Fiducial Markers, Saline, and Balloons to Locate and Stabilize the Prostate during Proton Therapy

Ross Zeitlin,Joseph Costa,Christopher R Williams,Nancy P Mendenhall,Zuofeng Li,Stephen Mandia,Stephanie Harris,Christopher G Morris,Matthew Mcphillips,Zhong Su

doi:10.14338/ijpt-15-00001

Abstract

Abstract Purpose: To determine the value of fiducials in daily image-guided prostate targeting for proton therapy (PT), to compare intrafraction motion between two stabilization strategies (rectal saline and balloon), and to determine the respective impacts of these combined strategies on planning target volume (PTV) expansions and smearing margins. Materials and Methods: Forty patients were randomly selected from a pool of low-risk prostate cancer patients with intraprostatic fiducials treated with proton therapy between 2006 and 2012, including 20 with intrarectal saline or 20 with endorectal balloons for daily prostate stabilization. Daily pre- and post-treatment orthovoltage (kV) films and digitally reconstructed radiographs (DRRs) were analyzed to determine prostate interfraction displacement, intrafraction motion, daily residual setup error in three axial dimensions (anterior-posterior, superior-inferior, and left-right), necessary population PTV expansions using van Herk's formula (2.5Σ + 0.7σ), an...

Highlights

In external-beam radiation therapy, the accuracy of tumor targeting and treatment delivery affect both the likelihood of tumor control and the likelihood of treatment complications related to normal tissue damage
An expansion beyond the actual target volume identified on 3-dimensional simulation imaging must be planned to account for both prostate interfraction and intrafraction motion to assure accurate targeting and treatment delivery, with highly conformal radiation techniques such as x-ray-based intensity-modulated radiation therapy (IMRT) or proton therapy
The purpose of the study reported is to evaluate the current strategy used at the University of Florida Health Proton Therapy Institute (UFHPTI, Jacksonville, FL) to account for interfraction motion, to compare two strategies used for minimizing intrafraction motion, and to determine the adequacy of the current planning target volume (PTV) expansion policy used in the prostate cancer program at UFHPTI

Summary

Introduction

In external-beam radiation therapy, the accuracy of tumor targeting and treatment delivery affect both the likelihood of tumor control and the likelihood of treatment complications related to normal tissue damage. Internal tumor targets may vary in position within the body on a daily basis (interfraction motion); for example, within the pelvis the degree of bladder and bowel filling may affect the location of the prostate relative to the bony pelvis and pelvic skin surface. The purpose of the study reported is to evaluate the current strategy used at the University of Florida Health Proton Therapy Institute (UFHPTI, Jacksonville, FL) to account for interfraction motion, to compare two strategies used for minimizing intrafraction motion, and to determine the adequacy of the current PTV expansion policy used in the prostate cancer program at UFHPTI

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Discussion

Conclusion