Intrafraction Prostate Motion Research Articles

Influence of Respiratory Phase during Image Acquisition on Prescribed Dose in Image Guided Radiation Therapy Using Implant Marker for Prostate Cancer

In image guided radiation therapy (IGRT) using implanted fiducial marker by two-dimensional radiography for prostate cancer, temporal positional relationship during treatment between the isocenter and the prostate is changed by respiratory phase at the time of image acquisition. We examined influence of the respiratory phase in the IGRT on dose variation by interplay effect. Intra-fractional prostate motions of patients who were implanted fiducial marker were measured using fluoroscopy, then we reconstructed plans considering for the respiratory phase in IGRT and the respiratory motion during volumetric modulated arc therapy. Averages of the intra-fractional prostate motion in left-right, anterior-posterior and superior-inferior direction were 0.039, 0.49 and 1.6 mm respectively. There was a patient whose intra-fractional prostate motion was larger than 4 mm that was planning target volume margin. By changing the respiratory phase like inspiration, exhalation and dispersing respiratory phase in each fraction, dose variation from original plan became smaller in order of the inspiration, exhalation and dispersion. The largest variations of dose indices in clinical target volume, bladder and rectum were 8.0%, 4.5% and 9.1% respectively when IGRT was done in inspiration. When the IGRT is performed by the same respiratory phase in each fraction, systematic dose variations may occur even if the respiratory phase at the timing of irradiation is changed. By dispersing the respiratory phase in each fraction, the variations in all dose indices were<1% from original plan. We realized that dispersing the respiratory phase in IGRT by each fraction is effective to reduce the dose variation caused by the respiratory phase in IGRT.

229P - Predictability of intra-fractional prostate motion

229P - Predictability of intra-fractional prostate motion

PO348 Designing and Evaluating the Efficacy of Mobile Cardiac Arrhythmia Simulator Application on Critical Care Nurses’ Knowledge and Satisfaction

To determine intrafraction prostate motion during volumetric modulated arc therapy (VMAT) using transperineal ultrasound (US) real-time tracking.770 US monitoring sessions in 38 prostate cancer patients' VMAT treatment series were retrospectively evaluated. Intrafraction motion assessment of the prostate was based on continuous position monitoring with a 4-dimensional US system along the 3 directions: left-right (LR), anterior-posterior (AP), and inferior-superior (SI). The overall mean values and standard deviations (SD) along with random and systematic errors were calculated.The mean duration of each monitoring session was 254 s. The mean (μ), the systematic error (Σ), and the random error (σ) of intrafraction prostate displacement were μ = (0.01, −0.08, 0.15) mm, Σ = (0.30, 0.34, 0.23) mm, and σ = (0.59, 0.73, 0.64) mm in the LR, AP and SI directions, respectively. The percentage of treatments for which prostate displacement was ≤2 mm was 97.01%, 92.24%, and 95.77% in the LR, AP, and SI directions, respectively. At 60 s, a vector length of prostate displacement >2 mm was present in 0.67% of the data. The percentage increased to 2.42%, 6.14%, and 9.35% at 120 s, 180 s, and 240 s, respectively.The magnitudes of intrafraction prostate motion along the SI and AP directions were comparable. On average, the smallest motion was in the LR direction and the largest in AP direction. Most of the prostate displacements were within a few millimeters. However, with increasing treatment time (eg, during hypofractionation), larger 3-dimensional prostate displacements up to 18.30 mm could be observed. Shortening treatment time can reduce the impact of intrafraction motion and potentially allows smaller safety margins.

Impact of Rectum and Bladder Anatomy in Intrafractional Prostate Motion During Hypofractionated Radiation Therapy

Impact of Rectum and Bladder Anatomy in Intrafractional Prostate Motion During Hypofractionated Radiation Therapy

Dosimetric and Radiobiological Evaluation of Delivered Dose Distribution with Intra-Fractional Motion in Prostate Stereotactic Radiation Therapy Treatments Using VMAT and Helical Tomotherapy

The implementation of motion-management techniques during intensity modulated radiation therapy (IMRT) is still under challenging issue. Moreover, the dose-per-fraction regime and beam-delivery methods affect the dose distribution owing to the interplay effect. Hypofractionation may be a uniquely appropriate treatment for prostate cancer because of a lower α/β ratio. Several prospective studies support the safety of moderate hypofractionation; however, extreme fractionation may lead to greater toxicity. It has been reported that respiratory motion during IMRT delivery of stereotactic body radiation therapy (SBRT) can lead to dosimetric errors in the target of up to ±20%. Therefore, intra-fractional prostate motion may occur unpredictably during IMRT and lead to under-treatment of the target. In this study, we evaluated the dosimetric and radiobiological effects of the SBRT dose distributions with patient-specific intra-fractional motion in prostate cancer for volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) using a commercially available six-dimensional (6D) motion system. Dose distributions with patient-specific prostate intra-fractional motion were evaluated using the 6D-motion simulator system, which was coupled to a biplanar diode array detector phantom. These bidirectional prostate motions were acquired from magnetic resonance (MR)-cine images. Then, these motions were continuously generated for approximately 4 min, and dose measurements were repeated 5 times to measure the uncertainty of prostate motion during irradiation. We tested two typical motion patterns: large (over 2.0 mm) and small (under 1.0 mm). The SBRT plan was created in VMAT and HT with a prescription of 36.25 Gy/5 fractions to D95% of the PTV. We compared dose distributions with static irradiations using the 3 dimensional gamma (3D-γ) analysis. Moreover, the equivalent uniform dose (EUD)-based tumor control probability (TCP) and normal tissue complication probability (NTCP) of the rectum were compared with 76 Gy/38 fractions, which is the standard prostate fractionation plan. In the results of the dosimetric evaluation, the pass rate of the γ-analysis (criterion of 2 mm, 3%) was degraded by 9.5% and 22.7% in VMAT and HT plans in the large motion patterns and 3.0% and 8.7% in the small motion patterns, respectively. However, degradation of the D99 for CTV was only 0.7% and 1.8% in VMAT and HT plans, respectively, even in the large motion patterns. Moreover, these errors were negligible in small motion patterns. For the radiobiological evaluation, no significant differences in TCP and NTCP degradations were found in VMAT and HT SBRT plans compared with the standard fractionation plan. SBRT dose distributions with intra-fractional motion over 2.0 mm in prostate cancer were more degraded in HT than those observed in VMAT; however, these dosimetric errors might not be clinically significant degradation for TCP and/or NTCP.

Assessment of Intra-Fraction Prostate Motion and Delivered Dose Accuracy in Prostate SBRT Using an in-House Real-Time Position Monitoring System

Assessment of Intra-Fraction Prostate Motion and Delivered Dose Accuracy in Prostate SBRT Using an in-House Real-Time Position Monitoring System

Combifix or Vacloc Bags, Which One Is Better for Prostate Patient Setup and Immobilization?

Compared to traditional used VacLoc bags, Combifix is a new patient setup and immobilization device for pelvic region treatment. It has adjustable kneefix and feetfix cushions. This study is to evaluate and compare these two device performance by analyzing patient pre-treatment setup and post-treatment radiographs from prostate patients treated with proton. Total 22 prostate patients were selected for the study, with 11 using Combifix and 11 using VacLoc bags for patient immobilization and setup. Pre-treatment setup radiographs and post-treatment radiographs were obtained to evaluate the setup residual errors and prostate intrafraction motion errors for both cohorts of patients. The systematic and random components of the residual errors and intrafraction motion errors were calculated and compared. Therapists were interviewed about their experiences using Combifix. For Combifix patients, the setup residual systematic errors are 0.02, 0.03 and 0.02cm in lateral (LR), longitudinal (SI) and Vertical (AP) directions, respectively. The residual random errors are 0.05, 0.07 and 0.07cm in LR, SI and AP directions, respectively. For VacLoc patients, the setup residual systematic errors are 0.0, 0.01 and 0.01cm in LR, SI and AP directions, respectively. The residual random errors are 0.02, 0.04 and 0.04cm in LR, SI and AP directions, respectively. The intrafraction motion errors are slightly larger than residual errors. For Combifix patients, the setup residual systematic errors are 0.04, 0.07 and 0.05cm in LR, SI and AP directions, respectively. The residual random errors are 0.08, 0.15 and 0.15cm in LR, SI and AP directions, respectively. For VacLoc patients, the setup residual systematic errors are 0.02, 0.05 and 0.05cm in LR, SI and AP directions, respectively. The residual random errors are 0.05, 0.12 and 0.11cm in LR, SI and AP directions, respectively. Therapists observed that there were less rotation errors but slightly more pitching errors at the beginning of patient setup. But after 1 or 2 corrections, the residual errors are very similar between the two immobilization devices. However, if multiple consecutive patients treated with Combifix device, it improves clinical flow. The error analyses of the patient initial setup and intrafraction motion showed that similar characteristics between the two patient immobilization devices. Nevertheless, improved clinical flow can be achieved by treating consecutive patients with Combifix devices.

Impact of rectum and bladder anatomy in intrafractional prostate motion during hypofractionated radiation therapy.

The objective was to determine the magnitude of the prostate intrafractional motion relative to bony pelvis anatomy, and to evaluate the relationship between this displacement and some clinical and anatomical variables. The prospective study consisted of 544 images (375 pre-treatment CBCT and 169 post-treatment CBCT) from 15 prostate adenocarcinoma patients that were used for intrafractional prostate motion determination. In addition, two radiation oncologists re-contoured the bladder and rectum on each CBCT according to the patient's anatomy of the day. ANOVA and correlation analysis followed by linear regression analysis were performed to identify clinical or anatomical variables that predict large prostate intrafractional motion. Prostate shift increased in patients with hormone therapy (p ≤ 0.02). The regression analysis showed that patients with large bladder intrafractional filling (p < 0.01) and a large bladder volume difference from planning CT were more likely to experience bigger longitudinal prostate motion (> 3mm). Recommended bladder size values: anterior-posterior size ≤ 10cm and anterior-posterior/cranio-caudal ratio ≤ 1.7, both parameters measured in the midsagittal prostate plane, were defined. The treatment margin should not be reduced for those patients who were treated with hormone therapy and/or whose rectum or bladder was far from complying the preparation protocol conditions.

Application of real-time transperineal ultrasound in radiotherapy of prostate cancer-4D analysis of intra-fractional prostate motion

Objective To apply real-time transperineal ultrasound (TPUS) to monitor the intra-fractional prostate motion, collect and analyze the data of the prostate motion, aiming to provide evidence for the optimization of the target area and plan of radiotherapy for prostate cancer. Methods TPUS is a non-invasive monitoring technique that utilizes an automatic scanning ultrasound probe to dynamically monitor and correct the motion of organs during radiotherapy. In this study, TPUS was utilized to collect 1588 intra-fractional data of 70 patients with prostate cancer. Prior to each cycle of radiotherapy, CBCT was adopted to correct the errors between intra-factional data by using VMAT. During radiotherapy, real-time (once per second) ultrasound images were acquired to monitor the 3D motion of the prostate on the x (left+ , right-), y (cranial+ , caudal-), and z (abdominal+ , dorsal-) axes, emphasizing the analysis of 4D motion of the prostate. Results All patients successfully completed the treatment and data collection. The median time of effective monitoring per faction was 179 seconds (132-286 seconds). During 95% of the monitoring time, the distance of prostate motion was 2.22 mm in the left direction, 2.17 mm in the right, 2.08 mm in the cranial, 1.98 mm in the caudal, 2.44 mm in the abdominal and 2.97 mm in the dorsal direction, respectively. In the x, y and z axes, the percentage of time in which the distance of prostate motion less than 1 mm among the total time was 83.07%, 85.46% and 78.27%, respectively, whereas 97.70%, 97.87% and 96.45% for<3 mm, respectively. Conclusions TPUS is a non-invasive real-time monitoring technique, which can detect the 4D motion of the prostate during radiotherapy. By using VMAT, the range of prostate motion is relatively small, and the motion range is less than 3 mm in each direction within 95% of the time. Key words: Prostate neoplasms; Transperineal ultrasound; Intra-fractional motion; Real-time monitoring

In Vivo Validation of Elekta's Clarity Autoscan for Ultrasound-based Intrafraction Motion Estimation of the Prostate During Radiation Therapy

PurposeOur purpose was to perform an in vivo validation of ultrasound imaging for intrafraction motion estimation using the Elekta Clarity Autoscan system during prostate radiation therapy. The study was conducted as part of the Clarity-Pro trial (NCT02388308).Methods and MaterialsInitial locations of intraprostatic fiducial markers were identified from cone beam computed tomography scans. Marker positions were translated according to Clarity intrafraction 3-dimensional prostate motion estimates. The updated locations were projected onto the 2-dimensional electronic portal imager plane. These Clarity-based estimates were compared with the actual portal-imaged 2-dimensional marker positions. Images from 16 patients encompassing 80 fractions were analyzed. To investigate the influence of intraprostatic markers and image quality on ultrasound motion estimation, 3 observers rated image quality, and the marker visibility on ultrasound images was assessed.ResultsThe median difference between Clarity-defined intrafraction marker locations and portal-imaged marker locations was 0.6 mm (with 95% limit of agreement at 2.5 mm). Markers were identified on ultrasound in only 3 of a possible 240 instances. No linear relationship between image quality and Clarity motion estimation confidence was identified. The difference between Clarity-based motion estimates and electronic portal–imaged marker location was also independent of image quality. Clarity estimation confidence was degraded in a single fraction owing to poor probe placement.ConclusionsThe accuracy of Clarity intrafraction prostate motion estimation is comparable with that of other motion-monitoring systems in radiation therapy. The effect of fiducial markers in the study was deemed negligible as they were rarely visible on ultrasound images compared with intrinsic anatomic features. Clarity motion estimation confidence was robust to variations in image quality and the number of ultrasound-imaged anatomic features; however, it was degraded as a result of poor probe placement.

Dosimetric impact of intra-fraction prostate motion under a tumour-tracking system in hypofractionated robotic radiosurgery.

For CyberKnife-mediated prostate cancer treatment, a tumour-tracking approach is applied to correct the target location by acquiring X-ray images of implanted fiducial markers intermittently. This study investigated the dosimetric impact of intra-fraction prostate motion during CyberKnife treatment. We retrospectively analyzed 16 patients treated using the CyberKnife (35 Gy delivered in five fractions). Using log files of recorded prostate motion, the intra-fraction prostate motion was simulated. We defined the worst-case intra-fraction prostate motion as the difference between pre- and post-deviation on log files and shifted structure sets according to the corresponding offsets for each beam. The dose–volume indices were calculated and compared with the original plan in terms of clinical target volume (CTV), planning target volume (CTV plus a 2-mm margin), rectum, bladder, and urethra. Prostate motions of >3, >5, and >10 mm were observed for 31.3, 9.1, and 0.5% of the 1929 timestamps, respectively. Relative differences between the simulated and original plans were mostly less than 1%. Although significant decreases were observed in D50% and D98% of the target, absolute dose differences were <0.1 Gy compared with the planned dose. The dosimetric impact of intra-fraction prostate motion may be small even with longer treatment durations, indicating that the tumour tracking using the CyberKnife could be a robust system for examining prostate motion.

EP-2017: Assessing the dosimetric impact of intra-fractional prostate motion during SBRT

EP-2017: Assessing the dosimetric impact of intra-fractional prostate motion during SBRT

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

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. 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). 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). 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.

Determination of Intrafraction Prostate Motion During External Beam Radiation Therapy With a Transperineal 4-Dimensional Ultrasound Real-Time Tracking System

To determine intrafraction prostate motion during volumetric modulated arc therapy (VMAT) using transperineal ultrasound (US) real-time tracking. 770 US monitoring sessions in 38 prostate cancer patients' VMAT treatment series were retrospectively evaluated. Intrafraction motion assessment of the prostate was based on continuous position monitoring with a 4-dimensional US system along the 3 directions: left-right (LR), anterior-posterior (AP), and inferior-superior (SI). The overall mean values and standard deviations (SD) along with random and systematic errors were calculated. The mean duration of each monitoring session was 254s. The mean (μ), the systematic error (Σ), and the random error (σ) of intrafraction prostate displacement were μ = (0.01, -0.08, 0.15) mm, Σ = (0.30, 0.34, 0.23) mm, and σ = (0.59, 0.73, 0.64) mm in the LR, AP and SI directions, respectively. The percentage of treatments for which prostate displacement was ≤2mm was 97.01%, 92.24%, and 95.77% in the LR, AP, and SI directions, respectively. At 60s, a vector length of prostate displacement >2mm was present in 0.67% of the data. The percentage increased to 2.42%, 6.14%, and 9.35% at 120s, 180s, and 240s, respectively. The magnitudes of intrafraction prostate motion along the SI and AP directions were comparable. On average, the smallest motion was in the LR direction and the largest in AP direction. Most of the prostate displacements were within a few millimeters. However, with increasing treatment time (eg, during hypofractionation), larger 3-dimensional prostate displacements up to 18.30mm could be observed. Shortening treatment time can reduce the impact of intrafraction motion and potentially allows smaller safety margins.

Obesity does not influence prostate intrafractional motion.

IntroductionMotion of the prostate is problematic in the accurate delivery of external beam radiation therapy (EBRT) for prostate cancer. This study investigated the relationship between body mass index (BMI), an easily measured indicator of obesity, and prostate motion.MethodsProstate motion during EBRT was assessed by measuring the displacement of fiducial markers implanted within the prostate in 130 prostate cancer patients. Interfractional motion was corrected on daily imaging through pre‐treatment cone‐beam‐computed tomography (CBCT) and intrafractional motion measured using movie sequences captured using an electronic portal imaging device (EPID) during treatment delivery.ResultsThere was no statistically significant relationship between the mean intrafractional motion and BMI, except in the left‐right (LR) translation (P = 0.049) over the study population. For each BMI category, there was no statistical significance (P > 0.05) between any of the translations/rotations except LR (P = 0.003).ConclusionWhile intrafractional motion is an important consideration, prostate motion cannot be reliably predicted through measurement of patient's BMI.

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

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. 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. 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). 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.

Intrafractional Prostate Motion and Dose Variation during Radiation Therapy for Prostate Cancer Using 4D-TPUS

More recently, noninvasive 4D transperineal ultrasound (4D-TPUS) has been introduced in tracking intrafractional prostate motion in radiotherapy. Compared to other tracking method, the ultrasound has its own advantage in precise identification of soft tissue without invasive procedure or extra radiation dose. In this study, we investigated the prostate motion model and dose variation during radiotherapy using a transperineal autoscan ultrasound system (Clarity®, Elekta Inc., Sweden). From July 2014 through December 2016, 57 prostate cancer patients were enrolled with a median age of 74 years (range 61-85). All patients were asked to have a full bladder and empty rectum before each treatment. A simultaneous CT and TPUS simulation was conducted to provide a fused CT/US reference. Before radiation delivery, prostates were localized using CBCT to determine setup offsets relative to the patients’ skin tattoos. During the treatment, real-time ultrasound images were acquired and data was collected for direct monitoring of 3D motion of the prostate. Then dose distributions were recalculated with the isocenter shifts relative to the simulation CT images according to the real-time data using the leaf sequences/MUs based on the original treatment plan. The doses were compared with the original doses planned on the simulation CT using the clinical acceptance criteria. A total of 1207 fractions were evaluated. The mean (±SD) of the infraction displacements were [mm]: I(+)/S: (0.03 ± 0.92); L(+)/R: (0.12 ± 1.03); and A(+)/P: (-0.01 ± 1.37), respectively. There were 41/1207 (3.4%), 29/1207 (2.4%), and 66/1207 (5.5%) fractions with deviation exceeded 3 mm in the IS, LR, and AP directions, respectively. The A/P direction has the largest extent of prostate displacement. The percentage of time with displacements 0-1mm, 1-2mm, 2-3mm and larger than 3 mm was 88.1%, 9.8%, 1.7% and 0.4% in the IS direction, 89.3%, 8.9%, 1.5% and 0.3 % in the LR direction, 84.5%, 11.1%, 3.7%, and 0.7% in the AP direction. We classified our patients into three groups according to the motion model: stable (n=50), irregular (n=3) and intention (n=4). The intention group was defined as persistent deviation to the same direction (the maximal displacement should exceed 3 mm) that repeated in at least 50% fractions. All these patients had obviously anxiety and urinary frequency and/or urgency. Recalculated dose distributions showed that all the 4 patients in the intention group did not meet our criterion of D95% of PTV prostate> 8000 cGy or V70 of rectum< 20%, which may leading to insufficient treatment and increased toxicity. The present study demonstrated that for over 90% of fractions, a CTV-PTV margin of 3 mm would be good coverage with the planned prescribed dose. However, it is important to identify the patients belonging to the intention group. Pre-treatment with anti-anxiety drugs and α receptor blocker may be useful in relief the prostate motion.

Real-time intrafraction prostate motion during linac based stereotactic radiotherapy with rectal displacement.

BackgroundKilovoltage Intrafraction Monitoring (KIM) is a method which determines the three‐dimensional position of the prostate from two‐dimensional kilovoltage (kV) projections taken during linac based radiotherapy treatment with real‐time feedback. Rectal displacement devices (RDDs) allow for improved rectal dosimetry during prostate cancer treatment. This study used KIM to perform a preliminary investigation of prostate intrafraction motion observed in patients with an RDD in place.MethodsTen patients with intermediate to high‐risk prostate cancer were treated with a Rectafix RDD in place during two boost fractions of 9.5–10 Gy delivered using volumetric modulated arc therapy (VMAT) on Clinac iX and Truebeam linacs. Two‐dimensional kV projections were acquired during treatment. KIM software was used following treatment to determine the displacement of the prostate over time. The displacement results were analyzed to determine the percentage of treatment time the prostate spent within 1 mm, between 1 and 2 mm, between 2 and 3 mm and greater than 3 mm from its initial position.Results KIM successfully measured displacement for 19 prostate stereotactic boost fractions. The prostate was within 1 mm of its initial position for 84.8%, 1–2 mm for 14%, 2–3 mm 1.2% and ≥3 mm only 0.4% of the treatment time.ConclusionsIn this preliminary study using KIM, KIM was successfully used to measure prostate intrafraction motion, which was found to be small in the presence of a rectal displacement device.Trial registrationThe Hunter New England Human Research Ethics Committee reference number is 14/08/20/3.01.

Prostate SBRT Intrafraction Monitoring With Transperineal Ultrasound

To quantify intra-fraction prostate motion during stereotactic radiation therapy (SBRT) with trans-perineal ultrasound and hence determine suitable intra-fraction margins. Ultrasound provided real-time monitoring of prostate position in 7 SBRT patients for a total of 33 tracking sessions. Average monitoring time was 9.4 minutes including cone-beam CT (CBCT) alignment and radiation delivery. Each patient had a rectal balloon. The raw displacement (shift) versus time data was smoothed with a moving average window of 2 s, to remove transient motion in the data. The average time spent within 1, 2 and 3 mm margins was determined. The time when the maximum shift occurred was also recorded, in order to compare to using just a post treatment CBCT to assess motion. Lastly, the times when the prostate position first left a 1, 2 and 3 mm margin was measured for each fraction. A Kaplan-Meier (KM) estimate was created with this data to give the probability that a fraction would be within a 1, 2 or 3 mm margin at a specific time. This can be used to select margins for those without real-time monitoring. Ultrasound successfully monitored intra-fraction prostate motion. It could be used to gate the treatment when the prostate is beyond the margin. Averaged over all 33 fractions, 95% of the first minute was spent within a 1 mm margin. Through the fifth minute of treatment, 55% of the time was spent within a 1 mm margin while 95% was within a 2 mm margin. The maximum shift for any fraction was 4.6 mm. The average maximum shift for a patient was 2.6 ± 1.0 mm. The final prostate position was within 0.2 mm of the maximum shift of the prostate for 45% of fractions, and was within 1 mm for 84%. This demonstrates that pre and post CBCTs do not fully capture the motion of the prostate, missing larger motion during treatment. A trend of increasing shifts with time was seen. Trends ranged from 0.00085 mm/s to 0.011 mm/s, indicating a large variability in prostate motion between patients. Further, the trend increased as treatment progressed. Patients’ trends were 4% to 192% higher in fractions 4 & 5 than fraction 1. The KM curves are summarized in the table, presenting the probability(%) of a fraction being always within a 1, 2, or 3 mm margin for a range of total treatment times. Eg, for a 5 minute treatment, there is a 90.6% probability that the prostate would stay entirely within a 3 mm margin. Ultrasound provides real-time position data for the prostate that could be used to gate the treatment. Our ultrasound motion data has determined suitable margins for clinics without ultrasound that treat prostate SBRT with a rectal balloon, based on their expected treatment length.Abstract 3719Monitoring Time (s)3060901201802403003604206001 mm Margin96.981.378.175.065.640.631.224.316.74.22 mm Margin10096.993.887.587.587.587.584.073.067.03 mm Margin10010010096.993.893.890.690.690.686.3 Open table in a new tab

Intrafraction monitoring of prostate motion during radiotherapy using the Clarity® Autoscan Transperineal Ultrasound (TPUS) system

IntroductionImplementation of the Clarity® Autoscan (Elekta) Transperineal Ultrasound (TPUS) system in Bristol is the first of its kind in the UK and we have already shown its utility in interfractional Image Guided Radiotherapy (IGRT).14 This study establishes the extent of intrafraction prostate motion as measured by Clarity and explores the potential benefits of TPUS for intrafraction monitoring. MethodsMonitoring data was analysed for 526 fractions from 20 localised prostate cancer patients. Intrafraction prostate displacements exceeding thresholds of 3 mm, 7 mm and 10 mm along patient axes were assessed for frequency and duration of motion. ResultsProstate motion exceeds the above displacement thresholds during 52%, 8%, and 2% of fractions analysed. Displacement at the 3 mm threshold occurred for 100% of patients, 60% at 7 mm and 35% at 10 mm. The mean frequency and duration of displacements is low for the overall population. In contrast specific patients exhibit much higher displacement values. Posterior motion is most common, averaging at 24% of the treatment time at 3 mm, 3% at 7 mm and 1% at 10 mm, ranging up to 92%, 35% and 10% for individual patients. ConclusionsIntrafraction monitoring with Clarity has the potential to improve accuracy through application of in-treatment motion correction. This is most beneficial for specific patients who exhibit a higher frequency and/or duration of prostate motion. Consideration must be given to the added time implications and radiographer workload in clinical practice to correct for prostate motion. Clarity could help facilitate future protocols using tighter treatment margins, although further research is required.