Intrafraction Motion and Margin Assessment for Ethos Online Adaptive Radiotherapy Treatments of the Prostate and Seminal Vesicles.

Purpose: Online adaptive radiation therapy (OART) uses daily imaging to identify changes in the patient's anatomy and generate a new treatment plan adapted to these changes for each fraction. The aim of this study was to determine the intrafraction motion and planning target volume (PTV) margins required for an OART workflow on the Varian Ethos system. Methods and Materials: Sixty-five fractions from 13 previously treated OART patients were analyzed for this retrospective study. The prostate and seminal vesicles were contoured by a radiation oncologist on 2 cone beam computed tomography scans (CBCT) for each fraction, the initial CBCT at the start of the treatment session, and the verification CBCT immediately before beam-on. In part 1 of the study, PTVs of different sizes were defined on the initial CBCT, and the geometric overlap with the clinical target volume (CTV) on the verification CBCT was used to determine the optimal OART margin. This was performed with and without a patient realignment shift by registering the verification CBCT to the initial CBCT. In part 2 of the study, the margins determined in part 1 were used for simulated Ethos OART treatments on all 65 fractions. The resultant coverage to the CTV on the verification CBCT, was compared with an image guided radiation therapy (IGRT) workflow with 7-mm margins. Results: Part 1 of the study found, if a verification CBCT and shift is performed, a 4-mm margin on the prostate and 5 mm on the seminal vesicles resulted in 95% of the CTV covered by the PTV in >90% of fractions, and 98% of the CTV covered by the PTV in >80% of fractions. Part 2 of the study found when these margins were used in an Ethos OART workflow, they resulted in CTV coverage that was superior to an IGRT workflow with 7-mm margins. Conclusions: A 4mm prostate margin and 5-mm seminal vesicles margin in an OART workflow with verification imaging are adequate to ensure coverage on the Varian Ethos system. Larger margins may be required if using an OART workflow without verification imaging.

Clinical assessment of a novel machine-learning automated contouring tool for radiotherapy planning.

Contouring has become an increasingly important aspect of radiotherapy due to inverse planning. Several studies have suggested that the clinical implementation of automated contouring tools can reduce inter-observer variation while increasing contouring efficiency, thereby improving the quality of radiotherapy treatment and reducing the time between simulation and treatment. In this study, a novel, commercial automated contouring tool based on machine learning, the AI-Rad Companion Organs RT™ (AI-Rad) software (Version VA31) (Siemens Healthineers, Munich, Germany), was assessed against both manually delineated contours and another commercially available automated contouring software, Varian Smart Segmentation™ (SS) (Version 16.0) (Varian, Palo Alto, CA, United States). The quality of contours generated by AI-Rad in Head and Neck (H&N), Thorax, Breast, Male Pelvis (Pelvis_M), and Female Pelvis (Pevis_F) anatomical areas was evaluated both quantitatively and qualitatively using several metrics. A timing analysis was subsequently performed to explore potential time savings achieved by AI-Rad. Results showed that most automated contours generated by AI-Rad were not only clinically acceptable and required minimal editing, but also superior in quality to contours generated by SS in multiple structures. In addition, timing analysis favored AI-Rad over manual contouring, indicating the largest time saving (753s per patient) in the Thorax area. AI-Rad was concluded to be a promising automated contouring solution that generated clinically acceptable contours and achieved time savings, thereby greatly benefiting the radiotherapy process.

Individualized breathing trace quality assurance for lung radiotherapy patients undergoing 4DCT simulation.

4DCT simulation is a popular solution for radiotherapy simulation of lung cancer patients as it allows the clinician to gain an appreciation for target motion during the patient breathing cycle. Resultant binning of images and production of the 4DCT dataset relies heavily on the recorded breathing trace; but quality assurance is not routinely performed on these and there lacks any substantial recommendations thereof. An application was created for Windows in C# that was able to analyze the VXP breathing trace files from Varian RPM/RGSC and quantify various metrics associated with the patient breathing cycle. This data was then used to consider errors in voluming of targets for several example cases in order to justify recommendations on quality assurance. For 281 real patient breathing traces from 4DCT simulation of lung targets, notable differences were found between RGSC and application calculations of phase data. For any new patient without individualized QA, the average marked phase calculation (which is used for 4DCT reconstruction) is only accurate to within 19% of the actual phases. The error in BPM within the scan due to breathing rate variation is 37%. The uncertainty in amplitude due to breathing variation is 34% in the mean. Phase uncertainty leads to misbinning which we have shown can lead to missing 66% of the target for gated treatment. Variation in inhalation/exhalation level leads to voluming errors which, without individualized QA, can be assumed to be 11% (PTV is smaller than actual). Without individualized quality assurance of patient breathing traces, large uncertainties have to be assumed for metrics of both phase and amplitude, leading to clinically significant uncertainties in treatment. It is recommended to perform individualized quality assurance as this provides the clinician with an accurate quantification of uncertainty for their patient.

Varian ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time.

The Varian Ethos system allows for online adaptive treatments through the utilization of artificial intelligence (AI) and deformable image registration which automates large parts of the anatomical contouring and plan optimization process. In this study, treatments of intact prostate and prostate bed, with and without nodes, were simulated for 182 online adaptive fractions, and then a further 184 clinical fractions were delivered on the Ethos system. Frequency and magnitude of contour edits were recorded, as well as a range of plan quality metrics. From the fractions analyzed, 11% of AI generated contours, known as influencer contours, required no change, and 81% required minor edits in any given fraction. The frequency of target and noninfluencer organs at risk (OAR) contour editing varied substantially between different targets and noninfluencer OARs, although across all targets 72% of cases required no edits. The adaptive plan was the preference in 95% of fractions. The adaptive plan met more goals than the scheduled plan in 78% of fractions, while in 15% of fractions the number of goals met was the same. The online adaptive recontouring and replanning process was carried out in 19 min on average. Significant improvements in dosimetry are possible with the Ethos online adaptive system in prostate radiotherapy.

A review of stereotactic body radiotherapy for the spine.

Radiation therapy of the spine, as recourse for spinal tumours, is an effective method of achieving pain reduction and local control. Hypofractionated techniques like stereotactic body radiation therapy and especially stereotactic radiosurgery are quickly becoming more popular as studies are published demonstrating their superior outcomes. This review concerns aspects of spinal radiotherapy of interest to the clinical medical physicist, with a focus on stereotactic techniques. The literature surveyed is mostly from the last two decades, concentrating particularly on studies from the last few years. Clinical aspects of spinal disease are covered to give context to the development of different radiotherapy techniques and thus the changing suitability criteria of patients. The latest studies concerning the treatment pathway are reviewed and summarised-from simulation and prescription to contouring, treatment planning and treatment delivery. This then leads into a discussion of the accuracy and uncertainties surrounding different methods of immobilisation and image guidance. Treatment planning algorithms and approaches are also reviewed. Finally, we survey the most recent outcomes and statistics concerning failures, toxicity, survivability and control rates. With careful consideration of the latest literature, patients suffering from spinal disease have a good chance of positive outcomes following radiotherapy.

An assessment of the ExacTrac intrafraction imaging capabilities for flattening filter free prostate stereotactic body radiotherapy.

The uncertainties associated with image matching using the ExacTrac® system (BrainLab, Munich, Germany) have been the subject of investigation in the literature for extra-cranial sites. However, the uncertainties involved in the use of ExacTrac in the presence of higher scatter conditions like that for intrafraction imaging of prostate stereotactic radiotherapy utilising unflattened beams is yet to be determined. A prostate phantom was created with 3 implanted gold fiducial markers. This phantom was shifted by 1 mm and 2 mm amounts in the translational planes and by 1° and 2° amounts in the rotational planes and subsequently imaged by ExacTrac during delivery of a clinical SBRT plan. ExacTrac auto-match results were compared to the known offsets with uncertainties calculated. Calculated shifts were shown to be accurate within one standard deviation of the known offsets. Uncertainties were found to vary considerably among the 6 dimensions with matching in the vertical and angle vertical directions having standard deviations of 0.7 mm and 1.3°, respectively. These results agreed with the literature cases for pre-treatment setup and lower scatter condition IMRT intrafraction delivery. Based on these values, probabilities of intrafraction inhibits were calculated based on patient movement and possible fusion tolerances. While the measured uncertainties are adequately defined in order to calculate appropriate target margins, their relatively large magnitudes made choice of intrafraction fusion tolerances problematic. A degree of compromise between the rate of false positives and false negatives is required when implementing ExacTrac into a SBRT prostate protocol.

Investigation of elastomeric materials for bolus using stereolithography printing technology in radiotherapy.

PURPOSE: An investigation was conducted of an elastomeric material, VisiJet M2 (3D systems, USA) for use as 3D bolus within high energy photon beams for radiotherapy. Personalized conformal bolus material on complex structures like the nose can be challenging. This material was evaluated for its clinical feasibility due to its pliability and comfort compared to alternatives. METHOD: Regular slabs of bolus were created of various thicknesses for dosimetric and non-dosimetric characterization. Verification culminated with the creation of a custom nose bolus for an end to end verification using an anthropomorphic head phantom. In vivo dosimetry using Gafchromic EBT3 (Ashland, USA) film validated delivered doses from a 6 MV conformal field and a pair of 6 MV volumetric modulated arc therapy (VMAT) beams. RESULTS & CONCLUSION: Non-dosimetric and dosimetric tests were conducted to assess clinical suitability. The bolus was precisely created using stereolithographic (SLA) methods and presented a compliant and uniform water equivalent material with elastic memory. Measurement yielded a physical density of 1.10 g cm-3 and 1.06 relative to water electron density, and the bolus to skin distance was measured to be a maximum of 3 mm. A maximum measured dose difference of <2% was observed for dynamic treatment. Based on the investigation conducted, and the benefits presented for patient comfort while being uniform and water equivalent, and correctly represented within the treatment planning system (TPS), this material has the potential for clinical use for patient specific custom bolus.

Linear accelerator bunker shielding for stereotactic radiotherapy.

Shielding protocols such as NCRP 151, IAEA SRS 47 and IPEM 47 are commonly used for the design of radiotherapy facilities. Some work has been accomplished in updating the basic formula with the advent of IMRT but little consideration has been made for unflattened beams and stereotactic techniques apart from for facilities housing devices like the CyberKnife. The inevitable scenario of a stereotactic-only linear accelerator was considered in this study. The necessary shielding requirements were determined based on stereotactic data from a year's worth treatments from one clinic as well as further measurements of leakage, scatter and use factors. These values were compared to recommendations in the literature. While tenth value layer amounts, workload and barrier widths could be kept at the status quo, major changes could be made to the parameters of leakage, scatter and use factors while still maintaining safety. Some differences could also be seen for the use of IMRT factors. Current shielding protocols were found to inadequately describe methodology for the shielding of a stereotactic-only radiotherapy linac bunker, producing overly-conservative wall thicknesses which is in disagreement with the principles of ICRP.

Conservatism in linear accelerator bunker shielding.

Conservatism in the shielding of linear accelerator bunkers is engrained in the methodology of international protocols and guidelines. However, the degree to which this cautious and prudent approach is necessary should be judged against the International Committee of Radiation Protection's principles of exposure justification and optimisation. Radiation survey data from 75 concrete barriers was aggregated and compared to exposure predictions from three popular protocols in order to assess any conservatism in factors used to calculate scatter, leakage and beam penetration. These findings, in addition to a list of common conservative practices, were then used to tally the possible fiscal impact of an over-conservative approach to linear accelerator bunker shielding. While primary beam penetration was accurately predicted, stated conservatisms in scatter and leakage was found to be largely misplaced. An estimated total factor of conservatism calculated from a tally was found to be in agreement with literature values of radiotherapist occupational exposure. This factor amounted to a cost increase of 43% for a single bunker if all conservative assumptions were made. There are aspects of linear accelerator shielding design that have been shown to be overly conservative, beyond what is justifiable by the International Committee of Radiation Protection. Some adjustment to international protocol methodology may be required.

Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study.

PURPOSE: Beam matching occurs on all linacs to some degree and when two are more are matched to each other, patients are able to be transferred between machines. Quality assurance of plans can also be performed "distributively" on any of the matched linacs. The degree to which machines are matched and how this translates to like delivery of plans has been the focus of a number of studies. This concept has not yet been explored for stereotactic techniques which require a higher degree of accuracy. This study proposes beam matching criteria which allows for the distributive delivery and quality assurance of stereotactic body radiotherapy (SBRT) plans. METHOD: Two clinically relevant and complex volumetric modulated arc therapy (VMAT) SBRT spine and lung plans were chosen as benchmarking cases. These were delivered on nine previously beam matched linacs with quality assurance performed through ArcCheck and film exposure in the sagittal plane. Measured doses were compared to their treatment planning system predictions through gamma analysis at a range of criteria. RESULTS: Despite differences in beam match parameters and variations in small fields, all nine linacs produced accurate deliveries with a tight deviation in the population sample. Pass rates were well above suggested tolerances at the recommended gamma criterion. Film was able to detect dose errors to a greater degree than ArcCheck. CONCLUSION: Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linacs is certainly feasible provided the linacs are matched to a strict protocol like that suggested in this study and regular quality assurance is performed on the matched fleet. Distributive quality assurance and delivery of SBRT provides the possibility of efficiency gains for physicists as well as treatment staff.

Effect of arc length on skin dose from hypofractionated volumetric modulated arc radiotherapy treatments of the lung and spine.

Due to large doses per fraction, stereotactic ablative radiotherapy of lung or spine can lead to skin tissue toxicity, the amount of which depends on a variety of factors such as target location, beam geometry, and immobilization. The effect of arc length on spreading out entrance and exit doses and the corresponding predictions of skin reactions has not yet been studied for stereotactic body radiotherapy volumetric modulated arc therapy (VMAT) treatments. 58 clinically relevant VMAT stereotactic body radiotherapy spine and lung plans were created for an anthropomorphic phantom utilizing a range of target locations, beam geometries and arc lengths. Skin dose was assessed by considering the National Cancer Institute skin reaction grades adjusted for 3 fraction treatments. While the skin volumes predicted to exhibit low grade reactions decreased with arc length, high grade reactions were found to increase at smaller arcs as well as at full arcs where a superposition of entrance and exit doses would occur. It is possible for skin dose to be effectively optimized by choice of arc length (within clinically relevant boundaries) and thus minimize the skin reaction. High skin doses are often attributed to effects arising from the distance between the planning target volume and patient surface but this study has demonstrated that VMAT arc length is of equal importance. Understanding this relationship will assist in minimizing skin reactions through modification of plan parameters and will provide clinicians more information for patient selection.

Improving accuracy for stereotactic body radiotherapy treatments of spinal metastases.

PURPOSE: Use of SBRT techniques is now a relatively common recourse for spinal metastases due to good local control rates and durable pain control. However, the technique has not yet reached maturity for gantry-based systems, so work is still required in finding planning approaches that produce optimum conformity as well as delivery for the slew of treatment planning systems and treatment machines. METHODS: A set of 32 SBRT spine treatment plans based on four vertebral sites, varying in modality and number of control points, were created in Pinnacle. These plans were assessed according to complexity metrics and planning objectives as well as undergoing treatment delivery QA on an Elekta VersaHD through ion chamber measurement, ArcCheck, film-dose map comparison and MLC log-file reconstruction via PerFraction. RESULTS: All methods of QA demonstrated statistically significant agreement with each other (r = 0.63, P < 0.001). Plan complexity and delivery accuracy were found to be independent of MUs (r = 0.22, P > 0.05) but improved with the number of control points (r = 0.46, P < 0.03); with use of 90 control points producing the most complex and least accurate plans. The fraction of small apertures used in treatment had no impact on plan quality or accuracy (r = 0.29, P > 0.05) but rather more complexly modulated plans showed poorer results due to MLC leaf position inaccuracies. Plans utilizing 180 and 240 control points produced optimal plan coverage with similar complexity metrics to each other. However, plans with 240 control points demonstrated slightly better delivery accuracy, with fewer MLC leaf position discrepancies. CONCLUSION: In contrast to other studies, MU had no effect on delivery accuracy, with the most impactful parameter at the disposal of the planner being the number of control points utilized.

A simple method to account for skin dose enhancement during treatment planning of VMAT treatments of patients in contact with immobilization equipment.

PURPOSE: The ability to accurately predict skin doses and thereby design radiotherapy treatments that balance the likelihood of skin reactions against other treatment objectives is especially important when hypofractionated prescription regimes are used. However, calculations of skin dose provided by many commercial radiotherapy treatment planning systems are known to be inaccurate, especially if the presence of immobilization equipment is not accurately taken into account. This study proposes a simple method by which the accuracy of skin dose calculations can be substantially improved, to allow informed evaluation of volumetric modulated arc therapy (VMAT) treatment plans. METHOD: A simple method was developed whereby dose calculation is split into grid regions, each with a correction factor which determines MU scaling for skin dose calculation. Correction factors were derived from film measurements made using a geometrically simple phantom in partial contact with a vacuum immobilization device. This method was applied to two different test treatments, planned for delivery to a humanoid phantom with a hypofractionated stereotactic body radiotherapy technique, and results were verified using film measurements of surface dose. RESULTS: Compared to the measured values, calculations of skin dose volumes corresponding to different grade tissue reactions were greatly improved through use of the method employed in this study. In some cases, the accuracy of skin dose evaluation improved by 76% and brought values to within 3% of those measured. CONCLUSION: The method of skin dose calculation in this study is simple, can be made as accurate as the user requires and is applicable for various immobilization systems. This concept has been verified through use on SBRT lung treatment plans and will aid clinicians in predicting skin response in patients.

Dose uncertainties associated with a set density override of unknown hip prosthetic composition.

The dosimetric uncertainties associated with radiotherapy through hip prostheses while overriding the implant to a set density within the TPS has not yet been reported. In this study, the uncertainty in dose within a PTV resulting from this planning choice was investigated. A set of metallic hip prosthetics (stainless steel, titanium, and two different Co-Cr-Mo alloys) were CT scanned in a water bath. Within the TPS, the prosthetic pieces were overridden to densities between 3 and 10 g/cm3 and irradiated on a linear accelerator. Measured dose maps were compared to the TPS to determine which density was most appropriate to override each metal. This was shown to be in disagreement with the reported literature values of density which was attributed to the TPS dose calculation algorithm and total mass attenuation coefficient differences in water and metal. The dose difference was then calculated for a set density override of 6 g/cm3 in the TPS and used to estimate the dose uncertainty beyond the prosthesis. For beams passing through an implant, the dosimetric uncertainty in regions of the PTV may be as high as 10% if the implant composition remains unknown and a set density override is used. These results highlight limitations of such assumptions and the need for careful consideration by radiation oncologist, therapist, and physics staff.

Post-upgrade testing on a radiotherapy oncology information system with an embedded record and verify system following the IAEA Human Health Report No. 7 recommendations.

Record and verify (R&V) systems have proven that their application in radiotherapy clinics leads to a significant reduction in mis-treatments of patients. The purpose of this technical note is to share our experience of acceptance testing, commissioning and setting up a quality assurance programme for the MOSAIQ® oncology information system and R&V system after upgrading from software version 2.41 to 2.6 in a multi-vendor, multi-site environment. Testing was guided primarily by the IAEA Human Report No. 7 recommendations, but complemented by other departmental workflow specific tests. To the best of our knowledge, this is the first time successful implementation of the IAEA Human Health Report Series No. 7 recommendations have been reported in the literature.

Comparison of effective I-131 half-life between thyroid hormone withdrawal and recombinant human thyroid-stimulating hormone for thyroid cancer: a retrospective study.

INTRODUCTION: Preparation for postoperative radioiodine ablation for differentiated thyroid carcinoma is performed by either thyroid hormone withdrawal or recombinant human thyroid-stimulating hormone (rhTSH) administration. There is little information on the impact of the method of preparation with respect to whole-body effective I-131 half-life and its potential clinical implications in the Australian setting. METHODS: A retrospective study was performed on patients admitted for adjuvant radioiodine ablation for non-metastatic differentiated thyroid carcinoma at the Royal Adelaide Hospital over a 4½-year period from 2009. Dose rate measurements were analysed for 19 rhTSH and 31 thyroid hormone withdrawal patients. RESULTS: The mean effective I-131 half-lives were 11.51 and 13.29 h for the rhTSH and thyroid hormone withdrawal groups, respectively, with no statistically significant difference between the two groups (P = 0.761). This result differs from previously published data where withdrawal periods were typically longer, resulting in slower renal clearance and longer half-lives for withdrawal patients. CONCLUSIONS: Our study did not demonstrate a significant difference in whole-body effective half-life of I-131 between the two methods of preparation for radioiodine ablation. This suggests that putative advantages of rhTSH over withdrawal in terms of whole-body radiation dose, duration of hospital admission and quality of life may be sensitive to duration of withdrawal.