Why do depth dose curves differ among different accelerators, even for the same nominal energy MV?

Depth dose curves differ among different accelerators due to the type of target used in each machine. The target material significantly affects the energy spectrum of the photons generated during the acceleration process, resulting in variations in the emitted beam’s quality and energy distribution. Each type of target—such as tantalum or gold—has unique properties that influence how the high-energy photons are produced and how they interact with tissues upon reaching the patient.

As a consequence, even if accelerators are set to deliver the same nominal energy, the physical characteristics of the target can lead to differences in dose distribution at various depths. This means that the dose delivered to tissues at different depths will vary, which is crucial for treatment planning and delivering precise radiation therapy. Understanding these variations helps medical dosimetrists ensure the effectiveness and safety of the treatment plan tailored for individual patients.