Which scenario allows the addition of doses in radiation treatment?

In the context of radiation treatment, the addition of doses is often guided by the principle of optimizing treatment while minimizing toxicity to surrounding healthy tissues. When considering multiple phases directed at the same volume with the use of external beam radiation therapy, different dose distributions can be generated across various phases. This approach allows for a cumulative dose that can enhance the therapeutic effect on the target while carefully managing dose limits to adjacent structures over time.

Staging treatment in phases can effectively escalate the total dose delivered without exceeding the maximum tolerable limit for any single session, optimizing the therapeutic ratio. Each phase can have a specific rationale based on the tumor's response, potential changes in patient anatomy, or treatment goals, thus justifying the addition of these doses.

Other scenarios may limit the addition of doses due to the nature of the modalities or techniques involved. For instance, in brachytherapy or a combination of modalities targeting the same volume, careful consideration must be given to dose overlaps and total radiation exposure to avoid over-treatment.