Abstract
Radiotherapy is a commonly applied treatment modality in head and neck cancer patients. However, because of set-up errors and anatomic changes during the course of radiotherapy, the dose actually given to the patient can deviate from the planned dose.
We transferred, checked and modified individual contours of target volumes and organs at risk from the planning CTs to each of 660 CBCTs using deformable registration in 20 consecutive patients with head and neck cancer undergoing image-guided radical radiotherapy with RapidArc using the LD 70 Gy dose in 33 fractions. The real dose distribution was calculated and the dose was summed from all 33 fractions.
We compared these resulting plans with the dose distribution from the original plan. We evaluated the median dose for both parotids (D mean), the planning target volume treated with the 70 Gy dose (PTV 70 D mean), and the maximum dose for spinal cord with a 7 mm margin (D max Margin 0.7).
The median dose difference was - 3.56 Gy to + 7.38 Gy for the left parotid, - 2.32 Gy to + 3.98 Gy for the right parotid and - 0.8 % to + 0.6 % for PTV 70 D mean. The maximum dose difference for D max Margin 0.7 ranged from - 2.55 Gy to + 8.78 Gy.
Adaptive radiotherapy is a promising technology that can further improve treatment outcomes by more accurate irradiation of target volumes while sparing the healthy tissues.