Impact of Real-Time Image Gating on Spot Scanning Proton Therapy for Lung Tumors: A Simulation Study.

Abstract

PURPOSE:

To investigate the effectiveness of real-time-image gated proton beam therapy for lung tumors and to establish a suitable size for the gating window (GW).

METHODS AND MATERIALS:

A proton beam gated by a fiducial marker entering a preassigned GW (as monitored by 2 fluoroscopy units) was used with 7 lung cancer patients. Seven treatment plans were generated: real-time-image gated proton beam therapy with GW sizes of ±1, 2, 3, 4, 5, and 8 mm and free-breathing proton therapy. The prescribed dose was 70 Gy (relative biological effectiveness)/10 fractions to 99% of the target. Each of the 3-dimensional marker positions in the time series was associated with the appropriate 4-dimensional computed tomography phase. The 4-dimensional dose calculations were performed. The dose distribution in each respiratory phase was deformed into the end-exhale computed tomography image. The D99 and D5 to D95 of the clinical target volume scaled by the prescribed dose with criteria of D99 >95% and D5 to D95 <5%, V20 for the normal lung, and treatment times were evaluated.

RESULTS:

Gating windows ≤ ±2 mm fulfilled the CTV criteria for all patients (whereas the criteria were not always met for GWs ≥ ±3 mm) and gave an average reduction in V20 of more than 17.2% relative to free-breathing proton therapy (whereas GWs ≥ ±4 mm resulted in similar or increased V20). The average (maximum) irradiation times were 384 seconds (818 seconds) for the ±1-mm GW, but less than 226 seconds (292 seconds) for the ±2-mm GW. The maximum increased considerably at ±1-mm GW.

CONCLUSION:

Real-time-image gated proton beam therapy with a GW of ±2 mm was demonstrated to be suitable, providing good dose distribution without greatly extending treatment time.

• Authors: Takahiro Kanehira, Taeko Matsuura, Seishin Takao, Yuka Matsuzaki, Yusuke Fujii, Takaaki Fujii, Yoichi M Ito, Naoki Miyamoto, Tetsuya Inoue, Norio Katoh, Shinichi Shimizu, Kikuo Umegaki, Hiroki Shirato
• Journal: International journal of radiation oncology, biology, physics (Int J Radiat Oncol Biol Phys) Vol. 97 Issue 1 Pg. 173-181 (01 01 2017) ISSN: 1879-355X [Electronic] United States
• PMID: 27856039 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2016 Elsevier Inc. All rights reserved.

Topics

• Carcinoma, Non-Small-Cell Lung (diagnostic imaging, pathology, radiotherapy)
• Fiducial Markers
• Four-Dimensional Computed Tomography (methods)
• Humans
• Lung Neoplasms (diagnostic imaging, pathology, radiotherapy)
• Movement
• Proton Therapy (instrumentation, methods)
• Radiotherapy Dosage
• Radiotherapy Planning, Computer-Assisted (methods)
• Respiration
• Simulation Training (methods)
• Time Factors