A proton beam therapy system dedicated to spot-scanning increases accuracy with moving tumors by real-time imaging and gating and reduces equipment size

• Published in: PloS one Vol. 9; no. 4; p. e94971
• Main Authors: Shimizu, Shinichi, Miyamoto, Naoki, Matsuura, Taeko, Fujii, Yusuke, Umezawa, Masumi, Umegaki, Kikuo, Hiramoto, Kazuo, Shirato, Hiroki
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01-04-2014; Public Library of Science (PLoS)
• Subjects: Biology and Life Sciences; Breathing; Cancer therapies; Carcinoma, Hepatocellular - diagnostic imaging; Carcinoma, Hepatocellular - physiopathology; Carcinoma, Hepatocellular - radiotherapy; Comparative analysis; Computed tomography; Criteria; Drug dosages; Engineering and Technology; Equipment costs; Fiducial Markers; Fluoroscopy; Gating; Health physics; Hepatocellular carcinoma; Housing; Humans; Imaging; Laboratories; Liver; Liver cancer; Liver Neoplasms - diagnostic imaging; Liver Neoplasms - physiopathology; Liver Neoplasms - radiotherapy; Markers; Medicine and Health Sciences; Methods; Movement; Patients; Physical Sciences; Polybutylene terephthalates; Proton beam radiotherapy; Proton beams; Proton Therapy - instrumentation; Proton Therapy - standards; R&D; Radiation therapy; Radiotherapy Dosage; Real time; Research & development; Respiration; Respiratory-Gated Imaging Techniques; Scanning; Scanning devices; Simulation; Studies; Synchrotrons; Tomography; Tomography, X-Ray Computed; Tumors; University graduates; Japan
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0094971

A proton beam therapy (PBT) system has been designed which dedicates to spot-scanning and has a gating function employing the fluoroscopy-based real-time-imaging of internal fiducial markers near tumors. The dose distribution and treatment time of the newly designed real-time-image gated, spot-scanning proton beam therapy (RGPT) were compared with free-breathing spot-scanning proton beam therapy (FBPT) in a simulation.
In-house simulation tools and treatment planning system VQA (Hitachi, Ltd., Japan) were used for estimating the dose distribution and treatment time. Simulations were performed for 48 motion parameters (including 8 respiratory patterns and 6 initial breathing timings) on CT data from two patients, A and B, with hepatocellular carcinoma and with clinical target volumes 14.6 cc and 63.1 cc. The respiratory patterns were derived from the actual trajectory of internal fiducial markers taken in X-ray real-time tumor-tracking radiotherapy (RTRT).
With FBPT, 9/48 motion parameters achieved the criteria of successful delivery for patient A and 0/48 for B. With RGPT 48/48 and 42/48 achieved the criteria. Compared with FBPT, the mean liver dose was smaller with RGPT with statistical significance (p<0.001); it decreased from 27% to 13% and 28% to 23% of the prescribed doses for patients A and B, respectively. The relative lengthening of treatment time to administer 3 Gy (RBE) was estimated to be 1.22 (RGPT/FBPT: 138 s/113 s) and 1.72 (207 s/120 s) for patients A and B, respectively.
This simulation study demonstrated that the RGPT was able to improve the dose distribution markedly for moving tumors without very large treatment time extension. The proton beam therapy system dedicated to spot-scanning with a gating function for real-time imaging increases accuracy with moving tumors and reduces the physical size, and subsequently the cost of the equipment as well as of the building housing the equipment.