Epid‐based in vivo dose verification for lung stereotactic treatments delivered with multiple breath‐hold segmented volumetric modulated arc therapy

Abstract

We evaluated an EPID‐based in‐vivo dosimetry (IVD) method for the dose verification and the treatment reproducibility of lung SBRT‐VMAT treatments in clinical routine. Ten patients with lung metastases treated with Elekta VMAT technique were enrolled. All patients were irradiated in five consecutive fractions, with total doses of 50 Gy. Set‐up was carried out with the Elekta stereotactic body frame. Eight patients were simulated and treated using the Active Breath Control (ABC) system, a spirometer enabling patients to maintain a breath‐hold at a predetermined lung volume. Two patients were simulated and treated in free‐breathing using an abdominal compressor. IVD was performed using the SOFTDISO software. IVD tests were evaluated by means of (a) ratio R between daily in‐vivo isocenter dose and planned dose and (b) γ‐analysis between EPID integral portal images in terms of percentage of points with γ‐value smaller than one (γ%) and mean γ‐values (γmean) using a 3%(global)/3 mm criteria. Alert criteria of ±5% for R ratio, γ% < 90%, and γmean > 0.67 were chosen. 50 transit EPID images were acquired. For the patients treated with ABC spirometer, the results reported a high level of accuracy in dose delivery with 100% of tests within ±5%. The γ‐analysis showed a mean value of γmean equal to 0.21 (range: 0.04–0.56) and a mean γ% equal to 96.9 (range: 78–100). Relevant discrepancies were observed only for the two patients treated without ABC, mainly due to a blurring dose effect due to residual respiratory motion. Our method provided a fast and accurate procedure in clinical routine for verifying delivered dose as well as for detecting errors.

In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

“…Although initially developed for patient setup verification, EPIDs show also useful dosimetric characteristics [36] , [37] , [38] , [39] that have made them suitable for the implementation of IVD verification solutions [8] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] . Beginning in the early 2000 s, the current generation of amorphous-silicon flat-panel EPID technology became commercially available from major linac manufacturers and today is a ubiquitous choice on newly purchased linacs.…”

Combined Use of a Transmission Detector and an EPID-Based In Vivo Dose Monitoring System in External Beam Whole Breast Irradiation: A Study with an Anthropomorphic Female Phantom

“…The strength of the combined use of the two systems in detecting all different kinds of errors, even when very small, has been evidenced in this work. Separate use of IQM or SoftDiso devices has been widely discussed for different irradiation modalities [43][44][45][46][47][48][49], but to our knowledge, no study exists of their combined use, in particular for breast irradiation. A clinical study of the SoftDiso-based quality assurance procedure for post-mastectomy IMRT and VMAT radiation therapy is reported in reference [50], where specific thresholds for R-value, γ PR and γ mean indexes were proposed, based on the clinical experience and validated with a phantom chest.…”

IPEM topical report: guidance for the clinical implementation of online treatment monitoring solutions for IMRT/VMAT

“…The growth in RT complexity introduces new sources of uncertainty or opportunity for error along the patient pathway. With this, advanced methods are required to provide verification of the entire treatment chain (Torres-Xirau et al 2018, Cilla et al 2019).…”