Adaptive intensity-modulated radiotherapy in head and neck cancer patients treated by chemoradiotherapy: To quantify temporal changes during the course of radiotherapy and to study the impact of these changes on the baseline treatment plans

Aims: The purpose of study was to evaluate the volumetric changes and dose perturbations, occurring in various target volumes and organs at risk during radiotherapy. Materials and Methods: Ten locally advanced head and neck cancer patients were recruited. The rate of volume change and dose perturbations for targets and organs at risk was calculated by superimposing repeatradiation treatment planning scans (RTPs) over baseline RTP-computerized tomography. Results: The mean volume regression for primary target was 19% (0–48.5) for first (repeat) RTP scan and 29.4% (4.5–52.8) for second (repeat) RTP scan; for nodal target, mean volume regression was 33.4% (3.4–67.2) and 52.9% (36.5–78.7), respectively; for the left parotid, mean volume regression was 24.4% (13.5–40.8) and 33.6% (9.4–52.4), respectively, and for right parotid, mean volume regression was 24.13% (9.4–52.4) and 35.55% (16–52), respectively. For the left parotid, mean displacement was 0.21 cm (0–0.5) for first repeat RTP and 0.28 cm (0–0.6) for second repeat RTP while for right parotid it was 0.26 cm (0–0.8) and 0.36 cm (0.1–1.0), respectively. These all movements for both parotids were in medial directions. Only one patient had crossed Dmax cord beyond 50 Gy, i.e., 54.07 Gy. For left parotid gland, mean dose was increased up to 26.7% (2–26.7) and 33% (2–33); right parotid, mean dose was increased up to 35% (1.6–35) and 48.9 (2–48.9), respectively. Conclusion: As a consequence of regression in tumor and parotid glands volumes resulted in dose perturbation of target volumes up to 21%. Similarly, parotid glands received up to 49% excess of planned dose, due to its medial migration.