Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled With Dynamic Multileaf Collimator Tracking: An Intensity-Modulated Radiation Therapy Feasibility Study

Smith, Ryan L.; Sawant, Amit; Santanam, Lakshmi; Venkat, Raghu B.; Newell, Laurence J.; Cho, Byung-chul; Poulsen, Per; Catell, Herbert; Keall, Paul J.; Parikh, Parag J.

doi:10.1016/j.ijrobp.2009.01.031

« Previous Next »International Journal of Radiation Oncology * Biology * Physics
Volume 74, Issue 3 , Pages 868-875, 1 July 2009

Integration of Real-Time Internal Electromagnetic Position Monitoring Coupled With Dynamic Multileaf Collimator Tracking: An Intensity-Modulated Radiation Therapy Feasibility Study

Ryan L. Smith
- Washington University Saint Louis, Saint Louis, MO
Amit Sawant, PhD.
- Stanford University, Palo Alto, CA
Lakshmi Santanam, PhD.
- Washington University Saint Louis, Saint Louis, MO
Raghu B. Venkat, MS.
- Stanford University, Palo Alto, CA
Laurence J. Newell, MS.
- Calypso® Medical Technologies, Inc., Seattle, WA
Byung-chul Cho, PhD.
- Stanford University, Palo Alto, CA
Per Poulsen, PhD.
- Stanford University, Palo Alto, CA
Herbert Catell
- Varian Medical Systems, Palo Alto, CA
Paul J. Keall, PhD.
- Stanford University, Palo Alto, CA
Parag J. Parikh, MD.
- Washington University Saint Louis, Saint Louis, MO
- Reprint request to: Parag J. Parikh, M.D., Department of Radiation Oncology, Washington University School of Medicine, 4921 Parkview Place, Saint Louis, MO 63110. Tel: (314) 747-9614; Fax: (314) 362-8521

Received 11 August 2008; received in revised form 22 January 2009; accepted 25 January 2009. published online 24 April 2009.

Purpose

Continuous tumor position measurement coupled with a tumor tracking system would result in a highly accurate radiation therapy system. Previous internal position monitoring systems have been limited by fluoroscopic radiation dose and low delivery efficiency. We aimed to incorporate a continuous, electromagnetic, three-dimensional position tracking system (Calypso 4D Localization System) with a dynamic multileaf collimator (DMLC)–based dose delivery system.

Methods and Materials

A research version of the Calypso System provided real-time position of three Beacon transponders. These real-time three-dimensional positions were sent to research MLC controller with a motion-tracking algorithm that changed the planned leaf sequence. Electromagnetic transponders were embedded in a solid water film phantom that moved with patient lung trajectories while being irradiated with two different plans: a step-and-shoot intensity-modulated radiation therapy (S-IMRT) field and a dynamic IMRT (D-IMRT) field. Dosimetric results were recorded under three conditions: no intervention, DMLC tracking, and a spatial gating system.

Results

Dosimetric accuracy was comparable for gating and DMLC tracking. Failure rates for gating/DMLC tracking are as follows: ±3 cGy 10.9/ 7.5% for S-IMRT, 3.3/7.2% for D-IMRT; gamma (3mm/3%) 0.2/1.2% for S-IMRT, 0.2/0.2% for D-IMRT. DMLC tracking proved to be as efficient as standard delivery, with a two- to fivefold efficiency increase over gating.

Conclusions

Real-time target position information was successfully integrated into a DMLC effector system to modify dose delivery. Experimental results show both comparable dosimetric accuracy as well as improved efficiency compared with spatial gating.

Radiation therapy, Intensity modulation, Lung, Cancer, DMLC, Tracking