When Should an Adaptive Plan be Considered for Head-and-neck Cancer Patients Undergoing Tomotherapy Treatment?

Changes in target-induced cold and hot spots may result in significant dose differences to some parts of a target, which might be related to clinical outcome. We suggest a guideline for adaptive planning using megavoltage CT (MVCT) during tomotherapy. Twenty-one head-and-neck cancer patients, including eight who experienced relatively large weight loss during tomotherapy treatment, were evaluated retrospectively with initial and final MVCT images to quantify the greatest weight-loss effects. Kilovoltage CTs (KVCTs) of five patients were obtained during radiation therapy (RT), and volumes of targets and organs were delineated on the KVCTs. Direct machine parameter optimization (DMPO) was used to generate intensity-modulated radiotherapy (IMRT) plans. The beam configurations of the initial plans were applied to the second KVCT images. We compared changes in target dose and organs with various parameters. We compared the initial and the final MVCTs of the 21 patients undergoing tomotherapy with the same initial target. We found that the average of the maximum and mean doses delivered to the gross tumor, increased. Data on modified targets and organs on KVCT imaging from five patients showed that the maximum and the mean doses delivered to the gross tumor increased and that the minimum dose decreased. Heterogeneity and coverage also decreased similarly when the overall results from the 21 patients were assessed. The relative thicknesses of the five patients were close to 0.9, and therapy for some patients required replanning. When the thickness value was less than 0.85, adaptive planning was recommended during tomotherapy even if the setup variation had also been considered. Attention should be paid to weight loss during tomotherapy treatment, and if a patient shows significant weight loss, an adaptive plan should be considered to achieve prescribed doses to targets and to spare nearby critical structures.