undergoing treatment; receiving medical treatment
Used for a person currently under medical care, or for a condition being treated. Often appears in phrases like 治療中です or 治療中のため.
He is currently undergoing treatment.
治療中のため、しばらく仕事を休みます。
I will be off work for a while because I am receiving treatment.
Compound of 治療 (treatment) + 中 (in the middle of).