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Arthrosis is a chronic degenerative disorder of unknow cause characterized by a loss of cartilage in knee and hips. This disease is most prevalent in patients older than 60 years that conforms the 10- 15% of population worldwide. The need for a non-invasive treatment is required as the increased of an aged population. Low dose radiotherapy is recommended in DEGRO Guidelines using a total dose of 3-6 Gy with dose per fraction of 0.5-1 Gy. The objective of this trial is to evaluate the non-inferiority efficacy of low dose radiotherapy 3 or 6 Gy to change in pain with VAS (Visual Analogue Scale).and WOMAC scale (Western Ontario MacMaster Questionnaire). Secondly, we evaluate skin toxicity.

We did a randomize control trial at 13 centers in Spain. Eligible patients were > 50 years old, diagnosed with Gonarthrosis or/and Coxarthrosis with at least 1 year of evolution, non-responsive to drug or surgery treatments and risk of collateral side effects due to the comorbidity with conventional treatments. The exclusion criteria were: previous high dose radiotherapy, Connective tissue disease, inherited Hypersensitivity Syndrome. We randomly allocated patients in a 1:1 single blind ratio to 3 Gy (Arm A) or 6 Gy (Arm B). Randomization was stratified by age, gonarthrosis or coxarthrosis, IMC and pain before treatment. The Arm A group received low dose radiotherapy (0.5 Gy in 6 fractions alternating days) and Arm B group received low dose radiotherapy (1 Gy in 6 fractions alternating days). An evaluation of pain relief and quality of life in 8-12 weeks was done if no effect the patient in Arm B was randomized again to 3 or 6 Gy and in Arm B retreated with 6 Gy. Skin toxicity was rated according to the RTOG scale. This trial is registered with ClinicalTrials.gov number NCT04424628.

230 patients were recruited from May 2019 to May 2021, and followed-up at 8 weeks, and 6-12 months after the end of the treatment. 68 were men (29.6%) and 162 women (70.4%), median age 72.7±9.1 years. Allocated groups were well balanced. 1 case of grade 1 skin toxicity was present in both arms. In ARM B, 2 cases of transient increased pain and 1 case of venous thrombosis in right lower limb were recorded. No grade 3-4 toxicity was recorded. 217 patients completed the treatment. 3.9% abandoned the study: 1 for death not related to the trial and 1 for fear of treatment, no patients for side effects. At 6 months, they were statistical differences were comparing improvement in VAS and WOMAC scale p= <0.001, but no statistical differences comparing both arms p=0.58. This result was stabled after a year of follow- up when comparing to basal. VAS scale; IC 95% (4%-23%) and WOMAC scale IC 95% (3%-16%), respectably. VAS and WOMAC evolution are shown in Figures 1 and 2.

Figure 1: VAS average.

Figure 2: WOMAC evolution.

3 Gy is non inferior to 6 Gy in knee and hip arthritis. There was no presence of grade 3-4 skin toxicity in both arms. The decrease of analgesics consumption analysis is in progress.