A patient undergoing external beam radiation therapy received a fractionated dose of 14 Gy in 2 Gray fractions to an area that was approximately 15.6 cm from the intended treatment site.
Root Cause
The treatment error was due to improper marking of the isocenter following laser alignment on the patient's external body contour. A CT scanner table movement was required to align the field set lasers with the anticipated isocenter. The actual direction of the table movement was in the opposite direction than assumed. At that point the isocenter was incorrectly marked. The treatment plan was correctly generated, and the treatment plan was reviewed and received physician and physics approval. Treatment port film verification on the first day of treatment was performed, but there was a failure to recognize the improper location of the isocenter and treatment commenced. A subsequent set of port films were again reviewed and erroneously approved. At the interval of the third porting of the treatment fields it was recognized that the isocenter was far inferior to the anticipated site. At this point treatment was paused.
Corrective Action
Corrective action includes re-training personnel on the use of the Tumor-Loc software used with the CT scanner, implementing a policy that all patients are to have the day before their first treatment dedicated to filming instead of trying to perform it on the same day as and immediately prior to their first treatment, and implementation of a double check policy that addresses isocenter placement on the patient, as visualized by the radiation therapist and physicist, dosimetrist or other therapist.
Effect on Patient
The facility reviewed the patient dosimetry with regard to the normal tissues unintentionally irradiated and expects no adverse effects in the short or long term related to the seven treatments delivered.
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