Julia Murray

Comparison of CT number calibration techniques for CBCT-based dose calculation

PurposeThe aim of this work was to compare and validate various computed tomography (CT) number calibration techniques with respect to cone beam CT (CBCT) dose calculation accuracy.MethodsCBCT dose calculation accuracy was assessed for pelvic, lung, and head and neck (H&N) treatment sites for two approaches: (1) physics-based scatter correction methods (CBCTr); (2) density override approaches including assigning water density to the entire CBCT (W), assignment of either water or bone density (WB), and assignment of either water or lung density (WL). Methods for CBCT density assignment within a commercially available treatment planning system (RSauto), where CBCT voxels are binned into six density levels, were assessed and validated. Dose-difference maps and dose-volume statistics were used to compare the CBCT dose distributions with the ground truth of a planning CT acquired the same day as the CBCT.ResultsFor pelvic cases, all CTN calibration methods resulted in average dose-volume deviations below 1.5u2009%. RSauto provided larger than average errors for pelvic treatments for patients with large amounts of adipose tissue. For H&N cases, all CTN calibration methods resulted in average dose-volume differences below 1.0u2009% with CBCTr (0.5u2009%) and RSauto (0.6u2009%) performing best. For lung cases, WL and RSauto methods generated dose distributions most similar to the ground truth.ConclusionThe RSauto density override approach is an attractive option for CTN adjustments for a variety of anatomical sites. RSauto methods were validated, resulting in dose calculations that were consistent with those calculated on diagnostic-quality CT images, for CBCT images acquired of the lung, for patients receiving pelvic RT in cases without excess adipose tissue, and for H&N cases.ZusammenfassungZielZiel dieser Arbeit ist der Vergleich und die Validierung mehrerer CT-Kalibrierungsmethoden zur Dosisberechnung auf der Grundlage von Kegelstrahlcomputertomographie(CBCT)-Aufnahmen.MethodenBei 4xa0Becken-, 3xa0Lungen- und 4xa0Kopf-Hals-Patienten wurde die Genauigkeit der Dosisberechnung auf der Basis von CBCT-Aufnahmen für die folgenden Ansätze untersucht: einerseits Rekonstruktion der CBCT-Aufnahmen mithilfe eines Streukorrekturalgorithmus (CBCTr) und andererseits 3 verschiedene Methoden zur expliziten Zuweisung der Elektronendichten auf Basis des CBCT-Datensatzes (W: Zuordnung von Wasserdichte auf dem gesamten CBCT, WB: Zuordnung von entweder Wasser- oder Knochendichte, WL: Zuordnung von entweder Wasser- oder Lungendichte) sowie der in einem kommerziellen Planungssystem implementierten Methode der automatischen Zuordnung von 6xa0Dichtestufen auf Basis der CBCT-Hounsfield-Werte (RSauto). Als Grundlage zur Evaluierung der Methoden diente die Dosisverteilung, welche anhand einer am gleichen Tag wie die CBCT aufgenommenen Planungs-CT berechnet wurde. Die Genauigkeit der einzelnen Ansätze wurde anhand von Dosis-Volumen-Statistiken und lokalen Dosisunterschieden beurteilt.ErgebnisseBei den Datensätzen mit Tumoren im Beckenbereich ist die mittlere Dosisabweichung für alle Kalibrierungsmethoden unter 1,5u2009%, wobei RSauto in einer überdurchschnittlichen Abweichung für Patienten mit einem höheren Anteil von Fettgewebe resultiert. Die mittlere Abweichung für Kopf-Hals-Patienten beträgt unter 1,0u2009%, wobei CBCTr (0,5u2009%) und RSauto (0,6u2009%) am besten abschneiden. WL und RSauto resultieren für die Patienten mit Lungentumoren in Dosisverteilungen, welche der Referenzdosisverteilung entsprechen.SchlussfolgerungRSauto zur Kalibrierung von CBCT-Aufnahmen zur Dosisberechnung ist eine aussichtsreiche Methode für die untersuchten Indikationen. Es wurde gezeigt, dass mithilfe von RSauto die Dosisberechnung auf der Basis von CBCT-Aufnahmen von Lungen- und Kopf-Hals-Erkrankungen sowie für Tumoren im Beckenbereich bei Patienten ohne ein Übermaß an Fettgewebe in einer akkuraten Dosisverteilung resultiert.

Rationale and development of image-guided intensity-modulated radiotherapy post-prostatectomy: the present standard of care?

The indications for post-prostatectomy radiotherapy have evolved over the last decade, although the optimal timing, dose, and target volume remain to be well defined. The target volume is susceptible to anatomical variations with its borders interfacing with the rectum and bladder. Image-guided intensity-modulated radiotherapy has become the gold standard for radical prostate radiotherapy. Here we review the current evidence for image-guided techniques with intensity-modulated radiotherapy to the prostate bed and describe current strategies to reduce or account for interfraction and intrafraction motion.

Slice Encoding for Metal Artefact Correction in magnetic resonance imaging examinations for radiotherapy planning

Background and purpose Magnetic resonance (MR) and computed tomography (CT) images are degraded in the presence of metallic implants. We investigate whether SEMAC (Slice Encoding for Metal Artifact Correction) MR is advantageous for radiotherapy (RT) planning. Methods Conventional and SEMAC MR protocols were compared (1.5 T). A spine fixation device suspended in gelatine, two patients with spine fixation devices and six patients with bilateral hip replacements were scanned with both conventional and SEMAC protocols. In spine patients the visibility of the spinal canal and spinal cord was assessed; in prostate patients, the visibility of the prostate, pelvic structures and the pelvic girdle. Results The signal loss volume surrounding the spine fixation device was reduced by approximately 20% when the SEMAC protocol was employed, and registration errors were reduced. For spine patients, the spinal canal was completely visible only using the SEMAC protocol. In hip replacement patients, metal artifacts were local; the signal loss extended to the internal surface of the acetabulum in eight implants with conventional protocols, but only in four using SEMAC. Conclusions SEMAC MR contributes towards correct co-registration of MR and CT images for RT planning, and is particularly relevant when the TV or OARs are close to implants.

Rising thyroglobulin tumour marker during pregnancy in a thyroid cancer patient: no cause for alarm?

inhibit mTOR are therefore a rational choice to trial in these tumours. Preliminary results of the use of everolimus in our patient with MTC have shown it to be well tolerated: disease that was previously progressive initially stabilized, and the rate of rise of the calcitonin level was reduced. Further observation will be required to demonstrate whether a durable response of tumour burden and biochemical parameters can be achieved, although one caveat is the choice of assessable tumour markers in these patients. The early trials of vandetanib suggest that the reduction in calcitonin levels seen in treated patients did not always correlate with radiological responses. It seems that RET expression may be necessary for ligand-induced calcitonin gene expression, and therefore it may be that carcinoembryonic antigen (CEA) will prove to be a more reliable marker in patients using tyrosine kinase inhibitors. This hypothesis may also prove applicable to patients being treated with mTOR inhibitors. The promising results here for the use of everolimus in MTC would suggest that more rigorous assessment in the form of a clinical trial would be helpful.

An Investigation of Dosimetric Correlates of Acute Toxicity in Prostate Stereotactic Body Radiotherapy: Dose to Urinary Trigone is Associated with Acute Urinary Toxicity

AIMSnThere are limited data on dosimetric correlates of toxicity in stereotactic body radiotherapy (SBRT) for prostate cancer. We aimed to identify potential relationships between dose and toxicity using conventional dose-volume histograms (DVHs) and dose-surface maps (DSMs).nnnMATERIALS AND METHODSnUrinary bladder trigone and rectum DSMs were produced for a single-institution service evaluation cohort of 50 patients receiving SBRT for localised prostate cancer, together with conventional DVHs for bladder and rectum. Patients had been prospectively recruited to this cohort and treated according to a pre-defined protocol to a dose of 36.25 Gy in five fractions. Radiation Therapy Oncology Group (RTOG) and International Prostate Symptom Score (IPSS) toxicity data were recorded prospectively. Logistic regression was used to identify dosimetric predictors of acute IPSS+10 (rise of 10 points or more above baseline) and grade 2+ RTOG toxicity.nnnRESULTSnOn univariate analysis, trigone area receiving 40 Gy and trigone Dmax were associated with IPSS+10 (odds ratio 1.06 [1.02-1.11], Pxa0=xa00.007 and odds ratio 1.54 [1.06-2.25], Pxa0=xa00.024, respectively). These two variables were highly correlated. In a multivariate model, including all baseline variables, trigone Dmax remained associated with IPSS+10 (odds ratio 1.91 [1.13-3.22], Pxa0=xa00.016). These findings were not significant with Holm-Bonferroni correction for multiple testing (corrected P value threshold 0.006). No associations were seen between rectal toxicity and DVH or DSM parameters.nnnCONCLUSIONSnOur study suggests a potential relationship between high doses to the urinary bladder trigone and patient-reported urinary toxicity in prostate SBRT, and is consistent with previous studies in conventionally fractionated radiotherapy, justifying further evaluation in larger cohorts.

EP-1899: Evaluation of SEMAC MRI metal artifact reduction for orthopaedic implants in radiotherapy planning

Royal Marsden NHS Foundation Trust, Radiotherapy Department, Sutton, United Kingdom Royal Marsden NHS Foundation Trust, Radiology Department, Sutton, United Kingdom Royal Marsden NHS Foundation Trust, Neuro-Oncology Unit, Sutton, United Kingdom Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Radiotherapy Department, Sutton, United Kingdom St Georges Hospital NHS Trust, OrthopaedicSurgery, London, United Kingdom Siemens Healthcare, Diagnostic Imaging, Erlagen, Germany