The impact of contouring uncertainty on rectal 3D dose-volume data: results of a dummy run in a multicenter trial (AIROPROS01-02)

Proposal for a Method for Assessing the Quality of an Updated Deep Learning-Based Automatic Segmentation Program

This study aimed to verify whether a commercial deep learning-based automatic segmentation (DLS) method can maintain contour geometric accuracy post-update and to propose a streamlined validation method that minimizes the burden on clinical workflows. This study included 109 participants. Radiation oncologists used computed tomography (CT) imaging to identify 28 organs located in the head and neck, chest, abdomen, and pelvic regions. Contours were delineated on CT images using AI-Rad Companion Organs RT (AIRC; Siemens Healthineers, Erlangen, Germany) versions VA30, VA50, and VA50. The Dice similarity coefficient, maximum Hausdorff distance, and mean distance to agreement were calculated to identify contours with significant differences among versions. To evaluate the identified contours, the ground truth was defined as the contour delineated by radiation oncologists, and the geometric indices for VA30, VA50, and VA60 were recalculated. Statistical analysis was performed on the geometric indices to verify differences between each version. Among the 28 contours evaluated, nine organs did not satisfy the established criteria. Statistical analysis revealed that the brain, rectum, and bladder contours differed substantially across AIRC versions. In particular, the pre-update rectum contour had a mean (range) Hausdorff distance of 0.76 (0.40-1.16), whereas the post-update rectum contour exhibited lower quality, with a Hausdorff distance of 1.13 (0.24-5.68). Therefore, commercial DLS methods that undergo regular updates must be reassessed for quality in each region of interest. The proposed method can help reduce the burden on clinical workflows while appropriately evaluating post-update DLS performance.

Experience and uncertainty analysis of CT-based adaptive radiotherapy for abdominal treatments

BACKGROUND

Online adaptive radiotherapy (ART) allows for daily replanning of treatment plans with adjustments according to current day anatomy. The purpose of this work is to present our methodology for using CT-based ART applied to abdominal cases along with our experience with this treatment. We additionally aim to estimate some of the uncertainties associated with the adaptive process.

METHODS AND MATERIALS

Analysis was performed on patients with abdominal targets (N = 41, 205 fractions), treated on a CT-based adaptive treatment unit; treatment sites were divided into 3 categories: pancreas, liver, and other (e.g., lymph nodes). Statistics regarding contouring time, planning target volume (PTV) coverage, and organ-at-risk (OAR) sparing are presented. Contouring uncertainty was estimated by expanding critical OARs and recalculating dose, and auto-registration uncertainty was estimated by adjusting the registration between the cone beam computed tomography scan and the dose cloud and recalculating dose.

RESULTS

Coverage for the planning optimization PTV (PTV_Opt) for adaptive plans was on average 94.7 ± 0.4 %, while for scheduled plans it was on average 92.0 ± 0.6 %. The average decrease in OAR maximum dose by using the adaptive plans was 11.6 ± 1.0 %. Contouring time was on average 23 ± 0 min. Uncertainty estimates for PTV V100% were on average 0.6 ± 0.4 %; combined uncertainties for maximum OAR dose were on average 4.6 ± 0.4 %.

CONCLUSION

Adaptive therapy on average led to plans with improved PTV coverage or OAR sparing, and our workflow allowed for treatment to be completed within a reasonable timeframe. The benefit of adaptive therapy largely outweighed estimates of uncertainty.

Gastrointestinal Toxicity Prediction Not Influenced by Rectal Contour or Dose-Volume Histogram Definition

PURPOSE

Rectal dose delivered during prostate radiation therapy is associated with gastrointestinal toxicity. Treatment plans are commonly optimized using rectal dose-volume constraints, often whole-rectum relative-volumes (%). We investigated whether improved rectal contouring, use of absolute-volumes (cc), or rectal truncation might improve toxicity prediction.

METHODS AND MATERIALS

Patients from the CHHiP trial (receiving 74 Gy/37 fractions [Fr] vs 60 Gy/20 Fr vs 57 Gy/19 Fr) were included if radiation therapy plans were available (2350/3216 patients), plus toxicity data for relevant analyses (2170/3216 patients). Whole solid rectum relative-volumes (%) dose-volume-histogram (DVH), as submitted by treating center (original contour), was assumed standard-of-care. Three investigational rectal DVHs were generated: (1) reviewed contour per CHHiP protocol; (2) original contour absolute volumes (cc); and (3) truncated original contour (2 versions; ±0 and ±2 cm from planning target volume [PTV]). Dose levels of interest (V30, 40, 50, 60, 70, 74 Gy) in 74 Gy arm were converted by equivalent-dose-in-2 Gy-Fr (EQD2α/β= 3 Gy) for 60 Gy/57 Gy arms. Bootstrapped logistic models predicting late toxicities (frequency G1+/G2+, bleeding G1+/G2+, proctitis G1+/G2+, sphincter control G1+, stricture/ulcer G1+) were compared by area-undercurve (AUC) between standard of care and the 3 investigational rectal definitions.

RESULTS

The alternative dose/volume parameters were compared with the original relative-volume (%) DVH of the whole rectal contour, itself fitted as a weak predictor of toxicity (AUC range, 0.57-0.65 across the 8 toxicity measures). There were no significant differences in toxicity prediction for: (1) original versus reviewed rectal contours (AUCs, 0.57-0.66; P = .21-.98); (2) relative- versus absolute-volumes (AUCs, 0.56-0.63; P = .07-.91); and (3) whole-rectum versus truncation at PTV ± 2 cm (AUCs, 0.57-0.65; P = .05-.99) or PTV ± 0 cm (AUCs, 0.57-0.66; P = .27-.98).

CONCLUSIONS

We used whole-rectum relative-volume DVH, submitted by the treating center, as the standard-of-care dosimetric predictor for rectal toxicity. There were no statistically significant differences in prediction performance when using central rectal contour review, with the use of absolute-volume dosimetry, or with rectal truncation relative to PTV. Whole-rectum relative-volumes were not improved upon for toxicity prediction and should remain standard-of-care.

Real-world validation of Artificial Intelligence-based Computed Tomography auto-contouring for prostate cancer radiotherapy planning

Background and purpose

Artificial Intelligence (AI)-based auto-contouring for treatment planning in radiotherapy needs extensive clinical validation, including the impact of editing after automatic segmentation. The aims of this study were to assess the performance of a commercial system for Clinical Target Volumes (CTVs) (prostate/seminal vesicles) and selected Organs at Risk (OARs) (rectum/bladder/femoral heads + femurs), evaluating also inter-observer variability (manual vs automatic + editing) and the reduction of contouring time.

Materials and methods

Two expert observers contoured CTVs/OARs of 20 patients in our Treatment Planning System (TPS). Computed Tomography (CT) images were sent to the automatic contouring workstation: automatic contours were generated and sent back to TPS, where observers could edit them if necessary. Inter- and intra-observer consistency was estimated using Dice Similarity Coefficients (DSC). Radiation oncologists were also asked to score the quality of automatic contours, ranging from 1 (complete re-contouring) to 5 (no editing). Contouring times (manual vs automatic + edit) were compared.

Results

DSCs (manual vs automatic only) were consistent with inter-observer variability (between 0.65 for seminal vesicles and 0.94 for bladder); editing further improved performances (range: 0.76-0.94). The median clinical score was 4 (little editing) and it was <4 in 3/2 patients for the two observers respectively. Inter-observer variability of automatic + editing contours improved significantly, being lower than manual contouring (e.g.: seminal vesicles: 0.83vs0.73; prostate: 0.86vs0.83; rectum: 0.96vs0.81). Oncologist contouring time reduced from 17 to 24 min of manual contouring time to 3-7 min of editing time for the two observers (p < 0.01).

Conclusion

Automatic contouring with a commercial AI-based system followed by editing can replace manual contouring, resulting in significantly reduced time for segmentation and better consistency between operators.

Validation of prediction models for radiation-induced late rectal bleeding: evidence from a large pooled population of prostate cancer patients

PURPOSE

To validate published models for the risk estimate of grade≥1 (G1+), grade≥2 (G2+) and grade=3 (G3) late rectal bleeding (LRB) after radical radiotherapy for prostate cancer in a large pooled population from three prospective trials.

MATERIALS AND METHODS

The external validation population included patients from Europe, and Oceanian centres enrolled between 2003 and 2014. Patients received 3DCRT or IMRT at doses between 66-80 Gy. IMRT was administered with conventional or hypofractionated schemes (2.35-2.65 Gy/fr). LRB was prospectively scored using patient-reported questionnaires (LENT/SOMA scale) with a 3-year follow-up. All Normal Tissue Complication Probability (NTCP) models published until 2021 based on the Equivalent Uniform Dose (EUD) from the rectal Dose Volume Histogram (DVH) were considered for validation. Model performance in validation was evaluated through calibration and discrimination.

RESULTS

Sixteen NTCP models were tested on data from 1633 patients. G1+ LRB was scored in 465 patients (28.5%), G2+ in 255 patients (15.6%) and G3 in 112 patients (6.8%). The best performances for G2+ and G3 LRB highlighted the importance of the medium-high doses to the rectum (volume parameters n=0.24 and n=0.18, respectively). Good performance was seen for models of severe LRB. Moreover, a multivariate model with two clinical factors found the best calibration slope.

CONCLUSION

Five published NTCP models developed on non-contemporary cohorts were able to predict a relative increase in the toxicity response in a more recent validation population. Compared to QUANTEC findings, dosimetric results pointed toward mid-high doses of rectal DVH. The external validation cohort confirmed abdominal surgery and cardiovascular diseases as risk factors.

A rapid review of influential factors and appraised solutions on organ delineation uncertainties reduction in radiotherapy

Background and purpose.Accurate volume delineation plays an essential role in radiotherapy. Contouring is a potential source of uncertainties in radiotherapy treatment planning that could affect treatment outcomes. Therefore, reducing the degree of contouring uncertainties is crucial. The role of utilized imaging modality in the organ delineation uncertainties has been investigated. This systematic review explores the influential factors on inter-and intra-observer uncertainties of target volume and organs at risk (OARs) delineation focusing on the used imaging modality for these uncertainties reduction and the reported subsequent histopathology and follow-up assessment.Methods and materials.An inclusive search strategy has been conducted to query the available online databases (Scopus, Google Scholar, PubMed, and Medline). 'Organ at risk', 'target', 'delineation', 'uncertainties', 'radiotherapy' and their relevant terms were utilized using every database searching syntax. Final article extraction was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. Included studies were limited to the ones published in English between 1995 and 2020 and that just deal with computed tomography (CT) and magnetic resonance imaging (MRI) modalities.Results.A total of 923 studies were screened and 78 were included of which 31 related to the prostate 20 to the breast, 18 to the head and neck, and 9 to the brain tumor site. 98% of the extracted studies performed volumetric analysis. Only 24% of the publications reported the dose deviations resulted from variation in volume delineation Also, heterogeneity in studied populations and reported geometric and volumetric parameters were identified such that quantitative synthesis was not appropriate.Conclusion.This review highlightes the inter- and intra-observer variations that could lead to contouring uncertainties and impede tumor control in radiotherapy. For improving volume delineation and reducing inter-observer variability, the implementation of well structured training programs, homogeneity in following consensus and guidelines, reliable ground truth selection, and proper imaging modality utilization could be clinically beneficial.

Interobserver variability in target volume delineation in definitive radiotherapy for thoracic esophageal cancer: a multi-center study from China

Purpose

To investigate the interobserver variability (IOV) in target volume delineation of definitive radiotherapy for thoracic esophageal cancer (TEC) among cancer centers in China, and ultimately improve contouring consistency as much as possible to lay the foundation for multi-center prospective studies.

Methods

Sixteen cancer centers throughout China participated in this study. In Phase 1, three suitable cases with upper, middle, and lower TEC were chosen, and participants were asked to contour a group of gross tumor volume (GTV-T), nodal gross tumor volume (GTV-N) and clinical target volume (CTV) for each case based on their routine experience. In Phase 2, the same clinicians were instructed to follow a contouring protocol to re-contour another group of target volume. The variation of the target volume was analyzed and quantified using dice similarity coefficient (DSC).

Results

Sixteen clinicians provided routine volumes, whereas ten provided both routine and protocol volumes for each case. The IOV of routine GTV-N was the most striking in all cases, with the smallest DSC of 0.37 (95% CI 0.32–0.42), followed by CTV, whereas GTV-T showed high consistency. After following the protocol, the smallest DSC of GTV-N was improved to 0.64 (95% CI 0.45–0.83, P = 0.005) but the DSC of GTV-T and CTV remained constant in most cases.

Conclusion

Variability in target volume delineation was observed, but it could be significantly reduced and controlled using mandatory interventions.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13014-020-01691-4.

Quality indicator selection for the Canadian Partnership against Cancer rectal cancer project: A modified Delphi study

AIM

It is well established that (i) magnetic resonance imaging, (ii) multidisciplinary cancer conference (MCCs), (iii) preoperative radiotherapy, (iv) total mesorectal excision surgery and (v) pathological assessment as described by Quirke are key processes necessary for high quality, rectal cancer care. The objective was to select a set of multidisciplinary quality indicators to measure the uptake of these clinical processes in clinical practice.

METHOD

A multidisciplinary panel was convened and a modified two-phase Delphi method was used to select a set of quality indicators. Phase 1 included a literature review with written feedback from the panel. Phase 2 included an in-person workshop with anonymous voting. The selection criteria for the indicators were strength of evidence, ease of capture and usability. Indicators for which ≥90% of the panel members voted 'to keep' were selected as the final set of indicators.

RESULTS

During phase 1, 68 potential indicators were generated from the literature and an additional four indicators were recommended by the panel. During phase 2, these 72 indicators were discussed; 48 indicators met the 90% inclusion threshold and included eight pathology, five radiology, 11 surgical, six radiation oncology and 18 MCC indicators.

CONCLUSION

A modified Delphi method was used to select 48 multidisciplinary quality indicators to specifically measure the uptake of key processes necessary for high quality care of patients with rectal cancer. These quality indicators will be used in future work to identify and address gaps in care in the uptake of these clinical processes.

Use of deformable image registration techniques to estimate dose to organs at risk following prostate external beam radiation therapy and high-dose-rate brachytherapy

PURPOSE

The purpose of this investigation was to examine differences in estimates of accumulated rectal dose when using deformable image registration (DIR) compared with rigid image registration (RIR) methods, and parameter addition methods for combined transrectal ultrasound (TRUS)-based high-dose-rate brachytherapy (HDR-BT) and external beam radiation therapy (EBRT) treatments of prostate cancer.

MATERIAL AND METHODS

In this retrospective study, data from 10 patients who had previously received HDR-BT in one 15 Gy fraction, followed by 46 Gy EBRT in twenty-three fractions were used. To estimate total combined dose to the rectum, dose accumulation using both DIR and RIR methods were compared with parameter addition methods, which assume the same region of rectal anatomy receives the maximum dose from both treatment modalities. For both rigid and deformable image registration techniques, the quality of image registration was evaluated through metrics, including mean distance to agreement and dice similarity coefficient of prostate contours. Total D1cc and D2cc for the rectum was calculated and compared using each method.

RESULTS

The parameter addition methods predicted the highest accumulated dose to the rectum. On average, the predicted D2cc dose was higher than that calculated by the DIR method by 6.59 Gy EQD2 (range, -3.03 to 13.68 Gy EQD2) for partial parameter addition (PPA), and 4.88 Gy EQD2 (range, -3.41 to 11.97 Gy EQD2) for the full parameter addition (FPA) methods. Similarly, RIR predicted higher average doses compared with DIR, with a difference of 3.46 Gy EQD2 (range, -5.50 to 7.90 Gy EQD2). The results showed a significant difference between DIR and parameter addition methods for dose estimation.

CONCLUSIONS

This retrospective study demonstrates significant differences in accumulated rectal dose prediction using different image registration methods. Each method has limitations in its application, and when used with real-time HDR-BT dose planning, awareness of these limitations is essential.

Reduction of inter-observer contouring variability in daily clinical practice through a retrospective, evidence-based intervention

BACKGROUND

Inter-observer variations (IOVs) arising during contouring can potentially impact plan quality and patient outcomes. Regular assessment of contouring IOV is not commonly performed in clinical practice due to the large time commitment required of clinicians from conventional methods. This work uses retrospective information from past treatment plans to facilitate a time-efficient, evidence-based intervention to reduce contouring IOV.

METHODS

The contours of 492 prostate cancer treatment plans created by four radiation oncologists were analyzed in this study. Structure volumes, lengths, and DVHs were extracted from the treatment planning system and stratified based on primary oncologist and inclusion of a pelvic lymph node (PLN) target. Inter-observer variations and their dosimetric consequences were assessed using Student's t-tests. Results of this analysis were presented at an intervention meeting, where new consensus contour definitions were agreed upon. The impact of the intervention was assessed one-year later by repeating the analysis on 152 new plans.

RESULTS

Significant IOV in prostate and PLN target delineation existed pre-intervention between oncologists, impacting dose to nearby OARs. IOV was also present for rectum and penile-bulb structures. Post-intervention, IOV decreased for all previously discordant structures. Dosimetric variations were also reduced. Although target contouring concordance increased significantly, some variations still persisted for PLN structures, highlighting remaining areas for improvement.

CONCLUSION

We detected significant contouring IOV in routine practice using easily accessible retrospective data and successfully decreased IOV in our clinic through a reflective intervention. Continued application of this approach may aid improvements in practice standardization and enhance quality of care.

Validation of a new open-source method for automatic delineation and dose assessment of the heart and LADCA in breast radiotherapy with simultaneous uncertainty estimation

Radiotherapy has been shown to increase risks of cardiotoxicities for breast cancer patients. Automated delineation approaches are necessary for consistent and efficient assessment of cardiac doses in large, retrospective datasets, while patient-specific estimation of the uncertainty in these doses provides valuable additional data for modelling and understanding risks. In this work, we aim to validate the consistency of our previously described open-source software model for automatic cardiac delineation in the context of dose assessment, relative to manual contouring. We also extend our software to introduce a novel method to automatically quantify the uncertainty in cardiac doses based on expected inter-observer variability (IOV) in contouring. This method was applied to a cohort of 15 left-sided breast cancer patients treated in Denmark using modern tangential radiotherapy techniques. On each image set, the whole heart and left anterior descending coronary artery (LADCA) were contoured by nine independent experts; the range of doses to these nine volumes provided a reference for the dose uncertainties generated from the automatic method. Local and external atlas sets were used to test the method. Results give confidence in the consistency of automatic segmentations, with mean whole heart dose differences for local and external atlas sets of -0.20 ± 0.17 and -0.10 ± 0.14 Gy, respectively. Automatic estimates of uncertainties in doses are similar to those from IOV for both the whole heart and LADCA. Overall, this study confirms that our automated approach can be used to accurately assess cardiac doses, and the proposed method can provide a useful tool in estimating dose uncertainties.

Standardizing Normal Tissue Contouring for Radiation Therapy Treatment Planning: An ASTRO Consensus Paper

PURPOSE

The comprehensive identification and delineation of organs at risk (OARs) are vital to the quality of radiation therapy treatment planning and the safety of treatment delivery. This guidance aims to improve the consistency of ontouring OARs in external beam radiation therapy treatment planning by providing a single standardized resource for information regarding specific OARs to be contoured for each disease site. The guidance is organized in table format as a quality assurance tool for practices and a training resource for residents and other radiation oncology students (see supplementary materials).

METHODS AND MATERIALS

The Task Force formulated recommendations based on clinical practice and consensus. The draft manuscript was peer reviewed by 16 reviewers, the American Society for Radiation Oncology (ASTRO) legal counsel, and ASTRO's Multidisciplinary Quality Assurance Subcommittee and revised accordingly. The recommendations were posted on the ASTRO website for public comment in June 2018 for a 6-week period. The final document was approved by the ASTRO Board of Directors in August 2018.

RESULTS

Standardization improves patient safety, efficiency, and accuracy in radiation oncology treatment. This consensus guidance represents an ASTRO quality initiative to provide recommendations for the standardization of normal tissue contouring that is performed during external beam treatment planning for each anatomic treatment site. Table 1 defines 2 sets of structures for anatomic sites: Those that are recommended in all adult definitive cases and may assist with organ selection for palliative cases, and those that should be considered on a case-by-case basis depending on the specific clinical scenario. Table 2 outlines some of the resources available to define the parameters of general OAR tissue delineation.

CONCLUSIONS

Using this paper in conjunction with resources that define tissue parameters and published dose constraints will enable practices to develop a consistent approach to normal tissue evaluation and dose documentation.

Developing and Evaluating Multimedia Patient Education Tools to Better Prepare Prostate-Cancer Patients for Radiotherapy Treatment (Randomized Study)

The purpose of this study is to determine the effectiveness of multimedia educational tools to improve CT planning preparation for intensity modulated radiotherapy (IMRT) for prostate cancer. Many patients are not prepared when given verbal preparation instructions to have a full bladder and empty rectum for their IMRT and require being rescanned, which results in additional costs for the patient and the hospital. A pamphlet and video outlining the proper preparation for prostate IMRT was created to decrease additional scans and the associated costs, while increasing patient satisfaction. A controlled, randomized experimental group study was conducted to examine the effectiveness of the multimedia tools (the video and the pamphlet), as compared to the pamphlet only, in preparing patients for their planning CT appointment. We found no statistical difference between the multimedia group and the pamphlet group in patients' preparedness for their appointments and the rescanning rate. However, patients in the multimedia group indicated that they felt more prepared about their treatment after watching the video and stated that they would recommend the video to other patients with prostate cancer. Furthermore, patients who had to wait longer for their planning CT appointment felt less prepared by the materials than those with a shorter wait time. We recommend reducing wait times between appointments as much as possible to increase patients' preparedness for the planning CT. We conclude that providing multimedia treatment information and minimizing wait times increases patients' feelings of preparedness leading to a more positive treatment experience and reducing costly rescans.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02410291.

Computational analysis of interfractional anisotropic shape variations of the rectum in prostate cancer radiation therapy

PURPOSE

To analyze the uncertainties of the rectum due to anisotropic shape variations by using a statistical point distribution model (PDM).

MATERIALS AND METHODS

The PDM was applied to the rectum contours that were delineated on planning computed tomography (CT) and cone-beam CT (CBCT) at 80 fractions of 11 patients. The standard deviations (SDs) of systematic and random errors of the shape variations of the whole rectum and the region in which the rectum overlapped with the PTV (ROP regions) were derived from the PDMs at all fractions of each patient. The systematic error was derived by using the PDMs of planning and average rectum surface determined from rectum surfaces at all fractions, while the random error was derived by using a PDM-based covariance matrix at all fractions of each patient.

RESULTS

Regarding whole rectum, the population SDs were larger than 1.0 mm along all directions for random error, and along the anterior, superior, and inferior directions for systematic error. The deviation is largest along the superior and inferior directions for systematic and random errors, respectively. For ROP regions, the population SDs of systematic error were larger than 1.0 mm along the superior and inferior directions. The population SDs of random error for the ROP regions were larger than 1.0 mm except along the right and posterior directions.

CONCLUSIONS

The anisotropic shape variations of the rectum, especially in the ROP regions, should be considered when determining a planning risk volume (PRV) margins for the rectum associated with the acute toxicities.

Comparison of different contouring definitions of the rectum as organ at risk (OAR) and dose-volume parameters predicting rectal inflammation in radiotherapy of prostate cancer: which definition to use?

OBJECTIVE

The objective of this retrospective planning study was to find a contouring definition for the rectum as an organ at risk (OAR) in curative three-dimensional external beam radiotherapy (EBRT) for prostate cancer (PCa) with a predictive correlation between the dose-volume histogram (DVH) and rectal toxicity.

METHODS

In a pre-study, the planning CT scans of 23 patients with PCa receiving definitive EBRT were analyzed. The rectum was contoured according to 13 different definitions, and the dose distribution was correlated with the respective rectal volumes by generating DVH curves. Three definitions were identified to represent the most distinct differences in the shapes of the DVH curves: one anatomical definition recommended by the Radiation Therapy Oncology Group (RTOG) and two functional definitions based on the target volume. In the main study, the correlation between different relative DVH parameters derived from these three contouring definitions and the occurrence of rectal toxicity during and after EBRT was studied in two consecutive collectives. The first cohort consisted of 97 patients receiving primary curative EBRT and the second cohort consisted of 66 patients treated for biochemical recurrence after prostatectomy. Rectal toxicity was investigated by clinical investigation and scored according to the Common Terminology Criteria for Adverse Events. Candidate parameters were the volume of the rectum, mean dose, maximal dose, volume receiving at least 60 Gy (V₆₀), area under the DVH curve up to 25 Gy and area under the DVH curve up to 75 Gy in dependence of each chosen rectum definition. Multivariable logistic regression considered other clinical factors such as pelvine lymphatics vs local target volume, diabetes, prior rectal surgery, anticoagulation or haemorrhoids too.

RESULTS

In Cohort 1 (primary EBRT), the mean rectal volumes for definitions "RTOG", planning target volume "(PTV)-based" and "PTV-linked" were 100 cm³ [standard deviation (SD) 43 cm³], 60 cm³ (SD 26 cm³) and 74 cm³ (SD 31 cm³), respectively (p < 0.01; analysis of variance). The mean rectal doses according to these definitions were 35 Gy (SD 8 Gy), 48 Gy (SD 4 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). In Cohort 2 (salvage EBRT), the mean rectal volumes were 114 cm³ (SD 47 cm³), 64 cm³ (SD 26 cm³) and 81 cm³ (SD 30 cm³) (p < 0.01) and the mean doses received by the rectum were 36 Gy (SD 8 Gy), 49 Gy (SD 5 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). Acute or subacute rectal inflammation occurred in 69 (71.9%) patients in Cohort 1 and in 43 (70.5%) in Cohort 2. We did not find a correlation between all investigated DVH parameters and rectal toxicity, irrespective of the investigated definition. By adding additional variables in multivariate analysis, the predictive ability was substantially improved. Still, there was essentially no difference in the probability of predicting rectal inflammation occurrence between the tested contouring definitions.

CONCLUSION

The RTOG anatomy-based recommendations are questionable in comparison with functional definitions, as they result in higher variances in several relative DVH parameters. Moreover, the anatomy-based definition is no better and no worse in the predictive value concerning clinical end points. Advances in knowledge: Functional definitions for the rectum as OAR are easier to apply, faster to contour, have smaller variances and do not offer less information than the anatomy-based RTOG definition.

Uncertainties in volume delineation in radiation oncology: A systematic review and recommendations for future studies

BACKGROUND AND PURPOSE

Volume delineation is a well-recognised potential source of error in radiotherapy. Whilst it is important to quantify the degree of interobserver variability (IOV) in volume delineation, the resulting impact on dosimetry and clinical outcomes is a more relevant endpoint. We performed a literature review of studies evaluating IOV in target volume and organ-at-risk (OAR) delineation in order to analyse these with respect to the metrics used, reporting of dosimetric consequences, and use of statistical tests.

METHODS AND MATERIALS

Medline and Pubmed databases were queried for relevant articles using keywords. We included studies published in English between 2000 and 2014 with more than two observers.

RESULTS

119 studies were identified covering all major tumour sites. CTV (n=47) and GTV (n=38) were most commonly contoured. Median number of participants and data sets were 7 (3-50) and 9 (1-132) respectively. There was considerable heterogeneity in the use of metrics and methods of analysis. Statistical analysis of results was reported in 68% (n=81) and dosimetric consequences in 21% (n=25) of studies.

CONCLUSION

There is a lack of consistency in conducting and reporting analyses from IOV studies. We suggest a framework to use for future studies evaluating IOV.

A pan-Canadian survey of peer review practices in radiation oncology

PURPOSE

Peer review (PR) of treatment plans has been recognized internationally as a key component of quality care in radiation oncology programs (ROPs). We conducted a survey of Canadian ROPs to describe current PR practices and identify barriers/facilitators to PR optimization.

METHODS AND MATERIALS

A 42-item e-survey was sent to all Canadian ROPs (n = 44). Survey development was guided by expert consensus, literature review, and existing guidelines. One multidisciplinary response per ROP was requested.

RESULTS

Response rate was 100.0% (44/44). All ROPs (100.0%) reported conducting some PR and rated its importance as 7/10 or higher (10 = extremely important). One-half of ROPs (52.3%) peer-reviewed >80% of curative treatment plans. ROPs reported performing PR "always/almost always" pretreatment (38.6%) or before 25% of radiation therapy delivery (52.3%). The majority of ROPs reported recommending major plan changes in <5% of plans (88.6%) and documenting findings in the medical record (58.1%). Barriers to PR were radiation oncologist availability (34.1%) and time constraints (27.3%). Facilitators included development of PR standards (97.7%) and education/support (90.9%).

CONCLUSIONS

The ROPs perceive PR as highly important, but substantial variation in the extent, timing, and documentation of PR exists. The understanding of current PR activities, barriers, and facilitators will inform the development of initiatives to optimize PR in radiation oncology.

A teaching intervention in a contouring dummy run improved target volume delineation in locally advanced non-small cell lung cancer: Reducing the interobserver variability in multicentre clinical studies

INTRODUCTION

Interobserver variability in the definition of target volumes (TVs) is a well-known confounding factor in (multicentre) clinical studies employing radiotherapy. Therefore, detailed contouring guidelines are provided in the prospective randomised multicentre PET-Plan (NCT00697333) clinical trial protocol. This trial compares strictly FDG-PET-based TV delineation with conventional TV delineation in patients with locally advanced non-small cell lung cancer (NSCLC). Despite detailed contouring guidelines, their interpretation by different radiation oncologists can vary considerably, leading to undesirable discrepancies in TV delineation. Considering this, as part of the PET-Plan study quality assurance (QA), a contouring dummy run (DR) consisting of two phases was performed to analyse the interobserver variability before and after teaching.

MATERIALS AND METHODS

In the first phase of the DR (DR1), radiation oncologists from 14 study centres were asked to delineate TVs as defined by the study protocol (gross TV, GTV; and two clinical TVs, CTV-A and CTV-B) in a test patient. A teaching session was held at a study group meeting, including a discussion of the results focussing on discordances in comparison to the per-protocol solution. Subsequently, the second phase of the DR (DR2) was performed in order to evaluate the impact of teaching.

RESULTS

Teaching after DR1 resulted in a reduction of absolute TVs in DR2, as well as in better concordance of TVs. The Overall Kappa(κ) indices increased from 0.63 to 0.71 (GTV), 0.60 to 0.65 (CTV-A) and from 0.59 to 0.63 (CTV-B), demonstrating improvements in overall interobserver agreement.

CONCLUSION

Contouring DRs and study group meetings as part of QA in multicentre clinical trials help to identify misinterpretations of per-protocol TV delineation. Teaching the correct interpretation of protocol contouring guidelines leads to a reduction in interobserver variability and to more consistent contouring, which should consequently improve the validity of the overall study results.

Predictors of breast radiotherapy plan modifications: quality assurance rounds in a large cancer centre

BACKGROUND AND PURPOSE

This study describes the process and outcomes of breast radiotherapy (RT) quality assurance (QA) rounds, seeking to identify variables associated with plan modifications.

MATERIALS AND METHODS

Real-time data were prospectively collected over 2 years. Descriptive statistics determined the proportion of cases requiring no (A), minor (B), or major (C) modifications, which were then subjected to univariate and multivariate analyses.

RESULTS

A total of 2223 breast cancer QA cases were reviewed; 47 cases (2.1%) underwent a minor, and 52 cases (2.3%) required a major modification. Common changes included boost, volume, seroma, and bolus. On univariate analysis, regional nodal irradiation (RNI), tumour size, and axillary node dissection were significantly associated with major modifications. Upon multivariate analysis, the only independent predictor was RNI (OR 2.12, p=0.0075). For patients with no RNI, <2 cm tumours, no axillary lymph node dissection, and no boosts (n=420); the likelihood of category C was only 1.4%.

CONCLUSIONS

It is feasible to conduct QA review for all breast cancer cases prior to commencing RT. Patients undergoing RNI had a higher likelihood of plan modifications; a group with low risk of modification was identified, which could direct future re-structuring of QA rounds.

Contouring variations and the role of atlas in non-small cell lung cancer radiation therapy: Analysis of a multi-institutional preclinical trial planning study

PURPOSE

To quantify variations in target and normal structure contouring and evaluate dosimetric impact of these variations in non-small cell lung cancer (NSCLC) cases. To study whether providing an atlas can reduce potential variation.

METHODS AND MATERIALS

Three NSCLC cases were distributed sequentially to multiple institutions for contouring and radiation therapy planning. No segmentation atlas was provided for the first 2 cases (Case 1 and Case 2). Contours were collected from submitted plans and consensus contour sets were generated. The volume variation among institution contours and the deviation of them from consensus contours were analyzed. The dose-volume histograms for individual institution plans were recalculated using consensus contours to quantify the dosimetric changes. An atlas containing targets and critical structures was constructed and was made available when the third case (Case 3) was distributed for planning. The contouring variability in the submitted plans of Case 3 was compared with that in first 2 cases.

RESULTS

Planning target volume (PTV) showed large variation among institutions. The PTV coverage in institutions' plans decreased dramatically when reevaluated using the consensus PTV contour. The PTV contouring consistency did not show improvement with atlas use in Case 3. For normal structures, lung contours presented very good agreement, while the brachial plexus showed the largest variation. The consistency of esophagus and heart contouring improved significantly (t test; P < .05) in Case 3. Major factors contributing to the contouring variation were identified through a survey questionnaire.

CONCLUSIONS

The amount of contouring variations in NSCLC cases was presented. Its impact on dosimetric parameters can be significant. The segmentation atlas improved the contour agreement for esophagus and heart, but not for the PTV in this study. Quality assurance of contouring is essential for a successful multi-institutional clinical trial.

Long term rectal function after high-dose prostatecancer radiotherapy: results from a prospective cohort study

PURPOSE

To prospectively evaluate long-term late rectal bleeding (lrb) and faecal incontinence (linc) after high-dose radiotherapy (RT) for prostate cancer in the AIROPROS 0102 population, and to assess clinical/dosimetric risk factors.

MATERIALS AND METHODS

Questionnaires of 515 patients with G0 baseline incontinence and bleeding scores (follow-up ≥6 years) were analysed. Correlations between lrb/linc and many clinical and dosimetric parameters were investigated by univariate and multivariate logistic analyses. The correlation between lrb/linc and symptoms during the first 3 years after RT was also investigated.

RESULTS

Of 515 patients lrb G1, G2 and G3 was found in 32 (6.1%), 2 (0.4%) and 3 (0.6%) patients while linc G1, G2 and G3 was detected in 50 (9.7%), 3 (0.6%) and 3 (0.6%), respectively. The prevalence of G2-G3 lrb events was significantly reduced compared to the first 3-years (1% vs 2.7%, p=0.016) ≥G1 lrb was significantly associated with V75 Gy (OR=1.07). In multivariate analysis, ≥G1 linc was associated with V40 Gy (OR=1.015), use of antihypertensive medication (OR=0.38), abdominal surgery before RT (OR=4.7), haemorrhoids (OR=2.6), and G2-G3 acute faecal incontinence (OR=4.4), a nomogram to predict the risk of long-term ≥G1 linc was proposed. Importantly, the prevalence of ≥G1 linc was significantly correlated with the mean incontinence score during the first 3 years after RT (OR=16.3).

CONCLUSIONS

Long-term (median: 7 years) rectal symptoms are prevalently mild and strongly correlated with moderate/severe events occurring in the first 3 years after RT. Linc was associated with several risk factors.

Which bowel preparation is best? Comparison of a high-fibre diet leaflet, daily microenema and no preparation in prostate cancer patients treated with radical radiotherapy to assess the effect on planned target volume shifts due to rectal distension

OBJECTIVE

We evaluated and compared a high-fibre diet leaflet, daily microenema and no preparation to establish how best to achieve consistent bowel preparation in prostate cancer patients being treated with radical radiotherapy.

METHODS

3 cohorts of 10 patients had different dietary interventions: no bowel preparation, high-fibre diet information leaflet and daily microenemas. The available cone beam CT (CBCT) scans of each patient were used to quantify interfractional changes in rectal distension (measured using average cross-sectional area-CSA), prostate shifts relative to bony anatomy compared with that at CT planning scan and rates of geometric miss (i.e. shifts of ≥5 mm). 85 CBCT scans were available in the pre-leaflet cohort, 89 scans in the post-leaflet, and 89 scans in the post-enema group.

RESULTS

Mean rectal CSA in the post-enema group was reduced compared with both pre-leaflet (p=0.010) and post-leaflet values (p=0.031). The magnitude of observed mean prostate shifts was significantly reduced in the post-enema group compared with the pre-leaflet group (p=0.014). The proportion of scans showing geometric miss (i.e. shift >5 mm) in the post-enema group (31%) was significantly lower than in the pre-leaflet (62%, p<0.001) or post-leaflet groups (56%, p<0.001).

CONCLUSION

This study indicates microenema to be an effective measure to achieve reduction in rectal CSA, prostate shift and reduce geometric miss of ≥5 mm. A further prospective randomised study is advocated to validate the results.

ADVANCES IN KNOWLEDGE

The use of microenema is effective in reducing prostate shift and rectal CSA, consequently decreasing the incidence of geographical miss.

Improving plan quality and consistency by standardization of dose constraints in prostate cancer patients treated with CyberKnife

Treatment plans for prostate cancer patients undergoing stereotactic body radiation therapy (SBRT) are often challenging due to the proximity of organs at risk. Today, there are no objective criteria to determine whether an optimal treatment plan has been achieved, and physicians rely on their personal experience to evaluate the plan's quality. In this study, we propose a method for determining rectal and bladder dose constraints achievable for a given patient's anatomy. We expect that this method will improve the overall plan quality and consistency, and facilitate comparison of clinical outcomes across different institutions. The 3D proximity of the organs at risk to the target is quantified by means of the expansion-intersection volume (EIV), which is defined as the intersection volume between the target and the organ at risk expanded by 5 mm. We determine a relationship between EIV and relevant dosimetric parameters, such as the volume of bladder and rectum receiving 75% of the prescription dose (V75%). This relationship can be used to establish institution-specific criteria to guide the treatment planning and evaluation process. A database of 25 prostate patients treated with CyberKnife SBRT is used to validate this approach. There is a linear correlation between EIV and V75% of bladder and rectum, confirming that the dose delivered to rectum and bladder increases with increasing extension and proximity of these organs to the target. This information can be used during the planning stage to facilitate the plan optimization process, and to standardize plan quality and consistency. We have developed a method for determining customized dose constraints for prostate patients treated with robotic SBRT. Although the results are technology specific and based on the experience of a single institution, we expect that the application of this method by other institutions will result in improved standardization of clinical practice.

A survey of radiation treatment planning peer-review activities in a provincial radiation oncology programme: current practice and future directions

OBJECTIVES

To describe current patterns of practice of radiation oncology peer review within a provincial cancer system, identifying barriers and facilitators to its use with the ultimate aim of process improvement.

DESIGN

A survey of radiation oncology programmes at provincial cancer centres.

SETTING

All cancer centres within the province of Ontario, Canada (n=14). These are community-based outpatient facilities overseen by Cancer Care Ontario, the provincial cancer agency.

PARTICIPANTS

A delegate from each radiation oncology programme filled out a single survey based on input from their multidisciplinary team.

OUTCOME MEASURES

Rated importance of peer review; current utilisation; format of the peer-review process; organisation and timing; case attributes; outcomes of the peer-review process and perceived barriers and facilitators to expanding peer-review processes.

RESULTS

14 (100%) centres responded. All rated the importance of peer review as at least 8/10 (10=extremely important). Detection of medical error and improvement of planning processes were the highest rated perceived benefits of peer review (each median 9/10). Six centres (43%) reviewed at least 50% of curative cases; four of these centres (29%) conducted peer review in more than 80% of cases treated with curative intent. Fewer than 20% of cases treated with palliative intent were reviewed in most centres. Five centres (36%) reported usually conducting peer review prior to the initiation of treatment. Five centres (36%) recorded the outcomes of peer review on the medical record. Thirteen centres (93%) planned to expand peer-review activities; a critical mass of radiation oncologists was the most important limiting factor (median 6/10).

CONCLUSIONS

Radiation oncology peer-review practices can vary even within a cancer system with provincial oversight. The application of guidelines and standards for peer-review processes, and monitoring of implementation and outcomes, will require effective knowledge translation activities.

Dosimetric impact of inter-observer variability for 3D conformal radiotherapy and volumetric modulated arc therapy: the rectal tumor target definition case

Background

To assess the dosimetric effect induced by inter-observer variability in target definition for 3D-conformal RT (3DCRT) and volumetric modulated arc therapy by RapidArc (RA) techniques for rectal cancer treatment.

Methods

Ten patients with rectal cancer subjected to neo-adjuvant RT were randomly selected from the internal database. Four radiation oncologists independently contoured the clinical target volume (CTV) in blind mode. Planning target volume (PTV) was defined as CTV + 7 mm in the three directions. Afterwards, shared guidelines between radiation oncologists were introduced to give general criteria for the contouring of rectal target and the four radiation oncologists defined new CTV following the guidelines. For each patient, six intersections (I) and unions (U) volumes were calculated coupling the contours of the various oncologists. This was repeated for the contours drawn after the guidelines. Agreement Index (AI = I/U) was calculated pre and post guidelines. Two RT plans (one with 3DCRT technique using 3–4 fields and one with RA using a single modulated arc) were optimized on each radiation oncologist’s PTV. For each plan the PTV volume receiving at least 95% of the prescribed dose (PTV V95%) was calculated for both target and non-target PTVs.

Results

The inter-operator AI pre-guidelines was 0.57 and was increased up to 0.69 post-guidelines. The maximum volume difference between the various CTV couples, drawn for each patient, passed from 380 ± 147 cm³ to 137 ± 83 cm³ after the introduction of guidelines. The mean percentage for the non-target PTV V95% was 93.7 ± 9.2% before and 96.6 ± 4.9%after the introduction of guidelines for the 3DCRT, for RA the increase was more relevant, passing from 86.5 ± 13.8% (pre) to 94.5 ± 7.5% (post). The OARs were maximally spared with VMAT technique while the variability between pre and post guidelines was not relevant in both techniques.

Conclusions

The contouring inter-observer variability has dosimetric effects in the PTV coverage. The introduction of guidelines increases the dosimetric consistency for both techniques, with greater improvements for RA technique.

A system for continual quality improvement of normal tissue delineation for radiation therapy treatment planning

PURPOSE

To implement the "plan-do-check-act" (PDCA) cycle for the continual quality improvement of normal tissue contours used for radiation therapy treatment planning.

METHODS AND MATERIALS

The CT scans of patients treated for tumors of the brain, head and neck, thorax, pancreas and prostate were selected for this study. For each scan, a radiation oncologist and a diagnostic radiologist, outlined the normal tissues ("gold" contours) using Radiation Therapy Oncology Group (RTOG) guidelines. A total of 30 organs were delineated. Independently, 5 board-certified dosimetrists and 1 trainee then outlined the same organs. Metrics used to compare the agreement between the dosimetrists' contours and the gold contours included the Dice Similarity Coefficient (DSC), and a penalty function using distance to agreement. Based on these scores, dosimetrists were re-trained on those organs in which they did not receive a passing score, and they were subsequently re-tested.

RESULTS

Passing scores were achieved on 19 of 30 organs evaluated. These scores were correlated to organ volume. For organ volumes <8 cc, the average DSC was 0.61 vs organ volumes ≥8 cc, for which the average DSC was 0.91 (P=.005). Normal tissues that had the lowest scores included the lenses, optic nerves, chiasm, cochlea, and esophagus. Of the 11 organs that were considered for re-testing, 10 showed improvement in the average score, and statistically significant improvement was noted in more than half of these organs after education and re-assessment.

CONCLUSIONS

The results of this study indicate the feasibility of applying the PDCA cycle to assess competence in the delineation of individual organs, and to identify areas for improvement. With testing, guidance, and re-evaluation, contouring consistency can be obtained across multiple dosimetrists. Our expectation is that continual quality improvement using the PDCA approach will ensure more accurate treatments and dose assessment in radiotherapy treatment planning and delivery.

Characterisation of rectal motion during neo-adjuvant radiochemotherapy for rectal cancer with image-guided tomotherapy: implications for adaptive dose escalation strategies

BACKGROUND

Interest in boosting the dose to the tumour during neo-adjuvant radiochemotherapy for rectal cancer is ever increasing, especially within the frame of adaptive radiotherapy. Rectal motion remains a potentially important obstacle to the full exploitation of this approach and needs to be carefully investigated.

MATERIAL AND METHODS

The main purposes of this work were to: a) quantify rectal motion on all fractions of a treatment course; and b) assess margins for adaptive boosting in the second part of the treatment in order to benefit of tumour reduction during treatment. Ten consecutive patients treated with image-guided tomotherapy (41.4 Gy, 18 fractions) were selected. The cranial half of the rectum (subject to motion) was contoured by a single observer on daily MVCTs. The variations of rectal volume and of the envelope of rectum positions were investigated (169 MVCTs). The impact of applying different margins to the rectum in including all its possible positions was also investigated when considering the planning kVCT, the first fraction MVCT, the half-treatment MVCT or the median rectal contours of the whole or second half of treatment as reference volumes.

RESULTS

Rectal volume reduced during treatment in all patients, with a significant time-trend in 6/10 patients. The median values of the envelope volumes were 129 cm(3) and 87 cm(3) in the first and second half of the treatment, respectively. On average, 95% of the rectal envelope was included by an isotropic expansion of 12 mm and 5 mm of the median contours when considering the whole or the second half of the treatment, respectively.

CONCLUSION

A significant reduction of rectal volume was found in the second part of the treatment where rectal mobility was limited. As a consequence, relatively small margins may be used around the residual tumour volume when adaptive boost is delivered in the second half of the treatment.

Late rectal bleeding after 3D-CRT for prostate cancer: development of a neural-network-based predictive model

The aim of this study was to develop a model exploiting artificial neural networks (ANNs) to correlate dosimetric and clinical variables with late rectal bleeding in prostate cancer patients undergoing radical radiotherapy and to compare the ANN results with those of a standard logistic regression (LR) analysis. 718 men included in the AIROPROS 0102 trial were analyzed. This multicenter protocol was characterized by the prospective evaluation of rectal toxicity, with a minimum follow-up of 36 months. Radiotherapy doses were between 70 and 80 Gy. Information was recorded for comorbidity, previous abdominal surgery, use of drugs and hormonal therapy. For each patient, a rectal dose-volume histogram (DVH) of the whole treatment was recorded and the equivalent uniform dose (EUD) evaluated as an effective descriptor of the whole DVH. Late rectal bleeding of grade ≥ 2 was considered to define positive events in this study (52 of 718 patients). The overall population was split into training and verification sets, both of which were involved in model instruction, and a test set, used to evaluate the predictive power of the model with independent data. Fourfold cross-validation was also used to provide realistic results for the full dataset. The LR was performed on the same data. Five variables were selected to predict late rectal bleeding: EUD, abdominal surgery, presence of hemorrhoids, use of anticoagulants and androgen deprivation. Following a receiver operating characteristic analysis of the independent test set, the areas under the curves (AUCs) were 0.704 and 0.655 for ANN and LR, respectively. When evaluated with cross-validation, the AUC was 0.714 for ANN and 0.636 for LR, which differed at a significance level of p = 0.03. When a practical discrimination threshold was selected, ANN could classify data with sensitivity and specificity both equal to 68.0%, whereas these values were 61.5% for LR. These data provide reasonable evidence that results obtained with ANNs are superior to those achieved with LR when predicting late radiotherapy-related rectal bleeding. The future introduction of patient-related personal characteristics, such as gene expression profiles, might improve the predictive power of statistical classifiers. More refined morphological aspects of the dose distribution, such as dose surface mapping, might also enhance the overall performance of ANN-based predictive models.

Inter-observer variability in contouring the penile bulb on CT images for prostate cancer treatment planning

Several investigations have recently suggested the existence of a correlation between the dose received by the penile bulb (PB) and the risk of erectile dysfunction (ED) after radical radiotherapy for clinically localized prostate carcinoma. A prospective multi-Institute study (DUE-01) was implemented with the aim to assess the predictive parameters of ED. Previously, an evaluation of inter-observer variations of PB contouring was mandatory in order to quantify its impact on PB dose-volume parameters by means of a dummy run exercise. Fifteen observers, from different Institutes, drew the PB on the planning CT images of ten patients; inter-observer variations were analysed in terms of PB volume variation and cranial/caudal limits. 3DCRT treatment plans were simulated to evaluate the impact of PB contouring inter-variability on dose-volume statistics parameters. For DVH analysis the values of PB mean dose and the volume of PB receiving more than 50 Gy and 70 Gy (V50 and V70, respectively) were considered. Systematic differences from the average values were assessed by the Wilcoxon test. Seven observers systematically overestimated or underestimated the PB volume with deviations from the average volumes ranging between -48% and +34% (p < 0.05). The analysis of the cranial and caudal borders showed a prevalence of random over systematic deviations. Inter-observer contouring variability strongly impacts on DVH parameters, although standard deviations of inter-patient differences were larger than inter-observer variations: 14.5 Gy versus 6.8 Gy for mean PB dose, 23.0% versus 11.0% and 16.8% versus 9.3% for V50 and V70 respectively. In conclusion, despite the large inter-observer variation in contouring PB, a large multi-centric study may have the possibility to detect a possible correlation between PB % dose-volume parameters and ED. The impact of contouring uncertainty could be reduced by "a posteriori" contouring from a single observer or by introducing Magnetic Resonance Imaging (MRI) in the planning procedures and/or in improving the skill of observers through post-dummy run tutoring of those observers showing large systematic deviations from the mean.

Is it time to tailor the prediction of radio-induced toxicity in prostate cancer patients? Building the first set of nomograms for late rectal syndrome

PURPOSE

Development of user-friendly tools for the prediction of single-patient probability of late rectal toxicity after conformal radiotherapy for prostate cancer.

METHODS AND MATERIALS

This multicenter protocol was characterized by the prospective evaluation of rectal toxicity through self-assessed questionnaires (minimum follow-up, 36 months) by 718 adult men in the AIROPROS 0102 trial. Doses were between 70 and 80 Gy. Nomograms were created based on multivariable logistic regression analysis. Three endpoints were considered: G2 to G3 late rectal bleeding (52/718 events), G3 late rectal bleeding (24/718 events), and G2 to G3 late fecal incontinence (LINC, 19/718 events).

RESULTS

Inputs for the nomogram for G2 to G3 late rectal bleeding estimation were as follows: presence of abdominal surgery before RT, percentage volume of rectum receiving >75 Gy (V75Gy), and nomogram-based estimation of the probability of G2 to G3 acute gastrointestinal toxicity (continuous variable, which was estimated using a previously published nomogram). G3 late rectal bleeding estimation was based on abdominal surgery before RT, V75Gy, and NOMACU. Prediction of G2 to G3 late fecal incontinence was based on abdominal surgery before RT, presence of hemorrhoids, use of antihypertensive medications (protective factor), and percentage volume of rectum receiving >40 Gy.

CONCLUSIONS

We developed and internally validated the first set of nomograms available in the literature for the prediction of radio-induced toxicity in prostate cancer patients. Calculations included dosimetric as well as clinical variables to help radiation oncologists predict late rectal morbidity, thus introducing the possibility of RT plan corrections to better tailor treatment to the patient's characteristics, to avoid unnecessary worsening of quality of life, and to provide support to the patient in selecting the best therapeutic approach.

A review of methods of analysis in contouring studies for radiation oncology

Inter-observer variability in anatomical contouring is the biggest contributor to uncertainty in radiation treatment planning. Contouring studies are frequently performed to investigate the differences between multiple contours on common datasets. There is, however, no widely accepted method for contour comparisons. The purpose of this study is to review the literature on contouring studies in the context of radiation oncology, with particular consideration of the contouring comparison methods they employ. A literature search, not limited by date, was conducted using Medline and Google Scholar with key words: contour, variation, delineation, inter/intra observer, uncertainty and trial dummy-run. This review includes a description of the contouring processes and contour comparison metrics used. The use of different processes and metrics according to tumour site and other factors were also investigated with limitations described. A total of 69 relevant studies were identified. The most common tumour sites were prostate (26), lung (10), head and neck cancers (8) and breast (7).The most common metric of comparison was volume used 59 times, followed by dimension and shape used 36 times, and centre of volume used 19 times. Of all 69 publications, 67 used a combination of metrics and two used only one metric for comparison. No clear relationships between tumour site or any other factors that may influence the contouring process and the metrics used to compare contours were observed from the literature. Further studies are needed to assess the advantages and disadvantages of each metric in various situations.

Feasibility of CBCT-based target and normal structure delineation in prostate cancer radiotherapy: multi-observer and image multi-modality study

BACKGROUND AND PURPOSE

In-room cone-beam CT (CBCT) imaging and adaptive treatment strategies are promising methods to decrease target volumes and to spare organs at risk. The aim of this work was to analyze the inter-observer contouring uncertainties of target volumes and organs at risks (oars) in localized prostate cancer radiotherapy using CBCT images. Furthermore, CBCT contouring was benchmarked against other image modalities (CT, MR) and the influence of subjective image quality perception on inter-observer variability was assessed.

METHODS AND MATERIALS

Eight prostate cancer patients were selected. Seven radiation oncologists contoured target volumes and oars on CT, MRI and CBCT. Volumes, coefficient of variation (COV), conformity index (cigen), and coordinates of center-of-mass (COM) were calculated for each patient and image modality. Reliability analysis was performed for the support of the reported findings. Subjective perception of image quality was assessed via a ten-scored visual analog scale (VAS).

RESULTS

The median volume for prostate was larger on CT compared to MRI and CBCT images. The inter-observer variation for prostate was larger on CBCT (CIgen=0.57±0.09, 0.61 reliability) compared to CT (CIgen=0.72±0.07, 0.83 reliability) and MRI (CIgen=0.66±0.12, 0.87 reliability). On all image modalities values of the intra-observer reliability coefficient (0.97 for CT, 0.99 for MR and 0.94 for CBCT) indicated high reproducibility of results. For all patients the root mean square (RMS) of the inter-observer standard deviation (σ) of the COM was largest on CBCT with σ(x)=0.4 mm, σ(y)=1.1 mm, and σ(z)=1.7 mm. The concordance in delineating OARs was much stronger than for target volumes, with average CIgen>0.70 for rectum and CIgen>0.80 for bladder. Positive correlations between CIgen and VAS score of the image quality were observed for the prostate, seminal vesicles and rectum.

CONCLUSIONS

Inter-observer variability for target volume delineation in prostate cancer is larger for CBCT-based contouring compared to CT and MRI. This factor of influence needs to be considered when defining safety margins for CBCT-based Adaptive Radiotherapy (ART).

Prospective randomized double-blind pilot study of site-specific consensus atlas implementation for rectal cancer target volume delineation in the cooperative group setting

PURPOSE

Variations in target volume delineation represent a significant hurdle in clinical trials involving conformal radiotherapy. We sought to determine the effect of a consensus guideline-based visual atlas on contouring the target volumes.

METHODS AND MATERIALS

A representative case was contoured (Scan 1) by 14 physician observers and a reference expert with and without target volume delineation instructions derived from a proposed rectal cancer clinical trial involving conformal radiotherapy. The gross tumor volume (GTV), and two clinical target volumes (CTVA, including the internal iliac, presacral, and perirectal nodes, and CTVB, which included the external iliac nodes) were contoured. The observers were randomly assigned to receipt (Group A) or nonreceipt (Group B) of a consensus guideline and atlas for anorectal cancers and then instructed to recontour the same case/images (Scan 2). Observer variation was analyzed volumetrically using the conformation number (CN, where CN = 1 equals total agreement).

RESULTS

Of 14 evaluable contour sets (1 expert and 7 Group A and 6 Group B observers), greater agreement was found for the GTV (mean CN, 0.75) than for the CTVs (mean CN, 0.46-0.65). Atlas exposure for Group A led to significantly increased interobserver agreement for CTVA (mean initial CN, 0.68, after atlas use, 0.76; p = .03) and increased agreement with the expert reference (initial mean CN, 0.58; after atlas use, 0.69; p = .02). For the GTV and CTVB, neither the interobserver nor the expert agreement was altered after atlas exposure.

CONCLUSION

Consensus guideline atlas implementation resulted in a detectable difference in interobserver agreement and a greater approximation of expert volumes for the CTVA but not for the GTV or CTVB in the specified case. Visual atlas inclusion should be considered as a feature in future clinical trials incorporating conformal RT.

Variations in target volume definition for postoperative radiotherapy in stage III non-small-cell lung cancer: analysis of an international contouring study

PURPOSE

Postoperative radiotherapy (PORT) in patients with completely resected non-small-cell lung cancer with mediastinal involvement is controversial because of the failure of earlier trials to demonstrate a survival benefit. Improved techniques may reduce toxicity, but the treatment fields used in routine practice have not been well studied. We studied routine target volumes used by international experts and evaluated the impact of a contouring protocol developed for a new prospective study, the Lung Adjuvant Radiotherapy Trial (Lung ART).

METHODS AND MATERIALS

Seventeen thoracic radiation oncologists were invited to contour their routine clinical target volumes (CTV) for 2 representative patients using a validated CD-ROM-based contouring program. Subsequently, the Lung ART study protocol was provided, and both cases were contoured again. Variations in target volumes and their dosimetric impact were analyzed.

RESULTS

Routine CTVs were received for each case from 10 clinicians, whereas six provided both routine and protocol CTVs for each case. Routine CTVs varied up to threefold between clinicians, but use of the Lung ART protocol significantly decreased variations. Routine CTVs in a postlobectomy patient resulted in V(20) values ranging from 12.7% to 54.0%, and Lung ART protocol CTVs resulted in values of 20.6% to 29.2%. Similar results were seen for other toxicity parameters and in the postpneumectomy patient. With the exception of upper paratracheal nodes, protocol contouring improved coverage of the required nodal stations.

CONCLUSION

Even among experts, significant interclinician variations are observed in PORT fields. Inasmuch as contouring variations can confound the interpretation of PORT results, mandatory quality assurance procedures have been incorporated into the current Lung ART study.

Broadening the scope of image-guided radiotherapy (IGRT)

The recent wave of enthusiasm for image guidance in radiation therapy is largely due to the advent of on-line imaging devices. The current narrow definition of image-guided radiotherapy (IGRT), in fact, essentially connotes the use of near real-time imaging during treatment delivery to reduce uncertainties in target position and should therefore be termed IGRT-D. However, a broader (and more appropriate) context of image-guidance should include: (1) detection and diagnosis, (2) delineation of target and organs at risk, (3) determining biological attributes, (4) dose distribution design, (5) dose delivery assurance and (6) deciphering treatment response through imaging i.e. the 6 D's of IGRT. Strategies to advance these areas will be discussed.

Clinical and Dosimetric Predictors of Late Rectal Syndrome After 3D-CRT for Localized Prostate Cancer: Preliminary Results of a Multicenter Prospective Study

PURPOSE

To assess the predictors of late rectal toxicity in a prospectively investigated group of patients treated at 70-80 Gy for prostate cancer (1.8-2 Gy fractions) with three-dimensional conformal radiotherapy.

METHODS AND MATERIALS

A total of 1,132 patients were entered into the study between 2002 and 2004. Three types of rectal toxicity, evaluated by a self-administered questionnaire, mainly based on the subjective objective management, analytic late effects of normal tissue system, were considered: stool frequency/tenesmus/pain, fecal incontinence, and bleeding. The data from 506 patients with a follow-up of 24 months were analyzed. The correlation between a number of clinical and dosimetric parameters and Grade 2 or greater toxicity was investigated by univariate and multivariate (MVA) logistic analyses.

RESULTS

Of the 1,132 patients, 21, 15, and 30 developed stool frequency/tenesmus/pain, fecal incontinence, and bleeding, respectively. Stool frequency/tenesmus/pain correlated with previous abdominal/pelvic surgery (MVA, p=0.05, odds ratio [OR], 3.3). With regard to incontinence, MVA showed the volume receiving>or=40 Gy (V40) (p=0.035, OR, 1.037) and surgery (p=0.02, OR, 4.4) to be the strongest predictors. V40 to V70 were highly predictive of bleeding; V70 showed the strongest impact on MVA (p=0.03), together with surgery (p=0.06, OR, 2.5), which was also the main predictor of Grade 3 bleeding (p=0.02, OR, 4.2).

CONCLUSIONS

The predictive value of the dose-volume histogram was confirmed for bleeding, consistent with previously suggested constraints (V50<55%, V60<40%, V70<25%, and V75<5%). A dose-volume histogram constraint for incontinence can be suggested (V40<65-70%). Previous abdominal/pelvic surgery correlated with all toxicity types; thus, a modified constraint for bleeding (V70<15%) can be suggested for patients with a history of abdominal/pelvis surgery, although further validation on a larger population with longer follow-up is needed.