A study of waiting times and waiting lists for radiation therapy patients

A simple mathematical model based on queueing theory is introduced, and used to obtain a sensitive measure of the capacity of a radiation therapy centre to provide service. The model illustrates the relationships among the relevant variables: the patient waiting time, the number on the waiting list, the rate at which requests for radiation therapy are received and the rate at which courses of treatment are commenced. In particular, the rate at which the waiting time increases is equal to the difference between the request rate and the start rate, expressed as a fraction of the start rate, and is therefore a measure of the deficiency in service capacity of a facility. A study of the records of patients treated on the linear accelerators of the Tom Baker Cancer Centre from January 1991 to June 1994 shows that this relationship holds to a high degree of accuracy for average values of the various parameters in spite of the considerable variation in these values, and particularly variation in the individual waiting times. This finding suggests that such an approach would be useful in assessing and comparing the performance of radiation therapy facilities.