Dwell time verification in brachytherapy based on time resolved in vivo dosimetry. (April 2019)

• Record Type: Journal Article
• Authors: Johansen, J.G.; Kertzscher, G.; Jørgensen, E.B.; Rylander, S.; Bentzen, L.; Hokland, S.B.; Søndergaard, C.S.; With, A.K.M.; Buus, S.; Tanderup, K.
• Is Part Of: Physica medica. Volume 60(2019)
• Page Start: 156
• Page End: 161
• Publication Date: 2019-04
• Subjects: BT Brachytherapy -- DAQ Data acquisition -- EBRT External beam radiotherapy -- HDR High dose rate -- IVD in vivo dosimetry -- MR Magnetic resonance -- MRI Magnetic resonance imaging -- OAR Organs at risk -- PMT Photomultiplier tube -- RL Radioluminescence -- SD Standard deviation; In vivo dosimetry -- HDR brachytherapy -- Prostate cancer -- Treatment verification -- Dwell times; 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.2019.03.031
• Languages: English
• ISSNs: 1120-1797

Abstract

Highlights: Real-time in vivo dosimetry in prostate cancer brachytherapy. Dwell times can be determined during patient treatment with in vivo dosimetry. Afterloader control of dwell time was demonstrated stable over a year. Incidences leading to dwell time offsets with a clinical impact can be caught by in vivo dosimetry. Abstract: Purpose: This paper presents a method to verify dwell times during High Dose Rate (HDR) Brachytherapy (BT) by means of in vivo dosimetry (IVD), and reports on an afterloader's stability in dwell time control. Methods: In vivo dosimetry was performed during 20 HDR prostate cancer treatments using a point detector based on a radio-luminescence crystal (Al2 O3 :C) coupled to a fiber-optic cable. The dose rate was recorded at either 10 Hz or 20 Hz during the treatments. The "time of transit" when the source moved between two dwell positions was identified using the difference in count rate between two measurements. The dwell times were then determined by subtracting two adjacent times of transit. The measured dwell times were matched with the planned dwell times and categorised into two groups: Dwell times matching a single dwell position (identified) and dwell times matching the sum of multiple dwell positions (unidentified). Deviations between measured and planned dwell times were calculated for the identified dwell positions. Results: A total of 3518 dwell positions were analysed. The amount of identified dwell positions were 82%, which increased to 89% if the short dwell times (<1 s) were omitted in the analysis. The largest deviation was −0.4 s seen for a single dwell position, and in 97.1% of the cases, the deviations were <0.15 s. Conclusion: The dwell times in BT are well controlled by the afterloader. It is shown that IVD facilitates the detection of dwell time offsets that could have a clinical impact.