Here is the design of a clinical trial:

Official Title: Intraoperative Radiotherapy During Kyphoplasty/Vertebroplasty (Kypho-IORT) Versus EBRT in the Treatment of Painful Vertebral Metastases - a Randomized Prospective Phase III Study -

Included conditions:
- Metastasis

Study Armgroups:
- {'label': 'Arm A: Kypho-IORT', 'type': 'EXPERIMENTAL', 'description': 'balloon kyphoplasty/vertebroplasty + intraoperative radiotherapy', 'interventionNames': ['Radiation: Kypho-IORT']}
- {'label': 'Arm B: EBRT', 'type': 'ACTIVE_COMPARATOR', 'description': 'external beam radiotherapy with 30 Gy during 10 days (3 Gy/day)', 'interventionNames': ['Radiation: EBRT']}

Interventions:
- {'type': 'RADIATION', 'name': 'Kypho-IORT', 'description': 'During kyphoplasty/vertebroplasty a intraoperative radiotherapy of the affected vertebrae is done with a miniature X-ray generator (INTRABEAM®, Carl Zeiss, Surgical, Oberkochen, Germany). The prescription dose will be 8 Gy in a distance of 13 mm from the isocenter of the radiation source. IORT will take about five minutes. After radiation the applicator will be removed and the operation will be finished as usual.', 'armGroupLabels': ['Arm A: Kypho-IORT']}
- {'type': 'RADIATION', 'name': 'EBRT', 'description': 'The external beam radiotherapy will be usually carried out as an outpatient procedure. All patients will receive a planning CT before the first irradiation. EBRT will be performed with 30 Gy, added in 3 Gy per fraction or 8 Gy single dose (only for international study centers, not permitted in Germany) on a conventional linear accelerator (LINAC).', 'armGroupLabels': ['Arm B: EBRT']}

Primary Outcomes:
- {'measure': 'pain evaluation', 'description': 'Evaluation of the percentage of patients with a pain reduction of VAS-3 points after Kypho-IORT vs. EBRT at day 1 (one day after Kypho-IORT; one day after the first EBRT)', 'timeFrame': 'day 1'}

Please estimate the sample size based on the assumption: 
Two-sided alpha of 0.05, power of 0.817, and a dropout rate of 20%.
Trial sample size
          This study is designed to test if the analgesic efficiency of Kypho-IORT is superior to standard-of-care EBRT in patients with painful vertebral metastases by comparing percentages of patients with a pain reduction of at least 3 points on VAS at defined points in time (day 1, week 2 and 6 after start of treatment).
          Assuming a pain reduction of VAS-3 points at day one (first day after Kypho-IORT, one day after the first EBRT) for 40% of the patients after Kypho-IORT vs 5% of the patients after EBRT under standard pain medication (no change of the pretherapeutic pain medication 12âh after Kypho-IORT or 24âh after the first EBRT), the study will require 22 patients in each arm in order to have a two-sided alpha of 0.05 and a power of 0.817. Including a dropout rate of 20% at least 54 patients have to be recruited. The effect size was estimated on the basis of the results of the preceded phase I/II trial [11] and the results of RTOG 9714 [3].