Clinical application of time factor principles in radiotherapy in compensation of radiation series interruptions

The time factor plays a key role in radiotherapy. The radiotherapy overall treatment time is one of the most important predictive factors in the treatment effectiveness and is associated with better local control and impact on the overall survival. The length of the time from the dia-gnosis to radical radiotherapy or from surgery to adjuvant radiotherapy or the use of alternative fractionation schemes shortening the total treatment time also play an important role. The prevention of prolongation of the radiation series remains a fundamental and well feasible way of applying the time factor in radiotherapy.

Interruption of radiotherapy usually occurs for technical reasons, due to factors at the patients side or for personnel reasons of the department. Standard procedures for the compensation for treatment breaks are part of the treatment protocols at radiotherapy departments. Possible risks of the discontinuation of radiotherapy are considered on the basis of the type and extent of the disease, the treatment intent and the condition of the patient, and the need of compensation for a break in the treatment is set. Patients are classified into three categories according to the above mentioned parameters. Compensation for the pause in radiotherapy is performed by calculating the equivalent dose in 2 Gy per fraction (EQD2); the preferred method of compensation is the one which enables observation of the planned total time of radiotherapy without extension. The benefit of local tumor control and the risk of increased acute or especially late toxicity should always be considered. In the current epidemiological situation, radiotherapy is often discontinued for COVID-19, and due to longer breaks in the treatment, it is necessary to combine multiple compensation methods in one patient.