Synchrotron X-ray microbeam dosimetry with a 20 micrometre resolution scintillator fibre-optic dosimeter

2018 ◽  
Vol 25 (3) ◽  
pp. 826-832 ◽  
Author(s):  
James Archer ◽  
Enbang Li ◽  
Marco Petasecca ◽  
Andrew Stevenson ◽  
Jayde Livingstone ◽  
...  

Cancer is one of the leading causes of death worldwide. External beam radiation therapy is one of the most important modalities for the treatment of cancers. Synchrotron microbeam radiation therapy (MRT) is a novel pre-clinical therapy that uses highly spatially fractionated X-ray beams to target tumours, allowing doses much higher than conventional radiotherapies to be delivered. A dosimeter with a high spatial resolution is required to provide the appropriate quality assurance for MRT. This work presents a plastic scintillator fibre optic dosimeter with a one-dimensional spatial resolution of 20 µm, an improvement on the dosimeter with a resolution of 50 µm that was demonstrated in previous work. The ability of this probe to resolve microbeams of width 50 µm has been demonstrated. The major limitations of this method were identified, most notably the low-light signal resulting from the small sensitive volume, which made valley dose measurements very challenging. A titanium-based reflective paint was used as a coating on the probe to improve the light collection, but a possible effect of the high-Zmaterial on the probes water-equivalence has been identified. The effect of the reflective paint was a 28.5 ± 4.6% increase in the total light collected; it did not affect the shape of the depth-dose profile, nor did it explain an over-response observed when used to probe at low depths, when compared with an ionization chamber. With improvements to the data acquisition, this probe design has the potential to provide a water-equivalent, inexpensive dosimetry tool for MRT.

2014 ◽  
Vol 105 (20) ◽  
pp. 203110 ◽  
Author(s):  
Jeffrey S. Souris ◽  
Shih-Hsun Cheng ◽  
Charles Pelizzari ◽  
Nai-Tzu Chen ◽  
Patrick La Riviere ◽  
...  

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Jessie A. Posar ◽  
Matthew Large ◽  
Saree Alnaghy ◽  
Jason R. Paino ◽  
Duncan J. Butler ◽  
...  

Spatially fractionated ultra-high-dose-rate beams used during microbeam radiation therapy (MRT) have been shown to increase the differential response between normal and tumour tissue. Quality assurance of MRT requires a dosimeter that possesses tissue equivalence, high radiation tolerance and spatial resolution. This is currently an unsolved challenge. This work explored the use of a 500 nm thick organic semiconductor for MRT dosimetry on the Imaging and Medical Beamline at the Australian Synchrotron. Three beam filters were used to irradiate the device with peak energies of 48, 76 and 88 keV with respective dose rates of 3668, 500 and 209 Gy s−1. The response of the device stabilized to 30% efficiency after an irradiation dose of 30 kGy, with a 0.5% variation at doses of 35 kGy and higher. The calibration factor after pre-irradiation was determined to be 1.02 ± 0.005 µGy per count across all three X-ray energy spectra, demonstrating the unique advantage of using tissue-equivalent materials for dosimetry. The percentage depth dose curve was within ±5% of the PTW microDiamond detector. The broad beam was fractionated into 50 microbeams (50 µm FHWM and 400 µm centre-to-centre distance). For each beam filter, the FWHMs of all 50 microbeams were measured to be 51 ± 1.4, 53 ± 1.4 and 69 ± 1.9 µm, for the highest to lowest dose rate, respectively. The variation in response suggested the photodetector possessed dose-rate dependence. However, its ability to reconstruct the microbeam profile was affected by the presence of additional dose peaks adjacent to the one generated by the X-ray microbeam. Geant4 simulations proved that the additional peaks were due to optical photons generated in the barrier film coupled to the sensitive volume. The simulations also confirmed that the amplitude of the additional peak in comparison with the microbeam decreased for spectra with lower peak energies, as observed in the experimental data. The material packaging can be optimized during fabrication by solution processing onto a flexible substrate with a non-fluorescent barrier film. With these improvements, organic photodetectors show promising prospects as a cost-effective high spatial resolution tissue-equivalent flexible dosimeter for synchrotron radiation fields.


2000 ◽  
Vol 93 (supplement_3) ◽  
pp. 37-41 ◽  
Author(s):  
William F. Regine ◽  
Roy A. Patchell ◽  
James M. Strottmann ◽  
Ali Meigooni ◽  
Michael Sanders ◽  
...  

Object. This investigation was performed to determine the tolerance and toxicities of split-course fractionated gamma knife radiosurgery (FSRS) given in combination with conventional external-beam radiation therapy (CEBRT). Methods. Eighteen patients with previously unirradiated, gliomas treated between March 1995 and January 2000 form the substrate of this report. These included 11 patients with malignant gliomas, six with low-grade gliomas, and one with a recurrent glioma. They were stratified into three groups according to tumor volume (TV). Fifteen were treated using the initial FSRS dose schedule and form the subject of this report. Group A (four patients), had TV of 5 cm3 or less (7 Gy twice pre- and twice post-CEBRT); Group B (six patients), TV greater than 5 cm3 but less than or equal to 15 cm3 (7 Gy twice pre-CEBRT and once post-CEBRT); and Group C (five patients), TV greater than 15 cm3 but less than or equal to 30 cm3 (7 Gy once pre- and once post-CEBRT). All patients received CEBRT to 59.4 Gy in 1.8-Gy fractions. Dose escalation was planned, provided the level of toxicity was acceptable. All patients were able to complete CEBRT without interruption or experiencing disease progression. Unacceptable toxicity was observed in two Grade 4/Group B patients and two Grade 4/Group C patients. Eight patients required reoperation. In three (38%) there was necrosis without evidence of tumor. Neuroimaging studies were available for evaluation in 14 patients. Two had a partial (≥ 50%) reduction in volume and nine had a minor (> 20%) reduction in size. The median follow-up period was 15 months (range 9–60 months). Six patients remained alive for 3 to 60 months. Conclusions. The imaging responses and the ability of these patients with intracranial gliomas to complete therapy without interruption or experiencing disease progression is encouraging. Excessive toxicity derived from combined FSRS and CEBRT treatment, as evaluated thus far in this study, was seen in patients with Group B and C lesions at the 7-Gy dose level. Evaluation of this novel treatment strategy with dose modification is ongoing.


10.37206/88 ◽  
2005 ◽  
Author(s):  
Ellen Yorke ◽  
Rodica Alecu ◽  
Li Ding ◽  
Doracy Fontenla ◽  
Andre Kalend ◽  
...  

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