Dosimetric Comparison of Postmastectomy Radiotherapy Plans for Synchronous Bilateral Breast Cancer, Including...

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Synchronous bilateral breast cancer (SBBC) presents unique challenges for postmastectomy radiotherapy (PMRT) planning.
• Optimizing radiotherapy plans is crucial for maximizing treatment efficacy while minimizing toxicity in SBBC patients.

Purpose of the Study:

• To determine the optimal radiotherapy technique for SBBC patients undergoing PMRT with regional lymph node irradiation (RNI).
• To compare the dosimetric and efficiency outcomes of three different radiotherapy planning techniques.

Main Methods:

• A retrospective study involving 10 SBBC patients who underwent bilateral mastectomy and received bilateral PMRT with RNI.
• Three single-isocenter plans were designed: 9-fixed-beam intensity-modulated radiation therapy (9F-IMRT), 2-field VMAT (2F-VMAT), and 3-field VMAT (3F-VMAT).
• Paired t-tests and Friedman's tests were used to compare planning target volumes (PTVs) and organs at risk (OARs).

Main Results:

• All three techniques achieved adequate target dose coverage.
• 3F-VMAT demonstrated significantly better sparing of the lungs, heart, coronary artery, and liver compared to 9F-IMRT and 2F-VMAT.
• 3F-VMAT resulted in comparable monitor units to 2F-VMAT but significantly reduced beam-on times (BOTs) compared to 9F-IMRT.

Conclusions:

• 3F-VMAT provides superior normal tissue dose sparing and enhanced treatment efficiency for SBBC patients undergoing PMRT with RNI.
• The 3F-VMAT technique is identified as the optimal radiotherapy approach for this patient population.