ABSTRACT
Introduction and Objective: Anatomic and volumetric changes occur in head-and-neck cancer during fractionated radiotherapy (RT), and the actual dose received by patient is considerably different from the original plan. The purpose of this study is to evaluate volumetric and dosimetric changes occurring during radiation therapy. Patients and Methods: Ten patients of locally advanced head-and-neck cancer, 6 oropharynx, 3 larynx, and 1 hypopharynx underwent computed tomography (CT) simulation before treatment and after 4 weeks during RT treatment. Original plan (OPLAN) was generated based on initial CT scan for the entire course of treatment. The initial plan is implemented on the second planning CT scan, and the dose distribution is recalculated. Beam configuration of OPLAN was applied onto the second CT scan and then hybrid plan (HPLAN30) was generated. RPLAN30 is the intensity-modulated RT replan generated on the second CT scan for the remaining 30 Gy. Dose and volume parameters between OPLAN30 (based on the first CT scan for the remaining 30 Gy), HPLAN30, and RPLAN30 were compared. Results: The volume reduction of planning target volume (PTV), ipsilateral and contralateral parotid after 4 weeks of RT, was statistically significant (P < 0.05). D2% and V > 107% of PTV were higher in HPLAN than that of RPLAN (P < 0.05). Hybrid plans showed increase in delivered dose to spinal cord. Mid treatment replanning reduced doses to spinal cord (Dmax and D1%), which is statistically significant (P < 0.05). Mean doses to ipsilateral and contralateral parotid of RPLAN (21.4 Gy and 16.74 Gy, respectively) were reduced when compared to that of HPLAN (22.99 Gy and 22 Gy, respectively). Conclusion: Interim CT scanning and replanning (adaptive) improves target volume coverage and normal tissue sparing