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INTRODUCTION Aimed to develop a simple and robust volumetric modulated arc radiotherapy (VMAT) solution for comprehensive lymph node (CLN) breast cancer without increase in low-dose wash. METHODS Forty CLN-breast patient data sets were utilised to develop a knowledge-based planning (KBP) VMAT model, which limits low-dose wash using iterative learning and base-tangential methods as benchmark. Another twenty data sets were employed to validate the model comparing KBP-generated ipsilateral VMAT (ipsi-VMAT) plans against the benchmarked hybrid (h)-VMAT (departmental standard) and bowtie-VMAT (published best practice) methods. Planning target volume (PTV), conformity/homogeneity index (CI/HI), organ-at-risk (OAR), remaining-volume-at-risk (RVR) and blinded radiation oncologist (RO) plan preference were evaluated. RESULTS Ipsi- and bowtie-VMAT plans were dosimetrically equivalent, achieving greater nodal target coverage (P

Purpose Locally advanced and oligometastatic cancer patients require radiotherapy treatment to multiple independently moving targets. There is no existing commercial solution that can simultaneously track and treat multiple targets. This study experimentally implemented and evaluated a real-time multi-target tracking system for locally advanced prostate cancer. Methods Real-time multi-target MLC tracking was integrated with 3D x-ray image guidance on a standard linac. Three locally advanced prostate cancer treatment plans were delivered to a static lymph node phantom and dynamic prostate phantom that reproduced three prostate trajectories. Treatments were delivered using multi-target MLC tracking, single-target MLC tracking, and no tracking. Doses were measured using Gafchromic film placed in the dynamic and static phantoms. Dosimetric error was quantified by the 2%/2 mm gamma failure rate. Geometric error was evaluated as the misalignment between target and aperture positions. The multi-target tracking system latency was measured. Results The mean (range) gamma failure rates for the prostate and lymph nodes, were 18.6% (5.2%, 28.5%) and 7.5% (1.1%, 13.7%) with multi-target tracking, 7.9% (0.7%, 15.4%) and 37.8% (18.0%, 57.9%) with single-target tracking, and 38.1% (0.6%, 75.3%) and 37.2% (29%, 45.3%) without tracking. Multi-target tracking had the lowest geometric error with means and standard deviations within 0.2 ± 1.5 for the prostate and 0.0 ± 0.3 mm for the lymph nodes. The latency was 730 ± 20 ms. Conclusion This study presented the first experimental implementation of multi-target tracking to independently track prostate and lymph node displacement during VMAT. Multi-target tracking reduced dosimetric and geometric errors compared to single-target tracking and no tracking.

Background To measure intra-fraction displacement (IFD) in post-prostatectomy patients treated with anisotropic margins and daily soft tissue matching. Methods Pre-treatment cone beam computed tomography (CBCT) scans were acquired daily and post-treatment CBCTs for the first week then weekly on 46 patients. The displacement between the scans was calculated retrospectively to measure IFD of the prostate bed (PB). The marginal miss (MM) rate, and the effect of time between imaging was assessed. Results A total of 392 post-treatment CBCT’s were reviewed from 46 patients. The absolute mean (95% CI) IFD was 1.5 mm (1.3–1.7 mm) in the AP direction, 1.0 mm (0.9–1.2 mm) SI, 0.8 mm (0.7–0.9 mm) LR, and 2.4 mm (2.2–2.5 mm) 3D displacement. IFD ≥ ± 3 mm and ≥ ± 5 mm was 24.7% and 5.4% respectively. MM of the PB was detected in 33 of 392 post-treatment CBCT (8.4%) and lymph nodes in 6 of 211 post-treatment CBCT images (2.8%). Causes of MM due to IFD included changes in the bladder (87.9%), rectum (66.7%) and buttock muscles (6%). A time ≥ 9 min between the pre and post-treatment CBCT demonstrated that movement ≥ 3 mm and 5 mm increased from 19.2 to 40.5% and 5 to 8.1% respectively. Conclusions IFD during PB irradiation was typically small, but was a major contributor to an 8.4% MM rate when using daily soft tissue match and tight anisotropic margins.

PurposeFor patients with locally advanced cancer, multiple targets are treated simultaneously with radiotherapy. Differential motion between targets can compromise the treatment accuracy, yet there are currently no methods able to adapt to independent target motion. This study developed a multileaf collimator (MLC) tracking algorithm for differential motion adaptation and evaluated it in simulated treatments of locally advanced prostate cancer.MethodsA multi-target MLC tracking algorithm was developed that consisted of three steps: (a) dividing the MLC aperture into two possibly overlapping sections assigned to the prostate and lymph nodes, (b) calculating the ideally shaped MLC aperture as a union of the individually translated sections, and (c) fitting the MLC positions to the ideal aperture shape within the physical constraints of the MLC leaves. The multi-target tracking method was evaluated and compared with two existing motion management methods: single-target tracking and no tracking. Treatment simulations of six locally advanced prostate cancer patients with three prostate motion traces were performed for all three motion adaptation methods. The geometric error for each motion adaptation method was calculated using the area of overexposure and underexposure of each field. The dosimetric error was estimated by calculating the dose delivered to the prostate, lymph nodes, bladder, rectum, and small bowel using a motion-encoded dose reconstruction method.ResultsMulti-target MLC tracking showed an average improvement in geometric error of 84% compared to single-target tracking, and 83% compared to no tracking. Multi-target tracking maintained dose coverage to the prostate clinical target volume (CTV) D98% and planning target volume (PTV) D95% to within 4.8% and 3.9% of the planned values, compared to 1.4% and 0.7% with single-target tracking, and 20.4% and 31.8% with no tracking. With multi-target tracking, the node CTV D95%, PTV D90%, and gross tumor volume (GTV) D95% were within 0.3%, 0.6%, and 0.3% of the planned values, compared to 9.1%, 11.2%, and 21.1% for single-target tracking, and 0.8%, 2.0%, and 3.2% with no tracking. The small bowel V57% was maintained within 0.2% to the plan using multi-target tracking, compared to 8% and 3.5% for single-target tracking and no tracking, respectively. Meanwhile, the bladder and rectum V50% increased by up to 13.6% and 5.2%, respectively, using multi-target tracking, compared to 2.7% and 1.9% for single-target tracking, and 11.2% and 11.5% for no tracking.ConclusionsA multi-target tracking algorithm was developed and tracked the prostate and lymph nodes independently during simulated treatments. As the algorithm optimizes for target coverage, tracking both targets simultaneously may increase the dose delivered to the organs at risk.

Since February 12, 2020, approximately 6.5 million cases of SARS-CoV-2 infection, the cause of coronavirus disease 2019 (COVID-19), and 190,000 SARS-CoV-2-associated deaths have been reported in the United States (1,2). Symptoms associated with SARS-CoV-2 infection are milder in children compared with adults (3). Persons aged

Introduction Accurate delivery of radiation while reducing dose to organs at risk is essential in prostate treatment. The Calypso motion management system detects and corrects both inter- and intra-fraction motion which offers potential benefits over standard alignment to fiducial markers. The aims of this study were to implement Calypso with Dynamic Edge™ gating and to assess both the motion seen, and interventions required. Methods An implementation group was formed which assessed changes needed to standard workflows. Three patients had Calypso beacons inserted into their prostate. All patients were treated using volumetric modulated arc therapy to a dose of 80 Gy in 40 fractions. Standard inter-fraction motion correction using either kilovoltage (kV) orthogonal paired imaging or cone beam computed tomography (CBCT) image-guided radiotherapy techniques, were used along with the Calypso system to compare accuracy. A gating threshold of >0.5 cm was used during treatment. Workflow variations along with inter- and intra-fraction motion and interventions required were assessed. Results A total of 116 fractions were treated using Calypso with Dynamic Edge™ gating. There was a strong concordance between aligning beacons using kV orthogonal imaging or CBCT and Calypso (mean variation ≤0.06 cm). The mean intra-fraction motion detected was ≤0.2 cm in all directions with the largest motion recorded being 2.2 cm in the left direction while the treatment beam was off. Prostate rotation was largest in the pitch direction and 28 fractions exceeded the 10° tolerance. A total of 78 couch shift corrections of ≥0.3 cm were required, usually following standard imaging, and before treatment starting. Three gating events due to intra-fraction motion occurred during treatment. Conclusions Intra-fraction motion monitoring with Calypso was successfully implemented. Greatest movement was seen between time of standard imaging and treatment starting with more than half the treatments requiring a ≥0.3 cm adjustment. This would not have been detected without intra-fraction monitoring.

Introduction We have previously demonstrated that daily soft tissue matching with reduced anisotropic margins provides an ideal balance between prostate bed coverage and meeting organ at risk constraints. The aim of this study was to evaluate the implementation of this approach in clinical practice. Methods Thirty‐eight radiation therapists (RTs) completed offline IGRT training involving six patients. After training was completed, this approach was implemented clinically. The first 24 patients were evaluated with a central review of match displacements and geographic miss (GM). An assessment of treatment times and planning parameters was also performed. Results During offline training, the anterior–posterior (AP) match discrepancy had the largest mean variation ranging from −0.46 to 0.06 cm and undetected geographic miss occurred in 17% of alignments. The mean time taken to treat the first 24 patients ranged from 12.2 to 20.6 min. The smaller anisotropic margin resulted in similar target coverage but achieved reduced doses to the bladder (V65Gy from 36% to 27%, V40Gy from 54% to 51%) and rectum (V65Gy from 20% to 19%, V60Gy from 27% to 24%, V40Gy from 42% to 38%). The matches of 806 CBCT images in 24 patients were reviewed. The mean match ranged from −0.12 to 0.17 cm AP, −0.14 to 0.14 cm superior–inferior (SI) and −0.04 to 0.04 cm left–right (LR). An undetected geographic miss was found in the prostate bed in 17 (2.1%) images and lymph nodes in 2 (0.2%) images. Conclusions Daily soft tissue IGRT with reduced anisotropic margins for post‐prostatectomy radiotherapy has been successfully implemented. RTs performed better with real‐time online matching than they did in offline training, perhaps influenced by having several RTs perform online matching. Daily soft tissue IGRT did not prolong treatment time., Daily soft tissue IGRT with reduced anisotropic PTV expansions for post‐prostatectomy radiotherapy has been successfully implemented following adequate offline training and careful audit of practice with high rates of tumour bed coverage and reduced OAR doses.

© 2018 Elsevier B.V. Purpose: Until now, real-time image guided adaptive radiation therapy (IGART) has been the domain of dedicated cancer radiotherapy systems. The purpose of this study was to clinically implement and investigate real-time IGART using a standard linear accelerator. Materials/methods: We developed and implemented two real-time technologies for standard linear accelerators: (1) Kilovoltage Intrafraction Monitoring (KIM) that finds the target and (2) multileaf collimator (MLC) tracking that aligns the radiation beam to the target. Eight prostate SABR patients were treated with this real-time IGART technology. The feasibility, geometric accuracy and the dosimetric fidelity were measured. Results: Thirty-nine out of forty fractions with real-time IGART were successful (95% confidence interval 87–100%). The geometric accuracy of the KIM system was −0.1 ± 0.4, 0.2 ± 0.2 and −0.1 ± 0.6 mm in the LR, SI and AP directions, respectively. The dose reconstruction showed that real-time IGART more closely reproduced the planned dose than that without IGART. For the largest motion fraction, with real-time IGART 100% of the CTV received the prescribed dose; without real-time IGART only 95% of the CTV would have received the prescribed dose. Conclusion: The clinical implementation of real-time image-guided adaptive radiotherapy on a standard linear accelerator using KIM and MLC tracking is feasible. This achievement paves the way for real-time IGART to be a mainstream treatment option.

Collected real-life clinical target volume (CTV) displacement data show that some patients undergoing external beam radiotherapy (EBRT) demonstrate significantly more fraction-to-fraction variability in their displacement ('random error') than others. This contrasts with the common assumption made by historical recipes for margin estimation for EBRT, that the random error is constant across patients. In this work we present statistical models of CTV displacements in which random errors are characterised by an inverse gamma (IG) distribution in order to assess the impact of random error variability on CTV-to-PTV margin widths, for eight real world patient cohorts from four institutions, and for different sites of malignancy. We considered a variety of clinical treatment requirements and penumbral widths. The eight cohorts consisted of a total of 874 patients and 27 391 treatment sessions. Compared to a traditional margin recipe that assumes constant random errors across patients, for a typical 4 mm penumbral width, the IG based margin model mandates that in order to satisfy the common clinical requirement that 90% of patients receive at least 95% of prescribed RT dose to the entire CTV, margins be increased by a median of 10% (range over the eight cohorts -19% to +35%). This substantially reduces the proportion of patients for whom margins are too small to satisfy clinical requirements.

Purpose: Kilovoltage intrafraction monitoring (KIM) is a real-time image guidance method that uses widely available radiotherapy technology, i.e., a gantry-mounted x-ray imager. The authors report on the geometric and dosimetric results of the first patient treatment using KIM which occurred on September 16, 2014. Methods: KIM uses current and prior 2D x-ray images to estimate the 3D target position during cancer radiotherapy treatment delivery. KIM software was written to process kilovoltage (kV) images streamed from a standard C-arm linear accelerator with a gantry-mounted kV x-ray imaging system. A 120° pretreatment kV imaging arc was acquired to build the patient-specific 2D to 3D motion correlation. The kV imager was activated during the megavoltage (MV) treatment, a dual arc VMAT prostate treatment, to estimate the 3D prostate position in real-time. All necessary ethics, legal, and regulatory requirements were met for this clinical study. The quality assurance processes were completed and peer reviewed. Results: During treatment, a prostate position offset of nearly 3 mm in the posterior direction was observed with KIM. This position offset did not trigger a gating event. After the treatment, the prostate motion was independently measured using kV/MV triangulation, resulting in a mean difference of less than 0.6 mm and standard deviation of less than 0.6 mm in each direction. The accuracy of the marker segmentation was visually assessed during and after treatment and found to be performing well. During treatment, there were no interruptions due to performance of the KIM software. Conclusions: For the first time, KIM has been used for real-time image guidance during cancer radiotherapy. The measured accuracy and precision were both submillimeter for the first treatment fraction. This clinical translational research milestone paves the way for the broad implementation of real-time image guidance to facilitate the detection and correction of geometric and dosimetric errors, and resultant improved clinical outcomes, in cancer radiotherapy.

This editorial is advocating that increasing consistency and accuracy in radiation therapy via educational interventions is important for radiation therapist. Education and training with ongoing refreshers is the key to maintaining consistency throughout the radiotherapy process, which in turn will ensure all patients receive accurate treatment.

Introduction Standard post-prostatectomy radiotherapy (PPRT) image verification uses bony anatomy alignment. However, the prostate bed (PB) moves independently of bony anatomy. Cone beam computed tomography (CBCT) can be used to soft tissue match, so radiation therapists (RTs) must understand pelvic anatomy and PPRT clinical target volumes (CTV). The aims of this study are to define regions of interest (ROI) to be used in soft tissue matching image guidance and determine their visibility on planning CT (PCT) and CBCT. Methods Published CTV guidelines were used to select ROIs. The PCT scans (n = 23) and CBCT scans (n = 105) of 23 post-prostatectomy patients were reviewed. Details on ROI identification were recorded. Results Eighteen patients had surgical clips. All ROIs were identified on PCTs at least 90% of the time apart from mesorectal fascia (MF) (87%) due to superior image quality. When surgical clips are present, the seminal vesicle bed (SVB) was only seen in 2.3% of CBCTs and MF was unidentifiable. Most other structures were well identified on CBCT. The anterior rectal wall (ARW) was identified in 81.4% of images and penile bulb (PB) in 68.6%. In the absence of surgical clips, the MF and SVB were always identified; the ARW was identified in 89.5% of CBCTs and PB in 73.7%. Conclusions Surgical clips should be used as ROIs when present to define SVB and MF. In the absence of clips, SVB, MF and ARW can be used. RTs must have a strong knowledge of soft tissue anatomy and PPRT CTV to ensure coverage and enable soft tissue matching.

Background and purpose Accuracy when delivering post-prostatectomy intensity modulated radiotherapy (IMRT) is crucial. The aims of this study were to quantify prostate bed movement and determine what amount of bladder or rectum size variation creates the potential for geographic miss. Methods and materials The Cone Beam CT (CBCT) images ( n =377) of forty patients who received post-prostatectomy IMRT with daily on-line alignment to bony anatomy were reviewed. Prostate bed movement was estimated using the location of surgical clips in the upper and lower sections of the PTV and correlated with rectal and bladder filling (defined as changes in the cross sectional diameter at defined levels). The number of potential geographic misses caused by bladder and rectum variation was calculated assuming a uniform CTV to PTV expansion of 1cm except 0.5cm posteriorly. Results Variations in bladder filling of >2cm larger, ±1cm, or >2cm smaller occurred in 3.4%, 56.2%, and 15.1% of images respectively with potential geographic misses in the upper prostate bed of 61.5%, 9.9% and 26.3% respectively. Variations in rectal filling in the upper prostate bed of >1.5cm larger, 1.5cm larger to 1cm smaller, and >1cm smaller occurred in 17.2%, 75.6%, and 7.2% of images respectively. These variations resulted in geographic misses in the upper prostate bed in 29.2%, 12.3%, and 63.0% of images respectively. Variations in bladder and rectal filling in the lower prostate bed region had minimal impact on geographic misses. Conclusions Bladder and rectal size changes at treatment affect prostate bed coverage, especially in the upper aspect of the prostate bed. The greatest potential for geographic miss occurred when either the bladder increased in size or when the rectum became smaller. Ensuring a full bladder and empty rectum at simulation will minimise this risk. Our data also support anisotropic PTV margins with larger margins superiorly than inferiorly.

Variations in rectal and bladder filling can create a tilt of the prostate bed, which generates the potential for a geographic miss during postprostatectomy radiotherapy. The aim of this study is to assess the effect that bladder and rectum filling has on planning target volume angle, to determine a method to assess prostate bed tilt leading to potential geographic miss, and to discuss possible implementation issues. The cone-beam computed tomography images (n = 377) of 40 patients who received postprostatectomy radiotherapy with intensity-modulated radiotherapy were reviewed. The amount of tilt in the prostate bed was defined as the angle change between 2 surgical clips, one in the upper prostate bed and another in the lower. A potential geographic miss was defined as movement of any clip of more than 1cm in any direction or 0.5 cm posteriorly when aligned to bone anatomy. Variations in bladder and rectum size were correlated with the degree of prostate bed tilt, and the rate of potential geographic miss was determined. A possible clinical use of prostate bed tilt was then assessed for different imaging techniques. A tilt of more than 10° was seen in 20.2% of images, which resulted in a 57.9% geographic miss rate of the superior clip. When tilt remained within 10°, there was only a 9% rate of geographic miss. Potential geographic miss of the inferior surgical clip was rare, occurring in only 1.9% of all images reviewed. The most common occurrence when the prostate bed tilt increased by more than 10° was a smaller bladder and larger rectum (6.4% of all images). The most common occurrence when the prostate bed tilt decreased by more than 10° was a larger bladder and smaller rectum (1.3% of all images). Significant prostate bed tilt (>± 10°) occurred in more than 20% of images, creating a 58% rate of geographic miss. Greatest prostate bed tilt occurred when the bladder size increased or reduced by more than 2 cm or the superior rectum size increased by more than 1.5 cm or reduced by more than 1cm from the planned size. Using prostate bed tilt could be an effective measurement for assessing potential geographic miss on orthogonal images if volumetric imaging is unavailable.

Introduction There is little data to guide radiation oncologists on appropriate margin selection in the post-prostatectomy setting. The aim of this study was to quantify interfraction variation in motion of the prostate bed to determine these margins. Methods The superior and inferior surgical clips in the prostate bed were tracked on pretreatment cone beam CT images (n = 377) for 40 patients who had received post-prostatectomy radiotherapy. Prostate bed motion was calculated for the upper and lower segments by measuring the position of surgical clips located close to midline relative to bony anatomy in the axial (translational) and sagittal (tilt) planes. The frequency of potential geographic misses was calculated for either 1 cm or 0.5 cm posterior planning target volume margins. Results The mean magnitude of movement of the prostate bed in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.50 cm, 0.28 cm, 0.10 cm; lower portion, 0.18 cm, 0.18 cm, 0.08 cm. The random and systematic errors, respectively, of the prostate bed motion in the anterior–posterior, superior–inferior and left–right planes, respectively, were as follows: upper portion, 0.47 cm and 0.50 cm, 0.28 cm and 0.27 cm, 0.11 cm and 0.11 cm; lower portion, 0.17 cm and 0.18 cm, 0.17 cm and 0.19 cm, 0.08 cm and 0.10 cm. Most geographic misses occurred in the upper prostate bed in the anterior–posterior plane. The median prostate bed tilt was 1.8° (range −23.4° to 42.3°). Conclusions Variability was seen in all planes for the movement of both surgical clips. The greatest movement occurred in the anterior–posterior plane in the upper prostate bed, which could cause geographic miss of treatment delivery. The variability in the movement of the superior and inferior clips indicates a prostate bed tilt that would be difficult to correct with standard online matching techniques. This creates a strong argument for using anisotropic planning target volume margins in post-prostatectomy radiotherapy.

Summary The aim of this paper is to detail the experience obtained in implementing an image-guided radiation therapy program at the Northern Sydney Cancer Centre. This required retrofitting a Varian Clinac 21EX with an on-board imager. The commissioning and quality assurance procedures, organisation of a multidisciplinary image guided radiation therapy group, and the development of clinical protocols for orthogonal kV and cone beam computed tomography implementation are described. Reassessment of the image-guided radiation therapy program has continued as new equipment and software versions were made available in the department.

Background There is limited information available on the optimal Planning Target Volume (PTV) expansions and image guidance for post-prostatectomy intensity modulated radiotherapy (PP-IMRT). As the prostate bed does not move in a uniform manner, there is a rationale for anisotropic PTV margins with matching to soft tissue. The aim of this study is to find the combination of PTV expansion and image guidance policy for PP-IMRT that provides the best balance of target coverage whilst minimising dose to the organs at risk. Methods The Cone Beam CT (CBCT) images (n = 377) of 40 patients who received PP-IMRT with daily online alignment to bony anatomy (BA) were reviewed. Six different PTV expansions were assessed: 3 published PTV expansions (0.5 cm uniform, 1 cm uniform, and 1 + 0.5 cm posterior) and 3 further anisotropic PTV expansions (Northern Sydney Cancer Centre (NSCC), van Herk, and smaller anisotropic). Each was assessed for size, bladder and rectum coverage and geographic miss. Each CBCT was rematched using a superior soft tissue (SST) and averaged soft tissue (AST) match. Potential geographic miss was assessed using all PTV expansions except the van Herk margin. Results The 0.5 cm uniform expansion yielded the smallest PTV (median volume = 222.3 cc) and the 1 cm uniform expansion yielded the largest (361.7 cc). The Van Herk expansion includes the largest amount of bladder (28.0 %) and rectum (36.0 %) and the 0.5 cm uniform expansion the smallest (17.1 % bladder; 10.2 % rectum). The van Herk PTV expansion had the least geographic miss with BA matching (4.2 %) and the 0.5 cm uniform margin (28.4 %) the greatest. BA matching resulted in the highest geographic miss rate for all PTVs, followed by SST matching and AST matching. Changing from BA to an AST match decreases potential geographic miss by half to two thirds, depending on the PTV expansion, to

There is little data to guide radiation oncologists on appropriate margin selection in the post-prostatectomy setting. The aim of this study was to quantify interfraction variation in motion of the prostate bed to determine these margins.The superior and inferior surgical clips in the prostate bed were tracked on pretreatment cone beam CT images (n = 377) for 40 patients who had received post-prostatectomy radiotherapy. Prostate bed motion was calculated for the upper and lower segments by measuring the position of surgical clips located close to midline relative to bony anatomy in the axial (translational) and sagittal (tilt) planes. The frequency of potential geographic misses was calculated for either 1 cm or 0.5 cm posterior planning target volume margins.The mean magnitude of movement of the prostate bed in the anterior-posterior, superior-inferior and left-right planes, respectively, were as follows: upper portion, 0.50 cm, 0.28 cm, 0.10 cm; lower portion, 0.18 cm, 0.18 cm, 0.08 cm. The random and systematic errors, respectively, of the prostate bed motion in the anterior-posterior, superior-inferior and left-right planes, respectively, were as follows: upper portion, 0.47 cm and 0.50 cm, 0.28 cm and 0.27 cm, 0.11 cm and 0.11 cm; lower portion, 0.17 cm and 0.18 cm, 0.17 cm and 0.19 cm, 0.08 cm and 0.10 cm. Most geographic misses occurred in the upper prostate bed in the anterior-posterior plane. The median prostate bed tilt was 1.8° (range -23.4° to 42.3°).Variability was seen in all planes for the movement of both surgical clips. The greatest movement occurred in the anterior-posterior plane in the upper prostate bed, which could cause geographic miss of treatment delivery. The variability in the movement of the superior and inferior clips indicates a prostate bed tilt that would be difficult to correct with standard online matching techniques. This creates a strong argument for using anisotropic planning target volume margins in post-prostatectomy radiotherapy.

Aim To compare online position verification strategies with offline correction protocols for patients undergoing definitive prostate radiotherapy. Materials and methods We analysed 50 patients with implanted fiducial markers undergoing curative prostate radiation treatment, all of whom underwent daily kilovoltage imaging using an on-board imager. For each treatment, patients were set-up initially with skin tattoos and in-room lasers. Orthogonal on-board imager images were acquired and the couch shift to match both bony anatomy and the fiducial markers recorded. The set-up error using skin tattoos and offline bone correction was compared with online bone correction. The fiducial markers were used as the reference. Results Data from 1923 fractions were analysed. The systematic error was ≤1mm for all protocols. The average random error was 2–3mm for online bony correction and 3–5mm for skin tattoos or offline-bone. Online-bone showed a significant improvement compared with offline-bone in the number of patients with >5mm set-up errors for >10% ( P 20% ( P Conclusions Online correction to bony anatomy reduces both systematic and random set-up error in patients undergoing prostate radiotherapy, and is superior to offline correction methods for those patients not suitable for fiducial markers or daily soft-tissue imaging.

Summary An audit was conducted on 20 randomly selected patients who had daily electronic portal imaging during the course of their radiotherapy treatment. The daily images were reviewed to determine whether they were within tolerance according to departmental protocol. If they were not, the actions that were taken were documented. Four treatment areas (spine, chest, breast and prostate) were compared among five patients belonging to each of these categories. The patients were also categorized according to their treatment intent (radical or palliative). A total of 889 electronic portal images of 475 fractions were audited and 33.5% of all fractions were outside tolerance. It was found that 95% of patients needed an action during their treatment and 80% of the patients needed a treatment centre move during the course of their treatment. We found that errors occurred throughout the treatment and it was not possible to predict patients who could have daily imaging omitted. Concordance between radiation therapists and radiation oncologists for identification of error was also investigated. Despite the use of familiar electronic portal imaging protocols, image reviewers (radiation therapists and radiation oncologists) disagreed in interpretation 10% of the time. Our results support the hypothesis that daily imaging may be a useful tool for patients undergoing radiotherapy and that imaging may be ideally carried out before each fraction. Image assessments would be ideally carried out by a team approach, with all images reviewed by both radiation therapists and radiation oncologists. This approach has significant resource implications and may require review of current Medicare and Health Program Grant reimbursements.

Summary 1 . The effects of intraventricular injection of 6-hydroxydopamine (6-OHDA) on tyrosine hydroxylase activity, uptake of 3H-noradrenaline and endogenous catecholamine concentration in rat hypothalamus and striatum were investigated at various times after the injection of 6-OHDA. 2 . In the hypothalamus after the injection of 250 μg of 6-OHDA there was a rapid decrease in tyrosine hydroxylase activity, 3H-noradrenaline uptake and noradrenaline content, which was essentially complete within 2 hours. 3 . In the striatum after this dose of 6-OHDA there was a much slower reduction in tyrosine hydroxylase activity and 3H-noradrenaline uptake during the first 48 h after drug injection. For the first 24 h the dopamine concentration in this brain area was increased significantly above control values, but had fallen below control values by 48 hours. 4 . After the injection of a smaller dose of 6-OHDA (25 μg) the only detectable change in the striatum was a rapid increase in the dopamine concentration. In the hypothalamus this dose induced a rapid depletion of noradrenaline, not accompanied initially by any significant reduction in tyrosine hydroxylase activity. 5 . These results are consistent with the hypothesis that 6-OHDA causes a rapid degeneration of catecholamine-containing nerve terminals in the central nervous system (CNS). These degenerative changes, indicated by the loss of tyrosine hydroxylase and noradrenaline uptake sites, did not appear to be preceded by an initial displacement of endogenous catecholamines by 6-OHDA, except possibly at early times after the administration of small doses of the drug.