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PurposeThis retrospective study aimed to evaluate the dosimetric effects of a rectal insertion of Kushen Ningjiao on rectal protection using deformable dose accumulation and machine learning–based discriminative modelling.Materials and MethodsSixty-two patients with cervical cancer enrolled in a clinical trial, who received a Kushen Ningjiao injection of 20 g into their rectum for rectal protection via high–dose rate brachytherapy (HDR-BT, 6 Gy/f), were studied. The cumulative equivalent 2-Gy fractional rectal surface dose was deformably summed using an in-house-developed topography-preserved point-matching deformable image registration method. The cumulative three-dimensional (3D) dose was flattened and mapped to a two-dimensional (2D) plane to obtain the rectal surface dose map (RSDM). For analysis, the rectal dose (RD) was further subdivided as follows: whole, anterior, and posterior 3D-RD and 2D-RSDM. The dose–volume parameters (DVPs) were extracted from the 3D-RD, while the dose geometric parameters (DGPs) and textures were extracted from the 2D-RSDM. These features were fed into 192 classification models (built with 8 classifiers and 24 feature selection methods) for discriminating the dose distributions between pre-Kushen Ningjiao and pro-Kushen Ningjiao.ResultsThe rectal insertion of Kushen Ningjiao dialated the rectum in the ambilateral direction, with the rectal column increased from pre-KN 15 cm3 to post-KN 18 cm3 (P < 0.001). The characteristics of DGPs accounted for the largest portions of the top-ranked features. The top-ranked dosimetric features extracted from the posterior rectum were more reliable indicators of the dosimetric effects/changes introduced by the rectal insertion of Kushen Ningjiao. A significant dosimetric impact was found on the dose–volume parameters D1.0cc–D2.5cc extracted on the posterior rectal wall.ConclusionsThe rectal insertion of Kushen Ningjiao incurs significant dosimetric changes on the posterior rectal wall. Whether this effect is eventually translated into clinical gains requires further long-term follow-up and more clinical data for confirmation.

AIMS: The innervation zone asymmetry of the external anal sphincter (EAS) has been investigated as a risk factor for the development of fecal incontinence (FI). This study aims to utilize an intra-rectal high-density surface electromyogram (HD-sEMG) recording and advanced HD-sEMG decomposition technique to characterize the effects of aging on the asymmetry of EAS functional innervation. METHODS: HD-sEMG signals were recorded intra-rectally from six healthy young and seven healthy elderly women during voluntary contractions of the EAS. EMG signals were decomposed into constituent motor unit action potentials (MUAPs) and the innervation zone of each decomposed motor unit was identified. Asymmetry index (AI) was defined and calculated for all subjects. The maximum squeezing pressures of the EAS were also measured for all subjects as a comparison. RESULTS: The HD-sEMG decomposition and AI calculation were successfully performed from EMG data acquired from all the subjects. The AI values were 28.7 ± 17.0% for the young group and 55.6 ± 18.8% for the elderly group. The AI and EAS contraction strength were found to be negatively correlated (P < 0.05). A two-tailed student’s t-test demonstrated a significant increase in AI with age by comparison between two groups (P < 0.05). CONCLUSIONS: Our work demonstrates, for the first time, that EAS functional innervation tends to become increasingly asymmetrical with advancing age, and this increase is associated with a compromised anorectal function. Results suggest that the intra-rectal HD-sEMG will serve as an advanced tool for assessing and monitoring the anorectal neuromuscular function minimally invasively under different pathophysiological conditions.

Purpose: Cluster models are newly developed normal-tissue complication probability models in which the spatial aspects of radiation-induced injury are taken into account by considering the size of spatially contiguous aggregates of damaged tissue units. The purpose of this study was to test the validity of a two-dimensional cluster model of late rectal toxicity based on maximum cluster size of damage to rectal surface. Methods and Materials: A paired case–control study was performed in which each of 9 patients experiencing Grade 2 or higher late rectal toxicity after intensity-modulated radiation therapy of localized prostate cancer was paired with a patient having a similar rectal dose–surface histogram but free of rectal toxicity. Numeric simulations were performed to determine the distribution of maximum cluster size on each rectal surface for each of many different choices of possible model parameters. Results: Model parameters were found for which patients with rectal toxicity were consistently more likely to have a significantly larger mean maximum cluster size than their matched controls. These parameter values correspond to a 50% probability of tissue-unit damage at doses near 30 Gy. Conclusions: This study suggests that a cluster model based on maximum cluster size of damage to rectal surface successfully incorporates spatial information beyond that contained in the rectal dose–surface histogram and may therefore provide a useful new tool for predicting rectal normal-tissue complication probability after radiotherapy.

Purpose: To identify and illustrate the potential problems with brachytherapy in obese patients. Methods and Materials: Three patients with body mass index greater than 30 were treated with prostate brachytherapy. Transrectal ultrasound (TRUS) was performed using a 6.0-MHz Siemens Sonoline Prima ultrasound machine and a Barzell-Whitmore stepper unit. The patients' weight required use of an accessory table support. Results: Once set up, there was ample room to maneuver, providing that the patient's legs were abducted fully. TRUS imaging of the prostate was unaffected by patients' obesity. The amount of periprostate adipose tissue visualized on TRUS appeared to be no different than that noted in nonobese patients. Similarly, there was no increased distance between the prostate and rectal surface, either on preimplant CT or transverse TRUS. To date, our experience is that the perineal skin to prostate distance was not so great that standard 20-cm applicator needles could not be used. For the 2 sub–350-pound patients who could be imaged on our CT scanner, postimplant target coverage (V100) was 88% and 95%. Conclusions: Standard TRUS and brachytherapy needles are sufficient to implant even the largest patients.

Purpose: To develop a method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy. Methods and Materials: Dose-surface histograms of the rectum, which state the rectal surface area irradiated to any given dose, were calculated for a group of 27 patients treated with a four-field box technique to a total (tumor minimum) dose ranging from 68 to 70 Gy. Occurrences of rectal toxicities as defined by the Radiation Therapy Oncology Group (RTOG) were recorded and examined in terms of dose and rectal surface area irradiated. For a specified end point of rectal complication, the complication probability was analyzed as a function of dose irradiated to a fixed rectal area, and as a function of area receiving a fixed dose. Lyman’s model of normal tissue complication probability (NTCP) was used to fit the data. Results: The observed occurrences of rectal complications appear to depend on the rectal surface area irradiated to a given dose level. The patient distribution of each toxicity grade exhibits a maximum as a function of percentage surface area irradiated, and the maximum moves to higher values of percentage surface area as the toxicity grade increases. The dependence of the NTCP for the specified end point on dose and percentage surface area irradiated was fitted to Lyman’s NTCP model with a set of parameters. The curvature of the NTCP as a function of the surface area suggests that the rectum is a parallel structured organ. Conclusions: The described method of analyzing rectal surface area irradiated yields interesting insight into understanding rectal complications in prostate conformal radiotherapy. Application of the method to a larger patient data set has the potential to facilitate the construction of a full dose-surface-complication relationship, which would be most useful in guiding clinical practice. Normal tissue complication probability (NTCP), Dose-surface histogram, Conformal radiotherapy, Prostate cancer.

We studied 73 patients treated with 3-dimensional conformal radiotherapy for prostate cancer to determine whether there is a correlation between dose per volume to either the whole rectum, rectal wall, rectal surface, or anal canal and the development of late rectal complications measured with prostate-specific quality-of-life (QOL) questionnaires. Given doses were 66.6 to 72 Gy. The prostate cancer modules used were the UCLA-Prostate Cancer Index module (UCLA-PCI) (5 questions), the Functional Assessment of Cancer Therapy-Prostate module (FACT-P) (1 question), and the European Organization for Research and Treatment of Cancer prostate cancer module (EORTC QLQ-PR25) (4 questions). A Spearman correlation analysis between the total toxicity score and the dose-volume histograms (DVHs) was performed. All statistical tests were 2-sided. Sixty-five (89%) patients returned the questionnaire, and 18 (28%) underwent endoscopy for rectal bleeding. We found that only patients who had had an endoscopy showed a correlation between rectal toxicity and dose per volume, as compared with the other patients who showed none. Correlation between rectal toxicity and dose per volume for all 4 structures was stronger for higher doses. For 70 Gy, all contours, except the anal canal, showed a significant dose-volume correlation. Our results indicate that only in cases of pronounced rectal toxicity is there a dose-volume correlation, especially for doses of 70 Gy or more. DVHs of the whole rectum, wall, or surface, but not the anal canal, are all equivalent in predicting late rectal toxicity.