Understanding the Radiation Dose Variability in Nasopharyngeal Cancer: An Organs-at-Risk Approach.

Objective This study aims to thoroughly assess the radiation dose distribution to critical organs in patients with nasopharyngeal carcinoma, focusing on the correlation between the radiation dosages for the various organs at risk (OARs) in nasopharyngeal cancer patients. Methods We meticulously analysed a dataset comprising 38 nasopharyngeal carcinoma patients, focusing on radiation dosages measured in Gray (Gy) and volumetric data in cubic centimetres (cc) of critical organs, including the lens, brainstem, spinal cord, optic nerve, optic chiasm, and cochlea. A detailed exploratory data analysis approach encompassed univariate, bivariate, and multivariate techniques. Results Our analysis revealed several key findings. The mean and median values across various dose measurements were closely aligned, indicating symmetrical distributions with minimal skewness. The histograms further corroborated this, showing evenly distributed dose values across different anatomical regions. The correlation matrix highlighted varying degrees of interrelationships between the doses, with some showing strong correlations while others exhibited minimal or no correlation. The 3D scatter plot provided a view of the multi-dimensional dose relationships, with a specific focus on the spinal cord, lens, and brainstem doses. The bivariate scatter plots revealed symmetrical distributions between the right and left lens doses and more complex relationships involving the brainstem and spinal cord, illustrating the intricacies of dose distribution in radiation therapy. Conclusion Our findings reveal distinct radiation exposure patterns to OARs of nasopharyngeal carcinoma. This research emphasises the need for tailored radiation therapy planning to achieve optimal clinical outcomes while safeguarding vital organs.

Continuous protein refolding and purification by two-stage periodic counter-current chromatography.

Matrix-assisted refolding (MAR) has been used as an alternative to conventional dilution-based refolding to improve recovery and reduce specific buffer consumption. Size exclusion chromatography (SEC) has been extensively used for MAR because of its ability to load and refold proteins at high concentrations. However, the SEC-based batch MAR processes have the disadvantages of requiring longer columns for better separation and product dilution due to a high column-to-sample volume ratio. In this work, a modified operational scheme is developed for continuous MAR of L-asparaginase inclusion bodies (IBs) using SEC-based periodic counter-current chromatography (PCC). The volumetric productivity of the modified SEC-PCC process is 6.8-fold higher than the batch SEC process. In addition, the specific buffer consumption decreased by 5-fold compared to the batch process. However, the specific activity of the refolded protein (110-130 IU/mg) was less due to the presence of impurities and additives in the refolding buffer. To address this challenge, a 2-stage process was developed for continuous refolding and purification of IBs using different matrices in sequential PCCs. The performance of the 2-stage process is compared with literature reports on single-stage IMAC-PCC and conventional pulse dilution processes for refolding L-asparaginase IBs. The 2-stage process resulted in a refolded protein with enhanced specific activity (175-190 IU/mg) and a high recovery of 84%. The specific buffer consumption (6.2 mL/mg) was lower than the pulse dilution process and comparable to the single-stage IMAC-PCC. A seamless integration of the two stages would considerably increase the throughput without compromising other parameters. High recovery, throughput, and increased operational flexibility make the 2-stage process an attractive option for protein refolding.

Continuous refolding of L-asparaginase inclusion bodies using periodic counter-current chromatography.

Chromatography-based refolding is emerging as a promising alternative to dilution-refolding of solubilized inclusion bodies (IBs). The advantages of this matrix-assisted refolding (MAR) lie in its ability to reduce aggregate formation, leading to better recovery of active protein, and enabling refolding at higher protein concentration. However, batch chromatography has the disadvantage of ineffective solvent utilization, under-utilization of resin, and low throughput. In this work, we overcome these challenges by using a 3-column Periodic Counter-current Chromatographic (PCC) system for continuous refolding of IBs, formed during the production of L-asparaginase by recombinant E. coli cultures. Initial experiments were conducted in batch processes using single-column immobilized metal-affinity chromatography. Different gradient operations were designed to improve the protein loading for the single-column, batch-MAR processes. Optimized conditions, based on the batch-MAR experiments, were used for designing the continuous-MAR processes using the PCC system. The continuous-MAR experiments were carried out over 3 cycles (∼ 30 h) in the PCC system. A detailed quantitative comparison based on recovery, throughput, buffer consumption, and resin utilization was made for the three modes of operation: pulse-dilution, single-column batch-MAR, and 3-Column PCC-based continuous-MAR processes. While recovery (73%) and throughput (11 mg/h) were the highest in PCC, specific buffer consumption (6.9 ml/mg) was the least. Also, during PCC operation, resin utilization improved by 92% in comparison to the single-column batch-MAR process. These quantitative comparisons clearly establish the advantages of the continuous-MAR process over the batch-MAR and other conventional refolding techniques.

Living donor liver transplantation for hepatocellular carcinoma in Indian patients- Is the scenario different?

BACKGROUND: Living donor liver transplant (LDLT) for hepatocellular carcinoma (HCC) has been controversial in terms of selection and outcome. We share our experience of LDLT for HCC in Indian patients. METHODS: Retrospective analysis of patients undergoing LDLT for HCC discovered either preoperatively or incidentally on explant pathology was done. Preoperative characteristics and explant histopathology findings were recorded. Overall, recurrence-free survival and factors predicting recurrence were analyzed. RESULTS: Six hundred and eleven LDLT were performed between June 2011 and October 2019. HCC constituted 6.5% (n = 53) of transplant activity. Forty had preoperative diagnosis, while 13 were detected incidentally. The median model for end-stage liver disease (MELD) score was 18 for patients with HCC. Only in 10 patients (19%), HCC was the primary indication for liver transplant (LT), and the rest had undergone transplant for progressive decompensation. Thirty-two patients were within up-to-7, while 21 were outside up-to-7 criteria. Overall 5-year survival was 85.4% and recurrence-free survival was 83.3% after a median follow-up of 35 months (13-59). This was similar to LDLT for other indications (81.2% at 5 years). Risk Estimation of Tumor Recurrence After Transplant (RETREAT) score was best able to predict recurrence (p = 0.03) with odds ratio of 6.8. CONCLUSION: Patients with HCC in India present late for liver transplant. Most patients have some form of decompensation before they undergo LT. In selected patients, overall survival was comparable with other indications for LDLT with acceptable recurrence rates. RETREAT score was best to predict recurrence.

Upfront pancreaticoduodenectomy in severely jaundiced patients: is it safe?

AIM: The aim of this study was to evaluate the outcomes following upfront pancreaticoduodenectomy (PD) in severely jaundiced (serum bilirubin level ≥15 mg/dl) patients with malignant distal common bile duct (CBD) obstruction. BACKGROUND: Recent studies have failed to show the benefits of preoperative biliary drainage (PBD) before PD. In addition, there is limited data on the impact of upfront PD on perioperative outcomes in severely jaundiced patients. METHODS: We reviewed the prospectively collected data of 177 patients who had undergone PD for the malignant distal CBD obstruction from May 2009 to May 2018. Study subjects were divided into Group A (severely jaundiced patients with upfront PD; n = 20), Group B (patients with serum bilirubin <15 mg/dl and no PBD; n = 88) and Group C (PBD prior to PD; n = 69). Overall morbidity, in-hospital mortality, and postoperative hospital stay were compared. RESULTS: No significant differences were noted between the three groups regarding sex, tumor size and stage, comorbidities, and surgical technique. The intra-operative blood loss was more in severely jaundiced patients as compared to Groups B and C (605 vs. 300 vs. 350 ml, P = 0.0001), but similar operative times, blood transfusions, and rates of post-pancreatectomy leak and hemorrhage. The infective complications were significantly less with upfront surgery. The overall morbidity, in-hospital mortality, and hospital stay were comparable between the three groups. Multiple logistic regression analysis failed to identify both the presence of preoperative jaundice and hyperbilirubinemia ≥15 mg/dl as independent risk factors for post-PD major morbidity. CONCLUSION: Upfront PD can be performed safely in the selected severely jaundiced patients and is associated with significantly lower infective complications.

Design of aqueous two-phase systems for purification of hyaluronic acid produced by metabolically engineered Lactococcus lactis.

Hyaluronic acid has a wide range of biomedical applications and its commercial value is highly dependent on its purity and molecular weight. This study highlights the utility of aqueous two-phase separation as a primary recovery step for hyaluronic acid and for removal of major protein impurities from fermentation broths. Metabolically engineered cultures of a lactate dehydrogenase mutant strain of Lactococcus lactis (L. lactis NZ9020) were used to produce high-molecular-weight hyaluronic acid. The cell-free fermentation broth was partially purified using a polyethylene glycol/potassium phosphate system, resulting in nearly 100% recovery of hyaluronic acid in the salt-rich bottom phase in all the aqueous two-phase separation experiments. These experiments were optimized for maximum removal of protein impurities in the polyethylene glycol rich top phase. The removal of protein impurities resulted in substantial reduction of membrane fouling in the subsequent diafiltration process, carried out with a 300 kDa polyether sulfone membrane. This step resulted in considerable purification of hyaluronic acid, without any loss in recovery and molecular weight. Diafiltration was followed by an adsorption step to remove minor impurities and achieve nearly 100% purity. The final hyaluronic acid product was characterized by Fourier-transform IR and NMR spectroscopy, confirming its purity.

Detector system dose verification comparisons for arc therapy: couch vs. gantry mount.

The aim of this study was to assess the performance of a gantry-mounted detector system and a couch set detector system using a systematic multileaf collimator positional error manually introduced for volumetric-modulated arc therapy. Four head and neck and esophagus VMAT plans were evaluated by measurement using an electronic portal imaging device and an ion chamber array. Each plan was copied and duplicated with a 1 mm systematic MLC positional error in the left leaf bank. Direct comparison of measurements for plans with and without the error permitted observational characteristics for quality assurance performance between detectors. A total of 48 different plans were evaluated for this testing. The mean percentage planar dose differences required to satisfy a 95% match between plans with and without the MLCPE were 5.2% ± 0.5% for the chamber array with gantry motion, 8.12% ± 1.04% for the chamber array with a static gantry at 0°, and 10.9%± 1.4% for the EPID with gantry motion. It was observed that the EPID was less accurate due to overresponse of the MLCPE in the left leaf bank. The EPID always images bank-A on the ipsilateral side of the detector, whereas for a chamber array or for a patient, that bank changes as it crosses the -90° or +90° position. A couch set detector system can reproduce the TPS calculated values most consistently. We recommend it as the most reliable patient specific QA system for MLC position error testing. This research is highlighted by the finding of up to 12.7% dose variation for H/N and esophagus cases for VMAT delivery, where the mere source of error was the stated clinically acceptability of 1 mm MLC position deviation of TG-142.

Role of step size and max dwell time in anatomy based inverse optimization for prostate implants.

In high dose rate (HDR) brachytherapy, the source dwell times and dwell positions are vital parameters in achieving a desirable implant dose distribution. Inverse treatment planning requires an optimal choice of these parameters to achieve the desired target coverage with the lowest achievable dose to the organs at risk (OAR). This study was designed to evaluate the optimum source step size and maximum source dwell time for prostate brachytherapy implants using an Ir-192 source. In total, one hundred inverse treatment plans were generated for the four patients included in this study. Twenty-five treatment plans were created for each patient by varying the step size and maximum source dwell time during anatomy-based, inverse-planned optimization. Other relevant treatment planning parameters were kept constant, including the dose constraints and source dwell positions. Each plan was evaluated for target coverage, urethral and rectal dose sparing, treatment time, relative target dose homogeneity, and nonuniformity ratio. The plans with 0.5 cm step size were seen to have clinically acceptable tumor coverage, minimal normal structure doses, and minimum treatment time as compared with the other step sizes. The target coverage for this step size is 87% of the prescription dose, while the urethral and maximum rectal doses were 107.3 and 68.7%, respectively. No appreciable difference in plan quality was observed with variation in maximum source dwell time. The step size plays a significant role in plan optimization for prostate implants. Our study supports use of a 0.5 cm step size for prostate implants.