Source position measurement by Cherenkov emission imaging from applicators for high-dose-rate brachytherapy.

PURPOSE: We developed a novel and simple method to measure the source positions in applicators directly for high-dose-rate (HDR) brachytherapy based on Cherenkov emission imaging, and evaluated the performance. METHODS: The light emission from plastic applicators used in cervical cancer treatments, irradiated by an 192 Ir γ-ray source, was captured using a charge-coupled device camera. Moreover, we attached plastics of different shapes, including tapes, tubes, and plates to a metal applicator, to use as screens for the Cherenkov imaging. We determined the source positions and dwell intervals from the light profiles along with the applicator and compared these with preset values and dummy marker measurements. RESULTS: The source positions and dwell intervals measured from the light images were comparable to the dummy marker measurements and preset values. The distance from the applicator tip to the first source positions agreed with the dummy marker measurements within 0.2 mm for the plastic tandem. The dwell intervals measured using the Cherenkov method agreed with the preset values within 0.6 mm. The distances measured with three plastic types on the metal applicator also agreed with the dummy marker measurements within 0.2 mm. The dwell intervals measured using the plastic tape agreed with the preset values within 0.7 mm. CONCLUSIONS: The proposed method should be suitable for rapid and easy quality assurance (QA) investigations in HDR brachytherapy, as it enables source position using a single image. The method allows for real-time, filmless measurements of the source positions to be obtained and is useful for rapid feedback in QA procedures.

Imaging Cherenkov emission for quality assurance of high-dose-rate brachytherapy.

With advances in high-dose-rate (HDR) brachytherapy, the importance of quality assurance (QA) is increasing to ensure safe delivery of the treatment by measuring dose distribution and positioning the source with much closer intervals for highly active sources. However, conventional QA is time-consuming, involving the use of several different measurement tools. Here, we developed simple QA method for HDR brachytherapy based on the imaging of Cherenkov emission and evaluated its performance. Light emission from pure water irradiated by an 192Ir γ-ray source was captured using a charge-coupled device camera. Monte Carlo calculations showed that the observed light was primarily Cherenkov emissions produced by Compton-scattered electrons from the γ-rays. The uncorrected Cherenkov light distribution, which was 5% on average except near the source (within 7 mm from the centre), agreed with the dose distribution calculated using the treatment planning system. The accuracy was attributed to isotropic radiation and short-range Compton electrons. The source positional interval, as measured from the light images, was comparable to the expected intervals, yielding spatial resolution similar to that permitted by conventional film measurements. The method should be highly suitable for quick and easy QA investigations of HDR brachytherapy as it allows simultaneous measurements of dose distribution, source strength, and source position using a single image.

Dosimetric factors associated with long-term patient-reported outcomes after definitive radiotherapy of patients with head and neck cancer.

BACKGROUND: The aim of this study was to explore the relationships between dosimetric parameters of organs at risk and patient-reported outcomes (PRO) after radiotherapy of patients with head and neck cancer. METHODS: PRO data of 53 patients with head and neck cancer treated with radiotherapy were prospectively collected. These data concerned health-related quality of life (HRQOL) and were collected using the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (QLQ-C30) and head and neck cancer module (QLQ-H&N35). Patients were divided into "severe-deterioration" and "mild-deterioration" groups on the basis of degree of deterioration HRQOL > 6 months after completing treatment. The relationships between HRQOL deteriorations and patient-related or dosimetry-related factors were evaluated. P < 0.0013 according to Bonferroni correction was considered to denote statistical significance. RESULTS: Regarding "trouble with social eating (HNSO)" and "coughing (HNCO)," there were significant differences between the severe-deterioration and mild-deterioration groups in mean dosages to the superior pharyngeal constrictor muscle (SPC) (HNSO: 62.5 Gy vs 54.2 Gy; p = 0.00029, and HNCO: 61.5 Gy vs 54.1 Gy; p = 0.0012) and parotid gland (HNSO: 24.1 Gy vs 20.5 Gy; p = 0.000056, and HNCO: 24.2 Gy vs 20.3 Gy; p = 0.00043). Regarding "nausea and vomiting," there was a significant difference between the two groups in the mean dosage to the middle pharyngeal constrictor muscle (MPC: 61.9 Gy vs. 58.4Gy; P = 0.00059). CONCLUSIONS: We found that dosages to the SPC and parotid gland were associated with severe deterioration in HRQOL attributable to difficulty in HNSO and HNCO, whereas dosage to the MPC was associated with severe deterioration attributable to nausea and vomiting.

Automated source tracking with a pinhole imaging system during high-dose-rate brachytherapy treatment.

The transportation accuracy of sealed radioisotope sources influences the therapeutic effect of high-dose-rate (HDR) brachytherapy. We have developed a pinhole imaging system for tracking an Ir-192 radiation source during HDR brachytherapy treatment. Our system consists of a dual-pinhole collimator, a scintillator, and a charge-coupled device (CCD) camera. We acquired stereo-shifted images to infer the source position in three dimensions using a dual pinhole collimator with 1.0 mm diameter pinholes. The CCD camera captured consecutive images of scintillation light that corresponds to the source positions every 2 s. The system automatically tracks scintillation light points using template-matching technique and measured the source positions therefrom. By integrating a series of CCD images, we could infer the source dwell time from the pixel values in the integrated image. We investigated the tracking accuracy of our system in monitoring simulated brachytherapy as it would be performed for cervical cancer by using water as a stand-in for human tissue. Ir-192 pellet was moved through a water tank using tandem and ovoid applicators. The CCD camera captured clear images of the scintillation light produced by the underwater Ir-192 source in conditions equivalent to common clinical situations. The differences between the measured and the reference 3D source positions and dwell times were 1.5 ± 0.7 mm and 0.8 ± 0.4 s, respectively. This system has the potential to track in vivo Ir-192 source in real time and may prove a useful tool for quality assurance during HDR brachytherapy treatments in clinical settings.