On 22 May 2001, the IAEA informed Contact Points identified under the Convention on Early Notification of a Nuclear Accident ("Early Notification Convention") and the Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency ("Assistance Convention") of a radiological emergency at a radiotherapy facility in the National Oncology Institute in Panama affecting 28 patients undergoing radiotherapy. On 2 June 2001, the Contact Points were provided with additional advisory information, which informed them of the preliminary conclusions of an expert team that had been sent by the IAEA to assist the Panamanian government under the auspices of the Assistance Convention.
The purpose of this advisory information is to inform Contact Points that the IAEA team has completed its mission and confirmed the preliminary conclusions included in the advisory information provided on 2 June 2001, and to provide some additional details of this emergency.
The experts found that the radiotherapy equipment had been working properly and had been adequately calibrated. The experts confirmed that the cause of the emergency lay with the entering of data into the computerized treatment planning system which is used at the Institute in question. Shielding blocks are used to protect healthy tissue of patients undergoing radiotherapy at the Institute, as is the normal practice. Data on the shielding blocks are entered into the computer, which calculates the dose distributions in patients and the treatment times.
Until August 2000, the practice had been to enter data in one batch for each shielding block. The treatment planning system has a limitation on the number of shielding blocks for which data can be entered in this way. It was reported that the practice at the facility was changed from August 2000 in order to overcome this limitation for some treatments that require more shielding blocks. For the 28 patients who were affected, data were entered in a batch for several shielding blocks at once. However, this approach apparently caused the treatment planning system to calculate incorrect radiation doses and, consequently, incorrect treatment times.
The team found that it was possible to enter data in one batch for several shielding blocks in different ways; and that for some ways of entering the data, which were accepted by the treatment planning system, the output values were calculated incorrectly. However, whichever way was used, the computer produced a printout drawing that showed the treatment field and the shielding blocks as if the data had been entered correctly. The isodose curves for a single treatment field are somewhat different, but for multiple treatment fields the differences are not so obvious. (It should be noted that, for irradiation treatments in the pelvic region, which was the region of treatment for all the patients concerned, multiple treatment fields are always used in the Institute .) These factors, together with an apparent omission of manual checking of computer calculations, resulted in the patients concerned being exposed at radiation levels that were set too high.
The IAEA team was informed that, of the 28 patients concerned, eight have since died; and the team confirmed that five of these deaths are probably attributable to the patientsÕ overexposure to radiation. Of the other three deaths, one is considered to have been related to the patientÕs cancer; while there was insufficient information available to draw conclusions in respect of the other two deaths. Of the surviving 20 patients, most injuries are related to the bowel, with a number of patients suffering persistent bloody diarrhoea, necrosis (tissue death), ulceration and anaemia. About three-quarters of the surviving 20 patients may be expected to develop serious complications, which in some cases may ultimately prove fatal.
The IAEA team provided the Government of Panama with a briefing on the findings and conclusions of the mission, which were consistent with those of the local group of investigators. The Government has agreed that the findings and conclusions identified be shared on an urgent basis with the international community in order to help prevent other overexposures where such an approach for treatment may be in use.
The Contact Points are requested to draw these findings and conclusions urgently to the attention of the relevant national authorities, who are encouraged to urge users to check that any relevant systems are being operated in accordance with an appropriate quality assurance programme. It is reiterated that particular emphasis should be given to the need:
- to follow written quality assurance procedures, which include:
- ensuring that the procedures require manual checks of the doses to the prescription points as calculated by computer, for each individual patient, before the first treatment; and
- performing verification measurements using a phantom in exceptional cases of complicated treatments, for which manual calculations may not be practicable.
The IAEA plans to publish a detailed report on the circumstances of this emergency and the lessons to be learned as soon as feasible.