Parotid sparing in RapidPlan Oropharynx models: To split or not to split

Area of Science:

• Radiation oncology
• Medical physics
• Radiotherapy planning

Background:

• Radiation planning quality varies due to factors like patient anatomy and planning objectives.
• Knowledge-based planning (KBP) aims to standardize and improve radiotherapy plans.

Purpose of the Study:

• To determine if treating parotid glands as combined or separate structures in KBP impacts oropharyngeal radiation plan quality.
• To evaluate dose received by parotid glands under different KBP modeling approaches.

Main Methods:

• Two RapidPlan (RP) models were developed: one with separate ipsilateral/contralateral parotids and one combined.
• Both models were validated using independent patient data (20 patients).
• Dose constraints, priorities, and an auto-generated line objective were consistently applied; parotid mean and V50 doses were compared.

Main Results:

• The combined parotid model achieved lower ipsilateral mean doses in 80% of cases and lower V50 doses in 75% of cases.
• Lower mean doses to the contralateral parotid were observed in 55% of plans using the combined model.
• V50 dose reductions for the contralateral parotid were evenly distributed between the two models.

Conclusions:

• A combined parotid gland model in RP enhances ipsilateral parotid sparing during oropharyngeal radiotherapy.
• The combined model shows promise for sparing the contralateral parotid, warranting further investigation.
• Optimizing KBP by combining parotid structures can lead to improved dose distribution in head and neck cancer radiotherapy.