Margriet Kwint

Intra anatomical changes during radiotherapy 73 4 Decision support system A team of dedicated CBCT RTTs, radiation oncologists and physicists evaluated examples of collected ITACs. Four types of urgency levels were defined ( figure 1 ): A protocol for communication and/or consultation was defined for each urgency level. 1. Action level red: The GTV is outside the PTV due to ITACs. The radiation oncologist is called immediately and treatment is only given when approved by the radiation oncologist. 2. Action level orange: The GTV is just inside the PTV due to ITACs. The radiation oncologist is notified by email and has to respond before the next fraction. Further diagnostics are considered as a result of the ITAC. 3. Action level yellow: There is an ITAC visible but the GTV is well inside the PTV. The radiation oncologist is notified by email about the ITAC but no response is necessary and treatment may continue. 4. Action level green: No change visible. No action needed. The Traffic Light Protocol is practical guideline to the RTTs visual inspection of the patients CBCT in the absence of the possibility to quantify the dosimetric influence of ITACs immediately after a CBCT is made. Note that a CBCT is not of diagnostic quality. A visual assessment that the CBCT visualized GTV is (well) within the PTV gives confidence but no guarantees that the tumor receives adequate dose. The traffic light color therefore reflects a risk assessment of the occurrence of clinically relevant dosimetric changes. In case of an ITAC, the RTT informs the radiation oncologist. The radiation oncologist and clinical physicist make an estimation of the dosimetric influence of the ITAC on the tumor and/or OAR. When is estimated that the dosimetric influence is relevant for treatment outcome, a new planning-CT and possibly adaptive treatment plan will be made.