Dosimetric effect of prostate motion during helical tomotherapy

Area of Science:

• Radiation oncology
• Medical physics

Background:

• Prostate cancer radiotherapy requires precise dose delivery.
• Intrafraction motion can potentially compromise treatment accuracy.
• Helical tomotherapy is an advanced radiation delivery technique.

Purpose of the Study:

• To evaluate the impact of intrafraction prostate motion on dose distributions in helical tomotherapy plans.
• To quantify the dosimetric consequences of prostate motion on target coverage.

Main Methods:

• Real-time prostate motion was tracked using an electromagnetic device in 515 fractions from 16 patients.
• Dose distributions were recalculated retrospectively using a 4D calculation engine based on motion data.
• Key dosimetric parameters, including D(95%), were analyzed for individual fractions and cumulative treatment effects.

Main Results:

• The average change in target D(95%) across all fractions was less than 1%.
• Individual fractions occasionally showed D(95%) reductions up to 20%.
• The cumulative dosimetric effect on target D(95%) remained small, approximately 1% after five fractions.

Conclusions:

• Intrafraction prostate motion typically has a minor dosimetric impact on helical tomotherapy plans.
• Severe dose degradations in single fractions are infrequent and their cumulative effect is mitigated by fractionation.