Prostate Motion Research Articles

Breathing-Induced Prostate Motion: Real-Time Data Show Second-Order Effects

Breathing-Induced Prostate Motion: Real-Time Data Show Second-Order Effects

Does body mass index or subcutaneous adipose tissue thickness affect interfraction prostate motion in patients receiving radical prostate radiotherapy?

AbstractAimIt is unclear whether body mass index (BMI) is a useful measurement for examining prostate motion. Patient’s subcutaneous adipose tissue thickness (SAT) and weight has been shown to correlate with prostate shifts in the left/right direction. We sought to analyse the relationship between BMI and interfraction prostate movement in order to determine planning target volume (PTV) margins based on patient BMI.Materials and methodsIn all, 38 prostate cancer patients with three implanted gold fiducial markers in their prostate were recruited. Height, mass and SAT were measured, and the extent of interfraction prostate movement in the left/right, superior/inferior and anterior/posterior directions was recorded during each daily fiducial marker-based image-guided radiotherapy treatment. Mean corrective shift in each direction for each patient, along with BMI values, were calculated.ResultsThe median BMI value was 28·4 kg/m2 (range 21·4–44·7). Pearson’s product-moment correlation analysis showed no significant relationship between BMI, mass or SAT and the extent of prostate movement in any direction. Linear regression analysis also showed no relationship between any of the patient variables and the extent of prostate movement in any direction (BMI: R2=0·006 (ρ=0·65), 0·002 (ρ=0·80) and 0·001 (ρ=0·86); mass: R2=0·001 (ρ=0·87), 0·010 (ρ=0·54) and 0·000 (ρ=0·99); SAT: R2=0·012 (ρ=0·51), 0·013 (ρ=0·50) and 0·047 (ρ=0·19) for shifts in the X, Y and Z axis, respectively). Patients were grouped according to BMI, as BMI<30 (n=25, 65·8%) and BMI≥30 (n=13, 34·2%). A two-tailed t-test showed no significant difference between the mean prostate shifts for the two groups in any direction (ρ=0·320, 0·839 and 0·325 for shifts in the X, Y and Z axis, respectively).FindingsBMI is not a useful parameter for determining individualised PTV margins. Gold fiducial marker insertion should be used as standard to improve treatment accuracy.

Development and validation of a software to evaluate breathing-induced prostate motion tracked with implanted electromagnetic transponders

Introduction A system (Calypso, Varian Medical Systems) based on the localization of electromagnetic transponders (ELM-TRNs) permanently implanted in the prostate allows real-time tracking during radiotherapy treatments. Purpose Development and validation of a dedicated software for ELM-TRNs signal analysis to quantify the amplitude of the intra-fraction prostate motion induced by patient’s breathing, both in supine and prone position. Materials and methods For each treatment session, the software automatically identifies the breathing frequency on the power density spectrum of the recorded signal and creates a bandpass filter around this frequency. The obtained filter is then applied to selectively compute the breathing-induced harmonic excursion of the prostate around its nominal position. The software was validated with a moving phantom (QUASAR, Modus Medical Devices), provided with home-made inserts containing three ELM-TRNs. Harmonic motions along the three main directions were tracked at several known frequencies and amplitudes. The calculated frequencies and amplitudes were compared to the expected ones. The software was then applied to signals of patients who underwent radiotherapy treatments in supine or prone position. Results The software automatically computed the correct frequencies and amplitudes within a 0.6% and a 110 μm uncertainty, respectively, without any significant difference among the three main directions. The software was demonstrated to properly work on signals acquired both with supine and prone patients. Conclusion A software to quantify prostate motion due to patient’s breathing was successfully developed, in-phantom validated and applied to supine and prone patients, highlighting significant motion differences between the two setups. Disclosure None. Work partially funded by AIRC-(IG-14300).

Determining intrafractional prostate motion using four dimensional ultrasound system.

BackgroundIn prostate radiotherapy, it is essential that the prostate position is within the planned volume during the treatment delivery. The aim of this study is to investigate whether intrafractional motion of the prostate is of clinical consequence, using a novel 4D autoscan ultrasound probe.MethodsTen prostate patients were ultrasound (US) scanned at the time of CT imaging and once a week during their course of radiotherapy treatment in an ethics-approved study, using the transperineal Clarity autoscan system (Clarity®, Elekta Inc., Stockholm, Sweden). At each US scanning session (fraction) the prostate was monitored for 2 to 2.5 min, a typical beam-on time to deliver a RapidArc® radiotherapy fraction. The patients were instructed to remain motionless in supine position throughout the US scans. They were also requested to comply with a bladder-filling protocol. In total, 51 monitoring curves were acquired. Data of the prostate motion in three orthogonal directions were analyzed. Finally, the BMI value was calculated to investigate correlation between BMI and the extent of prostate displacement.ResultsThe patients were cooperative, despite extra time for applying the TPUS scan. The mean (±1SD) of the maximal intrafractional displacements were [mm]; I(+)/S: (0.2 ± 0.9); L(+)/R: (−0.2 ± 0.8); and A(+)/P: (−0.2 ± 1.1), respectively. The largest displacement was 2.8 mm in the posterior direction. The percentage of fractions with displacements larger than 2.0 mm was 4 %, 2 %, and 10 % in the IS, LR, and AP directions, respectively. The mean of the maximal intrafractional Euclidean distance (3D vector) was 0.9 ± 0.6 mm. For 12 % of the fractions the maximal 3D vector displacements were larger than 2.0 mm. At only two fractions (4 %) displacements larger than 3.0 mm were observed. There was no correlation between BMI and the extent of the prostate displacement.ConclusionsThe prostate intrafractional displacement is of no clinically consequence for treatment times in the order of 2 – 2.5 min, which is typical for a RapidArc radiotherapy fraction. However, prostate motion should be considered for longer treatment times eg if applying conventional or IMRT radiotherapy.

SU‐G‐JeP1‐02: A New Intra‐Fractional Prostate Motion Tracking Method in Volumetric Modulated Arc Therapy (VMAT) Via 2D/3D Registration

Purpose:Intra‐fractional prostate motion leads uncertainty on delivered dose in radiotherapy and may cause significant dose deviation from the planned dose distribution. This is especially a concern in scenarios with a high dose per fraction and hence a long delivery time, e.g. stereotactic body radiotherapy. Knowledge about intra‐fractional prostate motion is valuable to address this problem, e.g. by reconstructing delivered dose and performing adaptation. This study proposes a new approach to determine intra‐fractional prostate motion in VMAT via 2D/3D maker registration.Methods:At our institution, each patient has three markers implanted in the prostate. During treatment delivery, kV triggered images were taken every three seconds to acquire 2D projection of 3D anatomy at the direction orthogonal to the therapeutic beam. Projected marker locations were identified on each projection image using template matching with geometric constraints. 3D prostate translation and rotation for each triggered image were obtained by solving an optimization problem, such that the calculated marker locations match the measured ones. Inter‐image motion smoothness was employed as a constraint. We tested this method in simulation studies with five realistic prostate motion trajectories acquired via Calypso and in real phantom experiments.Results:For the simulation case, the motion range for these patients was 0.5∼6.0 mm. Root mean square (RMS) error of calculated motion along left‐right (LR), anterior‐posterior (AP) and cranial‐caudal (CC) directions were 0.26mm, 0.36mm, and 0.016mm, respectively. The motion range in the phantom study along LR, AP, and CC directions were 15mm, 20mm and 10mm. The mean RMS errors along these directions were 1.99mm, 1.37mm and 0.22mm.Conclusion:A new prostate motion tracking algorithm based on kV triggered images has been developed and validated. Clinically acceptable accuracy has been achieved.

SU‐G‐JeP4‐10: Measurement of Prostate Motion Trajectories During Prostate SBRT Boost Treatments with a Rectafix

Purpose:To determine prostate motion during SBRT boost treatments with a Rectafix rectal sparing device in place using kV imaging during treatment.Methods:Patients each had three gold fiducial markers inserted into the prostate and received two VMAT boost fractions of 9.5–10 Gy under the PROMETHEUS clinical trial protocol with a Rectafix rectal retractor in place. Two‐dimensional kilovoltage images of fiducial markers were acquired continuously during delivery. Three patients were treated on a Varian Clinac iX linear accelerator (6X, 600 MU/min), where kV images were acquired at 5 Hz during treatment. Seven patients were treated on a Varian Truebeam linear accelerator (10XFFF, 2400 MU/min) where kV images were acquired every 3 seconds. Images were processed off‐line using the Kilovoltage Intrafraction Monitoring (KIM) software after treatment. KIM determines prostate position in three dimensions from 2D kV projections using a probability density model and a pre‐treatment kV arc. The 3D displacement of the prostate was quantified as a function of time throughout each fraction.Results:From all fractions analyzed, it was found that the prostate had moved less than 1 mm in any direction from its initial position 84.6% of the time. The prostate was between 1 and 2 mm from its initial position 14.2% of the time, between 2 and 3 mm of its initial position 0.8% of the time and was greater than 3 mm from its initial position only 0.4% of the time.Conclusion:The amount of prostate motion observed during prostate SBRT boost treatments with a Rectafix device in place was minimal and lower than that observed in non‐Rectafix studies. The Rectafix device reduces rectal dose as well as immobilizing the prostate. Kimberley Legge is the recipient of an Australian Postgraduate Award.

SU‐F‐T‐534: Using Daily Images to Verify Dosimetric Advantage of Dual‐Isocentric Technique for High‐Risk Prostate Cancer Treated with Pelvic Lymph Node

Purpose:To evaluate a dual‐isocentric technique to compensate for the daily independent movements of prostate and pelvic lymph nodes (PLN) of high‐risk prostate cancer patients.Methods:Three patients, who received 78 Gy to the prostate, 66 Gy to the seminal vesicle (SV), and 50.4 Gy to the PLN in 39 fractions under CT‐on‐rail (CTOR) imaging guidance, were retrospectively selected. Each patient was planned with volumetric modulated arc therapy (VMAT) techniques using (1) single isocenter with a 6 mm margin except 4 mm posteriorly (6/4 mm), to the prostate‐CTV and a uniform 5 mm margin to the PLN‐CTV, and (2) two isocenters, located at the centroids of the prostate or the PLN, with a 5/3 mm margin to the prostate‐CTV and a 5 mm uniform margin to the PLN‐CTV. Both plans met the established clinical guidelines, and were subsequently applied to the daily CTOR images, where prostate, SV, rectum and bladder were contoured by the same physician. On each of 117 CTOR images, two plans were created by registering only the bony anatomy for the single‐isocentric one, or by registering both the bony anatomy and the prostate for the dual‐isocentric one. These plans were then compared based on V78Gy of prostate‐CTV, V66Gy of SV‐CTV, and V50.4Gy of PLN‐CTV. The paired Student's t‐test was performed to test for significance.Results:The V78Gy of prostate‐CTV in the dual‐isocentric plans from 117 CTOR images was 99.32±0.89%, significantly (p<0.01) better than that in the single‐isocentric ones (98.29±2.11%). Both V66Gy of SV‐CTV and V50.4Gy of PLN‐CTV were increased from 99.15±3.28% and 99.38±0.74% in the dual‐isocentric plans to 99.31±2.02% and 99.48±0.90% in the single‐isocentric ones, respectively, but neither were statistically significant (p=0.47 and 0.34).Conclusion:By targeting prostate and PLN accordingly in the daily verification images, the dosimetric advantage of dual‐isocentric technique is verified even with a reduced margin.

The effect of rectal retractor on intrafraction motion of the prostate

Rectal retractors (RR) are used in prostate radiotherapy to retract part of the rectal wall further from the prostate in order to lower the rectal dose and toxicity. The aim of this study was to investigate the effect of RR on intrafraction motion of the prostate. Intrafraction motion of the prostate with RR and without it was recorded with electromagnetic real-time tracking system. Intrafractional motion data of 260 RR fractions and 351 non-RR fractions from 22 patients was analyzed. 3D and unidirectional motion patterns between RR and non-RR fraction datasets were compared in terms of percentage time at displacement ≥1, 2, 3, 4, 5 and 6 mm over 6 and 10 min of tracking time. Temporal patterns of the prostate motion were evaluated by re-binning the motion data in 1 min time intervals. The percentage time at displacement was larger in RR data compared to non-RR data in every direction (except anterior) and for every motion magnitude considered. For non-RR fractions the percentage of time of ≥1, 2, 3, 4, 5 and 6 mm 3D displacements within 10 min of tracking time were 44.8%, 16.0%, 6.4%, 2.9%, 1.4% and 0.5%, respectively. For RR fractions the corresponding percentages were 69.6%, 32.8%, 15.3%, 7.4%, 3.7% and 2.2%, respectively. The difference in 3D motion between the datasets was statistically significant (p < 0.03). Largest increase in the motion was seen in inferior and posterior directions when the RR was used. Motion increased linearly as a function of elapsed tracking time in both RR and non-RR datasets but the increase was more rapid in RR fractions. The use of RR increases the intrafraction motion of the prostate which can lead to inaccurate treatment localization and delivery thus questioning the justification of its use.

SU‐G‐BRA‐12: Development of An Intra‐Fractional Motion Tracking and Dose Reconstruction System for Adaptive Stereotactic Body Radiation Therapy in High‐Risk Prostate Cancer

Purpose:A clinical trial on stereotactic body radiation therapy (SBRT) for high‐risk prostate cancer is undergoing at our institution. In addition to escalating dose to the prostate, we have increased dose to intra‐prostatic lesions. Intra‐fractional prostate motion deteriorates well planned radiation dose, especially for the small intra‐prostatic lesions. To solve this problem, we have developed a motion tracking and 4D dose‐reconstruction system to facilitate adaptive re‐planning.Methods:Patients in the clinical trial were treated with VMAT using four arcs and 10 FFF beam. KV triggered x‐ray projections were taken every 3 sec during delivery to acquire 2D projections of 3D anatomy at the direction orthogonal to the therapeutic beam. Each patient had three implanted prostate markers. Our developed system first determined 2D projection locations of these markers and then 3D prostate translation and rotation via 2D/3D registration of the markers. Using delivery log files, our GPU‐based Monte Carlo tool (goMC) reconstructed dose corresponding to each triggered image. The calculated 4D dose distributions were further aggregated to yield the delivered dose.Results:We first tested each module in our system. MC dose engine were commissioned to our treatment planning system with dose difference of &lt;0.5%. For motion tracking, 1789 kV projections from 7 patients were acquired. The 2D marker location error was &lt;1 mm. For 3D motion tracking, root mean square (RMS) errors along LR, AP, and CC directions were 0.26mm, 0.36mm, and 0.01mm respectively in simulation studies and 1.99mm, 1.37mm, and 0.22mm in phantom studies. We also tested the entire system workflow. Our system was able to reconstruct delivered dose.Conclusion:We have developed a functional intra‐fractional motion tracking and 4D dose re‐construction system to support our clinical trial on adaptive high‐risk prostate cancer SBRT. Comprehensive evaluations have shown the capability and accuracy of our system.

SU‐G‐BRA‐17: Tracking Multiple Targets with Independent Motion in Real‐Time Using a Multi‐Leaf Collimator

Purpose:Multiple targets with large intrafraction independent motion are often involved in advanced prostate, lung, abdominal, and head and neck cancer radiotherapy. Current standard of care treats these with the originally planned fields, jeopardizing the treatment outcomes. A real‐time multi‐leaf collimator (MLC) tracking method has been developed to address this problem for the first time. This study evaluates the geometric uncertainty of the multi‐target tracking method.Methods:Four treatment scenarios are simulated based on a prostate IMAT plan to treat a moving prostate target and static pelvic node target: 1) real‐time multi‐target MLC tracking; 2) real‐time prostate‐only MLC tracking; 3) correcting for prostate interfraction motion at setup only; and 4) no motion correction. The geometric uncertainty of the treatment is assessed by the sum of the erroneously underexposed target area and overexposed healthy tissue areas for each individual target. Two patient‐measured prostate trajectories of average 2 and 5 mm motion magnitude are used for simulations.Results:Real‐time multi‐target tracking accumulates the least uncertainty overall. As expected, it covers the static nodes similarly well as no motion correction treatment and covers the moving prostate similarly well as the real‐time prostate‐only tracking. Multi‐target tracking reduces &gt;90% of uncertainty for the static nodal target compared to the real‐time prostate‐only tracking or interfraction motion correction. For prostate target, depending on the motion trajectory which affects the uncertainty due to leaf‐fitting, multi‐target tracking may or may not perform better than correcting for interfraction prostate motion by shifting patient at setup, but it reduces ∼50% of uncertainty compared to no motion correction.Conclusion:The developed real‐time multi‐target MLC tracking can adapt for the independently moving targets better than other available treatment adaptations. This will enable PTV margin reduction to minimize health tissue toxicity while remain tumor coverage when treating advanced disease with independently moving targets involved.The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.

SU‐G‐JeP1‐09: Evaluation of Transperineal Ultrasound Imaging as a Potential Solution for Target Tracking During Ablative Body Radiotherapy for Prostate Cancer

Purpose:Prostate SABR is emerging as a clinically viable, potentially cost effective alternative to prostate IMRT but its adoption is contingent on providing solutions for accurate tracking during beam delivery. Our goal is to evaluate the performance of the Clarity Autoscan ultrasound monitoring system for inter‐fractional prostate motion tracking in both phantoms and in‐vivo.Methods:In‐vivo evaluation was performed under IRB protocol to allow data collection in prostate patients treated with VMAT whereby prostate was imaged through the acoustic window of the perineum. The probe was placed before KV imaging and real‐time tracking was started and continued until the end of treatment. Initial absolute 3D positions of fiducials were estimated from KV images. Fiducial positions in MV images subsequently acquired during beam delivery were compared with predicted positions based on Clarity estimated motion.Results:Phantom studies with motion amplitudes of ±1.5, ±3, ±6 mm in lateral direction and ±2 mm in longitudinal direction resulted in tracking errors of −0.03 ± 0.3, −0.04 ± 0.6, −0.2 ± 0.9 mm, respectively, in lateral direction and −0.05 ± 0.30 mm in longitudinal direction. In phantom, measured and predicted fiducial positions in MV images were within 0.1 ± 0.6 mm. Four patients consented to participate in the study and data was acquired over a total of 140 fractions. MV imaging tracking was possible in about 75% of the time (due to occlusion of fiducials) compared to 100% with Clarity. Overall range of estimated motion by Clarity was 0 to 4.0 mm. In‐vivo fiducial localization error was 1.2 ± 1.0 mm compared to 1.8 ± 1.9 mm if not taking Clarity estimated motion into account.Conclusion:Real‐time transperineal ultrasound tracking reduces uncertainty in prostate position due to intrafractional motion.Research was supported by Elekta.

SU‐G‐JeP4‐13: Continuous Intra‐Fractional Monitoring of the Prostate Using Dynamic KV Collimation and Tube Current Modulation

Purpose:The focus of this work is to improve the available kV image quality for continuous intra‐fraction monitoring of the prostate. This is investigated using a novel blade collimation system enabling modulated volume‐of‐interest (VOI) imaging of prostate fiducial markers.Methods:A four‐blade dynamic kV collimator was used to track a VOI during gantry rotation. Planar image quality was investigated as a function of collimator dimension, while maintaining the same dose to isocenter, for a 22.2 cm diameter cylindrical water phantom with a 9 mm diameter bone insert. A sample prostate anatomy was defined in the planning system, including three fiducial markers within the CTV. The VOI margin around each marker was set to be 2σ of the population covariance matrix characterizing prostate motion. DRRs were used to calculate the kV attenuation for each VOI as a function of angle. The optimal marker and tube current were determined using kV attenuation. Monte Carlo simulations were used to calculate the imaging dose to the phantom and MV scatter dose to the imaging panel.Results:Preliminary measurements show an increase in CNR by a factor of 1.3 with the VOI method, when decreasing from an 6×6 to 2×2 cm2 field. Attenuation calculations show a change in kV fluence at the detector by a factor of 21.6 with fiducial optimization; resultant tube current modulation increases maximum dose by a factor of 1.4 compared to no modulation. MV scatter contribution to the kV detector changes by approximately a factor of two over a complete gantry rotation.Conclusion:The dynamic collimation system allows single fiducial marker tracking at a very low dose, with reduction of scatter and improvement of image quality, compared to imaging the entire prostate. The approach is compatible with tube current modulation, which enables consistent image quality throughout the range of gantry rotation.This project was funded by Varian Medical Systems.

TH-AB-202-12: The First Clinical Implementation of a Real-Time Six Degree of Freedom Tracking System During Radiation Therapy

Purpose: In current practice, imaging is typically performed prior to treatment; the cancer target motion during treatment is unknown. We present the first clinical implementation of real time Kilovoltage Intrafraction Monitoring (KIM) system which tracks the cancer target translational and rotational motions during treatment. Methods: KIM technology: KIM estimates the 3D position of the target tumour based on segmented 2D positions of the three implanted fiducials in each of the kV images (125 kV, 10 mA at 11 fps) taken continuously during the treatment arc. The 2D-3D target estimation is based on a probability distribution function, obtained during pre-treatment CBCT. Rotations about each axis with the centroid of the markers as the pivot were calculated using the iterative closest point algorithm in real time. Patient: A patient with prostate adenocarcinoma undergoing stereotactic body radiotherapy (SBRT) with 36.25 Gy delivered in 5 fractions (Varian TrueBeam, 6X, VMAT) was enrolled in the study. The trial complies with Australian ethical and regulatory standards. Results: Of the 5 fractions of treatment the patient received, KIM was utilised successfully in 4 fractions with 3 couch shifts due to large persistent prostate movements (>2mm for more than 5 seconds). KIM translational accuracy and precision in comparison with post treatment kV-MV triangulation are 0.28±0.59 mm, −0.19±0.25 mm and 0.23±0.69 mm in the Left-Right, Superior-Inferior and Anterior-Posterior directions, respectively. KIM rotational accuracy as compared with triangulation is: 0.429°±2.22°, −0.44°±4.7° and 0.06°±1.08° in the roll, pitch and yaw direction, respectively. Conclusion: The first six degree of freedom KIM system was successfully implemented clinically. The presented KIM system has sub-millimeters accuracy and precision in all three translational axes, and less than 1° of mean error in all three rotational axes. Acknowledgement: This work is supported by Cancer Australia grants APPXXX, APPYYY.

Quantification of the margin required for treating intraprostatic lesions.

Advances in magnetic resonance imaging (MRI) sequences allow physicians to define the dominant intraprostatic lesion (IPL) in prostate radiation therapy treatments allowing for dose escalation and potentially increased tumor control. This work quantifies the margin required around the MRI‐defined IPL accounting for both prostate motion and deformation. Ten patients treated with a simultaneous integrated intraprostatic boost (SIIB) were retrospectively selected and replanned with incremental 1 mm margins from 0‐5 mm around the IPL to determine if there were any significant differences in dosimetric parameters. Sensitivity analysis was then performed accounting for random and systematic uncertainties in both prostate motion and deformation to ensure adequate dose was delivered to the IPL. Prostate deformation was assessed using daily CBCT imaging and implanted fiducial markers. The average IPL volume without margin was 2.3% of the PTV volume and increased to 11.8% with a 5 mm margin. Despite these changes in volume, the only statistically significant dosimetric difference was found for the PTV maximum dose, which increased with increasing margin. The sensitivity analysis demonstrated that a 3.0 mm margin ensures >95% IPL coverage accounting for both motion and deformation. We found that a margin of 3.0 mm around the MRI defined IPL is sufficient to account for random and systematic errors in IPL position for the majority of cases.PACS number(s): 87.55.de

Potential benefits of dosimetric VMAT tracking verified with 3D film measurements.

To evaluate three different plan adaptation strategies using 3D film-stack dose measurements of both focal boost and hypofractionated prostate VMAT treatments. The adaptation strategies (a couch shift, geometric tracking, and dosimetric tracking) were applied for three realistic intrafraction prostate motions. A focal boost (35 × 2.2 and 35 × 2.7 Gy) and a hypofractionated (5 × 7.25 Gy) prostate VMAT plan were created for a heterogeneous phantom that allows for internal prostate motion. For these plans geometric tracking and dosimetric tracking were evaluated by ionization chamber (IC) point dose measurements (zero-D) and measurements using a stack of EBT3 films (3D). The geometric tracking applied translations, rotations, and scaling of the MLC aperture in response to realistic prostate motions. The dosimetric tracking additionally corrected the monitor units to resolve variations due to difference in depth, tissue heterogeneity, and MLC-aperture. The tracking was based on the positions of four fiducial points only. The film measurements were compared to the gold standard (i.e., IC measurements) and the planned dose distribution. Additionally, the 3D measurements were converted to dose volume histograms, tumor control probability, and normal tissue complication probability parameters (DVH/TCP/NTCP) as a direct estimate of clinical relevance of the proposed tracking. Compared to the planned dose distribution, measurements without prostate motion and tracking showed already a reduced homogeneity of the dose distribution. Adding prostate motion further blurs the DVHs for all treatment approaches. The clinical practice (no tracking) delivered the dose distribution inside the PTV but off target (CTV), resulting in boost dose errors up to 10%. The geometric and dosimetric tracking corrected the dose distribution's position. Moreover, the dosimetric tracking could achieve the planned boost DVH, but not the DVH of the more homogeneously irradiated prostate. A drawback of both the geometric and dosimetric tracking was a reduced MLC blocking caused by the rotational component of the MLC aperture corrections. Because of the used CTV to PTV margins and the high doses in the considered fractionation schemes, the TCP differed less than 0.02 from the planned value for all targets and all correction methods. The rectal NTCP constraints, however, could not be realized using any of these methods. The geometric and dosimetric tracking use only a limited input, but they deposit the dose distribution with higher geometric accuracy than the clinical practice. The latter case has boost dose errors up to 10%. The increased accuracy has a modest impact [Δ(NT)CP < 0.02] because of the applied margins and the high dose levels used. To allow further margin reduction tracking methods are vital. The proposed methodology could further be improved by implementing a rotational correction using collimator rotations.

EP-1729: The impact of CBCT-imaging and verification time on prostate motion using 4D TPUS Clarity system

EP-1729: The impact of CBCT-imaging and verification time on prostate motion using 4D TPUS Clarity system

EP-1777: MRT investigation of prostate and lymph nodes movements: implications on planning target volume?

EP-1777: MRT investigation of prostate and lymph nodes movements: implications on planning target volume?

PO-0878: The effect of rectal retractor on intra-fraction motion of prostate

PO-0878: The effect of rectal retractor on intra-fraction motion of prostate

EP-1750: Monitoring of intra-fraction prostate motion with a new 4D ultrasound device

EP-1750: Monitoring of intra-fraction prostate motion with a new 4D ultrasound device

EP-1731: Changes of the prostate motion errors in the intra-fraction early phase for prostate cancer patients

EP-1731: Changes of the prostate motion errors in the intra-fraction early phase for prostate cancer patients