A comparison of in-house and shared RapidPlan models for prostate radiation therapy planning.

Knowledge-based planning (KBP) can increase plan quality, consistency and efficiency. In this study, we assess the success of a using a publicly available KBP model compared with developing an in-house model for prostate cancer radiotherapy using a single, commercially available treatment planning system based on the ability of the model to achieve the centre's planning goals. Two radiation oncology centres each created a prostate cancer KBP model using the Eclipse RapidPlan software. These two models and a third publicly-available, shared model were tested at three centres in a retrospective planning study. The publicly-available model achieved lower rectum doses than the other two models. However, the planning-target-volume (PTV) doses did not meet the local planning goals and the model could not be adjusted to correct this. As a result, the plans most likely to satisfy local planning goals and requirements were created using an in-house model. For centres without an existing in-house model, a model created by another centre with similar planning goals was found to be preferred. Variations in local planning practices including contouring, treatment technique and planning goals can influence the relative performance of KBP. The value of publicly available KBP models could be enhanced through standardisation of planning goals and contouring guidelines, providing information related to the planning goals used to create the model and increased flexibility to allow local adaptation of the KBP model.

Clinical impact of removing respiratory motion during liver SABR.

BACKGROUND: Liver tumors are subject to motion with respiration, which is typically accounted for by increasing the target volume. The prescription dose is often reduced to keep the mean liver dose under a threshold level to limit the probability of radiation induced liver toxicity. A retrospective planning study was performed to determine the potential clinical gains of removal of respiratory motion from liver SABR treatment volumes, which may be achieved with gating or tumor tracking. METHODS: Twenty consecutive liver SABR patients were analysed. The treated PTV included the GTV in all phases of respiration (ITV) with a 5 mm margin. The goal prescription was 50Gy/5# (BED 100 Gy10) but was reduced by 2.5 Gy increments to meet liver dose constraints. Elimination of motion was modelled by contouring the GTV in the expiration phase only, with a 5 mm PTV margin. All patients were replanned using the no-motion PTV and tumor dose was escalated to higher prescription levels where feasible given organ-at-risk constraints. For the cohort of patients with metastatic disease, BED gains were correlated to increases in tumour control probability (TCP). The effect of the gradient of the TCP curve on the magnitude of TCP increase was evaluated by repeating the study for an additional prescription structure, 54Gy/3# (BED 151 Gy10). RESULTS: Correlation between PTV size and prescribed dose exists; PTVs encompassing < 10% of the liver could receive the highest prescription level. A monotonically increasing correlation (Spearman's rho 0.771, p = 0.002) between the degree of PTV size reduction and motion vector magnitude was observed for GTV sizes <100cm3. For 11/13 patients initially planned to a decreased prescription, tumor dose escalation was possible (5.4Gy10-21.4Gy10 BED) using the no-motion PTV. Dose escalation in excess of 20 Gy10 increased the associated TCP by 5% or more. A comparison of TCP gains between the two fractionation schedules showed that, for the same patient geometry, the absolute increase in BED was the overarching factor rather than the gradient of the TCP curve. CONCLUSIONS: In liver SABR treatments unable to be prescribed optimal dose due to exceeding mean liver thresholds, eliminating respiratory motion allowed dose escalation in the majority of patients studied and substantially increased TCP.

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams.

PURPOSE: Flattening filter free (FFF) beams are increasingly being considered for stereotactic radiotherapy (SRT). For the first time, the performance of a monolithic silicon array detector under 6 and 10 MV FFF beams was evaluated. The dosimeter, named "Octa" and designed by the Centre for Medical Radiation Physics (CMRP), was tested also under flattened beams for comparison. METHODS: Output factors (OFs), percentage depth-dose (PDD), dose profiles (DPs) and dose per pulse (DPP) dependence were investigated. Results were benchmarked against commercially available detectors for small field dosimetry. RESULTS: The dosimeter was shown to be a 'correction-free' silicon array detector for OFs and PDD measurements for all the beam qualities investigated. Measured OFs were accurate within 3% and PDD values within 2% compared against the benchmarks. Cross-plane, in-plane and diagonal DPs were measured simultaneously with high spatial resolution (0.3 mm) and real time read-out. A DPP dependence (24% at 0.021 mGy/pulse relative to 0.278 mGy/pulse) was found and could be easily corrected for in the case of machine specific quality assurance applications. CONCLUSIONS: Results were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side.

A Multidisciplinary Evaluation of a Web-based eLearning Training Programme for SAFRON II (TROG 13.01): a Multicentre Randomised Study of Stereotactic Radiotherapy for Lung Metastases.

AIMS: In technically advanced multicentre clinical trials, participating centres can benefit from a credentialing programme before participating in the trial. Education of staff in participating centres is an important aspect of a successful clinical trial. In the multicentre study of fractionated versus single fraction stereotactic ablative body radiotherapy in lung oligometastases (TROG 13.01), knowledge transfer of stereotactic ablative body radiotherapy techniques to the local multidisciplinary team is intended as part of the credentialing process. In this study, a web-based learning platform was developed to provide education and training for the multidisciplinary trial teams at geographically distinct sites. MATERIALS AND METHODS: A web-based platform using eLearning software consisting of seven training modules was developed. These modules were based on extracranial stereotactic theory covering the following discrete modules: Clinical background; Planning technique and evaluation; Planning optimisation; Four-dimensional computed tomography simulation; Patient-specific quality assurance; Cone beam computed tomography and image guidance; Contouring organs at risk. Radiation oncologists, medical physicists and radiation therapists from hospitals in Australia and New Zealand were invited to participate in this study. Each discipline was enrolled into a subset of modules (core modules) and was evaluated before and after completing each module. The effectiveness of the eLearning training will be evaluated based on (i) knowledge retention after participation in the web-based training and (ii) confidence evaluation after participation in the training. Evaluation consisted of a knowledge test and confidence evaluation using a Likert scale. RESULTS: In total, 130 participants were enrolled into the eLearning programme: 81 radiation therapists (62.3%), 27 medical physicists (20.8%) and 22 radiation oncologists (16.9%). There was an average absolute improvement of 14% in test score (P < 0.001) after learning. This score improvement compared with initial testing was also observed in the long-term testing (>4 weeks) after completing the modules (P < 0.001). For most there was significant increase in confidence (P < 0.001) after completing all the modules.

Dose enhancement in radiotherapy of small lung tumors using inline magnetic fields: A Monte Carlo based planning study.

PURPOSE: To report on significant dose enhancement effects caused by magnetic fields aligned parallel to 6 MV photon beam radiotherapy of small lung tumors. Findings are applicable to future inline MRI-guided radiotherapy systems. METHODS: A total of eight clinical lung tumor cases were recalculated using Monte Carlo methods, and external magnetic fields of 0.5, 1.0, and 3 T were included to observe the impact on dose to the planning target volume (PTV) and gross tumor volume (GTV). Three plans were 6 MV 3D-CRT plans while 6 were 6 MV IMRT. The GTV's ranged from 0.8 to 16 cm(3), while the PTV's ranged from 1 to 59 cm(3). In addition, the dose changes in a 30 cm diameter cylindrical water phantom were investigated for small beams. The central 20 cm of this phantom contained either water or lung density insert. RESULTS: For single beams, an inline magnetic field of 1 T has a small impact in lung dose distributions by reducing the lateral scatter of secondary electrons, resulting in a small dose increase along the beam. Superposition of multiple small beams leads to significant dose enhancements. Clinically, this process occurs in the lung tissue typically surrounding the GTV, resulting in increases to the D98% (PTV). Two isolated tumors with very small PTVs (3 and 6 cm(3)) showed increases in D98% of 23% and 22%. Larger PTVs of 13, 26, and 59 cm(3) had increases of 9%, 6%, and 4%, describing a natural fall-off in enhancement with increasing PTV size. However, three PTVs bounded to the lung wall showed no significant increase, due to lack of dose enhancement in the denser PTV volume. In general, at 0.5 T, the GTV mean dose enhancement is around 60% lower than that at 1 T, while at 3 T, it is 5%-60% higher than 1 T. CONCLUSIONS: Monte Carlo methods have described significant and predictable dose enhancement effects in small lung tumor plans for 6 MV radiotherapy when an external inline magnetic field is included. Results of this study indicate that future clinical inline MRI-guided radiotherapy systems will be able to deliver a dosimetrically superior treatment to small (PTV < 15 cm(3)), isolated lung tumors over non-MRI-Linac systems. This increased efficacy coincides with the reimbursement in the United States of lung CT screening and the likely rapid growth in the number of patients with small lung tumors to be treated with radiotherapy.

Calculating integral dose using data exported from a commercial record and verify system.

Integral dose has been useful in investigations into the incidence of second primary malignancies in radiotherapy patients. This note outlines an approach to calculation of integral dose for a group of prostate patients using only data exported from a commercial record and verify system. Even though it was necessary to make some assumptions about patient anatomy, comparison with integral dose calculated from data exported from the planning system showed good agreement.

Predictors of respiratory-induced lung tumour motion measured on four-dimensional computed tomography.

AIMS: The delivery of radical radiotherapy in lung cancer is complicated by respiratory-induced tumour motion. The aim of the study was to correlate tumour motion characteristics with tumour and patient factors, particularly the anatomical lobe and pulmonary zone. MATERIALS AND METHODS: Lung tumour volumes on four-dimensional computed tomography were delineated by a single observer at maximal expiration and propagated through all 10 phases of the breathing cycle. Movements were tracked in the superior-inferior (SI), anterior-posterior (AP) and medio-lateral (ML) directions by changes in the tumour centroid coordinates. Tumour motion characteristics were correlated with anatomical lobe, pulmonary zone, tumour volume, T-stage, smoking status and spirometry. RESULTS: In 101 consecutive patients, the median magnitude of tumour motion in the SI direction was significantly larger in tumours located in lower lobes compared with upper lobes and middle/lingular lobes (0.70 cm versus 0.09 cm versus 0.26 cm, P < 0.01). No significant difference was found in median tumour motion between lower, upper and middle/lingular lobes in the AP (0.16 cm versus 0.13 cm versus 0.16 cm, P = 0.45) and ML (0.08 cm versus 0.08 cm versus 0.13 cm, P = 0.32) directions, respectively. When assessed by zone, the median tumour displacement in the SI direction was significantly larger in the lower zones (0.81 cm) as compared with the middle zones (0.30 cm) and upper zones (0.11 cm), P < 0.01. No difference was observed in the AP (P = 0.45) and ML (P = 0.73) directions. Tumour volume, T-stage and forced expiratory ratio were not statistically significant predictors of respiratory-induced tumour motion. CONCLUSION: Respiratory-induced tumour motion in the SI direction was significantly greater in lower lobe and lower pulmonary zone tumours compared with apical tumours. Tumour volume, T-stage and spirometry did not correlate with the magnitude or direction of respiratory-induced tumour motion. During curative radiotherapy in lung cancer, attention should be paid to motion management, especially for lower lobe tumours.

Comparison of margins, integral dose and interfraction target coverage with image-guided radiotherapy compared with non-image-guided radiotherapy for bladder cancer.

AIMS: To measure the difference in cumulative doses received by the bladder (target) and integral doses with different clinical target volume (CTV) to planning target volume (PTV) margins, comparing set-up to skin tattoos versus image-guided radiotherapy to bone or soft tissue. MATERIALS AND METHODS: Four plans were generated on each planning computed tomography dataset using the CTV with 5, 10, 15, 20 mm PTV margins using a three-dimensional conformal four-field technique. Set-up data based on skin, bone and soft tissue to the bladder on pre-treatment cone beam computed tomography (CBCT) were recorded. In total, 316 CBCTs were evaluable from 10 bladder cancer patients. Each CBCT was fused to the planning computed tomography dataset using the isocentre corresponding to each of the three pre-treatment matching conditions. The target was contoured on each CBCT and called the CTV of the day and the plan was re-calculated to determine the dose to this. RESULTS: The mean D95 with CTV to PTV margins of 5, 10, 15 and 20 mm for skin set-up was 89.4, 93.0, 97.2, 98.6; for bone 88.8, 92.6, 96.7, 98.6; and for soft tissue 96.3, 98.6, 98.7, 99.5. With soft-tissue matching, the mean (standard deviation) volume of normal tissue receiving 5 Gy with 5, 10, 15 and 20 mm margins was 3899 (1022), 4561 (1142), 5663 (1304) and 6315 (1426) in cm(3). CONCLUSION: Soft-tissue matching results in superior target coverage and a reduced integral dose to the surrounding tissues. With soft-tissue matching, increasing CTV to PTV margins progressively beyond 5 mm results in modest improvement in CTV coverage, but a large increase in integral dose.

EBT2 radiochromic film for quality assurance of complex IMRT treatments of the prostate: micro-collimated IMRT, RapidArc, and TomoTherapy.

In response to the clinical need for a dosimetry system with both high resolution and minimal angular dependence, this study demonstrates the utility of Gafchromic EBT2 radiochromic dosimetry film for the quality assurance of micro-collimated IMRT, RapidArc and TomoTherapy treatments. Firstly, preliminary measurements indicated that the dose response of EBT2 film does not appreciably vary with either the angle of incidence of the radiation beam or the depth in water at which the film is placed. Secondly, prostate treatment plans designed for delivery using static-beam IMRT (collimated using the BrainLab m3 microMLC), RapidArc and TomoTherapy were investigated by comparing dose planes obtained from treatment planning calculations with EBT2 film measurements. For all treatment plans, the proportion of dose points agreeing with the film measurements to within γ (3%,3 mm) was found to be above 95%, with all points agreeing within 5%. The film images provided sufficient information to verify that the treatments could be delivered with an acceptable level of accuracy, while also providing additional information on low-level dose variations that were not predicted by the treatment planning systems. This information included: the location and extent of dose from inter-leaf leakage (in the RapidArc plan) and helical field junctioning (in the TomoTherapy plan), as well as the existence of small regions where the treatment planning system under-predicted the dose from very small treatment segments (in the micro-collimated IMRT plan).

Independent quality assurance of a helical tomotherapy machine using the dose magnifying glass.

PURPOSE: Helical tomotherapy is a complex delivery technique, integrating CT image guidance and intensity modulated radiotherapy in a single system. The integration of the CT detector ring on the gantry not only allows patient position verification but is also often used to perform various QA procedures. This convenience lacks the rigor of a machine-independent QA process. METHODS: In this article, a Si strip detector, known as the Dose Magnifying Glass (DMG), was used to perform machine-independent QA measurements of the multileaf collimator alignment, leaf open time threshold, and leaf fluence output factor (LFOF). RESULTS: The DMG measurements showed good agreements with EDR2 film for the MLC alignment test while the CT detector agrees well with DMG measurements for leaf open time threshold and LFOF measurements. The leaf open time threshold was found to be approximately 20 ms. The LFOF measured with the DMG agreed within error with the CT detector measured LFOF. CONCLUSIONS: The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit.

Rectal dose reduction with IMRT for prostate radiotherapy.

Dose escalation in radiation therapy has led to increased control rates with some clinical trial evidence that rectal toxicity may be reduced when using intensity-modulated radiotherapy (IMRT) over 3D conformal radiotherapy (3DCRT) for dose-escalated prostate radiotherapy. However, IMRT for prostate patients is not yet standard in many Australian radiation oncology centres. This study investigates dosimetric changes that can be observed between IMRT and 3DCRT in prostate radiotherapy. Fifteen patients were selected for analysis. Two target definitions were investigated--prostate-only and prostate plus seminal vesicles (p + SVs). A five-field 3DCRT and seven-field IMRT plan were created for each patient and target definition. The planning target volume coverage was matched for both plans. Doses to the rectum, bladder and femoral heads were compared using dose volume histograms. The rectal normal tissue complication probabilities (NTCPs) were calculated and compared for the 3DCRT and IMRT plans. The delivery efficiency was investigated. The IMRT plans resulted in reductions in the V25, V50, V60, V70 and V75 Gy values for both the prostate-only and p + SVs targets. Rectal NTCP was reduced with IMRT for three different sets of model parameters. The reductions in rectal dose and NTCP were much larger for the p + SVs target. Delivery of IMRT plans was less efficient than for 3DCRT plans. IMRT resulted in superior plans based on dosimetric and biological endpoints. The dosimetric gains with IMRT were greater for the more complex p + SVs target. The gains made came at the cost of decreased delivery efficiency.

Monte carlo study of MOSFET packaging, optimised for improved energy response: single MOSFET filtration.

Monte Carlo simulations of the energy response of a conventionally packaged single metal-oxide field effect transistors (MOSFET) detector were performed with the goal of improving MOSFET energy dependence for personal accident or military dosimetry. The MOSFET detector packaging was optimised. Two different 'drop-in' design packages for a single MOSFET detector were modelled and optimised using the GEANT4 Monte Carlo toolkit. Absorbed photon dose simulations of the MOSFET dosemeter placed in free-air response, corresponding to the absorbed doses at depths of 0.07 mm (D(w)(0.07)) and 10 mm (D(w)(10)) in a water equivalent phantom of size 30 x 30 x 30 cm(3) for photon energies of 0.015-2 MeV were performed. Energy dependence was reduced to within + or - 60 % for photon energies 0.06-2 MeV for both D(w)(0.07) and D(w)(10). Variations in the response for photon energies of 15-60 keV were 200 and 330 % for D(w)(0.07) and D(w)(10), respectively. The obtained energy dependence was reduced compared with that for conventionally packaged MOSFET detectors, which usually exhibit a 500-700 % over-response when used in free-air geometry.

Multileaf collimator end leaf leakage: implications for wide-field IMRT.

The multi-leaf collimator (MLC) of a particular linear accelerator vendor (Millennium MLC, Varian Medical Systems, Palo Alto, CA, USA) has a maximum leaf extension of 14.5 cm. To achieve intensity modulated radiotherapy (IMRT) for fields wider than 14.5 cm all closed leaf pairs are restricted to placement inside the field. Due to the rounded leaf end design of the MLC end leaf leakage will occur in the treatment field. The implementation of direct aperture optimization in the IMRT module of a radiotherapy treatment planning system (Pinnacle, Philips Radiation Oncology Systems, Milpitas, CA) has facilitated the delivery of IMRT fields wider than 14.5 cm. The end leaf leakage of the Millennium MLC has been characterized for 6 MV photons using gafchromic and radiographic film, and the accuracy of the planning system verified. The maximum leakage measured for a single field was 0.39 cGy MU(-1) for a 0 mm leaf gap and 0.51 cGy MU(-1) for a 0.6 mm leaf gap. For a clinical IMRT field leaf end leakage contributed an additional 2-3 Gy over the course of treatment. The planning system underestimated the magnitude of end leaf leakage by 20-40%. The ability to deliver IMRT fields wider than 14.5 cm with the Millennium MLC has improved the efficiency and flexibility of IMRT treatments; however, significant extra dose can be introduced due to end leaf leakage. Caution should be exercised when delivering wide field IMRT as it is not a complete panacea. Any significant occurrences of end leaf leakage predicted by the planning system should be independently verified prior to delivery.

Alopecia in association with severe seborrhoeic dermatitis following combination antiretroviral therapy for acute retroviral syndrome.

We present a case where alopecia occurred with severe seborrhoeic dermatitis associated with the commencement of combination antiretroviral therapy for acute retroviral syndrome. We postulate that the eruption could represent a novel manifestation in association with immunological response to antiretroviral therapy.

Best evidence topic report. Humeral fractures and non-accidental injury in children.

A short cut review was carried out to establish whether proximal humeral fractures in children are indicative of non-accidental injury. Altogether 44 papers were found using the reported search, of which two presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated.