The Estimated Difference in Biologically Effective Dose Between Two-Opposing-Fields-Per-Day and...

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Carbon ion radiation therapy (CIRT) is an advanced treatment modality.
• Optimizing dose delivery to minimize normal tissue toxicity is crucial in CIRT for prostate cancer.

Purpose of the Study:

• To compare the biologically effective dose (BED) to normal tissues between two-opposing-fields-per-day (2-fields-per-day) and one-alternating-field-per-day (1-field-per-day) CIRT approaches for prostate cancer.

Main Methods:

• BED was calculated using the linear-quadratic model and the modified microdosimetric kinetic model (mMKM) with varying parameters.
• Ten patients undergoing CIRT (54 Gy [RBE] in 12 fractions) were analyzed.
• Dosimetric differences in organs at risk (OARs) were compared between the two fractionation schedules.

Main Results:

• The 2-fields-per-day approach significantly reduced BED in noncentrally located OARs, notably the femoral head, skin, and bone marrow (up to 17% reduction).
• Centrally located OARs like the bladder and rectum showed minimal BED differences (<3%).
• Variations in BED reduction were observed depending on the calculation method used.

Conclusions:

• The 2-fields-per-day CIRT strategy results in lower BED for noncentrally located OARs compared to the 1-field-per-day approach.
• The clinical significance of this BED reduction needs further investigation.
• The choice of BED calculation method influences the observed differences.