Elsevier

Physica Medica

Volume 30, Issue 5, July 2014, Pages 555-558
Physica Medica

Original paper
Preliminary analysis for integration of spot-scanning proton beam therapy and real-time imaging and gating

https://doi.org/10.1016/j.ejmp.2014.04.002Get rights and content

Abstract

Purpose

Spot-scanning proton beam therapy (PBT) can create good dose distribution for static targets. However, there exists larger uncertainty for tumors that move due to respiration, bowel gas or other internal circumstances within the patients. We have developed a real-time tumor-tracking radiation therapy (RTRT) system that uses an X-ray linear accelerator gated to the motion of internal fiducial markers introduced in the late 1990s. Relying on more than 10 years of clinical experience and big log data, we established a real-time image gated proton beam therapy system dedicated to spot scanning.

Materials and methods

Using log data and clinical outcomes derived from the clinical usage of the RTRT system since 1999, we have established a library to be used for in-house simulation for tumor targeting and evaluation. Factors considered to be the dominant causes of the interplay effects related to the spot scanning dedicated proton therapy system are listed and discussed.

Results/conclusions

Total facility design, synchrotron operation cycle, and gating windows were listed as the important factors causing the interplay effects contributing to the irradiation time and motion-induced dose error. Fiducial markers that we have developed and used for the RTRT in X-ray therapy were suggested to have the capacity to improve dose distribution. Accumulated internal motion data in the RTRT system enable us to improve the operation and function of a Spot-scanning proton beam therapy (SSPT) system. A real-time-image gated SSPT system can increase accuracy for treating moving tumors. The system will start clinical service in early 2014.

Introduction

Proton beam therapy (PBT) has the potential to provide better dose distributions to the target being treated and reduce the dose to the target at risk (OAR) than X-ray therapy in many situations [1]. Spot-scanning proton beam therapy (SSPT) is expected to be more suitable to create more complex dose distributions to the target volume and also expected to be safer in terms of reducing the neutron contamination [2]. The SSPT has been considered disadvantageous to the conventional passive scattering PBT because of larger uncertainty in the dose distribution for the moving target due to interplay effects. The existence of the internal motion mainly from respiration is an issue to be discussed when we consider using the SSPT especially to treat lung and liver tumors.

We developed the real-time tumor-tracking radiation therapy (RTRT) system in 1999 and have been using it in the X-ray clinic for over 10 years [3]. The system can gate therapeutic x-rays according to the internal location of a fiducial in or near the tumor. The 3D trajectory of the fiducial marker is observed and calculated 30 times per second. We have started to develop a spot-scanning dedicated PBT system integrated with the RTRT system. The aim of this integration is to accurately treat tumors with SSPT that have respiratory movement. As the internal motion of lung and liver tumors is often different from the external surface motion of the chest or abdominal wall [4], it is insufficient to use surface motion for accurate estimation of target motion. In this study, a real time 3D fiducial location database obtained from the clinical experience using the RTRT system is used for simulation study of SSPT.

Section snippets

Materials and methods

Two orthogonal sets of X-ray fluoroscopes are installed in the gantry of the system to observe internal fiducials or bony structures before and during the beam delivery (Fig. 1). As an SSPT system does not require compensators and collimators, the X-ray images can be acquired simultaneously with proton beam irradiation at any beam angle, and their fields of view will not be narrowed by these field-shaping devices. The system supports the gating function of the therapeutic beam to the real-time

Results

Three factors are considered to be the main problems in developing a SSPT dedicated gating system from our imaging perspective and comparison with our experience of photon treatment through the clinical usage of the RTRT system. They are 1. synchrotron operation cycle, 2. gating window, and 3. precise targeting.

  • 1.

    Synchrotron operation cycle is a new factor that was not a problem when we developed the RTRT system for x-ray therapy. For the integration of SSPT and RTRT, we realized that the

Discussion

SSPT is considered a promising system that can deliver to the target volume high dose conformity with reducing secondary neutron dose and realizing a reduction of the total facility size [6]. Existence of interplay effects, however, during beam delivery is considered to be one of the important problems to perform SSPT clinically. In the present study, we investigated the relationship between the organ motion and SSPT. The details of the analysis of the internal motion of fiducial markers can be

Conclusion

We are currently integrating the real-time tumor-monitoring system with the spot-scanning dedicated PBT system. Data from the RTRT system and its clinical use enable us to improve the operation and function of the PBT system and to decide the proper parameters. A proton beam therapy system dedicated to spot-scanning can increase accuracy for moving tumors with real-time imaging and gating. The system will be introduced to clinical service in early 2014.

Conflicts of interest

Dr. Shirato has a patent “MOVING BODY PURSUIT IRRADIATING DEVICE AND POSITIONING METHOD USING THIS DEVICE” licensed to Hokkaido University, Japan. The other authors declare that they have no conflicts of interest.

Acknowledgements

This research has been supported in part by a grant from the Ministry of Education, Science, Sports, and Culture, Japan (No. 24591829) and the Japan Society for the Promotion of Science (JSPS) through the ‘‘Funding Program for World-Leading Innovative R&D on Science and Technology’’ (FIRST Program).

References (7)

There are more references available in the full text version of this article.

Cited by (27)

  • A treatment planning study of urethra-sparing intensity-modulated proton therapy for localized prostate cancer

    2021, Physics and Imaging in Radiation Oncology
    Citation Excerpt :

    This retrospective planning study was approved by the Institutional Review Board of the Hokkaido University Hospital for Clinical Research (approval number: 018–0221). We included 13 patients with prostate cancer who had undergone real-time-image-gated-spot-scanning proton beam therapy (RGPT) (with three fiducial markers inserted into the prostate gland) at our institution between October 2019 and 2020 [14–17]. Written informed consent was obtained from all patients.

  • Impact of Spot Size and Spacing on the Quality of Robustly Optimized Intensity Modulated Proton Therapy Plans for Lung Cancer

    2018, International Journal of Radiation Oncology Biology Physics
    Citation Excerpt :

    Interplay effects may severely perturb the resulting dose distribution (15-26). Many efforts have been made to minimize this effect, such as range-adapted internal target volume (ITV) (27-29), breath hold (30), gating (31-33), tumor tracking (28, 34), repainting (16, 22, 23, 25, 35-39), and 4-dimensional (4D) treatment planning (40-44). Some studies have shown that the geometric and radiologic variation due to respiratory motion have limited dosimetric impacts on target coverage and target dose homogeneity of the robustly optimized IMPT plans in lung cancer treatments (14, 45) if the motion amplitude is small.

  • Empowering Intensity Modulated Proton Therapy Through Physics and Technology: An Overview

    2017, International Journal of Radiation Oncology Biology Physics
    Citation Excerpt :

    However, online motion tracking and synchronization are technically highly challenging (94, 95). Respiratory gating using tracking of implanted fiducial markers is being investigated (96-99). However, “shadows” created by the markers in the target dose distributions are a matter of concern, which may be mitigated by further development of markers with low atomic numbers.

View all citing articles on Scopus
View full text