of the planned course (approximately 3 weeks)
Incidence and Severity of Adverse Events
Adverse events occurring from the first radiotherapy fraction through Day 90 will be recorded and graded according to the Common Terminology Criteria for Adverse Events (CTCAE), version 5.0. For each event, the event term, severity grade, onset and resolution dates, relationship to radiotherapy, actions taken, treatment required, and outcome will be documented. The incidence and severity of adverse events will be summarized.
Time frame: From the first radiotherapy fraction through Day 90 (90 ± 14 days after the last radiotherapy fraction)
Plan to share: No — Pega esta versión: There is no plan for routine public sharing of individual participant data because access is subject to applicable data protection requirements, ethics approvals, and institutional agreements. However, justified requests for access to study data may be evaluated by the study team and the responsible institutions on a case-by-case basis, provided that appropriate ethical, legal, and data protection requirements are met.
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