Initial clinical experience with Epid-based in-vivo dosimetry for VMAT treatments of head-and-neck tumors.
We evaluated an EPID-based in-vivo dosimetry algorithm (IVD) for complex VMAT treatments in clinical routine. 19 consecutive patients with head-and-neck tumors and treated with Elekta VMAT technique using Simultaneous Integrated Boost strategy were enrolled. In-vivo tests were evaluated by means of (i) ratio R 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 (γmean), using a global 3%-3 mm criteria. Alert criteria of ±5% for R ratio, γ% < 90% and γmean > 0.67 were chosen. A total of 350 transit EPID images were acquired during the treatment fractions. The overall mean R ratio was equal to 1.002 ± 0.019 (1 SD), with 95.9% of tests within ±5%. The 2D portal images of γ-analysis showed an overall γmean of 0.42 ± 0.16 with 93.3% of tests within alert criteria, and a mean γ% equal to 92.9 ± 5.1% with 85.9% of tests within alert criteria. Relevant discrepancies were observed in three patients: a set-up error was detected for one patient and two patients showed major anatomical variations (weight loss/tumor shrinkage) in the second half of treatment. The results are supplied in quasi real-time, with IVD tests displayed after only 1 minute from the end of arc delivery. This procedure 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 between measured and planned dose.
Medical Physics Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy; Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma Tre, Roma, Italy. Electronic address: savino.cilla@fgps.it.
Savino
S
Cilla
Medical Physics Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy.
Daniela
D
Meluccio
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma Tre, Roma, Italy; Medical Physics Unit, Policlinico A. Gemelli, Università Cattolica del Sacro Cuore, Roma, Italy.
Andrea
A
Fidanzio
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma Tre, Roma, Italy; Medical Physics Unit, Policlinico A. Gemelli, Università Cattolica del Sacro Cuore, Roma, Italy.
Luigi
L
Azario
Medical Physics Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy.
Anna
A
Ianiro
Radiotherapy Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy.
Gabriella
G
Macchia
Radiotherapy Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy.
Cinzia
C
Digesù
Radiotherapy Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy.
Francesco
F
Deodato
Radiotherapy Unit, Fondazione di Ricerca e Cura "Giovanni Paolo II", Campobasso, Italy; Radiotherapy Department, Policlinico A. Gemelli, Università Cattolica del Sacro Cuore, Roma, Italy.
Vincenzo
V
Valentini
Radiation Oncology Center, Department of Experimental, Diagnostic and Specialty Medicine - DIMES University of Bologna, S. Orsola-Malpighi Hospital, Bologna, Italy.
Alessio G
AG
Morganti
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Roma Tre, Roma, Italy; Medical Physics Unit, Policlinico A. Gemelli, Università Cattolica del Sacro Cuore, Roma, Italy.
Angelo
A
Piermattei
D000465:Algorithms; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D019300:Medical Errors; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011446:Prospective Studies; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012984:Software; D014057:Tomography, X-Ray Computed
EPID; Head-neck; In-vivo dosimetry; VMAT