Evaluation and clinical implementation of in vivo dosimetry for kV radiotherapy using radiochromic film and micro-silica bead thermoluminescent detectors. (October 2017)

• Record Type: Journal Article
• Authors: Palmer, Antony L.; Jafari, Shakardokht M.; Mone, Ioanna; Muscat, Sarah
• Is Part Of: Physica medica. Volume 42(2017)
• Page Start: 47
• Page End: 54
• Publication Date: 2017-10
• Subjects: kV -- In vivo -- Film -- Silica bead; 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.2017.08.009
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Uncertainty in manual calculations for inhomogeneous, irregular kV treatments. Novel in vivo dosimetry verification of complex kV radiotherapy is presented. Radiochromic film and silica bead TLDs are introduced for kV in vivo. Accuracy and uncertainty of clinical kV treatments is demonstrated and discussed. Air cavities, underlying bone and lack of scatter can modify treatment dose. Abstract: Purpose: kV radiotherapy treatment calculations are based on flat, homogenous, full-scatter reference conditions. However, clinical treatments often include surface irregularities and inhomogeneities, causing uncertainty. Therefore, confirmation of actual delivered doses in vivo is valuable. The current study evaluates, and implements, radiochromic film and micro silica bead TLD for in vivo kV dosimetry. Methods: The kV energy and dose response of EBT3 film and silica bead TLD was established and uncertainty budgets determined. In vivo dosimetry measurements were made for a consecutive series of 30 patients using the two dosimetry systems. Results: Energy dependent calibration factors were required for both dosimetry systems. The standard uncertainty estimate for in vivo measurement with film was 1.7% and for beads was 1.5%. The mean measured dose was −2.1% for film and −2.6% for beads compared to prescription. Deviations up to −9% were found in cases of large surface irregularity, or with underlying air cavities or bone. Dose shielding by beads could be clinically relevant at low kV energies and superficial depths. Conclusions: Both film and beads may be used to provide in vivo verification of delivered doses in kV radiotherapy, particularly for complex situations that are not well represented by standard reference condition calculations.