Surface and superficial dose dosimetric verification for postmastectomy radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Dosimetry

Background:

• Postmastectomy radiotherapy (PMRT) involves treating the chest wall, a region with high dosimetric uncertainty due to thin tissue and underlying lung.
• Accurate dose delivery to the chest wall while minimizing dose to superficial tissues is crucial for effective treatment and reducing side effects.

Purpose of the Study:

• To measure and evaluate surface and superficial doses for patients undergoing PMRT using different treatment techniques.
• To compare the dosimetric characteristics of tangential wedged fields (TWFs) and 4-field intensity-modulated radiation therapy (IMRT) for PMRT.

Main Methods:

• A phantom simulating the chest wall and lung was used with varying thicknesses.
• Computed tomography (CT) imaging, clinical target volumes (CTVs), and planning target volumes (PTVs) were defined.
• TWF and 4-field IMRT plans were created with a prescribed dose of 180 cGy per fraction.
• Radiochromic external beam therapy (EBT) films were used to measure dose profiles at various depths (0-5 mm).

Main Results:

• TWF plans showed underdoses in median and lateral regions, with surface doses around 52% of the prescribed dose and maximum doses up to 118%.
• 4-field IMRT plans demonstrated more uniform dose distributions within the PTV (>94% at >1 mm depth) and a mean surface dose of approximately 65%.
• Maximum doses in IMRT plans were below 118.4% of the prescribed dose.

Conclusions:

• The choice of treatment technique significantly impacts surface and superficial dose distribution in PMRT.
• IMRT plans provide more uniform PTV coverage and potentially better skin sparing compared to TWF.
• Consideration of bolus, treatment technique, and target coverage is essential for optimizing PMRT and managing skin reactions.