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Radiochromic material used in recent commercial films has been suggested as a candidate for in vivo dosimetry because of its dose sensitivity, real-time response, and atomic composition. It was observed that its sensitive material, lithium pentacosa-10,12-diynoate (LiPCDA), can have two distinct forms, with main absorbance peaks at ∼635 and ∼674 nm. The spectrum of the latter is similar to that of pentacosa-10,12-diynoic acid (PCDA) used in the commercial predecessor, obtained through desiccation of the commercial film. Water was suggested to be a part of the crystal structure and thus its presence or absence would affect dosimetric parameters. The objective of this study is to: (a) investigate how desiccated commercial films compared to the native form in terms of macroscopic crystal structure, dose-response, signal linearity, and post-exposure kinetics; (b) demonstrate proof-of-concept that the two versions can be combined into one optical dosimeter and measured simultaneously.Commercial radiochromic film, EBT-3, was desiccated for 10 days at 45°C. Using a 6 MV LINAC beam and standard setup of 100 Source to Axis Distance (SAD), 10 cm × 10 cm field size, and 1.5 cm depth, commercial and desiccated films were irradiated to 50, 100, 200, 500, 1000, 2000, 3000 cGy and the latter to 4000, 5000, and 7000 cGy. A custom phantom equipped with optical fibers for real-time read-out was used for all measurements. Absorbance spectra were collected at ∼1 Hz before, during, and after irradiation. Data were collected for ∼1 h after the end of irradiation for 200 cGy experiments. The radiation-induced change in optical density (∆OD) was calculated with a 10 nm band around the primary absorbance peak. The post-exposure percent optical density change was calculated and compared to ∆OD at the end of irradiation. Both commercial and desiccated films were also irradiated and measured simultaneously as proof-of-concept for using two materials within one optical path. For electron microscopy imaging, active materials from commercial and desiccated films were imaged on a scanning electron microscope at an accelerating voltage of 10 kV.Scanning electron microscope images showed that desiccated film was similar in topographical structure to the commercial EBT-3 form. It maintained a non-linear ∆OD with dose but resulted in ∼1/3 signal compared to the commercial film. Evaluation of post-exposure response showed significantly lower percent increase in ∆OD for desiccated film initially, with no statistically significant difference at 1 h after the end of irradiation. Combining both films and simultaneously measuring their absorbance illustrated that the two absorbance peaks were identifiable and resolvable to allow for an independent determination of dose from each.Water is implicated in the crystal structure of the EBT-3 radiochromic film, with its removal through desiccation affecting both dosimetric and spectroscopic characteristics of the material. The two forms of radiochromic material (with and without water) are spectrally resolvable allowing for independent dose determination from each, opening up possibilities for dose measurements at different locations along a single fiber.

Purpose The purpose of this study was to implement a machine learning model to predict skin dose from targeted intraoperative (TARGIT) treatment resulting in timely adoption of strategies to limit excessive skin dose. Methods A total of 283 patients affected by invasive breast carcinoma underwent TARGIT with a prescribed dose of 6 Gy at 1 cm, after lumpectomy. Radiochromic films were used to measure the dose to the skin for each patient. Univariate statistical analysis was performed to identify correlation of physical and patient variables with measured dose. After feature selection of predictors of in vivo skin dose, machine learning models stepwise linear regression (SLR), support vector regression (SVR), ensemble with bagging or boosting, and feed forward neural networks were trained on results of in vivo dosimetry to derive models to predict skin dose. Models were evaluated by tenfold cross validation and ranked according to root mean square error (RMSE) and adjusted correlation coefficient of true vs predicted values (adj-R2 ). Results The predictors correlated with in vivo dosimetry were the distance of skin from source, depth-dose in water at depth of the applicator in the breast, use of a replacement source, and irradiation time. The best performing model was SVR, which scored RMSE and adj-R2 , equal to 0.746 [95% confidence intervals (CI), 95% CI 0.737,0.756] and 0.481 (95% CI 0.468,0.494), respectively, on the tenfold cross validation. Conclusion The model trained on results of in vivo dosimetry can be used to predict skin dose during setup of patient for TARGIT and this allows for timely adoption of strategies to prevent of excessive skin dose.

Purpose. To report our experience with high dose rate endobronchial brachytherapy (HDR-EBBT) and to assess its efficacy and tolerability with possibility of its use in selected cases with curative intent.Method. Retrospective review of patients with endobronchial tumors treated at our institution in 2007–2013 with HDR-EBBT. Subjective response and treatment related toxicity were extracted from patients’ records. Clinical response was evaluated by chest CT +/− bronchoscopy 2-3 months after treatment. Local control (LC) and overall survival (OS) were analyzed.Results. Overall 23 patients were identified. Ten patients were treated with curative intent, in 8 of them HDR-EBBT was combined with external beam radiotherapy. Short term palliation was as follows: dyspnea (13/15), cough (12/14), and hemoptysis (3/3). Seventeen patients were evaluated, of whom 9 (53%) showed complete response. Four patients developed local failure (only 1 of them treated with curative intent) and were salvaged with HDR-EBBT (n=1), chemotherapy (n=2), and laser (n=1). Among patients treated with curative intent, the 2-year LC and OS were 89% and 67%, respectively, and 2 out of 4 deaths were cancer-related. Late toxicity included bronchial stenosis (n=1). Only 1 patient had fatal hemoptysis and postmortem examination indicated local recurrence.Conclusion. HDR-EBBT is promising treatment with tolerable complication if used in properly selected patients.

The effects of temperature on real time changes in optical density (DeltaOD) of GAFCHROMIC EBT film were investigated. The spectral peak of maximum change in absorbance (lambdamax) was shown to downshift linearly when the temperature of the film was increased from 22 to 38 degrees C. The DeltaOD values were also shown to decrease linearly with temperature, and this decrease could not be attributed to the shift in lambdamax. A compensation scheme using lambdamax and a temperature-dependent correction factor was investigated, but provided limited improvement. Part of the reason may be the fluctuations in hydration of the active component, which were found to affect both position of absorbance peaks and the sensitivity of the film. To test the effect of hydration, laminated and unlaminated films were desiccated. This shifted both the major and minor absorbance peaks in the opposite direction to the change observed with temperature. The desiccated film also exhibited reduced sensitivity to ionizing radiation. Rehydration of the desiccated films did not reverse the effects, but rather gave rise to another form of the polymer with absorbance maxima upshifted further 20 nm. Hence, the spectral characteristics and sensitivity of the film can be dependent on its history, potentially complicating both real-time and conventional radiation dosimetry.