BACKGROUND AND PURPOSE:Dose effects of intrafraction motion during prone prostate radiotherapy are unknown.
We compared prone and supine treatment using real-time tracking data to model dose coverage.
MATERIAL AND METHODS:Electromagnetic tracking data were analyzed for 10 patients treated prone, and 15 treated supine, with IMRT for localized prostate cancer. Plans were generated using 0mm, 3mm, and 5mm PTV expansions. Manual beam-hold interventions were applied to reposition the patient when translations exceeded a predetermined threshold. A custom software application (SWIFTER) used intrafraction tracking data acquired during beam-on model delivered prostate dose, by applying rigid body transformations to the prostate structure contoured at simulation within the planned dose cloud. The delivered minimum prostate dose as a percentage of planned dose (Dmin%), and prostate volume covered by the prescription dose as a percentage of the planned volume (VRx%) were compared for prone and supine treatment.
RESULTS:Dmin% was reduced for prone treatment for 0 (p=0.02) and 3mm (p=0.03) PTV margins. VRx% was reduced for prone treatment only for 0mm margins (p=0.002). No significant differences were found using 5mm margins.
CONCLUSIONS: Intrafraction motion has a greater impact on target coverage for prone compared to supine prostate radiotherapy. PTV margins of 3mm or less correlate with a significant decrease in delivered dose for prone treatment.
Written by:
Olsen JR, Parikh PJ, Watts M, Noel CE, Baker KW, Santanam L, Michalski JM. Are you the author?
Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, USA.
Reference: Radiother Oncol. 2012 Jul 16. Epub ahead of print.
doi: 10.1016/j.radonc.2012.06.008
PubMed Abstract
PMID: 22809590
UroToday.com Prostate Cancer Section
