An Assessment of PTV Margin Definitions for Patients Undergoing Conformal 3D External Beam Radiation Therapy for Prostate Cancer Based on an Analysis of 10,327 Pretreatment Daily Ultrasound Localizations

Conclusion: Our study has revealed systematic intertreatment uncertainties that would have required a nonuniform PTV margin ranging in dimensions between 2.7 mm anterior, 14.9 mm posterior, 7.7 mm right, 6.7 mm left, 11 mm superior, and 7 mm inferior to encompass the prostate for 95% of our sample if the ultrasound localization system were not used. In the absence of systematic uncertainties, a uniform PTV margin of 9 mm would suffice.