Epid-based in vivo dosimetry for complex VMAT treatments dose verification in clinical routine. (September 2016)

• Record Type: Journal Article
• Authors: Cilla, Savino; Ianiro, Anna; Deodato, Francesco; Macchia, Gabriella; Fidanzio, Andrea; Azario, Luigi; Valentini, Vincenzo; Morganti, Alessio G.; Piermattei, Angelo
• Is Part Of: Physica medica. Volume 32(2016)Supplement 3
• Page Start: 254
• Page End: 255
• Publication Date: 2016-09
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2016.07.545
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Introduction: Due to the increasing complexity of radiotherapy treatments, comprehensive quality assurance programs are mandatory to check the proper functioning of the whole radiotherapy chain. In vivo dosimetry (IVD), a direct method of measuring radiation doses to cancer patients during treatment, has shown unique features to trace deviations between planned and actually delivered dose distributions. Purpose: To assess the usefulness of EPID-based IVD for complex VMAT treatments in clinical routine. Materials and methods: 80 patients (30 with head-neck tumor, 30 with pelvic tumors and 20 patients with extracranial metastases) treated with Elekta were enrolled. IVD tests were evaluate by means of (i) R ratio between daily in-vivo isocenter dose and planned dose and (ii) γ -analysis between EPID integral portal images in terms of percentage of points with γ -value smaller than one ( γ %) and mean γ -values ( γ mean), using a global 3%-3 mm criteria. Alert criteria of ±5% for R ratio, γ % <90% and γ mean >0.67 were chosen. Results: A total of 980 transit EPID images were acquired. The mean R ratio was equal to 1.001 ± 0.015 for all patients with more than 95% of tests were within 5%. For HN, pelvic and SBRT treatments, γ % and γ mean metrics reported 85.9%, 83.1% and 95.4%, and 93.3%, 92.1% and 98.1% of tests within alert criteria, respectively. The systematic use of IVD revealed relevant discrepancies in a few H–N patients due to major anatomical variations and variations due to random anatomical changes in terms of filling of rectum/bladder in pelvic tumors. No discrepancies were detected in SBRT patients. Conclusion: IVD was able to detect when delivery was inconsistent with the original plans, allowing physics and medical staff to promptly act in case of major deviations.