An investigation into the INTRABEAM miniature x‐ray source dosimetry using ionization chamber and radiochromic film measurements. Issue 9 (23rd July 2018)

• Record Type: Journal Article
• Authors: Watson, Peter G. F.; Bekerat, Hamed; Papaconstadopoulos, Pavlos; Davis, Stephen; Seuntjens, Jan
• Is Part Of: Medical physics. Volume 45:Issue 9(2018)
• Page Start: 4274
• Page End: 4286
• Publication Date: 2018-07-23
• Subjects: electronic brachytherapy -- gafchromic film -- kV dosimetry; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1002/mp.13059
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: Intraoperative radiotherapy using The INTRABEAM System (Carl Zeiss Meditec AG, Jena, Germany), a miniature low‐energy x‐ray source, has proven to be an effective modality in the treatment of breast cancer. However, some uncertainties remain in its dosimetry. In this work, we investigated the INTRABEAM system dosimetry by performing ionization chamber and radiochromic film measurements of absorbed dose in a water phantom. Methods: Ionization chamber measurements were performed with a PTW 34013 parallel‐plate soft x‐ray chamber at source to detector distances of 5 to 30 mm calculated using (a) the dose formula consistent with the TARGIT breast protocol (TARGIT), (b) the formula recommended by the manufacturer (Zeiss), and (c) the recently proposed C Q formalism of Watson et al. ( Physics in Medicine & Biology, 2018;63:015016) EBT3 Gafchromic film measurements were made at the same depths in water. To account for the energy dependence of EBT3 film, multiple dose response calibration curves were employed across a range of photon beam qualities relevant to the INTRABEAM spectrum in water. Results: At all depths investigated, the TARGIT dose was significantly lower than that measured by the Zeiss and C Q methods, as well as film. These dose differences ranged from 14% to as large as 80%. In general, the doses measured by film, and the Zeiss and C Q methods were in good agreement to within measurement uncertainties (5–6%). Conclusions: These results suggest that the TARGIT dose underestimates the physical dose to water from the INTRABEAM source. Understanding the correlation between the TARGIT and physical dose is important for any studies wishing to make dosimetric comparisons between the INTRABEAM and other radiation emitting devices.