SU-E-J-147: Dosimetric Consequences of Intrafraction Prostate Motion: Comparison Between Phantom Measurements and...

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Intrafraction motion significantly impacts dose delivery accuracy in prostate radiotherapy.
• Accurate dose calculation methods are needed to account for intra-fraction motion during Intensity-Modulated Radiation Therapy (IMRT).

Purpose of the Study:

• To evaluate and compare different computational methods for modifying radiation doses based on intrafraction prostate motion.
• To establish the accuracy of these methods using radiochromic film measurements as the ground truth.

Main Methods:

• Intrafraction motion data from 4 prostate IMRT patients (35 fractions each) were collected using the Calypso tumor tracking system.
• A phantom platform reproduced patient motion, with radiochromic films used for dose verification against three calculation methods: segment-shifted plans and two convolution techniques.

Main Results:

• The segment-shifted plan method achieved >90% gamma index (3%/3mm) agreement with film measurements across all patients.
• Convolution methods also yielded >90% agreement, with a slight decrease to 89% only for the patient exhibiting the largest intrafraction motion.

Conclusions:

• Segment-shifted target point recalculation is a reliable method for assessing the dosimetric impact of intrafraction prostate motion.
• Convolution methods provide acceptable results for dose estimation when segment-shifted calculations are not feasible.
• These findings can aid in optimizing treatment margins and dose prescription strategies under various motion conditions.