Inter- and intra-observer variation of patient setup shifts derived using the 4D TPUS Clarity system for prostate radiotherapy

Impact of transperineal ultrasound on perineal skin dose in prostate radiation therapy

Introduction

This study investigated the relationship between anatomical compression introduced via ultrasound probe pressure and maximum perineum dose in prostate radiotherapy patients using the Clarity transperineal ultrasound (TPUS) system.

Methods

115 patient ultrasound and computed tomography scans were retrospectively analysed. The probe to prostate apex distance (PPA), probe to inferior corpus spongiosum distance (PICS) and maximum perineum dose were calculated. Compression was represented by the PICS and the calculated corpus to prostate ratio (CPR). Demographics included treatment technique, image quality, body mass index (BMI) and age. Multiple linear regression analysis assessed the relationship between compression measures and perineum dose.

Results

The maximum dose to perineum ranged from 1.81 to 45.56 Gy, with a median of 5.87 Gy (Interquartile range (IQR) 3.17). The PICS distance and CPR recorded was 1.67 cm (IQR 0.63) and 0.51 (range 0.29-0.85) respectively. Regression analysis demonstrated both PICS and CPR were significant predictors of maximum dose to the perineum (p < 0.001). Patient-specific factors, including age, BMI, treatment technique and ultrasound image quality, were not factors that significantly impacted the maximum perineum dose.

Conclusion

There was a statistically significant association between increased anatomical compression and perineal dose measurements. A PICS of 1.2 cm or greater is recommended, with compression reduced as much as possible without losing anatomical US definition. Future investigations would be beneficial to evaluate the optimal balance between ultrasound image quality and transducer compression considering the perineum dose.

Men's preferences for image-guidance in prostate radiation therapy: A discrete choice experiment

INTRODUCTION

There are several options for real-time prostate monitoring during radiation therapy including fiducial markers (FMs) and transperineal ultrasound (TPUS). However, the patient experience for these procedures is very different. This study aimed to determine patient preferences around various aspects of prostate image-guidance, focusing on FMs and TPUS.

METHODS

A discrete choice experiment (DCE) was conducted, describing the image-guidance approach by: pain, cost, accuracy, side effects, additional appointments, and additional time. Participants were males with prostate cancer (PCa) and from the general Australian population. A DCE survey required participants to make hypothetical choices in each of 8 choice sets. Multinomial logit modelling and Latent Class Analysis (LCA) were used to analyse the responses. Marginal willingness to pay (mWTP) was calculated.

RESULTS

476 respondents completed the survey (236 PCa patients and 240 general population). The most important attributes for both cohorts were pain, cost and accuracy (p < 0.01). PCa patients were willing to pay more to avoid the worst pain than the general population, and willing to pay more for increased accuracy. LCA revealed 3 groups: 2 were focused more on the process-related attributes of pain and cost, and the third was focused on the clinical efficacy attributes of accuracy and side effects.

CONCLUSION

Both cohorts preferred less cost and pain and improved accuracy, with men with PCa valuing accuracy more than the general population. In addition to the clinical and technical evidence, radiation oncology centres should consider the preferences of patients when considering choice of image-guidance techniques.

Technical considerations for positioning and placement of a transperineal ultrasound probe during prostate radiotherapy

This technical evaluation aims to provide practice 'how to' guidelines for radiation therapists (RTs) when positioning a transperineal ultrasound (TPUS) probe during prostate radiotherapy. Recommendations and practical tips will be provided for the best practice in TPUS-guided workflow to obtain optimal ultrasound images for accurate interpretation and registration of the prostate gland. This will assist the RTs in making consistent and accurate clinical decision in an ultrasound-guided radiotherapy workflow for prostate treatment. The implementation process and the associated successes and challenges will also be described to assist institutions who may be investigating the potential of implementing this system.

Factors affecting accuracy and precision in ultrasound guided radiotherapy

BACKGROUND AND PURPOSE

Transperineal ultrasound (TPUS) is used clinically for directly assessing prostate motion. Factors affecting accuracy and precision in TPUS motion estimation must be assessed to realise its full potential.

METHODS AND MATERIALS

Patients were imaged using volumetric TPUS during the Clarity-Pro trial (NCT02388308). Prostate motion was measured online at patient set-up and offline by experienced observers. Cone beam CT with markers was used as a comparator and observer performance was also quantified. The influence of different clinical factors was examined to establish specific recommendations towards efficacious ultrasound guided radiotherapy.

RESULTS

From 330 fractions in 22 patients, offline observer random errors were 1.5 mm, 1.3 mm, 1.9 mm (left-right, superior-inferior, anteroposterior respectively). Errors increased in fractions exhibiting poor image quality to 3.3 mm, 3.3 mm and 6.8 mm. Poor image quality was associated with inconsistent probe placement, large anatomical changes and unfavourable imaging conditions within the patient. Online matching exhibited increased observer errors of: 3.2 mm, 2.9 mm and 4.7 mm. Four patients exhibited large systematic residual errors, of which three had poor quality images. Patient habitus showed no correlation with observer error, residual error, or image quality.

CONCLUSIONS

TPUS offers the unique potential to directly assess inter- and intra-fraction motion on conventional linacs. Inconsistent image quality, inexperienced operators and the pressures of the clinical environment may degrade precision and accuracy. Experienced operators are essential and cross-centre standards for training and QA should be established that build upon current guidance. Greater use of automation technologies may further minimise uncertainties.

A deep learning framework for prostate localization in cone beam CT-guided radiotherapy

PURPOSE

To develop a deep learning-based model for prostate planning target volume (PTV) localization on cone beam computed tomography (CBCT) to improve the workflow of CBCT-guided patient setup.

METHODS

A two-step task-based residual network (T2 RN) is proposed to automatically identify inherent landmarks in prostate PTV. The input to the T2 RN is the pretreatment CBCT images of the patient, and the output is the deep learning-identified landmarks in the PTV. To ensure robust PTV localization, the T2 RN model is trained by using over thousand sets of CT images with labeled landmarks, each of the CTs corresponds to a different scenario of patient position and/or anatomy distribution generated by synthetically changing the planning CT (pCT) image. The changes, including translation, rotation, and deformation, represent vast possible clinical situations of anatomy variations during a course of radiation therapy (RT). The trained patient-specific T2 RN model is tested by using 240 CBCTs from six patients. The testing CBCTs consists of 120 original CBCTs and 120 synthetic CBCTs. The synthetic CBCTs are generated by applying rotation/translation transformations to each of the original CBCT.

RESULTS

The systematic/random setup errors between the model prediction and the reference are found to be <0.25/2.46 mm and 0.14/1.41° in translation and rotation dimensions, respectively. Pearson's correlation coefficient between model prediction and the reference is higher than 0.94 in translation and rotation dimensions. The Bland-Altman plots show good agreement between the two techniques.

CONCLUSIONS

A novel T2 RN deep learning technique is established to localize the prostate PTV for RT patient setup. Our results show that highly accurate marker-less prostate setup is achievable by leveraging the state-of-the-art deep learning strategy.

Analysis of intra-fraction prostate motion and derivation of duration-dependent margins for radiotherapy using real-time 4D ultrasound

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Investigates the magnitude of intra-fraction prostate motion using real time monitoring.

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A motion-time trend analysis was presented.

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A duration-dependent margin was recommended.

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Larger margins are required around the prostate in the inferior and posterior directions.

Background and purpose

During radiotherapy, prostate motion changes over time. Quantifying and accounting for this motion is essential. This study aimed to assess intra-fraction prostate motion and derive duration-dependent planning margins for two treatment techniques.

Material and methods

A four-dimension (4D) transperineal ultrasound Clarity® system was used to track prostate motion. We analysed 1913 fractions from 60 patients undergoing volumetric-modulated arc therapy (VMAT) to the prostate. The mean VMAT treatment duration was 3.4 min. Extended monitoring was conducted weekly to simulate motion during intensity-modulated radiation therapy (IMRT) treatment (an additional seven minutes). A motion-time trend analysis was conducted and the mean intra-fraction motion between VMAT and IMRT treatments compared. Duration-dependent margins were calculated and anisotropic margins for VMAT and IMRT treatments were derived.

Results

There were statistically significant differences in the mean intra-fraction motion between VMAT and the simulated IMRT duration in the inferior (0.1 mm versus 0.3 mm) and posterior (−0.2 versus −0.4 mm) directions respectively (p ≪ 0.01). An intra-fraction motion trend inferiorly and posteriorly was observed. The recommended minimum anisotropic margins are 1.7 mm/2.7 mm (superior/inferior); 0.8 mm (left/right), 1.7 mm/2.9 mm (anterior/posterior) for VMAT treatments and 2.9 mm/4.3 mm (superior/inferior), 1.5 mm (left/right), 2.8 mm/4.8 mm (anterior/posterior) for IMRT treatments. Smaller anisotropic margins were required for VMAT compared to IMRT (differences ranging from 1.2 to 1.6 mm superiorly/inferiorly, 0.7 mm laterally and 1.1–1.9 mm anteriorly/posteriorly).

Conclusions

VMAT treatment is preferred over IMRT as prostate motion increases with time. Larger margins should be employed in the inferior and posterior directions for both treatment durations. Duration-dependent margins should be applied in the presence of prolonged imaging and verification time.

Reduction of intra-fraction prostate motion - Determining optimal bladder volume and filling for prostate radiotherapy using daily 4D TPUS and CBCT

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An optimal bladder volume and filling protocol is proposed.

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The current hydration protocol was well-accepted and tolerated.

Background and purpose

Inconsistent bladder and rectal volumes have been associated with motion uncertainties during prostate radiotherapy. This study investigates the impact of these volumes to determine the optimal bladder volume.

Materials and methods

60 patients from two Asian hospitals were recruited prospectively. 1887 daily cone-beam computed tomography (CBCT) images were analysed. Intra-fraction motion of the prostate was monitored real-time using a four-dimension transperineal ultrasound (4D TPUS) Clarity® system. The impact of planned bladder volume, adequacy of daily bladder filling, and rectum volume on mean intra-fraction motion of the prostate was analysed. Patients’ ability to comply with the full bladder hydration protocol and level of frustration was assessed using a questionaire. Acute side effects were assessed using the Common Terminology Criteria for Adverse Events (CTCAE) version 3.0 and quality of life (QoL) assessed using the International Prostate Symptom Score (IPSS).

Results

The mean (SD) bladder and rectum volumes achieved during daily treatment were 139.7 cm³ (82.4 cm³) and 53.3 cm³ (18 cm³) respectively. Mean (SD) percentage change from planned CT volumes in bladder volume was reduced by 8.2% (48.7%) and rectum volume was increased by 12.4% (42.2%). Linear Mixed effect model analysis revealed a reduction in intra-fraction motion in both the Sup/Inf (p = 0.008) and Ant/Post (p = 0.0001) directions when the daily bladder was filled between 82 and 113% (3rd Quartiles) of the planned CT volumes. A reduction in intra-fraction motion of the prostate in the Ant/Post direction (z-plane) (p = 0.03) was observed when the planned bladder volume was greater than 200 ml. Patients complied well with the hydration protocol with minimal frustration (mean (SD) scores of 2.1 (1.4) and 1.8 (1.2) respectively). There was a moderate positive correlation (0.496) between mean bladder volume and IPSS reported post-treatment urinary straining (p = 0.001).

Conclusions

A planned bladder volume >200 cm³ and daily filling between 82 and 113%, reduced intra-fraction motion of the prostate. The hydration protocol was well tolerated.

The Use of Ultrasound Imaging in the External Beam Radiotherapy Workflow of Prostate Cancer Patients

External beam radiotherapy (EBRT) is one of the curative treatment options for prostate cancer patients. The aim of this treatment option is to irradiate tumor tissue, while sparing normal tissue as much as possible. Frequent imaging during the course of the treatment (image guided radiotherapy) allows for determination of the location and shape of the prostate (target) and of the organs at risk. This information is used to increase accuracy in radiation dose delivery resulting in better tumor control and lower toxicity. Ultrasound imaging is harmless for the patient, it is cost-effective, and it allows for real-time volumetric organ tracking. For these reasons, it is an ideal technique for image guidance during EBRT workflows. Review papers have been published in which the use of ultrasound imaging in EBRT workflows for different cancer sites (prostate, breast, etc.) was extensively covered. This new review paper aims at providing the readers with an update on the current status for prostate cancer ultrasound guided EBRT treatments.