Clinical implementation of a knowledge based planning tool for prostate VMAT.

BACKGROUND: A knowledge based planning tool has been developed and implemented for prostate VMAT radiotherapy plans providing a target average rectum dose value based on previously achievable values for similar rectum/PTV overlap. The purpose of this planning tool is to highlight sub-optimal clinical plans and to improve plan quality and consistency. METHODS: A historical cohort of 97 VMAT prostate plans was interrogated using a RayStation script and used to develop a local model for predicting optimum average rectum dose based on individual anatomy. A preliminary validation study was performed whereby historical plans identified as "optimal" and "sub-optimal" by the local model were replanned in a blinded study by four experienced planners and compared to the original clinical plan to assess whether any improvement in rectum dose was observed. The predictive model was then incorporated into a RayStation script and used as part of the clinical planning process. Planners were asked to use the script during planning to provide a patient specific prediction for optimum average rectum dose and to optimise the plan accordingly. RESULTS: Plans identified as "sub-optimal" in the validation study observed a statistically significant improvement in average rectum dose compared to the clinical plan when replanned whereas plans that were identified as "optimal" observed no improvement when replanned. This provided confidence that the local model can identify plans that were suboptimal in terms of rectal sparing. Clinical implementation of the knowledge based planning tool reduced the population-averaged mean rectum dose by 5.6Gy. There was a small but statistically significant increase in total MU and femoral head dose and a reduction in conformity index. These did not affect the clinical acceptability of the plans and no significant changes to other plan quality metrics were observed. CONCLUSIONS: The knowledge-based planning tool has enabled substantial reductions in population-averaged mean rectum dose for prostate VMAT patients. This suggests plans are improved when planners receive quantitative feedback on plan quality against historical data.

IGRT/ART phantom with programmable independent rib cage and tumor motion.

PURPOSE: This paper describes the design and experimental evaluation of the Methods and Advanced Equipment for Simulation and Treatment in Radiation Oncology (MAESTRO) thorax phantom, a new anthropomorphic moving ribcage combined with a 3D tumor positioning system to move target inserts within static lungs. METHODS: The new rib cage design is described and its motion is evaluated using Vicon Nexus, a commercial 3D motion tracking system. CT studies at inhale and exhale position are used to study the effect of rib motion and tissue equivalence. RESULTS: The 3D target positioning system and the rib cage have millimetre accuracy. Each axis of motion can reproduce given trajectories from files or individually programmed sinusoidal motion in terms of amplitude, period, and phase shift. The maximum rib motion ranges from 7 to 20 mm SI and from 0.3 to 3.7 mm AP with LR motion less than 1 mm. The repeatability between cycles is within 0.16 mm root mean square error. The agreement between CT electron and mass density for skin, ribcage, spine hard and inner bone as well as cartilage is within 3%. CONCLUSIONS: The MAESTRO phantom is a useful research tool that produces programmable 3D rib motions which can be synchronized with 3D internal target motion. The easily accessible static lungs enable the use of a wide range of inserts or can be filled with lung tissue equivalent and deformed using the target motion system.

A pre-clinical assessment of an atlas-based automatic segmentation tool for the head and neck.

BACKGROUND AND PURPOSE: Accurate conformal radiotherapy treatment requires manual delineation of target volumes and organs at risk (OAR) that is both time-consuming and subject to large inter-user variability. One solution is atlas-based automatic segmentation (ABAS) where a priori information is used to delineate various organs of interest. The aim of the present study is to establish the accuracy of one such tool for the head and neck (H&N) using two different evaluation methods. MATERIALS AND METHODS: Two radiotherapy centres were provided with an ABAS tool that was used to outline the brainstem, parotids and mandible on several patients. The results were compared to manual delineations for the first centre (EM1) and reviewed/edited for the second centre (EM2), both of which were deemed as equally valid gold standards. The contours were compared in terms of their volume, sensitivity and specificity with the results being interpreted using the Dice similarity coefficient and a receiver operator characteristic (ROC) curve. RESULTS: Automatic segmentation took typically approximately 7min for each patient on a standard PC. The results indicated that the atlas contour volume was generally within +/-1SD of each gold standard apart from the parotids for EM1 and brainstem for EM2 that were over- and under-estimated, respectively (within +/-2SD). The similarity of the atlas contours with their respective gold standard was satisfactory with an average Dice coefficient for all OAR of 0.68+/-0.25 for EM1 and 0.82+/-0.13 for EM2. All data had satisfactory sensitivity and specificity resulting in a favourable position in ROC space. CONCLUSIONS: These tests have shown that the ABAS tool exhibits satisfactory sensitivity and specificity for the OAR investigated. There is, however, a systematic over-segmentation of the parotids (EM1) and under-segmentation of the brainstem (EM2) that require careful review and editing in the majority of cases. Such issues have been discussed with the software manufacturer and a revised version is due for release.

Evaluation of margining algorithms in commercial treatment planning systems.

INTRODUCTION: During commissioning of the Pinnacle (Philips) treatment planning system (TPS) the margining algorithm was investigated and was found to produce larger PTVs than Plato (Nucletron) for identical GTVs. Subsequent comparison of PTV volumes resulting from the QA outlining exercise for the CHHIP (Conventional or Hypofractionated High Dose IMRT for Prostate Ca.) trial confirmed that there were differences in TPS's margining algorithms. Margining and the clinical impact of the different PTVs in seven different planning and virtual simulation systems (Pinnacle, Plato, Prosoma (MedCom), Eclipse (7.3 and 7.5) (Varian), MasterPlan (Nucletron), Xio (CMS) and Advantage Windows (AW) (GE)) is investigated, and a simple test for 3D margining consistency is proposed. METHODS: Using each TPS, two different sets of prostate GTVs on 2.5mm and 5mm slices were margined according to the CHHIP protocol to produce PTV3 (prostate+5 mm/0 mm post), PTV2 (PTV3+5 mm) and PTV1 (prostate and seminal vesicles+10 mm). GTVs and PTVs were imported into Pinnacle for volume calculation. DVHs for 5mm slice plans, created using the smallest PTVs, were recalculated on the largest PTV dataset and vice versa. Since adding a margin of 50 mm to a structure should give the same result as adding five margins of 10 mm, this was tested for each TPS (consistency test) using an octahedron as the GTV and CT datasets with 2.5 mm and 5 mm slices. RESULTS: The CHHIP PTV3 and PTV1 volumes had a standard deviation, across the seven systems, of 5% and PTV2 (margined twice) 9%, on the 5 mm slices. For 2.5 mm slices the standard deviations were 4% and 6%. The ratio of the Pinnacle and the Eclipse 7.3 PTV2 volumes was 1.25. Rectal doses were significantly increased when encompassing Pinnacle PTVs (V(50)=42.8%), compared to Eclipse 7.3 PTVs (V(50)=36.4%). Conversely, fields that adequately treated an Eclipse 7.3 PTV2 were inadequate for a Pinnacle PTV2. AW and Plato PTV volumes were the most consistent (0.3%) and (-0.4%). However, the 1x50mm margin in Pinnacle produced a 15.9% larger volume than 5 x 10 mm margins, while for Eclipse 7.3 the single margined volume was 14.3% smaller. These inconsistencies were reduced to approximately 5% by adjusting the superior/inferior margins. CONCLUSIONS: Accurate margin algorithms are necessary to ensure that volume expansion does not add extra uncertainty to the radiotherapy planning process. We have found significant differences in the 3D margining algorithms of TPSs, devised a simple test to predict inconsistency and suggested corrective action to minimise the variation.

Bridges to life: evaluation of an in-prison restorative justice intervention.

Restorative justice initiatives have been identified as primarily, if not exclusively, useful as a "front-end" diversionary option reserved for non violent property crimes and minor assaults. In-prison restorative justice programs are rare and have not been examined for their impact on recidivism. Bridges to Life (BTL) is a voluntary, manualized, ecumenical faith-based restorative justice program offered to incarcerated offenders who are within nine months of their release. A survey of BTL graduates (n=1021) found an appreciatively lower recidivism rate than the general population of released inmates. Quantitative and qualitative analyses suggest that BTL helps break through offenders' denial and self-centeredness, exposing them to the impact of their actions and helping them feel the pain their crimes created. Possible reasons for the positive nature of participants' responses are advanced. The use of in-prison restorative justice programs to facilitate offender re-entry is also discussed.

Tolerance levels for quality assurance of electron density values generated from CT in radiotherapy treatment planning.

Methods are described which relate the uncertainty in relative electron density derived from CT numbers to the uncertainty in treatment plan calculation for both photon and electron beams. These relationships are used to generate tolerance levels for electron density quality assurance measurements. These tolerance levels are dependent on treatment beam energy and tissue thickness, and are generally broader than current recommendations. The predicted treatment plan errors associated with these tolerance levels are shown to be consistent with calculations made using two commercial treatment planning systems. The tolerance levels are also shown to be practical by comparison against quality assurance measurements made on a conventional CT scanner and a treatment simulator CT system over a 12-month period. The results demonstrate that broader tolerances than are currently recommended can be justified in all situations except for electron beam treatments in which the therapeutic range falls within lung tissue.