Quality assurance of radiotherapy in the ongoing EORTC 1420 "Best of" trial for early stage oropharyngeal, supraglottic and hypopharyngeal carcinoma: results of the benchmark case procedure

INTRODUCTION

The current phase III EORTC 1420 Best-of trial (NCT02984410) compares the swallowing function after transoral surgery versus intensity modulated radiotherapy (RT) in patients with early-stage carcinoma of the oropharynx, supraglottis and hypopharynx. We report the analysis of the Benchmark Case (BC) procedures before patient recruitment with special attention to dysphagia/aspiration related structures (DARS).

MATERIALS AND METHODS

Submitted RT volumes and plans from participating centers were analyzed and compared against the gold-standard expert delineations and dose distributions. Descriptive analysis of protocol deviations was conducted. Mean Sorensen-Dice similarity index (mDSI) and Hausdorff distance (mHD) were applied to evaluate the inter-observer variability (IOV).

RESULTS

65% (23/35) of the institutions needed more than one submission to achieve Quality assurance (RTQA) clearance. OAR volume delineations were the cause for rejection in 53% (40/76) of cases. IOV could be improved in 5 out of 12 OARs by more than 10 mm after resubmission (mHD). Despite this, final IOV for critical OARs in delineation remained significant among DARS by choosing an aleatory threshold of 0.7 (mDSI) and 15 mm (mHD).

CONCLUSIONS

This is to our knowledge the largest BC analysis among Head and neck RTQA programs performed in the framework of a prospective trial. Benchmarking identified non-common OARs and target delineations errors as the main source of deviations and IOV could be reduced in a significant number of cases after this process. Due to the substantial resources involved with benchmarking, future benchmark analyses should assess fully the impact on patients' clinical outcome.

Sequential 18F-FDG PET/CT imaging parameters for differentiating benign from malignant lymph nodes in head and neck carcinoma

OBJECTIVE

The aim of this study was to differentiate between benign and malignant head and neck lymph nodes by sequential imaging.

SUBJECTS AND METHODS

The total of 56 retrospectively analysed patients with suspected or histopathologically confirmed head and neck malignancy (nasopharyngeal cancers mainly; 28 patients), before any treatment, underwent sequential fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) examinations for staging purposes. Remaining 28 patients with physiologic and histopathologically confirmed inflammatory (of non-specified origin) lymph nodes were included into this analysis. Patients underwent sequential PET/CT scans 60 and 90min post injection (p.i.) of the ¹⁸F-FDG. Semi-quantitative analysis of metabolic activity within lymph nodes was based on the standardized uptake value (SUV) evaluation. To compare the metabolic activity fluctuation over time, the retention index (RI) was used. For SUV value and RI cut-off evaluation, the receiver operating characteristic (ROC) analysis was performed.

RESULTS

The SUVmax value at 60min p.i. of physiologic, inflammatory and malignant (metastatic) lymph nodes were 1.09±0.33, 2.36±0.60 and 6.31±2.74, respectively. The SUVmax value at 90min p.i. were: 1.01±0.32, 2.48±0.61, and 7.17±2.91, respectively, and there was statistically significant difference between physiologic and inflammatory and physiologic and the metastatic lymph nodes (P<0.001). The values of early and delayed SUVmax were significantly different between physiologic and inflammatory and physiologic and metastatic lymph nodes (P<0.001). The SUVmax, SUVmean values at 60 and at 90min p.i. between malignant and inflammatory lymph nodes were statistically insignificant (P=0.33). The RI at 60 and at 90min p.i. was: -6%±16% for physiologic, 6%±14% for inflammatory and 15%±13% for the metastatic lymph nodes. The SUVmax changes over time (the RI) were statistically significant for physiologic and metastatic and physiologic and inflammatory lymph nodes (P<0.001) and significant between malignant and inflammatory lymph nodes (P=0.02).

CONCLUSION

Sequential delayed ¹⁸F-FDG PET/CT examinations may increase specificity of this scan and provide information for the differentiation benign and malignant lymph nodes in the cases of head and neck cancer.

Impact of the Intra- and Inter-observer Variability in the Delineation of Parotid Glands on the Dose Calculation During Head and Neck Helical Tomotherapy

The intra- and inter-observer variability in delineation of the parotids on the kilo-voltage computed tomography (kVCT) and mega-voltage computed tomography (MVCT) were examined to establish their impact on the dose calculation during adaptive head and neck helical tomotherapy (HT). Three observers delineated left and right parotids for ten randomly selected patients with oropharynx cancer treated on HT. The pre-treatment kVCT and the MVCT from the first fraction of irradiation were selected to delineation. The delineation procedure was repeated three times by each observer. The parotids were delineated according to the institutional protocol. The analyses included intra-observer reproducibility and inter-structure, -observer and -modality variability of the volume and dose. The differences between the left and right parotid outlines were not statistically significant (p > 0.3). The reproducibility of the delineation was confirmed for each observer on the kVCT (p > 0.2) and on the MVCT (p > 0.1). The inter-observer variability of the outlines was significant (p < 0.001) as well as the inter-modality variability (p < 0.006). The parotids delineated on the MVCT were 10% smaller than on the kVCT. The inter-observer variability of the parotids delineation did not affect the average dose (p = 0.096 on the kVCT and p = 0.176 on the MVCT). The dose calculated on the MVCT was higher by 3.3% than dose from the kVCT (p = 0.009). Usage of the institutional protocols for the parotids delineation reduces intra-observer variability and increases reproducibility of the outlines. These protocols do not eliminate delineation differences between the observers, but these differences are not clinically significant and do not affect average doses in the parotids. The volumes of the parotids delineated on the MVCT are smaller than on the kVCT, which affects the differences in the calculated doses.

Tomotherapy: implications on daily workload and scheduling patients based on three years' institutional experience

Helical tomotherapy (HT) was introduced at the Greater Poland Cancer Centre (GPCC) in April 2009. Retrospective analysis included data from the treatments performed for the first 656 patients treated with HT between May 2009 and May 2012 at the GPCC. In order to evaluate the implications on daily workload and scheduling of patients, stepwise regression and time analysis for each component of the overall treatment time, such as positioning, imaging, registration, and irradiation were performed. A detailed analysis included: (1) learning curves and optimized time needed for positioning and registration; (2) relation between irradiation time and parameters used for plan creation; and (3) average time of daily imaging. The irradiation component has the highest influence on the overall treatment time (R = 0.911). The lowest influence was observed for the imaging (R = 0.670). The learning curve for positioning was 7 months while the reduction of the average daily time needed for registration was observed even after two years. The irradiation time strongly depends on the planning parameters. Changing the pitch from 0.215 to 0.287 for pelvic cancer cases decreased the average daily beam-on time per patient by about 2 minutes. Similar changes for head and neck reduced this time by 1.3 minutes. The limitation in the usage of 1 cm field width only for complex cases, lower than 10 cm in the cranio-caudal direction, reduced the beam-on time per patient by 2 minutes. The average overall treatment time decreased from 21.5 minutes per patient in the first year of the HT usage to 13.8 minutes per patient in current practice. Our current practice shows that for a group of patients including mainly those with pelvis and head and neck cancers, the HT treatment takes approximately 15 minutes per patient allowing 40 patients to be treated within 10 hours.

B-Spline Registration Based on New Concept of an Intelligent Masking Procedure and GPU Computations for the Head and Neck Adaptive Tomotherapy

The deformable image registration (DIR) procedure has been optimized for helical tomotherapy. The data on registration shifts obtained on matching planning image with pre-treatment megavoltage CT are used in our software for acceleration of the first step (rigid registration) of the DIR procedure and for implementation of the B-Spline algorithm with intelligent masking. Priorities of the masks were automatically calculated based on disagreement detected during rigid registration. Evaluation tasks included: (a) comparison of accuracy and rate for schemes of pre-registered and non-registered images; (b) qualification of the effectiveness of the intelligent masking process, and (c) determination of acceleration of achievable with GPU computing. A specially designed head and neck phantom used for evaluation included structures with controlled changes of position, volume, density, and shape. Re-contouring procedures were performed with an Adaptive Planning software (Tomotherapy Inc.). No statistical difference was observed in accuracy of DIR based on structure position match on the tomotherapy unit and non pre-registered images (p > 0.7). Using pre-registered data reduces the total time required for execution of the elastic registration procedure by 5%. These data are also necessary for intelligent masking procedure during B-Spine registration. Intelligent masking procedure increases accuracy of the registration for a masked structure (p < 0.04) without decreasing the accuracy in non-masked tissues and additionally reduces the total time by 13%. GPU computations speed up procedure 30 times. GPU computing of the DIR in current status of our investigation could be realized in a relatively short time after pre-treatment imaging. The proposed approach can be used in the routine assessment of anatomic changes occurring in healthy tissue during the course of radiotherapy. Further developments will be concentrated on the full integration of DIR computations in the imaging and treatment process of helical tomotherapy.