45 chest, 1.7-3.6mm for abdomen and 1.6-3.8mm for pelvis. Rotation systematic and random errors that ranged from 0.5-0.8° were comparable among the 5 body sites. Calculated 3D vector means were ranged from 4.3-8.3mm. The magnitudes of systematic and random errors in radiotherapy treatment were regions depended and the calculated result can be a reference in deciding optimal PTV margin. 15.14. A Dosimetric Comparison of Helical Tomotherapy versus Volumetric-modulated Arc Therapy in Radiosurgery for Single and Multiple Intracranial Lesions Presenter: Man Man Fan, Hong Kong Sanatorium & Hospital Authors: K. C. Chan, R. W. M. Luo, H. Y. Yip, G. Chiu Introduction: Radiosurgery (RS) is to deliver single, very high-dose fraction in a small volume with sub-millimeter accuracy. The effectiveness of radiosurgery is partially related to the use of high radiation dose to control tumor repopulation. Thus the treatment aims to achieve a sharp dose gradient between lesions and normal tissues, sparing adjacent radiosensitive tissues, and thereby minimizing the risk of radiation-induced toxicity. Radiosurgery can be delivered using various equipment and techniques including Gamma Knife, linacs, Cyberknife and helical Tomotherapy (TOMO). Volumetric-modulated arc therapy (VMAT) delivered by the linacs could be an alternative to TOMO. Data comparing the dosimetry of TOMO and other equipments/techniques for intracranial radiosurgery are limited. The aim of this study was to compare the dosimetric characteristics and treatment time between TOMO and VMAT for radiosurgery of single and multiple intracranial lesions. Twenty-two patients with either single and multiple intracranial lesions who were previously treated with TOMO RS were replanned for VMAT and evaluated in this study. Methods: Conformation number (CN) was used to assess the target conformity and homogeneity index (HI, D5%-D95%) to assess dose homogeneity. The percentage volumes of non-target brain tissue receiving 12Gy (V12) were also recorded. Results: VMAT plans showed comparable dose conformity in PTVs for single brain lesions. For multiple brain lesions, VMAT plans achieved better dose conformity. For target dose homogeneity, TOMO plans were superior for both single and multiple intracranial lesions. VMAT plans yielded lower V12 to the normal brain tissues for multiple lesions. It might imply that the possibility of late complications of the brain would be lower in VMAT plans. VMAT would be a preference for RS of multiple intracranial lesions. 15.15. Evaluation of in-house manufactured 99mTc-ECDG tumour detection in nude mice Presenter: Je'nine Horn-Lodewyk, Department of Nuclear Medicine, Universitas Hospital, Bloemfontein, South-Africa Authors: J. Horn-Lodewyk, A.C. Otto, J.M. Wagener, J.R. Zeevaart and G. Joubert Introduction: In-house manufactured (IHM) Technetium-99-metastablepertechnetate Ethylenedicysteine-deoxyglucose (99mTc-ECDG) was developed with a new synthesis route and radiolabelling procedure for possible tumour detection. The aim of the study was to evaluate the tumour-to-muscle-, tumour-to-brain- and tumour-to-lung ratio of the IHM 99mTc-ECDG compared and Fluorine-18-fluorodeoxyglucose (18F-FDG). Methods: Xenografts (n=18) injected with IHM 99mTc-ECDG or 18F-FDG were sacrificed at time points. In vivo percentage of injected dose per gram of wet tissue weight and tumour-to-non-tumour tissue ratios are presented as means + standard errors of the means. Results:The IHM 99mTc-ECDG showed better tumour-to-muscle ratio and tumour-to-lung ratio than the 99mTc-ECDG found in the literature (tumour-to-brain ratio for 99mTc-ECDG was not reported in literature). The IHM 99mTc-ECDG showed better tumour-to-muscle ratio, tumour-tobrain and tumour-to-lung ratio than 18F-FDG. IHM 99mTc-ECDG may be utilised as a possible low dose and low cost glucose metabolism imaging agent for the detection of muscle, brain and lung tumours. 15.16. Mepilex Lite dressing for the prevention of radiotehrapy-related skin reactions - a case study Presenter: Mervi Rytilahti, Department of Radiotherapy/Oulu University Hospital, Finland Authors: Mervi Rytilahti, A. Suomela , U. Viinikka Introduction: A large amount of patients still experience side effects from radiation treatment despite new improvements in irradiation techniques. The severity of radiotherapy-associated skin reactions varies according to treatments- and patient-related factors (e.g. total radiation dose, volume of tissue irradiated, chemotherapy). To date there is no consensus or universal skin care guidelines to prevent or treat radiation-induced skin reactions. These reactions are typically managed with a variety of topical agents such as water-based moisturizing creams or lotions, topical steroids, anti-inflammatory emulsions and wound dressings. Previous case studies have shown that Mepilex Lite dressings decrease the severity of skin reactions. However, the preventative effect of Mepilex Lite was not investigated in these studies. The aim of this study was to compare the effectiveness of Mepilex Lite dressings as a preventative aid with our department´s standard skin care guidelines for breast cancer patients receiving electron beam therapy. 98 women participated in this study but ten patients were withdrawn. The study was conducted during February 2013 and February 2014. The Mepilex Lite dressing was positioned on half of the electron field area before the first fraction at the first treatment appointment; the other half of the treatment field was treated with the standard departmental care guidelines (e.g. base moisturizing lotion, hydrocortisone cream (1%)). Mepilex Lite dressings (15x15 cm) were donated by Molnlycke Health Care. Methods: The material was collected by using observation and questionnaires. The patients filled out the questionnaires with baseline demographic during the first treatment appointment. Since the Mepilex Lite dressing was positioned before the first fraction, it was to be used through the whole treatment session. However, dressing changes were performed if needed. After the treatment session was completed patients filled out the rest of the questionnaire assessing their own symptoms. Digital photographs of the skin reactions were taken after the last fraction and a group of three radiation therapist evaluated the skin reactions upon photos. Results: Preliminary results show that Mepilex Lite dressing reduces effectively the severe acute skin reactions compared to our standard departmental skin care guidelines. No significant results were observed in minor skin reactions. The analysis of the study is not completed yet; the final results will be ready in spring 2014. According to the results of this study Mepilex Lite can be recommended to be used during radiotherapy for breast cancer patients as a preventative method for acute skin reactions. 15.17. Validation of implanted fiducial gold markers for set up verification of breast cancer patients during radiotherapy Presenter: R.Steenberg, Netherlands Authors: R. Kattevilder, R. Steenberg, V. Althof, D. Koopman, T. Eiland, M. Kramer Introduction: Introduction To investigate if fiducial gold markers, implanted during breast conserving surgery, accurately represent the position of the lumpectomy cavity and whether they improve accuracy of patient setup in an EPID protocol during treatment. Fiducial gold markers represent the position of the lumpectomy cavity. CT analysis of the lumpectomy volumes supported a decrease in inter-marker distance between the CT studies suggesting a shrinkage of the volume of the lump cavity during radiotherapy treatment. 3D COM displacement results were consistent with 2D EPID analysis. Using EPID: patient set up in the cranial/caudal direction based on fiducial markers is preferred above set up based on bony anatomy Methods: 25 patients enrolled in a prospective study protocol. Three fiducial gold markers were placed in the lumpectomy cavity during surgery, following study protocol. For each patient, 3 CT-studies (before, halfway and directly after radiotherapy) and 6 orthogonal MV control images (anterior/posterior and lateral; EPID Theraview NT) were acquired during radiotherapy. Variations in lump volume in the CT studies were assessed. Variations in inter-marker distances and the position of the Centre of Mass (COM) were assessed by an application written in Matlab. Results: Results are presented as mean ± 1SD in mm. EPID set up results for 3 different marker sets were compared, using external fiducials placed on the patient skin, internal gold fiducials and bony anatomy. Until now 17 patients completed the study protocol. The inter-marker distance, measured in the CT studies, decreased in 16 out of 17 patients (94%) with an average of 4.0 mm, suggesting lumpectomy cavity shrinkage during radiotherapy. The largest change in inter-marker distances was found between the first and second CT study. A decrease in lumpectomy volume between CT1 and CT2 of 51% was found for lumpectomy volumes over 11
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