Development of a Tumor Growth-responsive Robust Planning Method for Head and Neck Cancer in Carbon-ion Radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Particle therapy offers precise dose delivery for head and neck cancers.
• Tumor growth during treatment can compromise dose distribution and treatment efficacy.
• Robust treatment planning methods are crucial to adapt to such biological changes.

Purpose of the Study:

• To evaluate a novel treatment planning method robust against tumor growth in particle therapy.
• To assess the effectiveness of this method in head and neck cancer patients undergoing carbon ion radiotherapy.

Main Methods:

• A treatment planning method was developed, optimizing dose distribution by using a tumor-equivalent relative stopping power ratio (rSPR) in the clinical target volume (CTV) cavity region.
• The method was evaluated in 10 head and neck cancer patients treated with carbon ion radiotherapy.
• Treatment plans were recalculated using in-room CT images, comparing doses between the proposed method (Condition 1) and the initial plan (Condition 2).

Main Results:

• The proposed method (Condition 1) demonstrated improved CTV coverage compared to the initial plan (Condition 2), with a lower CTV V95% reduction (1.3%±2.9% vs. 2.6%±3.7%).
• Subgroup analysis indicated that faster-growing tumors, such as mucosal melanoma, experienced greater changes in target coverage, highlighting the method's sensitivity to tumor growth rates.
• The replacement condition (Condition 1) consistently provided superior CTV coverage.

Conclusions:

• The developed treatment planning method enhances robustness in carbon ion radiotherapy for head and neck cancer by adjusting for tumor growth.
• This approach ensures consistent dose delivery to the tumor and maintains safety for organs at risk.
• The method shows particular benefit for fast-growing tumors, potentially improving treatment outcomes.