External irradiation treatment process.

The purpose of this article is to describe the external irradiation process and updated recommendations of the French society for radiation oncology for patient follow-up.

Delineation of organs at risk.

The delineation of organs at risk is the basis of radiotherapy oncologists' work. Indeed, the knowledge of this delineation enables to better identify the target volumes and to optimize dose distribution, involving the prognosis of the patients but also their future. The learning of this delineation must continue throughout the clinician's career. Some contour changes have appeared with better imaging, some volumes are now required due to development of knowledge of side effects. In addition, the increasing survival time of patients requires to be more systematic and precise in the delineations, both to avoid complications until now exceptional but also because re-irradiations are becoming more and more frequent. We present the update of the recommendations of the French Society for Radiation Oncology (SFRO) on new findings or adaptations to volumes at risk.

A Study to Assess the Dosimetric Impact of the Anatomical Changes Occurring in the Parotid Glands and Tumour Volume during Intensity Modulated Radiotherapy using Simultaneous Integrated Boost (IMRT-SIB) in Head and Neck Squamous Cell Cancers.

BACKGROUND: Anatomical variations in head and neck cancer during IMRT leads to volume shrinkage, results in dosimetric variations in tumour and normal tissue including parotid glands, with a risk of radiation toxicities. METHODS: 30 patients with a stage II-IV head and neck squamous cell carcinoma (HNSCC) were treated with definitive IMRT-SIB and concomitant chemotherapy. Volumetric and dosimetric variations were evaluated during the period of IMRT by recalculating and obtaining dose-volume histograms of re-contoured target volumes and parotid glands on repeat CT scans taken multiple times during treatment (CT1, CT2, CT3 and CT4). RESULTS: Result showed significant (p < 0.001) mean decrease in both primary and nodal tumors volume with time whereas increase (p < 0.01 or p < 0.001) in respective V100 (%) and D2% (Gy). The mean parotid gland dose increased (p < 0.01 or p < 0.001) with time, whereas parotid gland volume and distance between plan isocenter and centre of mass of parotid glands decreased (p < 0.05 or p < 0.001) with time. Patient's mean weight and neck circumference both decrease (p < 0.001) with time whereas ECOG score increase (p < 0.001) with time. The mucosal toxicity increased significantly (p < 0.001) with time. The change in both weight and neck circumference showed significant (p < 0.001) and direct (positive correlation) association with change in parotid gland volume. CONCLUSION: If the PTV and normal anatomy are changing with time, adaptive IMRT would be beneficial radiation dose delivery where possible.

Dosimetric impact of rectum and bladder anatomy and intrafractional prostate motion on hypofractionated prostate radiation therapy.

OBJECTIVE: The objective of this study was to evaluate the dosimetric impact on hypofractionated prostate radiation therapy of two geometric uncertainty sources: rectum and bladder filling and intrafractional prostate motion. MATERIALS AND METHODS: This prospective study included 544 images (375 pre-treatment cone-beam CT [CBCT] and 169 post-treatment CBCT) from 15 prostate adenocarcinoma patients. We recalculated the dose on each pre-treatment CBCT once the positioning errors were corrected. We also recalculated two dose distributions on each post-treatment CBCT, either using or not intrafractional motion correction. A correlation analysis was performed between CBCT-based dose and rectum and bladder filling as well as intrafraction prostate displacements. RESULTS: No significant differences were found between administered and planned rectal doses. However, we observed an increase in bladder dose due to a lower bladder filling in 66% of treatment fractions. These differences were reduced at the end of the fraction since the lower bladder volume was compensated by the filling during the treatment session. A statistically significant reduction in target volume coverage was observed in 27% of treatment sessions and was correlated with intrafractional prostate motion in sagittal plane > 4 mm. CONCLUSIONS: A better control of bladder filling is recommended to minimize the number of fractions in which the bladder volume is lower than planned. Fiducial mark tracking with a displacement threshold of 5 mm in any direction is recommended to ensure that the prescribed dose criteria are met.

Evaluation of margins in pelvic lymph nodes and prostate radiotherapy and the impact of bladder and rectum on prostate position.

PURPOSE: The aims of this study were: determination of the CTV to PTV margins for prostate and pelvic lymph nodes. Investigation of the impact of registration modality (pelvic bones or prostate) on the CTV to PTV margins of pelvic lymph nodes. Investigation of the variations of bladder and rectum over the treatment course. Investigation of the impact of bladder and rectum variations on prostate position. PATIENTS AND METHODS: This study included 15 patients treated for prostate adenocarcinoma. Daily kilo voltage images and weekly CBCT scans were performed to assess prostate displacements and common and external iliac vessels motion. These data was used to calculate the CTV to PTV margins using Van Herk equation in the setting of a daily bone registration. We also compared the CTV to PTV margins of pelvic lymph nodes according to registration method; based on pelvic bone or prostate. We delineated bladder and rectum on all CBCT scans to assess their variations over treatment course at 4 anatomic levels [1.5cm above pubic bone (PB), superior edge, mid- and inferior edge of PB]. RESULTS: Using Van Herk equation, the prostate CTV to PTV margins (bone registration) were 8.03mm, 5.42mm and 8.73mm in AP, ML and SI direction with more than 97% of prostate displacements were less than 5mm. The CTV to PTV margins ranged from 3.12mm to 3.25mm for external iliac vessels and from 3.12mm to 4.18mm for common iliac vessels. Compared to registration based on prostate alignment, bone registration resulted in an important reduction of the CTV to PTV margins up to 54.3% for external iliac vessels and up to 39.6% for common iliac vessels. There was no significant variation of the mean bladder volume over the treatment course. There was a significant variation of the mean rectal volume before and after the third week of treatment. After the third week, the mean rectal volume seemed to be stable. The uni- and multivariate analysis identified the anterior wall of rectum as independent factor acting on prostate motion in AP direction at 2 levels (superior edge of, mid PB). The right rectal wall influenced the prostate motion in ML direction at inferior edge of PB. The bladder volume tends toward significance as factor acting on prostate motion in AP direction. CONCLUSIONS: We recommend CTV to PTV margins of 8mm, 6mm and 9mm in AP, ML and SI directions for prostate. And, we suggest 4mm and 5mm for external and common iliac vessels respectively. We also prefer registration based on bony landmarks to minimize bowel irradiation. More CBCT scans should be performed during the first 3weeks and especially the first week to check rectum volume.

Improving automatic delineation for head and neck organs at risk by Deep Learning Contouring.

INTRODUCTION: Adequate head and neck (HN) organ-at-risk (OAR) delineation is crucial for HN radiotherapy and for investigating the relationships between radiation dose to OARs and radiation-induced side effects. The automatic contouring algorithms that are currently in clinical use, such as atlas-based contouring (ABAS), leave room for improvement. The aim of this study was to use a comprehensive evaluation methodology to investigate the performance of HN OAR auto-contouring when using deep learning contouring (DLC), compared to ABAS. METHODS: The DLC neural network was trained on 589 HN cancer patients. DLC was compared to ABAS by providing each method with an independent validation cohort of 104 patients, which had also been manually contoured. For each of the 22 OAR contours - glandular, upper digestive tract and central nervous system (CNS)-related structures - the dice similarity coefficient (DICE), and absolute mean and max dose differences (|Δmean-dose| and |Δmax-dose|) performance measures were obtained. For a subset of 7 OARs, an evaluation of contouring time, inter-observer variation and subjective judgement was performed. RESULTS: DLC resulted in equal or significantly improved quantitative performance measures in 19 out of 22 OARs, compared to the ABAS (DICE/|Δmean dose|/|Δmax dose|: 0.59/4.2/4.1 Gy (ABAS); 0.74/1.1/0.8 Gy (DLC)). The improvements were mainly for the glandular and upper digestive tract OARs. DLC significantly reduced the delineation time for the inexperienced observer. The subjective evaluation showed that DLC contours were more often preferable to the ABAS contours overall, were considered to be more precise, and more often confused with manual contours. Manual contours still outperformed both DLC and ABAS; however, DLC results were within or bordering the inter-observer variability for the manual edited contours in this cohort. CONCLUSION: The DLC, trained on a large HN cancer patient cohort, outperformed the ABAS for the majority of HN OARs.

Development and evaluation of an auto-segmentation tool for the left anterior descending coronary artery of breast cancer patients based on anatomical landmarks.

This study describes the development and evaluation of an auto-segmentation tool for the left anterior descending coronary artery (LAD), on non-contrast planning computed tomography scans of breast cancer patients. The dosimetric parameters of the auto-segmented LAD contours are highly correlated with those of manual contours (R2-values ≥0.89).

Pancreatic cancer treated with SBRT: Effect of anatomical interfraction variations on dose to organs at risk.

BACKGROUND AND PURPOSE: Interfraction shape and position variations of organs at risk (OARs) may increase uncertainty in dose delivery during stereotactic body radiotherapy (SBRT), potentially leading to overirradiation or concessions in planned tumor dose and/or coverage to prevent clinical constraints violation. The aim of our study was to quantitatively analyze the impact of anatomical interfraction variations on dose to OARs in pancreatic cancer (PC) treated by SBRT using a CyberKnife with integrated CT-on-rails. MATERIALS AND METHODS: Thirty-five PC patients treated with SBRT (40 Gy/5 fractions) underwent a CT-scan in treatment position before each of the first three fractions using the CT-on-rails system. OARs (stomach, duodenum, bowel) were manually delineated and concatenated to one structure (Gastro-Intestinal Organ, GIO). To overlay the planned dose distribution, fiducial-based alignment of the fraction CT with the planning CT was performed. Planned DVH parameters of the OAR were compared to the parameters calculated in the fractions CTs. RESULTS: Compared to the treatment plan, the median V35, D2, D5, D10 and Dmax of the fraction CTs in the GIO was increased by 1.0 (IQR: 0.2-2.6), 4.4% (0.4-10.8), 2.3% (0.2-7.5), 3.3% (-0.4 to 7.1), and 12.0% (5.0-18.9) respectively. Median increase was statistically significant for all parameters in GIO and for V35 in all critical structures at Wilcoxon test. CONCLUSIONS: Anatomical interfraction variations increase OAR dose during SBRT for pancreatic cancer daily imaging using integrated CT/CyberKnife may allow to implement strategies to reduce the risk of OAR overirradiation during pancreatic SBRT.

Dose to the penile bulb and individual patient anatomy are predictive of erectile dysfunction in men treated with 125I low dose rate brachytherapy for localized prostate cancer.

Background: To evaluate the occurrence of erectile dysfunction at 3 years (3yED) after prostate brachytherapy (BT) and to predict 3yED after treatment based on patients and treatments characteristics. Material and methods: From September 2007 to July 2015, 117 men with mild or no ED [International Index of Erectile Function (IIEF-5) > 16] underwent 125Iodine real-time ultrasound-guided low-dose rate BT to a total dose of 160 Gy for low-risk or favorable intermediate-risk prostate adenocarcinoma, and were followed prospectively during 3 years. Median age was 63 years (51-79). The post-implant dosimetric parameters on the postoperative computer tomography were derived from the dose-volume histogram of the prostate and the penile bulb (PB), crura, neurovascular bundles (NVBs) and internal pudendal arteries (IPAs). Potential clinical confounding factors were collected. Additionally, anatomical indexes reflecting the prostate anatomical location within the pelvis were studied. These variables were compared between patients with and without 3yED. 3yED was defined as an IIEF-5 score change to the lower category between baseline, with or without medication. Results: The 3yED rate was 59% (62% maintained an IIEF-5 > 16). On multivariate analysis, prostate D90% (p > .5) and pretreatment characteristics including age (p > .5), pre-implant potency (p > .5), diabetes (p = .08) and high cardiovascular risk rates (p = .1) did not influence the occurrence of 3yED. Only the PB dose especially the D10% > 51 Gy was associated with 3yED (p = .005). Conversely, dose to the crura, IPAs or NVBs did not seem to impact the erectile function. The prostate position, especially the apex location varied significantly between potent and impotent patients and 3yED was significantly associated with close position of the prostate apex to PB (p = .008). Conclusion: The most predictive factor of 3yED was the dose to the PB. This may be explained by variation in individual patients' anatomy and this could allow for the development of better strategies to prevent ED.

Including anatomical variations in robust optimization for head and neck proton therapy can reduce the need of adaptation.

BACKGROUND AND PURPOSE: Classical robust optimization considers uncertainties in patient setup and particle range. However, anatomical changes occurring during the treatment are neglected. Our aim was to compare classical robust optimization (cRO) with anatomical robust optimization (aRO), to quantify the influence of anatomical variations during the treatment course, and to assess the need of adaptation. MATERIALS AND METHODS: Planning CT and weekly control CTs (cCTs) from 20 head and neck patients were analysed. Three intensity-modulated proton therapy (IMPT) plans were compared: conventional PTV-based plan; cRO, using solely the planning CT, and aRO, including additionally the first 2 cCTs in the optimization. Weekly and total cumulative doses, considering anatomical variations during the treatment, were calculated and compared with the nominal plans. RESULTS: Nominal plans fulfilled clinical specifications for target coverage (D98% ≥95% of prescribed dose). The PTV-based and cRO approaches were not sufficient to account for anatomical changes during the treatment in 10 and 5 patients, respectively, resulting in the need of plan adaptation. With the aRO approach, in all except one patient the target coverage was conserved, and no adaptations were necessary. CONCLUSION: In 25% of the investigated cases, classical robust optimization is not sufficient to account for anatomical changes during the treatment. Adding additional information of random anatomical variations in the optimization improves plan robustness.

Geometric and dosimetric evaluation of atlas based auto-segmentation of cardiac structures in breast cancer patients.

BACKGROUND AND PURPOSE: Auto-segmentation represents an efficient tool to segment organs on CT imaging. Primarily used in clinical setting, auto-segmentation plays an increasing role in research, particularly when analyzing thousands of images in the "big data" era. In this study we evaluate the accuracy of cardiac dosimetric endpoints derived from atlas based auto-segmentation compared to gold standard manual segmentation. MATERIAL AND METHODS: Heart and cardiac substructures were manually delineated on 54 breast cancer patients. Twenty-seven patients were used to build the auto-segmentation atlas, the other 27 to validate performance. We evaluated accuracy of the auto-segmented contours with standard geometric indices and assessed dosimetric endpoints. RESULTS: Auto-segmented contours overlapped geometrically with manual contours of the heart and chambers with Dice-similarity coefficients of 0.93 ±â€¯0.02 (mean ±â€¯standard deviation) and 0.79 ±â€¯0.07 respectively. Similarly, there was a strong link between dosimetric parameters derived from auto-segmented and manual contours (R2 = 0.955-1.000). On the other hand, the left anterior descending artery had little geometric overlap (Dice-similarity coefficient 0.09 ±â€¯0.07), though acceptable representation of dosimetric parameters (R2 = 0.646-0.992). CONCLUSIONS: The atlas based auto-segmentation approach delineates heart structures with sufficient accuracy for research purposes. Our results indicate that quality of auto-segmented contours cannot be determined by geometric values only.

Bridging the Gap in Global Advanced Radiation Oncology Training: Impact of a Web-Based Open-Access Interactive Three-Dimensional Contouring Atlas on Radiation Oncologist Practice in Russia.

Radiation oncologists in Russia face a number of unique professional difficulties including lack of standardized training and continuing medical education. To combat this, under the auspices of the Russian Society of Clinical Oncology (RUSSCO), our group has developed a series of ongoing in-person interactive contouring workshops that are held during the major Russian oncology conferences in Moscow, Russia. Since November 2016 during each workshop, we utilized a web-based open-access interactive three-dimensional contouring atlas as part of our didactics. We sought to determine the impact of this resource on radiation oncology practice in Russia. We distributed an IRB-approved web-based survey to 172 practicing radiation oncologists in Russia. We inquired about practice demographics, RUSSCO contouring workshop attendance, and the clinical use of open-access English language interactive contouring atlas (eContour). The survey remained open for 2 months until November 2017. Eighty radiation oncologists completed the survey with a 46.5% response rate. Mean number of years in practice was 13.7. Sixty respondents (75%) attended at least one RUSSCO contouring workshop. Of those who were aware of eContour, 76% were introduced during a RUSSCO contouring workshop, and 81% continue to use it in their daily practice. The greatest obstacles to using the program were language barrier (51%) and internet access (38%). Nearly 90% reported their contouring practices changed since they started using the program, particularly for delineation of clinical target volumes (57%) and/or organs at risk (46%). More than 97% found the clinical pearls/links to cooperative group protocols in the software helpful in their daily practice. The majority used the contouring program several times per month (43%) or several times per week (41%). Face-to-face contouring instruction in combination with open-access web-based interactive contouring resource had a meaningful impact on perceived quality of radiation oncology contours among Russian practitioners and has the potential to have applications worldwide.

Functional Swallowing Units (FSUs) as organs-at-risk for radiotherapy. PART 1: Physiology and anatomy.

BACKGROUND AND PURPOSE: When optimising radiotherapy treatments today, the pharyngeal constrictor muscles and the larynx are usually regarded as the swallowing organs at risk (SWOARs). The purpose of this study was to identify and describe additional, previously undefined groups of muscles (functional units) involved in crucial components of swallowing (hyolaryngeal elevation (HLE), tongue base retraction (TBR) and tongue motion), and to emphasise their relevance in radiation-induced dysphagia. MATERIAL AND METHODS: Based on available literature on human anatomy and swallowing physiology, the functional units of muscles involved in HLE, TBR and tongue motion have been identified and described. RESULTS AND CONCLUSION: Functional swallowing units (FSUs) were defined as groups of swallowing muscles sharing their function, that are in close proximity to each other. Seven FSUs involved in HLE, TBR and tongue motion were identified: floor of mouth, thyrohyoid muscles, posterior digastric/stylohyoid muscles complex, longitudinal pharyngeal muscles, hyoglossus/styloglossus muscles complex, genioglossus muscles, intrinsic tongue muscles. The swallowing physiology and anatomy of the FSUs described in this paper will lead to a greater understanding of radiation-induced dysphagia mechanisms and, consequently, to an improvement in the development of swallowing sparing strategies. This article (PART 1) serves as the theoretical foundation for a subsequent article (PART 2), which provides detailed delineation guidelines for FSUs.

Fast and robust adaptation of organs-at-risk delineations from planning scans to match daily anatomy in pre-treatment scans for online-adaptive radiotherapy of abdominal tumors.

PURPOSE: To validate a novel deformable image registration (DIR) method for online adaptation of planning organ-at-risk (OAR) delineations to match daily anatomy during hypo-fractionated RT of abdominal tumors. MATERIALS AND METHODS: For 20 liver cancer patients, planning OAR delineations were adapted to daily anatomy using the DIR on corresponding repeat CTs. The DIR's accuracy was evaluated for the entire cohort by comparing adapted and expert-drawn OAR delineations using geometric (Dice Similarity Coefficient (DSC), Modified Hausdorff Distance (MHD) and Mean Surface Error (MSE)) and dosimetric (Dmax and Dmean) measures. RESULTS: For all OARs, DIR achieved average DSC, MHD and MSE of 86%, 2.1 mm, and 1.7 mm, respectively, within 20 s for each repeat CT. Compared to the baseline (translations), the average improvements ranged from 2% (in heart) to 24% (in spinal cord) in DSC, and 25% (in heart) to 44% (in right kidney) in MHD and MSE. Furthermore, differences in dose statistics (Dmax, Dmean and D2%) using delineations from an expert and the proposed DIR were found to be statistically insignificant (p > 0.01). CONCLUSION: The validated DIR showed potential for online-adaptive radiotherapy of abdominal tumors as it achieved considerably high geometric and dosimetric correspondences with the expert-drawn OAR delineations, albeit in a fraction of time required by experts.

Risk of Late Urinary Complications Following Image Guided Adaptive Brachytherapy for Locally Advanced Cervical Cancer: Refining Bladder Dose-Volume Parameters.

PURPOSE: To study correlations between dose-volume parameters of the whole bladder and bladder trigone and late urinary toxicity in locally advanced cervical cancer patients treated with pulsed-dose-rate brachytherapy. METHODS AND MATERIALS: Patients with locally advanced cervical cancer treated with chemoradiation therapy and pulsed-dose-rate brachytherapy from 2004 to 2015 were included. Cumulative dose-volume parameters of the whole bladder and bladder trigone were converted into 2-Gy/fraction equivalents (EQD2, with α/ß = 3 Gy); these parameters, as well as clinical factors, were analyzed as predictors of toxicity in patients without local relapse. RESULTS: A total of 297 patients fulfilled the inclusion criteria. The median follow-up period was 4.9 years (95% confidence interval 4.5-5.3 years). In patients without local relapse (n = 251), the Kaplan-Meier estimated grade 2 or higher urinary toxicity rates at 3 years and 5 years were 25.4% and 32.1%, respectively. Minimal dose to the most exposed 2 cm3 of the whole bladder [Formula: see text] , bladder International Commission on Radiation Units & Measurements (ICRU) (BICRU) dose, and trigone dose-volume parameters correlated with grade 2 or higher toxicity. At 3 years, the cumulative incidence of grade 2 or higher complications was 22.8% (standard error, 2.9%) for bladder [Formula: see text]  < 80 GyEQD2 versus 61.8% (standard error, 12.7%) for [Formula: see text]  ≥ 80 GyEQD2 (P = .001). In the subgroup of patients with bladder [Formula: see text]  ≤ 80 GyEQD2, a trigone dose delivered to 50% of the volume (D50%) > 60 GyEQD2 was significant for grade 2 or higher toxicity (P = .027). The probability of grade 3 or higher toxicities increased with bladder [Formula: see text]  > 80 GyEQD2 (16.7% vs 1.6%; hazard ratio [HR], 5.77; P = .039), BICRU dose > 65 GyEQD2 (4.9% vs 1.3%; HR, 6.36; P = .018), and trigone D50% > 60 GyEQD2 (3.1% vs 1.2%; HR, 6.29; P = .028). Pearson correlation coefficients showed a moderate correlation between bladder [Formula: see text] , BICRU dose, and bladder trigone D50% (P < .0001). CONCLUSIONS: These data suggest that [Formula: see text]  ≤ 80 GyEQD2 should be advised for minimizing the risk of severe urinary complications (<15%). Bladder trigone dose was also predictive of severe late urinary toxicity. These constraints need further confirmation in a multicenter prospective setting.

Clinical evaluation of atlas and deep learning based automatic contouring for lung cancer.

BACKGROUND AND PURPOSE: Contouring of organs at risk (OARs) is an important but time consuming part of radiotherapy treatment planning. The aim of this study was to investigate whether using institutional created software-generated contouring will save time if used as a starting point for manual OAR contouring for lung cancer patients. MATERIAL AND METHODS: Twenty CT scans of stage I-III NSCLC patients were used to compare user adjusted contours after an atlas-based and deep learning contour, against manual delineation. The lungs, esophagus, spinal cord, heart and mediastinum were contoured for this study. The time to perform the manual tasks was recorded. RESULTS: With a median time of 20 min for manual contouring, the total median time saved was 7.8 min when using atlas-based contouring and 10 min for deep learning contouring. Both atlas based and deep learning adjustment times were significantly lower than manual contouring time for all OARs except for the left lung and esophagus of the atlas based contouring. CONCLUSIONS: User adjustment of software generated contours is a viable strategy to reduce contouring time of OARs for lung radiotherapy while conforming to local clinical standards. In addition, deep learning contouring shows promising results compared to existing solutions.

The effect of catheter displacement and anatomical variations on the dose distribution in MRI-guided focal HDR brachytherapy for prostate cancer.

PURPOSE: The aim of this study was to analyze the effect of catheter displacement and anatomical variations of prostate and organs at risk on dose distribution in MRI-guided 19 Gy single fraction focal high-dose-rate brachytherapy (HDR-BT) of the prostate. METHODS AND MATERIALS: Seventeen patients with localized prostate cancer were enrolled in a prospective trial investigating focal HDR-BT in a 1.5 T MRI-HDR-BT facility. The diagnostic MRI delineations were registered with intraoperative MR scan, and a single fraction of 19 Gy was applied to the visible tumor. Self-anchoring umbrella catheters were used for HDR-BT delivery. A 1.5 T MRI was performed directly after ultrasound (US)-guided catheter placement for treatment planning. After treatment and before removal of catheters, a posttreatment 1.5 T MRI was performed. Regions of interest were also delineated on the posttreatment MR images and the catheters of 17 patients were reconstructed. The dose plan was constructed for the posttreatment MRI scan to assess the influence of catheter migration and anatomical variation on the dose delivered to the target and the organs at risk. Also on the posttreatment MRI, the complete catheter reconstruction was reassessed, to correct for, for example, bending of the catheters. The displacement of catheters between the MRI scans was determined by comparing the catheter tip positions on the treatment planning and posttreatment 1.5 T MRI scans. RESULTS: The displacements of 241 catheters were investigated. Average (range) displacements of the umbrella catheters are 0.6 (0-2.9) mm in the x-direction, 0.5 (0-2.1) mm in the y-direction, and 0.9 (0-5.5) mm in the z-direction. In 3 patients, the displacement was >4 mm and up to 5.5 mm. This occurred in respectively 1/13, 1/16, and 1/18 catheters in these patients. The dosimetric differences between the intraoperative treatment and the posttreatment plans were in most patients less than 1.5 Gy. In 4 patients, a dose difference in clinical target volume D95 of >2 Gy up to 5.8 Gy was reported. No discrimination can be made between dose differences due to catheter displacement and/or organ movement/anatomy changes. CONCLUSIONS: In general, catheter displacements were in the order of a mm and differences in dose to the clinical target volume and the organs at risk between the treatment and posttreatment plans smaller than 1.5 Gy. In some patients, dose differences up to 5.8 Gy were determined, due to either individual larger catheter displacement and/or anatomy changes. A longer followup is necessary to assess the clinical implications of individual large dose differences.

Emphasis on Repair, Not Just Avoidance of Injury, Facilitates Prudent Stereotactic Ablative Radiotherapy.

Stereotactic ablative radiotherapy (SAbR) is a potent, hypofractionated treatment against cancer which puts adjacent normal tissue in potential peril. Accurate delineation of normal tissue injury risks from SAbR has been challenging, and lack of clear understanding of SAbR tolerance continues to limit its potential. In this review, we contend that SAbR effects on normal tissue could be akin to a surgical "wound," and that adequate wound repair of organs at risk is an essential component of effective SAbR therapy. To mitigate risks of clinical relevance from an SAbR wound, in addition to the traditional views on architectural organization and functional organization of an organ at risk, one should also consider the organ's predominant wound healing tendencies. We also propose that avoidance of SAbR injury to organs at risk must involve careful thought to minimize risk factors that could further impair wound healing. It is imperative that efforts aimed at determining appropriate dose constraints based on predicted SAbR wound injury repair mechanisms for a particular organ to be studied as a critically important step to furthering our understanding of SAbR-related normal tissue tolerances. This can be best achieved through thoughtful design of prospective phase I dose-escalation studies.

Deformable image registration for cervical cancer brachytherapy dose accumulation: Organ at risk dose-volume histogram parameter reproducibility and anatomic position stability.

PURPOSE: The purpose of this study was to determine the effect of deformable image registration (DIR) on cumulative organ at risk dose-volume histogram (DVH) parameter summation for more than three brachytherapy fractions. The reproducibility of different methods of DIR was tested. DIR was then used to assess the stability of the anatomic position of the DVH parameters within the bladder and rectum. METHODS AND MATERIALS: DIR was completed for 39 consecutive cervical cancer brachytherapy patients' planning CTs. Accumulated DVH parameters (D2cc and D0.1cc) for bladder and rectum were compared with dose summation without DIR. Reproducibility of DIR results was assessed for different methods of implementation based on adding contour biases added to the DIR algorithm. VolD2cc and VolD0.1cc structures were created from the overlap of the D2cc and D0.1cc isodose and the bladder or rectum, respectively. The overlap of VolD2cc and VolD0.1cc structures was calculated using the Dice similarity coefficient. RESULTS: DIR accumulated D2cc and D0.1cc decreased by an average of 2.9% and 4.2% for bladder and 5.08% and 2.8% for rectum compared with no DIR. DIR was most reproducible when the bladder or rectum contour was masked. The average Dice similarity coefficient was 0.78 and 0.61 for the bladder D2cc and D0.1cc as well as 0.83 and 0.62 for rectal D2cc and D0.1cc, respectively. CONCLUSIONS: Dose decreases were observed for accumulated DVH parameters using DIR. Adding contour-based biases to the algorithm increases the reproducibility of D2cc and D0.1cc accumulation. The anatomic position of VolD2cc was more stable than VolD0.1cc.

Ultrasound registration: A review.

This article is a review of registration algorithms for use between ultrasound images (monomodal image-based ultrasound registration). Ultrasound is safe, inexpensive, and real-time, providing many advantages for clinical and scientific use on both humans and animals, but ultrasound images are also notoriously noisy and subject to several unique artifacts/distortions. This paper introduces the topic and unique aspects of ultrasound-to-ultrasound image registration, providing a broad introduction and summary of the literature and the field. Both theoretical and practical aspects are introduced. The first half of the paper is theoretical, organized according to the basic components of a registration framework, namely preprocessing, image-similarity metrics, optimizers, etc. It further subdivides these methods between those suitable for elastic (non-rigid) vs. inelastic (matrix) transforms. The second half of the paper is organized by anatomy and is practical in nature, presenting and discussing the complete published systems that have been validated for registration in specific anatomic regions.