More optimal dose distributions for moving lung tumours: a planning study

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Moving lung tumors require larger target volumes, increasing the risk of lung complications.
• Intensity modulated radiotherapy (IMRT) offers precise dose distributions.
• Dose distributions based on tumor motion probability density function (PDF) may improve lung sparing.

Purpose of the Study:

• To compare conformal radiotherapy (CRT) encompassing full motion, CRT at the modal position, and IMRT based on tumor PDF.
• To evaluate dose distributions for moving lung tumors.
• To assess the impact on tumor dose and normal tissue complication probabilities (NTCPs).

Main Methods:

• A 5 cm spherical target in a lung phantom was simulated with 3 cm superior-inferior sinusoidal motion.
• Parallel-opposed beams with a 1.5 cm margin were used.
• Equivalent Uniform Dose (EUD) and NTCP for radiation pneumonitis were calculated for different dose distributions.

Main Results:

• Equivalent Uniform Doses (EUDs) were 60.0 Gy (CRT full motion), 48.5 Gy (CRT modal position), and 57.9 Gy (IMRT PDF).
• Normal Tissue Complication Probabilities (NTCPs) for radiation pneumonitis were 5% (CRT full motion), 1% (CRT modal position), and 3% (IMRT PDF).

Conclusions:

• Optimized dose distributions for moving lung targets are feasible.
• IMRT based on tumor PDF shows potential to reduce lung complications with minimal impact on EUD.
• Further investigation into these advanced radiotherapy techniques is warranted.