Therapy Misadministrations in 2010

Summary A patient undergoing external beam radiation therapy to the head and neck area received 3 of 35 fractions to the wrong treatment site. Because of the error an unintended dose of 4.63 and 4.89 Gy was administered to the right and left eyes of the patient which were 10 cm inferior to the intended treatment site. The original planned mean dose to the eyes was 0.6 Gy and 0.42 Gy.
Root Cause The normal procedure for a head and neck patient at the facility is to make a custom aquaplast mask to hold the patient's head. After the completion of the simulation CT, the therapist places a crosshair mark on the mask to identify a daily set-up point for laser alignment in the treatment room. Common practice is to place this CT mark on the mask 10 cm superiorly to the central axis point and then to identify the shift direction and shift distance on the mask itself. This avoids any unsightly marking on the patient's skin.

The misalignment of the patient was caused by the failure of the therapist to apply a 10 cm shift from the mark placed on the patient's mask. During the original patient set-up, the therapist failed to write the direction and amount of shift needed on the mask or on the patient chart. A verification simulation was also performed on the Linac to verify field placement before the treatment began. These pre-treatment films were performed with the appropriate 10 cm inferior shift from the CT crosshair mark. The Linac therapist did not notice the missing shift direction and shift distance on the mask or in the set-up notes. When the patient came in for the first treatment the Linac therapists forgot to apply the appropriate shift and used the CT crosshair marks as the treatment central axis for three days. Daily treatment alignment is normally verified with cone beam CT images (CBCT) but the imager was not working for the first three treatments. On the fourth day the CBCT imager was working and used for setup verification before treatment and it was found that the patient was treated for three fractions with the inappropriate setup.
Corrective Action In the future the facility will clearly indicate the treatment location with a different color and symbol on the patient if possible rather than relying on the CT cross hair mark with a shift amount written on the mask. The facility will require two sets of imaging on the day of patient verification simulation which will include orthogonal setup MV portal images and either a CBCT or KV/KV matched images. CBCT or KV/KV images should be done on daily set ups. If the CBCT is not working a set of orthogonal set up portal images should be used. If no Image Modality is available, a hard film copy should be implemented.
Effect on Patient The patient was been informed of this incident and the treatment plan was been adjusted. The facility believes there will be no significant clinical complications to the patient from this event.

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