Peripheral doses from noncoplanar IMRT for pediatric radiation therapy.

Area of Science:

• Medical Physics
• Radiation Oncology
• Pediatric Oncology

Background:

• Noncoplanar intensity-modulated radiation therapy (IMRT) offers potential advantages in critical organ sparing due to greater beam angle flexibility.
• However, noncoplanar IMRT may lead to elevated peripheral doses compared to coplanar techniques, a factor not previously quantified.
• Peripheral dose quantification is crucial for understanding the full implications of noncoplanar IMRT in clinical practice, especially in pediatric patients.

Purpose of the Study:

• To investigate and quantify the peripheral dose associated with noncoplanar IMRT in pediatric radiation therapy.
• To compare the peripheral doses delivered by noncoplanar IMRT versus coplanar IMRT in pediatric head and neck cancer cases.
• To assess the potential impact of noncoplanar IMRT on radiation-sensitive organs and secondary cancer risk in young patients.

Main Methods:

• Five pediatric head and neck cancer cases were planned using both coplanar and noncoplanar IMRT techniques.
• Treatment plans were optimized for comparable tumor coverage, conformality, and dose uniformity between the two techniques.
• Peripheral doses were measured using thermoluminescent dosimeters placed in 10 organs within a pediatric anthropomorphic phantom.

Main Results:

• Noncoplanar IMRT resulted in peripheral doses to the spinal cord, bone marrow, lung, and breast that were 1.8-2.5 times higher than those from coplanar IMRT.
• The increase in peripheral dose is primarily attributed to additional internal scatter from noncoplanar beams.
• While noncoplanar IMRT can spare specific organs like optic nerves, lens, or inner ears, it significantly elevates doses to organs such as bone marrow and breast.

Conclusions:

• Noncoplanar IMRT in pediatric patients can lead to substantially increased peripheral doses to critical organs like bone marrow and breast.
• The elevated peripheral dose from noncoplanar IMRT may increase the risk of secondary malignancies in young patients.
• Oncologists must carefully weigh the benefits of organ sparing against the increased peripheral dose and potential long-term risks when selecting noncoplanar IMRT for pediatric radiation therapy.