Does variable RBE affect toxicity risks for mediastinal lymphoma patients? NTCP-based evaluation after proton therapy...

Area of Science:

• Radiation oncology
• Medical physics
• Oncology

Background:

• Mediastinal lymphoma (ML) predominantly affects young individuals, necessitating treatments that balance efficacy with minimized long-term toxicity.
• Modern therapeutic strategies aim for high survival rates and extended life expectancy, highlighting the critical need to reduce treatment-related side effects.

Purpose of the Study:

• To quantify the organ-specific toxicity risks in ML patients undergoing intensity-modulated proton therapy (IMPT).
• To evaluate the impact of variable relative biological effectiveness (RBE) on predicted normal tissue complication probabilities (NTCP).
• To identify patients at higher risk of treatment-related toxicities.

Main Methods:

• Treatment plans for ten ML patients were re-analyzed using a Monte Carlo code (TOPAS) to determine linear energy transfer (LET) and estimate variable RBE.
• Published NTCP models were employed to calculate toxicity risks for hypothyroidism, heart valve defects, coronary heart disease, and lung fibrosis.
• NTCP calculations were performed using both constant and variable RBE values, with individual radiosensitivity uncertainties addressed by sampling alpha/beta ratios.

Main Results:

• Variable RBE had a minimal effect on hypothyroidism risk for most patients, but increased it significantly (up to 24%) in three individuals.
• Lung fibrosis risk was only slightly impacted by variable RBE (maximum ~1% increase).
• Heart valve dysfunction risk showed a similar minor impact, except for one patient with a ~10% increase potentially linked to larger heart volume and D1 dose.

Conclusions:

• Utilizing NTCP models effectively identifies ML patients at elevated risk of treatment-related toxicities.
• Incorporating variable RBE into treatment plan evaluations may be beneficial for high-risk patient stratification.
• This approach aids in optimizing IMPT strategies to mitigate long-term adverse effects in young ML survivors.