Note 3 - Property and Equipment (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Net Income (Loss) Attributable to Parent, Total	$ 194,000	$ (7,058,000)
Earnings Per Share, Diluted, Total (in dollars per share)	$ 0.03	$ (1.14)
Gain (Loss) on Sale of Assets and Asset Impairment Charges	$ (105,000)	$ (8,264,000)
Two MEVION S250i Proton Beam Radiation Therapy Systems [Member]
Long Term Purchase Commitment Deposits for Assets		2,250,000
Accumulated Capitalized Interest Costs		1,613,000
Gamma Knife Units [Member]
Impairment of Long-Lived Assets to be Disposed of		3,051,000
Asset Retirement Obligation, Liabilities Incurred		1,350,000
Asset Retirement Obligation, Liabilities Settled	618,000	80,000
Tangible Asset Impairment Charges, Total	4,401,000
Proton Beam Radiation Therapy PBRT [Member]
Tangible Asset Impairment Charges, Total	0	3,863,000
Salvage Value [Member]
Net Income (Loss) Attributable to Parent, Total	$ 342,000
Earnings Per Share, Diluted, Total (in dollars per share)	$ 0.06
Non-US [Member]
Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization, Total	$ 2,697,000	$ 3,195,000