AMERICAN SHARED HOSPITAL SERVICES ANNOUNCES $2 MILLION EQUITY INVESTMENT IN DEVELOPER OF PROTON BEAM RADIATION THERAPY DEVICE AMS Also Purchases Option to Acquire Two Proton Beam Radiation Therapy Systems San Francisco,

AMERICAN SHARED HOSPITAL SERVICES

ANNOUNCES $2 MILLION EQUITY INVESTMENT IN DEVELOPER OF

PROTON BEAM RADIATION THERAPY DEVICE

AMS Also Purchases Option to Acquire Two Proton Beam Radiation Therapy Systems

San Francisco, CA, April 11, 2006 AMERICAN SHARED HOSPITAL SERVICES (AMEX,PCX:AMS), the leading

provider of Gamma Knife radiosurgery services, announced today that it has invested $2 million for

an equity interest in Still River Systems, Inc., a development-stage company based in Littleton,

Massachusetts, which in collaboration with scientists from MIT s Plasma Science and Fusion Center

is developing a medical device for the treatment of cancer patients using proton beam radiation

therapy (PBRT). AMS also purchased for $1 million an option to acquire two Clinatron-250 PBRT

systems from Still River Systems for anticipated delivery in 2008.

Proton beam radiation therapy is widely regarded as the optimal radiation treatment for a wide

variety of cancers because of its significant clinical advantages compared to conventional high

energy X-rays, said Ernest A. Bates, Chairman and CEO of AMS. Whereas X-rays deposit dose all

along their path and continue to deposit dose beyond the depth of the tumor, PBRT deposits most of

its dose at a specific depth, determined by the initial energy of the beam, and then stops

entirely. This allows the physician to deposit far more dose in a tumor and far less in

surrounding normal tissue, limiting collateral damage and increasing tumor control rates.

Bates continued, Unfortunately, the PBRT systems available today cost at least $100 million, and

consist of three or more dedicated treatment rooms. As a result, deployment of this

Medicare-approved treatment modality has so far been limited to only a handful of large

institutions. According to Still River Systems, the device it is developing is a

single-treatment-room PBRT system incorporating proprietary technology that it believes may

dramatically reduce the cost of implementing this exciting therapy.

More than half of all cancer patients now receive radiation therapy each year, and more than one

million new cancer patients are diagnosed annually in the United States. So we see tremendous

growth potential in Still River Systems cost-effective PBRT device, especially when coupled with

AMS s innovative financing programs. We are pleased to support the development of this next major

advance in radiation oncology, which we see as a natural complement to our Gamma Knife business.

Marc Buntaine, Chief Executive Officer of Still River Systems, said, As a leader in providing

radiotherapy devices, AMS is an ideal partner for Still River Systems. We welcome AMS s support

and look forward to working with them as we complete development of our PBRT system.

The Still River Clinatron-250 PBRT system is not FDA approved, nor can there be any assurance that

this system will obtain FDA approval.

About Still River Systems

Still River Systems, Inc., a development stage company based in Littleton, Massachusetts, is

developing a medical device for the treatment of cancer patients using proton beam radiotherapy

(PBRT). Still River is dedicated to providing physicians and their patients access to high

quality, cost-effective proton beam radiation therapy solutions, and helping establish this

superior treatment modality as a standard of care for patients worldwide.

American Shared Hospital Services is building a profitable medical services company in an

underserved niche turnkey technology solutions for advanced radiosurgical procedures. The

Company s core business is supplying hospitals with the Gamma Knife a non-invasive treatment for

malignant and benign brain tumors, vascular malformations and trigeminal neuralgia (facial pain).

The Gamma Knife, the gold standard in radiosurgery, reduces surgical risk and patient discomfort,

resulting in shorter hospital stays and lower risk of complications. In most cases, Gamma Knife

patients resume their normal activities within a few days of treatment, compared to weeks or months

for patients who undergo conventional surgery. More than 250,000 patients worldwide have already

received this treatment. American Shared Hospital Services is the world leader in providing Gamma

Knife radiosurgery services.

Safe Harbor Statement

This press release may be deemed to contain certain forward-looking statements with respect to

the financial condition, results of operations and future plans of American Shared Hospital

Services, which involve risks and uncertainties including, but not limited to, the risks of the

Gamma Knife business, the risks of developing the Company s IMRT and The Operating Room for the

21st Century programs, and the risks of investing in a development-stage company, Still River

Systems, without a proven commercial product. Further information on potential factors that could

affect the financial condition, results of operations and future plans of American Shared Hospital

Services is included in the Company s filings with the Securities and Exchange Commission,

including the Company s Annual Report on Form 10-K for the year ended December 31, 2005, and the

definitive Proxy Statement for the Annual Meeting of Shareholders held on June 16, 2005.

American Shared Hospital Services:

Ernest A. Bates, M.D., 415-788-5300

Neil Berkman, 310-277-5162

Still River Systems:

978-486-1006 ext. 113