Radiotherapy

Von Willebrand Disease in the Netherlands (Doctoral Thesis)

Wee, E.M. de — 2011-10-26T00:00:00Z

Based on previous epidemiologic studies it is estimated that in the Netherlands the referral based prevalence of moderate to severe von Willebrand disease (VWD) is approximately 1 in 10,000 (1650 patients). This does not include patients with mild type 1 disease (VWF levels 30-50 U/dL), or individuals with borderline VWF levels with a mild bleeding phenotype, of which the prevalence is higher and may even reach 1:100 individuals. Despite the frequency of the disease only a limited number of studies have been performed on clinical presentation, determinants of bleeding phenotype and Quality of Life (QoL). Therefore we have initiated a nationwide study on moderate and severe VWD in the Netherlands, the Willebrand in the Netherlands study, the WiN study.

Image-Guided Intensity-Modulated Radiotherapy for Single Vocal Cord Irradiation in Early Glottic Cancers (Doctoral Thesis)

Osman, S.O.S. — 2011-10-21T00:00:00Z

The larynx anatomy is graphically presented in figure 1.1 . The vocal cords in the center of the larynx are muscular bands covered by thin mucosa layers. Together, the right and left vocal cords have a V-shape, when viewed from cranial. The vocal cords play key roles in the control of the airflow during breathing, the protection of airway, and in the production of sound for speech. Cancer of the larynx is one of the most common cancers in Europe, with about 52,000 new cases annually, 90% occurring in men. 95% of all cancers of the larynx are squamous cell carcinomas [65]. Cancer of the larynx is mainly caused by consumption of tobacco and alcohol. Nevertheless, tobacco dominates the risk for cancer of the vocal cords. Over 90% of the present incidences of laryngeal cancers could be prevented by avoiding smoking and alcohol consumption. The most common symptoms observed in early glottic cancers are; the presence of hoarseness, sore throat, shortness of breath, and the feeling of a lump in the throat. Hoarseness, which is a an early symptom for glottic lesions, is the main symptom which causes patients to seek medical consultation [65]. A complete ear, nose, and throat check (with mirrors and laryngscopes) and histology examination are common steps in the examination of suspected laryngeal cancer patients. Vocal cord mobility and exact tumor extension are carefully assessed to aid specifying the exact stage (TNM staging) of the tumor [65]. The stage of the tumor is important for establishing the treatment policy. This thesis discusses treatment of early stage glottic cancers (Carcinoma in situ (Tis), and tumors limited to one vocal cord (T1a), with no regional/distant lymph node metastasis (N0M0)).

Quality Assurance of Superficial Hyperthermia Treatments Superficial Hyperthermia Treatments (Doctoral Thesis)

Bruijne, M. de — 2011-09-21T00:00:00Z

In hyperthermia, tumour-loaded tissue is heated to a supraphysiological level of 40-45 °C. Hyperthermia is a well-established adjuvant to radiotherapy and/or chemotherapy. Hyperthermia causes direct cytotoxicity and has effect on tumour blood flow and oxygenation, which may enhance the other treatment modality. Further, hyperthermia sensitizes cells to both radiotherapy and chemotherapy, among other things by inhibition of DNA repair processes. The efficacy of hyperthermia has been demonstrated in randomized trials for multiple cancer types [1-18]. Several heating techniques and devices exist to heat tumours at different sites: deepregional and part-body hyperthermia, local hyperthermia, interstitial and endocavitary hyperthermia, and whole body hyperthermia [19]. The Erasmus MC – Daniel den Hoed Cancer Center has three treatment modes available, all of which use electromagnetic waves to heat tissue. Tumours in the pelvic region (deep hyperthermia) can be heated using the BSD-2000 system (BSD Medical, USA). The in-house developed Lucite cone applicator system can heat tumours at the body surface (superficial hyperthermia). Recently, also a specific system has been developed to heat tumours in the head and neck region [20]. The scope of this thesis is limited to superficial hyperthermia (SHT). Therefore, the next sections will focus on the clinical context and quality assurance of SHT treatments.

Incidence, treatment, and case-fatality of non-traumatic subarachnoid haemorrhage in the Netherlands (Article)

Risselada, R. — 2011-07-01T00:00:00Z

Background: Non-traumatic subarachnoid haemorrhage (SAH) is a devastating disorder and in the majority of cases it is caused by rupture of an intracranial aneurysm. No actual data are available on the incidence of non-traumatic SAH and aneursymal SAH (aSAH) in the Netherlands and little is known about treatment patterns of aSAH. Our purpose was therefore to assess the incidence, treatment patterns, and case-fatality of non-traumatic (a)SAH within the Dutch general population. Methods: Two population based data sources were used for this retrospective cohort study. One was the nationwide hospital discharge registry (National Medical Registration, LMR). Cases were patients hospitalized for SAH (ICD-9-code 430) in 2001-2005. The second source was the Integrated Primary Care Information (IPCI) database, a medical record database allowing for case validation. Cases were patients with validated non-traumatic (a)SAH in 1996-2006. Incidence, treatment, and case-fatality were assessed. Results: The incidence rate (IR) of non-traumatic SAH was 7.12 per 100,000 PY (95%CI: 6.94-7.31) and increased with age. The IR of aSAH was 3.78 (95%CI: 2.98-4.72). Women had a twofold increased risk of non-traumatic SAH; this difference appeared after the fourth decade. Non-traumatic SAH fatality was 30% (95%CI: 29-31%). Of aSAH patients 64% (95%CI: 53-74%) were treated with a clipping procedure, and 26% (95%CI: 17-37%) with coiling. Conclusion: Non-traumatic SAH is a rare disease with substantial case-fatality; rates in the Netherlands are similar to other countries. Case-fatality is also similar as well as age and sex patterns in incidence.

Genome-wide association studies of cerebral white matter lesion burden (Article)

Fornage, M. — 2011-07-01T00:00:00Z

Objective: White matter hyperintensities (WMHs) detectable by magnetic resonance imaging are part of the spectrum of vascular injury associated with aging of the brain and are thought to reflect ischemic damage to the small deep cerebral vessels. WMHs are associated with an increased risk of cognitive and motor dysfunction, dementia, depression, and stroke. Despite a significant heritability, few genetic loci influencing WMH burden have been identified. Methods: We performed a meta-analysis of genome-wide association studies (GWASs) for WMH burden in 9,361 stroke-free individuals of European descent from 7 community-based cohorts. Significant findings were tested for replication in 3,024 individuals from 2 additional cohorts. Results: We identified 6 novel risk-associated single nucleotide polymorphisms (SNPs) in 1 locus on chromosome 17q25 encompassing 6 known genes including WBP2, TRIM65, TRIM47, MRPL38, FBF1, and ACOX1. The most significant association was for rs3744028 (pdiscovery= 4.0 × 10-9; preplication= 1.3 × 10-7; pcombined= 4.0 × 10-15). Other SNPs in this region also reaching genome-wide significance were rs9894383 (p = 5.3 × 10-9), rs11869977 (p = 5.7 × 10-9), rs936393 (p = 6.8 × 10-9), rs3744017 (p = 7.3 × 10-9), and rs1055129 (p = 4.1 × 10-8). Variant alleles at these loci conferred a small increase in WMH burden (4-8% of the overall mean WMH burden in the sample). Interpretation: This large GWAS of WMH burden in community-based cohorts of individuals of European descent identifies a novel locus on chromosome 17. Further characterization of this locus may provide novel insights into the pathogenesis of cerebral WMH. Copyright

The role of mycophenolate mofetil in the management of autoimmune hepatitis and overlap syndromes (Article)

Baven-Pronk, A.M.C. — 2011-07-01T00:00:00Z

Background Treatment failure occurs in 20% of autoimmune hepatitis patients on prednisolone and azathioprine (AZA). There is no established second line treatment. Aim To assess the efficacy of mycophenolate mofetil as second line treatment after AZA-intolerance or AZA-nonresponse in autoimmune hepatitis and overlap syndromes. Methods Consecutive patients from the Dutch Autoimmune Hepatitis Group cohort, consisting of 661 patients, with autoimmune hepatitis or overlap syndromes, AZA-intolerance or AZA-nonresponse and past or present use of mycophenolate mofetil were included. Primary endpoint of mycophenolate mofetil treatment was biochemical remission. Secondary endpoints were biochemical response (without remission), treatment failure and prevention of disease progression. Results Forty-five patients treated with mycophenolate mofetil were included. In autoimmune hepatitis remission or response was achieved in 13% and 27% in the AZA-nonresponse group compared to 67% and 0% in the AZA-intolerance group (P = 0.008). In overlap-syndromes remission or response was reached in 57% and 14% in the AZA-nonresponse group and 63% and 25% of the AZA-intolerance group (N.S.); 33% had side effects and 13% discontinued mycophenolate mofetil. Overall 38% had treatment failure; this was 60% in the autoimmune hepatitis AZA-nonresponse group. Decompensated liver cirrhosis, liver transplantations and death were only seen in the autoimmune hepatitis AZA-nonresponse group (P < 0.001). Conclusions Mycophenolate mofetil induced response or remission in a majority of patients with autoimmune hepatitis and azathioprine-intolerance and with overlap syndromes, irrespective of intolerance or nonresponse for azathioprine. In autoimmune hepatitis with azathioprine nonresponse mycophenolate mofetil is less often effective.

Stereotactic Radiotherapy for Stage I Non-Small Cell Lung Cancer using Real-Time Tumor Tracking (Doctoral Thesis)

Voort van Zyp, N.C.M-G. van der — 2011-06-14T00:00:00Z

Lung cancer is the most commonly diagnosed cancer world-wide (1.61 million; 12.7% of the total) and also the leading cause of cancer death (1.38 million; 18.2% of the total). In the Netherlands, lung cancer was diagnosed in almost 11,000 patients in 2007 (website Netherlands Cancer Registry; www.ikcnet.nl). The majority of these patients (77%) have non-small cell lung cancer (NSCLC) and of these patients approximately 20% present with a resectable tumor (website Netherlands Cancer Registry; www.ikcnet.nl). Although surgery is the treatment of choice for patients with resectable tumors, many patients are inoperable due to smoking-related comorbidity. These patients were commonly treated with conventional radiotherapy (≥60 Gy in 2 Gy fractions), but the results were disappointing (51% local tumor control rate and a 15% survival rate at 5 years). Stereotactic body radiotherapy (SBRT) is an alternative treatment currently used for inoperable patients with stage I NSCLC. SBRT delivers a high radiation dose to the tumor in a small number of fractions over a short overall treatment time (typically 48-60 Gy in 3-6 fractions). Although the total dose may seem equal to that in conventional radiotherapy, the high dose per fraction of SBRT (20 Gy versus 2 Gy) is biologically more potent. Thus the biological effective dose (BED) is greater in SBRT than in conventional radiotherapy (BED >100 Gy versus 60 Gy).

Multispectral MRI centerline tracking in carotid arteries (Article)

Tang, H. — 2011-06-09T00:00:00Z

We propose a minimum cost path approach to track the centerlines of the internal and external carotid arteries in multispectral MR data. User interaction is limited to the annotation of three seed points. The cost image is based on both a measure of vessel medialness and lumen intensity similarity in two MRA image sequences: Black Blood MRA and Phase Contrast MRA. After intensity inhomogeneity correction and noise reduction, the two images are aligned using affine registration. The two parameters that control the contrast of the cost image were determined in an optimization experiment on 40 training datasets. Experiments on the training datasets also showed that a cost image composed of a combination of gradient-based medialness and lumen intensity similarity increases the tracking accuracy compared to using only one of the constituents. Furthermore, centerline tracking using both MRA sequences outperformed tracking using only one of these MRA images. An independent test set of 152 images from 38 patients served to validate the technique. The centerlines of 148 images were successfully extracted using the parameters optimized on the training sets. The average mean distance to the reference standard, manually annotated centerlines, was 0.98 mm, which is comparable to the in-plane resolution. This indicates that the proposed method has a high potential to replace the manual centerline annotation.

Region based level set segmentation of the outer wall of the carotid bifurcation in CTA (Article)

Vukadinovic, D. — 2011-06-09T00:00:00Z

This paper presents a level set based method for segmenting the outer vessel wall and plaque components of the carotid artery in CTA. The method employs a GentleBoost classification framework that classifies pixels as calcified region or not, and inside or outside the vessel wall. The combined result of both classifications is used to construct a speed function for level set based segmentation of the outer vessel wall; the segmented lumen is used to initialize the level set. The method has been optimized on 20 datasets and evaluated on 80 datasets for which manually annotated data was available as reference. The average Dice similarity of the outer vessel wall segmentation was 92%, which compares favorably to previous methods.

Automated versus manual segmentation of atherosclerotic carotid plaque volume and components in CTA: associations with cardiovascular risk factors (Article)

Vukadinovic, D. — 2011-05-26T00:00:00Z

The purpose of this study was to validate automated atherosclerotic plaque measurements in carotid arteries from CT angiography (CTA). We present an automated method (three initialization points are required) to measure plaque components within the carotid vessel wall in CTA. Plaque components (calcifications, fibrous tissue, lipids) are determined by different ranges of Hounsfield Unit values within the vessel wall. On CTA scans of 40 symptomatic patients with atherosclerotic plaque in the carotid artery automatically segmented plaque volume, calcified, fibrous and lipid percentages were 0.97 ± 0.51 cm3, 10 ± 11%, 63 ± 10% and 25 ± 5%; while manual measurements by first observer were 0.95 ± 0.60 cm3, 14 ± 16%, 63 ± 13% and 21 ± 9%, respectively and manual measurement by second observer were 1.05 ± 0.75 cm3, 11 ± 12%, 61 ± 11% and 27 ± 10%. In 90 datasets, significant associations were found between age, gender, hypercholesterolemia, diabetes, smoking and previous cerebrovascular disease and plaque features. For both automated and manual measurements, significant associations were found between: age and calcium and fibrous tissue percentage; gender and plaque volume and lipid percentage; diabetes and calcium, smoking and plaque volume; previous cerebrovascular disease and plaque volume. Significant associations found only by the automated method were between age and plaque volume, hypercholesterolemia and plaque volume and diabetes and fibrous tissue percentage. Significant association found only by the manual method was between previous cerebrovascular disease and percentage of fibrous tissue. Automated analysis of plaque composition in the carotid arteries is comparable with the manual analysis and has the potential to replace it.

Lobar distribution of cerebral microbleeds: The Rotterdam Scan Study (Article)

Mesker, D.J. — 2011-05-01T00:00:00Z

Objective: To investigate the distribution of lobar microbleeds over the different lobes, taking into account lobar volume and clustering effects of multiple microbleeds. Design: Population-based, cross-sectional analysis. Setting: The Rotterdam Scan Study. Participants: A total of 198 persons (age range, 61-95 years) with lobar microbleeds. Main Outcome Measures: Distribution of microbleeds over different lobes. Results:Wefoundthat lobar cerebralmicrobleedsoccurred significantlymoreoften inthetemporallobe, aregionknown to be more affected in cerebral amyloid angiopathy. Conclusion: This study corroborates the presumed association of lobar microbleeds with cerebral amyloid angiopathy.

Image-guided surgery in head and neck cancer: Current practice and future directions of optical imaging (Article)

Keereweer, S. — 2011-04-06T00:00:00Z

A key aspect for the postoperative prognosis of patients with head and neck cancer is complete tumor resection. In current practice, the intraoperative assessment of the tumor-free margin is dependent on visual appearance and palpation of the tumor. Optical imaging has the potential of traversing the gap between radiology and surgery by providing real-time visualization of the tumor, thereby allowing for image-guided surgery. The use of the near-infrared light spectrum offers 2 essential advantages: increased tissue penetration of light and an increased signal-to-background ratio of contrast agents. In this review, the current practice and limitations of image-guided surgery by optical imaging using intrinsic fluorescence or contrast agents are described. Furthermore, we provide an overview of the various molecular contrast agents targeting specific hallmarks of cancer that have been used in other fields of oncologic surgery, and we describe perspectives on its future use in head and neck cancer surgery.

Nonrigid registration of dynamic medical imaging data using nD+t B-splines and a groupwise optimization approach (Article)

Metz, C.T. — 2011-04-01T00:00:00Z

A registration method for motion estimation in dynamic medical imaging data is proposed. Registration is performed directly on the dynamic image, thus avoiding a bias towards a specifically chosen reference time point. Both spatial and temporal smoothness of the transformations are taken into account. Optionally, cyclic motion can be imposed, which can be useful for visualization (viewing the segmentation sequentially) or model building purposes. The method is based on a 3D (2D. +. time) or 4D (3D. +. time) free-form B-spline deformation model, a similarity metric that minimizes the intensity variances over time and constrained optimization using a stochastic gradient descent method with adaptive step size estimation. The method was quantitatively compared with existing registration techniques on synthetic data and 3D. +. t computed tomography data of the lungs. This showed subvoxel accuracy while delivering smooth transformations, and high consistency of the registration results. Furthermore, the accuracy of semi-automatic derivation of left ventricular volume curves from 3D. +. t computed tomography angiography data of the heart was evaluated. On average, the deviation from the curves derived from the manual annotations was approximately 3%. The potential of the method for other imaging modalities was shown on 2D. +. t ultrasound and 2D. +. t magnetic resonance images. The software is publicly available as an extension to the registration package elastix.

Practical Use of the Extended No Action Level (eNAL) Correction Protocol for Breast Cancer Patients with Implanted Surgical Clips (Article)

Penninkhof, J. — 2011-03-18T00:00:00Z

Purpose: To describe the practical use of the extended No Action Level (eNAL) setup correction protocol for breast cancer patients with surgical clips and evaluate its impact on the setup accuracy of both tumor bed and whole breast during simultaneously integrated boost treatments. Methods and Materials: For 80 patients, two orthogonal planar kilovoltage images and one megavoltage image (for the mediolateral beam) were acquired per fraction throughout the radiotherapy course. For setup correction, the eNAL protocol was applied, based on registration of surgical clips in the lumpectomy cavity. Differences with respect to application of a No Action Level (NAL) protocol or no protocol were quantified for tumor bed and whole breast. The correlation between clip migration during the fractionated treatment and either the method of surgery or the time elapsed from last surgery was investigated. Results: The distance of the clips to their center of mass (COM), averaged over all clips and patients, was reduced by 0.9 ± 1.2 mm (mean ± 1 SD). Clip migration was similar between the group of patients starting treatment within 100 days after surgery (median, 53 days) and the group starting afterward (median, 163 days) (p = 0.20). Clip migration after conventional breast surgery (closing the breast superficially) or after lumpectomy with partial breast reconstructive techniques (sutured cavity). was not significantly different either (p = 0.22). Application of eNAL on clips resulted in residual systematic errors for the clips' COM of less than 1 mm in each direction, whereas the setup of the breast was within about 2 mm of accuracy. Conclusions: Surgical clips can be safely used for high-accuracy position verification and correction. Given compensation for time trends in the clips' COM throughout the treatment course, eNAL resulted in better setup accuracies for both tumor bed and whole breast than NAL.

Variable Circular Collimator in Robotic Radiosurgery: a Time-Efficient Alternative to a Mini-Multileaf Collimator? (Article)

Water, S. van de — 2011-03-07T00:00:00Z

Purpose: Compared with many small circular beams used in CyberKnife treatments, beam’s eye view-shaped fields are generally more time-efficient for dose delivery. However, beam’s eye view-shaping devices, such as a mini-multileaf collimator (mMLC), are not presently available for CyberKnife, although a variable-aperture collimator (Iris, 12 field diameters; 5–60 mm) is available. We investigated whether the Iris can mimic noncoplanar mMLC treatments using a limited set of principal beam orientations (nodes) to produce time-efficient treatment plans. Methods and Materials: The data from 10 lung cancer patients and the beam-orientation optimization algorithm ‘‘Cycle’’ were used to generate stereotactic treatment plans (3 x 20 Gy) for a CyberKnife virtually equipped with a mMLC. Typically, 10–16 favorable beam orientations were selected from 117 available robot node positions using beam’s eye view-shaped fields with uniform fluence. Second, intensity-modulated Iris plans were generated by inverse optimization of nonisocentric circular candidate beams targeted from the same nodes selected in the mMLC plans. The plans were evaluated using the mean lung dose, lung volume receiving ≥20 Gy, conformality index, number of nodes, beams, and monitor units, and estimated treatment time. Results: The mMLC plans contained an average of 12 nodes and 11,690 monitor units. For a comparable mean lung dose, the Iris plans contained 12 nodes, 64 beams, and 21,990 monitor units. The estimated fraction duration was 12.2 min (range, 10.8–13.5) for the mMLC plans and 18.4 min (range, 12.9–28.5) for the Iris plans. In contrast to the mMLC plans, the treatment time for the Iris plans increased with an increasing target volume. The Iris plans were, on average, 40% longer than the corresponding mMLC plans for small targets (<80 cm3) and ≤121% longer for larger targets. For a comparable conformality index, similar results were obtained. Conclusion: For stereotactic lung irradiation, time-efficient and high-quality plans were obtained for robotic controlled noncoplanar treatments using a mMLC. Iris is a time-efficient alternative for small targets, with similar or better plan quality.

Accurate Targeting of Liver Tumors in Stereotactic Radiation Therapy (Doctoral Thesis)

Wunderink, W. — 2011-03-04T00:00:00Z

This doctoral thesis concerns the treatment of liver cancer patients using external beam radiotherapy. The quality of this treatment greatly depends on delivering a high radiation dose to the tumor while keeping the dose as low as possible to surrounding healthy tissues. One of the major challenges is locating the tumor at the moment of dose delivery. In this ork, the uncertainty of locating the tumor was investigated. For this purpose, gold markers were implanted in the liver tissue and visualized on X-ray images. The markers were used to measure day-to-day tumor mobility and motion due to respiration. Furthermore, it was found that major improvements in the targeting accuracy can be achieved by using the markers for guiding the treatment procedure.

Impact of von Willebrand disease on health-related quality of life in a pediatric population (Article)

Wee, E.M. de — 2011-03-01T00:00:00Z

Background: Von Willebrand disease (VWD) is the most frequent inherited bleeding disorder. Whether VWD is associated with health-related quality of life (HR-QoL) in children is unknown. Objectives: This nationwide cross-sectional study measured HR-QoL in children with moderate or severe VWD. Our primary aim was to compare HR-QoL of VWD patients with that of reference populations. Additionally, we studied the impact of bleeding phenotype and VWD type on HR-QoL. Methods: HR-QoL was assessed with the Infant/Toddler QoL Questionnaire (0-5 years) and Child Health Questionnaire (6-15 years), and compared with reference population scores. Multivariate analysis was used to evaluate the influence of type of VWD and bleeding phenotype on HR-QoL scores. Results: Preschool children (0-5 years, n=46) with VWD had lower HR-QoL scores for general health perceptions and parental time than reference populations. School children (6-15 years, n=87) with VWD had lower scores for physical functioning, role functioning - emotional/behavioral, general health perceptions, and physical summary. Type of VWD was associated with HR-QoL in school children for bodily pain, general health perceptions, parental emotion, family activities, and physical summary. Scores of children with type 3 VWD were, on average, 15 points lower than those of the reference population on the above-mentioned scales. A more severe bleeding phenotype was associated with a lower score on 11/15 physical, emotional and social scales. Conclusion: HR-QoL is lower in VWD children than in reference populations, in particular in school children. The negative impact of VWD is sensitive to type of VWD and bleeding phenotype; as well as physical scales, emotional and social scales are affected.

Does atlas-based autosegmentation of neck levels require subsequent manual contour editing to avoid risk of severe target underdosage? A dosimetric analysis (Article)

Voet, P.W.J. — 2011-03-01T00:00:00Z

Background and purpose: To investigate the dosimetric impact of not editing auto-contours of the elective neck and organs at risk (OAR), generated with atlas-based autosegmentation (ABAS) (Elekta software) for head and neck cancer patients. Materials and methods: For nine patients ABAS auto-contours and auto-contours edited by two observers were available. Based on the non-edited auto-contours clinically acceptable IMRT plans were constructed (designated 'ABAS plans'). These plans were then evaluated for the two edited structure sets, by quantifying the percentage of the neck-PTV receiving more than 95% of the prescribed dose (V95) and the near-minimum dose (D99) in the neck PTV. Dice coefficients and mean contour distances were calculated to quantify the similarity of ABAS auto-contours with the structure sets edited by observer 1 and observer 2. To study the dosimetric importance of editing OAR auto-contours a new IMRT plan was generated for each patient-observer combination, based on the observer's edited CTV and the non-edited salivary gland auto-contours. For each plan mean doses for the non-edited glands were compared with doses for the same glands edited by the observer. Results: For both observers, edited neck CTVs were larger than ABAS auto-contours (p ≤ 0.04), by a mean of 8.7%. When evaluating ABAS plans on the PTVs of the edited structure sets, V95reduced by 7.2% ± 5.4% (1 SD) (p < 0.03). The mean reduction in D99was 14.2 Gy (range 1-54 Gy). Even for Dice coefficients >0.8 and mean contour distances <1 mm, reductions in D99up to 11 Gy were observed. For treatment plans based on observer PTVs and non-edited auto-contoured salivary glands, the mean doses in the edited glands differed by only -0.6 Gy ± 1.0 Gy (p = 0.06). Conclusions: Editing of auto-contoured neck CTVs generated by ABAS is required to avoid large underdosages in target volumes. Often used similarity measures for evaluation of auto-contouring algorithms, such as dice coefficients, do not predict well for expected PTV underdose. Editing of salivary glands is less important as mean doses achieved for non-edited glands predict well for edited structures.

Nasal reconstruction after malignant tumor resection: An algorithm for treatment (Article)

Moolenburgh, S.E. — 2011-03-01T00:00:00Z

Shortening treatment time in robotic radiosurgery using a novel node reduction technique (Article)

Water, S. van de — 2011-02-18T00:00:00Z

Abstract. PURPOSE: The fraction duration of robotic radiosurgery treatments can be reduced by generating more time-efficient treatment plans with a reduced number of node positions, beams, and monitor units (MUs). Node positions are preprogramed locations where the robot can position the focal spot of the x-ray beam. As the time needed for the robot to travel between node positions takes up a large part of the treatment time, the aim of this study was to develop and evaluate a node reduction technique in order to reduce the treatment time per fraction for robotic radiosurgery. METHODS: Node reduction was integrated into the inverse planning algorithm, developed in-house for the robotic radiosurgery modality. It involved repeated inverse optimization, each iteration excluding low-contribution node positions from the planning and resampling new candidate beams from the remaining node positions. Node reduction was performed until the exclusion of a single node position caused a constraint violation, after which the shortest treatment plan was selected retrospectively. Treatment plans were generated with and without node reduction for two lung cases of different complexity, one oropharyngeal case and one prostate case. Plan quality was assessed using the number of node positions, beams and MUs, and the estimated treatment time per fraction. All treatment plans had to fulfill all clinical dose constraints. Extra constraints were added to maintain the low-dose conformality and restrict skin doses during node reduction. RESULTS: Node reduction resulted in 12 residual node positions, on average (reduction by 77%), at the cost of an increase in the number of beams and total MUs of 28% and 9%, respectively. Overall fraction durations (excluding patient setup) were shortened by 25% (range of 18%-40%), on average. Dose distributions changed only little and dose in low-dose regions was effectively restricted by the additional constraints. CONCLUSIONS: The fraction duration of robotic radiosurgery treatments can be reduced considerably by node reduction with minimal changes in dosimetrical plan quality. Additional constraints are required to guarantee low-dose conformality and to avoid unacceptable skin dose.