Single-fraction spine SBRT end-to-end testing on TomoTherapy, Vero, TrueBeam, and CyberKnife treatment platforms using a novel anthropomorphic phantom.

Spine SBRT involves the delivery of very high doses of radiation to targets adjacent to the spinal cord and is most commonly delivered in a single fraction. Highly conformal planning and accurate delivery of such plans is imperative for successful treatment without catastrophic adverse effects. End-to-end testing is an important practice for evaluating the entire treatment process from simulation through treatment delivery. We performed end-to-end testing for a set of representative spine targets planned and delivered using four different treatment planning systems (TPSs) and delivery systems to evaluate the various capabilities of each. An anthropomorphic E2E SBRT phantom was simulated and treated on each system to evaluate agreement between measured and calculated doses. The phantom accepts ion chambers in the thoracic region and radiochromic film in the lumbar region. Four representative targets were developed within each region (thoracic and lumbar) to represent different presentations of spinal metastases and planned according to RTOG 0631 constraints. Plans were created using the TomoTherapy TPS for delivery using the Hi·Art system, the iPlan TPS for delivery using the Vero system, the Eclipse TPS for delivery using the TrueBeam system in both flattened and flattening filter free (FFF), and the MultiPlan TPS for delivery using the CyberKnife system. Delivered doses were measured using a 0.007 cm3 ion chamber in the thoracic region and EBT3 GAFCHROMIC film in the lumbar region. Films were scanned and analyzed using an Epson Expression 10000XL flatbed scanner in conjunction with FilmQAPro2013. All treatment platforms met all dose constraints required by RTOG 0631. Ion chamber measurements in the thoracic targets delivered an overall average difference of 1.5%. Specifically, measurements agreed with the TPS to within 2.2%, 3.2%, 1.4%, 3.1%, and 3.0% for all three measureable cases on TomoTherapy, Vero, TrueBeam (FFF), TrueBeam (flattened), and CyberKnife, respectively. Film measurements for the lumbar targets resulted in average global gamma index passing rates of 100% at 3%/3 mm, 96.9% at 2%/2mm, and 61.8% at 1%/1 mm, with a 10% minimum threshold for all plans on all platforms. Local gamma analysis was also performed with similar results. While gamma passing rates were consistently accurate across all platforms through 2%/2 mm, treatment beam-on delivery times varied greatly between each platform with TrueBeam FFF being shortest, averaging 4.4 min, TrueBeam using flattened beam at 9.5 min, TomoTherapy at 30.5 min, Vero at 19 min, and CyberKnife at 46.0 min. In spite of the complexity of the representative targets and their proximity to the spinal cord, all treatment platforms were able to create plans meeting all RTOG 0631 dose constraints and produced exceptional agreement between calculated and measured doses. However, there were differences in the plan characteristics and significant differences in the beam-on delivery time between platforms. Thus, clinical judgment is required for each particular case to determine most appropriate treatment planning/delivery platform.

Gitelman Syndrome Presenting with Cerebellar Ataxia and Tetany.

Gitelman syndrome (GS) is salt-losing tubulopathy characterized by hypokalemia, hypomagnesemia, hypocalciuria, hyperreninemia, hyperaldosteronemia, metabolic alkalosis, and rarely hypocalcemia. Here, we describe the case of a 54-year-old man who presented with cerebellar signs and tetany. On investigation, he was found to have hypokalemia, hypocalcemia, hypomagnesemia, metabolic alkalosis, and high urinary chloride levels. On correction of metabolic parameters, he became asymptomatic. In cases of unexplained recurrent hypokalemia, hypocalcemia and hypomagnesemia, the diagnosis of GS should be considered.

Biological effect of different IMRT delivery techniques: SMLC, DMLC, and helical tomotherapy.

PURPOSE: Intensity-modulated radiotherapy (IMRT) is delivered using a variety of techniques with differing temporal dose characteristics. Spatial dose metrics are generally used to evaluate treatment plan quality. However, the use of this information alone neglects the effects of the significant differences in dose delivery duration and dose accumulation patterns, both of which can impact cell survival. This study uses the linear-quadratic model with dose protraction corrections to evaluate the biological effectiveness of different IMRT delivery techniques, including fixed gantry IMRT in SMLC (step-and-shoot) and DMLC (sliding window) modes and a rotational IMRT technique (helical tomotherapy) for the treatment of prostate and head/neck sites. METHODS: The temporal dose pattern was measured using a small volume ion chamber (A1SL--0.057 cm3) to calculate the protraction factor, and biological equivalent dose (BED) was calculated for a range of repair half-times and alpha/beta ratios. The treatment BED is compared to an ideal delivery of the target prescription dose, in which dose is delivered instantaneously (G(t0) = 1), to evaluate loss in biological effectiveness due to protraction in delivery. In the case of a conventional prescription, the loss in biological effectiveness was further evaluated using published tumor control probability (TCP) data. RESULTS: With SMLC and DMLC IMRT delivery, for both prostate and head/neck, the expected additional loss in BED is about 1% compared to 3D CRT, which corresponds to a predicted 2%-3% reduction in TCP. For tomotherapy, the prostate BED loss is smaller in comparison to 3D CRT; hence, the authors expect a TCP increase of the order of 2%-3%. The aforementioned differences are due to the dose accumulation time. CONCLUSIONS: While it is theoretically possible to compensate for changes in biologically effective dose, this would be hindered by large uncertainties in parameters used for such calculations; therefore, it is advantageous to irradiate target volume elements as rapidly as possible. The results of this study indicate that temporal dose delivery pattern is an important component in determining the biological effects of IMRT treatment.