Dose-response relationships of the sigmoid for urgency syndrome after gynecological radiotherapy

Effect of carbons' structure and type on AC electrical properties of polymer composites: predicting the percolation threshold of permittivity through different models

The AC electrical properties of EVA- and NBR-based composites filled with different conductive fillers were investigated. Result shows several magnitudes of increment in AC electrical conductivity and dielectric permittivity after the addition of these conductive fillers, indicating that these materials can be used as supercapacitors. The magnitude of increment was varied according to polymer and filler types. Herein, we also have tested the applicability of different sigmoidal models to find out the percolation threshold value of permittivity for these binary polymer composite systems. It is observed that except sigmoidal-Boltzmann and sigmoidal-dose-response models, other sigmoidal models exhibit different values of percolation threshold when considered for any particular polymer composite system. The paper discusses the variation in results of percolation threshold with an emphasis on the advantages, disadvantages and limitations of these models. We also have applied the classical percolation theory to predict the percolation threshold of permittivity and compared with all the reported sigmoidal models. To judge the unanimous acceptability of these models, they tested vis-à-vis the permittivity results of various polymer composites reported in published literature. To comprehend, all the models except the sigmoidal-logistic-1 model were successfully applicable for predicting the percolation threshold of permittivity for polymer composites.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00396-023-05120-2.

Dosimetric and Clinical Predictors for Acute and Late Gastrointestinal Toxicity Following Chemoradiotherapy of Locally Advanced Anal Cancer

AIMS

To analyse dosimetric and clinical predictors for acute and late gastrointestinal toxicity following chemoradiotherapy of anal cancer.

MATERIALS AND METHODS

Consecutive patients with locally advanced (T2 ≥4 cm - T4 or N+) anal cancer were selected from an institutional database (n = 114). All received intensity-modulated radiotherapy with concomitant 5-fluorouracil and mitomycin C. Gastrointestinal toxicity was retrospectively graded according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and bowel cavity, small bowel and large bowel were contoured. Dosimetric and clinical variables were tested for associations with acute grade ≥3 gastrointestinal toxicity and late grade ≥2 gastrointestinal toxicity using the Mann-Whitney test, area under receiver operating characteristic curve (AUC) and logistic regression.

RESULTS

The median follow-up was 40 months. Acute grade ≥3 gastrointestinal toxicity was seen in 51 (44.7%) of the patients; late grade ≥2 gastrointestinal toxicity was seen in 36 of the patients (39.6% of 91 patients with >1 year recurrence-free follow-up). Bowel cavity V30Gy was the best dosimetric predictor for acute gastrointestinal toxicity (AUC 0.633; P = 0.02). Large bowel V20Gy was the best dosimetric predictor for late gastrointestinal toxicity (AUC 0.698; P = 0.001) but showed no association with acute gastrointestinal toxicity. In multivariate logistic regression, increasing age was significantly associated with acute gastrointestinal toxicity; smoking and large bowel V20Gy were significantly associated with late gastrointestinal toxicity. Patients who experienced acute grade ≥3 gastrointestinal toxicity were not at an increased risk of late grade ≥2 gastrointestinal toxicity (odds ratio 1.3; P = 0.55).

CONCLUSIONS

Factors of importance for acute and late gastrointestinal toxicity were not the same. Bowel cavity V30Gy is a good metric to use for the prediction of acute gastrointestinal toxicity, but the results of our study indicate that individual large and small bowel loops need to be contoured for better prediction of late gastrointestinal toxicity. The role of the large bowel as an important organ at risk for late gastrointestinal toxicity merits further research.

Dose-Volume Predictors for Patient-reported Late Diarrhoea, Faecal Incontinence and Urgency after Pelvic Radiotherapy

AIMS

Pelvic radiotherapy adds significantly to the curative treatment of many pelvic malignancies. However, this cure comes at a cost for many patients, where late bowel toxicities, such as faecal incontinence, urgency and diarrhoea, adversely affect quality of life. Despite the implementation of advanced radiotherapy techniques in many centres, there are deficiencies in our knowledge of how to make best use of these techniques to minimise these late toxicities, with dose-volume constraints specifically for late effects needing definition. The aims of this study were to establish dose-volume predictors for patient-reported late bowel toxicities and derive constraints for clinical use to reduce the risk of these toxicities.

MATERIALS AND METHODS

All radiotherapy patients treated in our institution between 2012 and 2014 for gynaecological and urological cancers (bladder, prostate where pelvic nodes are treated) were identified. Patients were sent patient-reported toxicity questionnaires at 12 and 24 months after treatment. Planning computed tomography scans were retrospectively contoured with different definitions of bowel as organs at risk (OARs). Dose-volume data for each OAR were collected and predictors of these toxicities found using multivariate analysis. For those dose-volume predictors found to be significant on multivariate analysis, statistically significant and clinically relevant dose-volume constraints were derived. Furthermore, data collected were used to validate constraints from published studies.

RESULTS

Faecal urgency, incontinence and diarrhoea rates were found in 52, 23.5 and 18.7% of the 203 patients included at 12 months following radiotherapy. Dose-volume parameters for sigmoid colon and large bowel were significant for these toxicities, and constraints for these OARs were derived, which are promising. A previously published constraint for bowel loops was validated with our data.

CONCLUSIONS

The sigmoid colon and large bowel are important OARs for the development of faecal urgency, incontinence and diarrhoea. Promising constraints for these OARs were derived, which require further validation before prospective clinical use.

Evaluation of plan quality and robustness of IMPT and helical IMRT for cervical cancer

BACKGROUND

Both plan quality and robustness were investigated through comparing some dosimetric metrics between intensity modulated proton therapy (IMPT) and helical tomotherapy based intensity modulated radiotherapy (IMRT) for cervical cancer.

METHODS

Both a spot-scanning robust (SRO) IMPT plan and a helical tomotherapy robust (TRO) IMRT plan were generated for each of 18 patients. In order to evaluate the quality of nominal plans without dose perturbations, planning scores (PS) on clinical target volume (CTV) and five organs at risk (OARs) based on clinical experience, and normal tissue complication probabilities (NTCP) of rectum and sigmoid were calculated based on Lyman-Kutcher-Burman (LKB) model. Dose volume histogram bands width (DVHBW) were calculated in 28 perturbed scenarios to evaluate plan robustness.

RESULTS

Compared with TRO, the average scores of SRO nominal plans were higher in target metrics [V46.8Gy, V50Gy, Conformity and Homogeneity](16.5 vs. 15.1), and in OARs metrics (60.9 vs. 53.3), including bladder [V35,V45, Dmean,D2cc], rectum [V40,V45,D2cc,Dmax], bowel [V35,V40,V45, Dmax], sigmoid [V40,Dmax] and femoral heads [V30,Dmax]. Meanwhile, NTCP calculation showed that the toxicities of rectum and sigmoid in SRO were lower than those in TRO (rectum: 2.8% vs. 4.8%, p < 0.05; sigmoid: 5.2% vs. 5.7%, p < 0.05). DVHBW in target coverage for the SRO plan was smaller than that for the TRO plan (0.6% vs. 2.1%), which means that the SRO plan generated a more robust plan in target.

CONCLUSION

Better CTV coverage and OAR Sparing were obtained in SRO nominal plan. Based on NTCP calculation, SRO was expected to allow a small reduction in rectal toxicity. Furthermore, SRO generated a more robust plan in CTV target coverage.