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MRI guided radiotherapy devices are currently in clinical use. Detector responses are affected by the magnetic field and need to be characterized in terms of absorbed dose to water, Dw, against primary standards under these conditions. The aim of this study was to commission a water calorimeter, accepted as the Dutch national standard for Dw in MV photons and to validate its claimed standard uncertainty of 0.37% in the 7 MV photon beam of a pre-clinical MRI-linac in a 1.5 T magnetic field. To evaluate the primary standard on a fundamental basis, realisation of Dw at 1.5 T was evaluated parameter by parameter. A thermodynamic description was given to demonstrate potential temperature effects due to the magneto-caloric effect (MCE). Methods were developed for measurement of depth, variation in detector distance and beam output in the bore of the MRI-linac. This resulted in Dw measurements with a magnetic field of 1.5 T and, after ramp-down, without magnetic field. It was shown that the measurement of ΔTw and calorimeter corrections are either independent of or can be determined in a magnetic field. The chemical heat defect, h, was considered zero within its stated uncertainty, as for 0 T. Evaluation of the MCE and measurements done during magnet ramp-down, indicated no changes in the specific heat capacity of water. However, variations of the applied monitor system increased the uncertainty on beam output normalization. This study confirmed that the uncertainty for measurement of Dw with a water calorimeter in a 1.5 T magnetic field is estimated to be the same as under conventional reference conditions. The VSL water calorimeter can be applied as a primary standard for Dw in magnetic fields and is currently the only primary standard operable in a magnetic field that provides direct access to the international traceability framework. [ABSTRACT FROM AUTHOR]

Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers' advice on reference conditions should be followed. Beam quality specification of TPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are k Q msr Q 0 f msr f ref , a correction for beam quality and k B → , Q msr f msr , for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for k B → , Q msr f msr are given. It is important to note that this is a developing field and these recommendations should be used together with a review of current literature. [ABSTRACT FROM AUTHOR]

Prostate cancer oligometastatic disease can be treated using stereotactic body radiotherapy (SBRT) in order to postpone start of systemic treatments such as androgen deprivation therapy (ADT). 68Ga-PSMA-PET/CT imaging allows for diagnosis of oligometastases at lower PSA values. We analysed a cohort of patients with prostate cancer lymph node oligometastases detected on PSMA-PET/CT. Ninety patients with metachronous oligometastatic prostate cancer received SBRT for 1–3 lymph node metastases diagnosed on 68Ga-PSMA-PET/CT. The primary end point was progression free survival (PFS), with disease progression defined as occurrence of either target lesion progression, new metastatic lesion or biochemical progression. Secondary outcomes were biochemical PFS (BPFS), ADT-free survival (ADT-FS), toxicity and quality of life (QoL). Baseline patient characteristics were tested for association with PFS and a preliminary risk score was created. Median follow-up was 21 months (interquartile range 10–31 months). Median PFS and BPFS were 16 and 21 months, respectively. Median ADT-FS was not reached (73% (95%-CI 62–86%) at 24 months). In multivariable analysis, younger age, higher PSA prior to SBRT and extrapelvic location were associated with shorter PFS. Grade 1 fatigue was the most predominant acute toxicity (34%). Highest grade toxicity was grade 2 for acute and late events. QoL analysis showed mild, transient increase in fatigue at 1–4 weeks after SBRT. A median PFS of 16 months was attained after SBRT for patients with PSMA-PET positive oligometastatic lymph nodes from prostate cancer. Higher pre-SBRT PSA, younger age and extrapelvic location were found to be predictors of shorter PFS. [ABSTRACT FROM AUTHOR]

Abstract: A study was undertaken to explore the use of volumetric modulated arc therapy (VMAT) for total body irradiation (TBI). Five patient plans were created in Pinnacle3 using nine 6 MV photon dynamic arcs. A dose of 12 Gy in six fractions was prescribed. The planning target volume (PTV) was split into four subsections for the head, chest, abdomen, and pelvis. The head and chest beams were optimized together, followed by the abdomen and pelvis beams. The last stage of the planning process involved turning all beams on and performing a final optimization to achieve a clinically acceptable plan. Beam isocenters were shifted by 3 or 5 mm in the left–right, anterior–posterior, and superior–inferior directions to simulate the effect of setup errors on the dose distribution. Treatment plan verification consisted of ArcCheck measurements compared to calculated doses using a global 3%/3 mm gamma analysis. All five patient plans achieved the planning aim of delivering 12 Gy to at least 90% of the target. The mean dose in the PTV was 12.7 Gy. Mean lung dose was restricted to 8 Gy, and a dose reduction of up to 40% for organs such as the liver and kidneys proved feasible. The VMAT technique was found to be sensitive to patient setup errors particularly in the superior–inferior direction. The dose predicted by the planning system agreed with measured doses and had an average pass rate of 99.2% for all arcs. VMAT was found to be a viable treatment technique for total body irradiation. [ABSTRACT FROM AUTHOR]

Background The survival rates for patients diagnosed with uveal melanoma in Australia are unknown. Few long-term studies of uveal melanoma are available, and it is unclear whether their results are applicable to the Australian population. Design Retrospective population-based study. Participants Patients diagnosed with uveal melanoma between 1981 and 2005 in Western Australia. Methods Three hundred eight cases were included. Relative survival and Cox regression were performed. Variables tested for their predictive ability included patient age and sex, tumour-specific variables, and treatment modality. Main Outcome Measures All-cause survival rates and relative survival rates of patients with diagnosed uveal melanoma. Results Relative survival rates for the entire cohort were 88.2%, 81.4% and 71.4% at 3, 5 and 10 years, respectively. Predictors of worse survival included mixed-cell tumour morphology (hazard ratio [HR] = 2.1; P-value = 0.002), tumour location at the ciliary body (HR = 1.7; P-value = 0.029) and tumour apical height more than 5 mm (HR 1.9, P-value = 0.026). Of all patients who underwent enucleation, those diagnosed in 1998-2005 died twice as fast (HR = 2.3; P-value = 0.004). In the 17 patients with metastasis, the median survival time from date of diagnosis of metastasis was 3.1 months. Conclusions These survival estimates are comparable to those reported for the USA, and more optimistic than those reported for most European-based studies. Tumour apical height, tumour site, tumour morphology and having an enucleation in certain calendar periods of diagnosis were independent predictors of survival. Survival prognosis for patients with diagnosed metastatic uveal melanoma is very poor. [ABSTRACT FROM AUTHOR]

The author focuses on the effort of the Arrhythmia Alliance (AA) to increase the public's awareness about arrhythmia in Great Britain. He claims that part of the organization's campaign is to assess the efficiency of the implementation of Chapter 8, which concerns arrhythmias and sudden cardiac death, of the National Service Framework (NSF) for Coronary Heart Disease. Currently, it strives for an increased access to arrhythmia services.

Wound dressings are used during patient radiotherapy treatments, particularly in cases of radiation induced lesions. Potentially, the presence of a dressing may increase the dose to the skin, further aggravating the skin reaction and decrease the dose at depth. The changes are dependent on linear accelerator beam type and beam quality and were determined for 4 and 10 MV photon energies and 6 and 15 MeV electron energies using a slab phantom and fixed separation parallel plate chambers. Since these dressings have been designed to be used on exuding wounds, measurements were taken under eight different wound dressings in both dry and wet state. Irradiations with photon energies increased the skin dose significantly (max. increase: 68.1 %; average increase: 48 %) with little or no change to dose at depth. Electron beam energies showed little or no change to doses at the surface, but the dose distribution was shifted towards the surface. The maximum decrease in dose at depth was 3.6 % for 6 and 15 MeV through all dressings except one and was therefore considered to be clinically insignificant. A change in dose at surface of 9.7 % and at R of 25.9 %, equivalent to a shift of dose towards the surface of 7.5 mm, was measured for one dressing. This demonstrates that it is possible for a wet dressing to significantly alter electron beam dosimetry. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to incorporate a statistical process control tool, the cumulative sum (CUSUM) method, in the nonzero fixed action level setup correction strategy for the detection and correction of systematic shifts in prostate position during prostate image-guided radiotherapy. Methods: A daily nonzero action level setup correction strategy using CUSUM chart was proposed and tested retrospectively on 34 nonrandomized patients with prostate-implanted fiducial markers in situ plus daily localization via stereoscopic electronic portal imaging. A cumulative error index, which monitors a cumulative process index over time, was implemented in parallel with the localization offsets of the prostate. A value of this index exceeding a decision interval H indicated that a systematic change in the mean value of localization had occurred. When a value of the index exceeding H was recorded, the magnitude of the systematic shift was estimated and the subsequent prescribed offsets were corrected to account for the new setup positions. With the new protocol, the authors produced simulated treatment histories in which the detection of systematic shifts and the frequency of localization offset exceeding action level were evaluated. The protocol was examined against three levels of mean systematic shifts of localization for detection (μ1) of 3, 5, and 7 mm. Results: The overall rates of detection of systematic shifts using this algorithm were relatively high. The level μ1 = 3 mm resulted in the highest rate of detection of systematic offset change, in 42% of the charts. For larger values of μ1, the overall detection numbers fell to 18% and 12% of the charts for μ1 = 5 and 7 mm, respectively. The mean magnitude of change in systematic offset at time of detection was 3.1, 4.4, and 5.2 mm for μ1 = 3, 5, and 7 mm, respectively. By adapting the setup position for any change in systematic localization offset over a course of treatment using the new protocol, it has been shown that the frequency of localization offsets exceeding action levels was reduced. For the optimal choice of intervention levels for correction and μ1, the number of localization offsets exceeding action levels has been reduced by approximately half. Conclusions: The nonzero fixed action level setup correction strategy incorporating CUSUM charts has been shown to provide an objective method for (i) detecting a systematic shift of a patient localization offset, (ii) quantifying the magnitude of a systematic change based on previous observations, and (iii) correcting the prescribed offset by accounting for the systematic shift(s) in patient setup position. [ABSTRACT FROM AUTHOR]

The positional accuracy of multileaf collimators (MLC) is crucial in ensuring precise delivery of intensity-modulated radiotherapy (IMRT). The aim of this planning study was to investigate the dosimetric impact of systematic MLC positional errors on step and shoot IMRT of prostate cancer. A total of 12 perturbations of MLC leaf banks were introduced to six prostate IMRT treatment plans to simulate MLC systematic positional errors. Dose volume histograms (DVHs) were generated for the extraction of dose endpoint parameters. Plans were evaluated in terms of changes to the defined endpoint dose parameters, conformity index (CI) and healthy tissue avoidance (HTA) to planning target volume (PTV), rectum and bladder. Negative perturbations of MLC had been found to produce greater changes to endpoint dose parameters than positive perturbations of MLC ( p < 0.01). Negative and positive asynchronised MLC perturbations of −1 mm resulted in median changes in D of −1.2 and 0.9% respectively. Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in D of −2.3 and 1.8% respectively. Doses to rectum were generally more sensitive to systematic MLC errors compared to bladder ( p < 0.01). Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in endpoint dose parameters of rectum and bladder from 1.0 to 2.5%. Maximum reduction of −4.4 and −7.3% were recorded for conformity index (CI) and healthy tissue avoidance (HTA) respectively due to synchronised MLC perturbation of 1 mm. MLC errors resulted in dosimetric changes in IMRT plans for prostate. [ABSTRACT FROM AUTHOR]

By combining magnetic resonance imaging (MRI) scanners and radiotherapy treatment units the need arises for new radiation measurement equipment that can be used in the magnetic field of the MRI. This study describes the investigation of the influence of the 1.5 T magnetic field from an MRI linac on the STARCHECKMAXI MR, a large 2D ionization chamber detector panel. Measurements were performed on an MRI linac and a conventional linac to investigate the behaviour of the detector panel with and without the 1.5 T magnetic field. We measured reproducibility, linearity, warm-up effect, saturation/recombination and chamber orientation. A comparison with gafchromic film was performed and the effect of motion of the panel during measurements inside a magnetic field was investigated. The reproducibility, linearity, warm-up effect, saturation/recombination show no significant deviations with or without magnetic field. An absolute difference in reading of 2.1% was found between off-axis chambers on different axes. The comparison with film shows good agreement. Spurious readings are induced while the panel is undergoing a motion in the magnetic field during measurements. The STARCHECKMAXI MR is suited for use in a 1.5 T MRI linac. Care must be taken when comparing un-normalized profiles from different axes of the detector panel and when the panel is undergoing motion during measurements. [ABSTRACT FROM AUTHOR]