Study on surface dose generated in prostate intensity-modulated radiation therapy treatment.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Prostate intensity-modulated radiation therapy (IMRT) is a widely used technique.
• Understanding surface dose is crucial for predicting and mitigating potential skin toxicity.
• Comparing IMRT with traditional 4-beam box (FBB) techniques is essential for optimizing treatment planning.

Purpose of the Study:

• To measure and compare surface doses from 6- and 15-MV prostate IMRT and 15-MV FBB irradiations.
• To investigate the contribution of the dynamic multileaf collimator (MLC) to surface dose.
• To evaluate the effects of photon beam energy and the number of beams on surface dose in IMRT.

Main Methods:

• Utilized Pinnacle treatment planning system (version 6) with CT scans from a Rando Phantom.
• Generated IMRT plans using 5, 7, and 9 beams with 6- and 15-MV photon beams (step-and-shoot technique).
• Employed metal oxide semiconductor field effect transistor detectors for surface dose measurements at the central beam axis.

Main Results:

• 6-MV IMRT yielded higher surface doses than 15-MV IMRT for the same number of beams.
• Increasing the number of beams in 15-MV IMRT increased surface dose (0.86% to 1.19%); for 6-MV IMRT, it decreased slightly (1.33% to 1.24%).
• IMRT generally resulted in 15%-30% higher surface doses than 15-MV FBB, attributed to beam count and monitor units.

Conclusions:

• Prostate IMRT, particularly with more beams, can lead to increased surface dose compared to FBB.
• Despite higher average surface dose, IMRT's even distribution avoids focal hot spots, potentially reducing skin complications.
• Dynamic MLC movement influences surface dose distribution, highlighting the importance of dose-intensity mapping.