It was meant to be a routine treatment for cancer patients. The beams of radiation were directed exactly to kill the patients´ tumours. Instead, 115 patients were overdosed with radiation at a hospital in Costa Rica in September 1996. Nineteen patients died from the overdose.
Getting the "dose" correct in radiotherapy is vital to avoid such accidents. At the IAEA´s Dosimetry Laboratory near Seibersdorf, Austria, a team of medical physicists and technicians verifies that the beams emitted from radiotherapy equipment will deliver an accurate dose of radiation: to harm and kill tumours, not patients.
Known as "dosimetry", it is a precise art of measurement, to determine the dose - or the amount of radiation energy deposited in the cancer tissue - that is delivered to the patient.
Getting the "dose correct" starts with the calibration of the radiotherapy beams used to treat patients. This is done by a qualified medical physicist using a properly calibrated instrument. If the beam calibration is wrong, due to untrained staff or incorrectly calibrated instruments, then many patients can be given the wrong dose of radiation.
Each year the IAEA´s Dosimetry Lab calibrates more than 50 ionization chamber systems and independently checks and verifies some 450 beams emitted from radiotherapy equipment in hospitals dotted across the globe.
The calibration allows users to measure the dose, so that it accords with international standards. A "dosimetry audit" then verifies that the job’s been done properly.
How does it work?
For the dose audit, the hospitals are asked to irradiate a tiny plastic detector called a "TLD", to 2-Grays. At the IAEA´s Dosimetry lab, medical physicists like Joanna Izewska analyze the detectors to see that the 2-Gray dose is correct. "If it deviates more than 5%, that signals a problem," says Ms. Izewska, who is the Unit Head of the Dosimetry Lab. The IAEA then immediately alerts the hospital that their equipment may not be properly calibrated.
"Of the 450 hospital beams we check a year, typically we´ll discover about 20 having problems," says Ms. Izewska. Of the anomalies that the lab uncovers, 50% relate to too great a dose, the other 50% to too small a dose.
"Under dosing is more sinister," says Mr. Ken Shortt, a medical physicist and Section Head of the Dosimetry and Medical Radiation Physics group in the IAEA´s Division of Human Health. "It´s terrible for patients who go to the physician with the expectation and hope that they are being treated to cure their cancer. But because the equipment is not properly calibrated, they do not get the therapy they need. It is not a story that shows up in the media. It remains hidden unless you have programs like the one we offer," Mr. Shortt said.
The service is vital for many countries without appropriate laboratories that cannot afford calibration services offered in Europe or the US. In Africa, for example, there are only three national calibration laboratories that can conduct calibrations of radiotherapy instruments.
The IAEA works with the World Health Organization (WHO) to offer the TLD audits. The service supports 1500 hospitals in 116 countries that lack the infrastructure to conduct their own such checks and balances to international standards.
To keep pace with growing requests, the IAEA recently opened a $1 million irradiation bunker at Seibersdorf. Encased in thick concrete walls and accessed through lead-lined doors, the lab is used to safely conduct the necessary tests. The new bunker expands the IAEA’s dosimetry services to help countries measure radiation doses at national laboratories and hospitals; conduct more dose audits; and check if therapy machines have correctly calibrated radiation beams. The IAEA also supports the training of medical physicists carried out at the IAEA laboratory in Seibersdorf, under the directorship of Ms. Gabriele Voigt.
"As countries expand their cancer treatment capabilities, it´s led to many more requests for the Agency to provide dosimetry calibration and auditing services," Mr. Werner Burkart, Deputy Director General and Head of the IAEA Department of Nuclear Sciences and Applications, said.
Since 1980 the IAEA has worked in some 100 developing countries to improve access to safe and effective cancer treatment. The number of new cancer cases in the developing world is predicted to jump from 5 million in the year 2000 to nearly 10 million per year by 2020, the WHO reports. The expansion of the Dosimetry lab will help to meet ever growing needs.
"Cancer tissue in Africa needs the same dose as a cancer in Europe. The right dose will destroy the cancer, too little or too much will kill or maim the patient, be it through cancer growth or radiation damage to healthy organs," Mr. Burkart said.
The accident that killed 19 patients in Costa Rica, would have been prevented by the checks performed at the Seibersdorf Lab. It was caused by an error in calculating the dose rate for a newly installed radiotherapy Cobalt 60 source. If a TLD audit had been conducted before initiating treatments of the patients, says Ms Izewska, severe overdosage of the 115 patients would have been avoided.
"What we do at the Dosimetry Lab is to raise alarm bells before accidents occur. We improve quality controls and standardize dosimetry practices globally", she said. It is work to ensure cancer patients, whether they are in Zambia or Chile, get the safe and effective therapy they need.