Introducing new plan evaluation indices for prostate dose painting IMRT plans based on apparent diffusion coefficient...

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-guided Therapy

Background:

• Conventional plan quality indices are insufficient for complex prostate Intensity-Modulated Radiation Therapy (IMRT) dose painting due to varied dose prescriptions.
• Evaluating dose distribution conformity and homogeneity requires advanced metrics that account for tumoral cell density and lesion volume variations.

Purpose of the Study:

• To introduce novel Intensity-Optimized Evaluation (IOE) indices for assessing dose distribution conformity and homogeneity in prostate IMRT dose painting.
• To evaluate these new indices by comparing them with conventional methods and assessing their correlation with tumor control probability (TCP).

Main Methods:

• CT and MRI scans from 20 prostate cancer patients were used for Intensity-Modulated Radiation Therapy (IMRT) dose painting planning.
• Apparent diffusion coefficient (ADC) images were utilized to automatically delineate tumor sub-volumes (CTV70Gy, CTV60Gy, CTV53Gy) based on ADC values.
• New homogeneity (IOE(H)) and conformity (IOE(C)) indices were developed, incorporating relative lesion volume and cellular density from ADC data, and compared against conventional metrics and TCP.

Main Results:

• The novel IOE indices, particularly IOE(H) considering cellular density, showed significantly lower values compared to conventional indices (P < 0.05).
• Tumor control probability (TCP) demonstrated a stronger relationship with IOE(H) incorporating cell density (R² = -0.415) and IOE(C) without cell density (R² = 0.624).

Conclusions:

• The proposed IOE plan evaluation indices are effective for assessing prostate IMRT dose painting plans.
• Incorporating cellular density into the IOE(H) calculation is recommended, while IOE(C) is best calculated without considering cellular density.