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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Neue Verfahren der Präzisions-Strahlentherapie / New methods of precision radiotherapy

Baumann, Michael, Enghardt, Wolfgang, Herrmann, Thomas, Lehmann, Dietmar, Pawelke, Jörg, Pönisch, Falk, Sauerbrey, Roland 11 October 2008 (has links) (PDF)
Das Ziel strahlentherapeutischer Behandlung ist es, Tumoren zu vernichten und dabei das gesunde Gewebe weitgehend zu schonen. Eine Präzisions-Radiotherapie erfordert eine möglichst konforme Bestrahlung des Tumors mit der für die Heilung notwendigen Dosis. Für die heute gebräuchlichsten therapeutischen Strahlenquellen – Elektronen-Linearbeschleuniger, welche Elektronen- und harte Röntgenstrahlen bereitstellen – wurden dafür die Methoden der intensitätsmodulierten und bildgeführten Radiotherapie entwickelt. Der nächste Schritt zur Verbesserung der Tumorkonformität ist die klinische Anwendung von Partikelstrahlen (Protonen, leichte Ionen). Entsprechende Anlagen erfordern einen hohen Investitionsaufwand. Eine Reduktion dieses Aufwandes könnte der Einsatz außerordentlich kompakter Beschleunigungsstrukturen eröffnen, welche auf der Wechselwirkung hochintensiver Laserstrahlen mit Materie beruhen. / The goal of radiotherapeutic treatment is complete tumour destruction, while sparing the healthy tissue as far as possible. Precision radiotherapy requires tumour-conform irradiation with a curative dose. For electron linear accelerators, the most common therapeutic radiation source at present, delivering beams of electrons and hard X-rays, the methods of intensity-modulated and imageguided radiotherapy have been developed. The next level in improving tumour conformity is the clinical application of particle beams (protons and light ions). Such facilities require substantial investments. The outlay could be reduced, however, by using very compact accelerating structures based upon the interaction of highly intensive laser beams with matter.

Prevalence of side-effects and change in nutritional status during radical radiotherapy for head and neck malignancies at Tygerberg Academic Hospital, Western Cape, South Africa /

De Pomeroy-Legg, Jeanita. January 2008 (has links)
Thesis (MNutr)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Radiation safety practices in interventional radiology : the importance of oversight /

Lally, Mary T. January 1900 (has links)
Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 45-50). Also available on the World Wide Web.

Image-guided adaptive radiotherapy for nasopharyngeal carcinoma

Cheng, Chi-yuen, Harry., 鄭致遠. January 2011 (has links)
Nasopharyngeal carcinoma (NPC) is an endemic malignant disease in Southern China. Intensity-modulated radiotherapy (IMRT) has been employed as a standard treatment for NPC because it delivers highly conformal dose distribution to target volumes and spares organs at risk (OARs). The success of radiotherapy depends on the accurate delivery of the planned doses throughout the treatment. This can be achieved with the help of advanced image-guided adaptive radiotherapy (IGART) such as kilovoltage (kV) cone beam computed tomography (CBCT) which can reduce the geometric setup uncertainty, monitor the intra-course anatomic and dosimetric changes and adjust the treatment plan. The aim of this thesis is to study the role of repeat imaging for NPC and the radiation dose from CBCT to patients. The objectives of this thesis are to evaluate the volumetric and dosimetric changes during a course of IMRT for loco-regionally advanced NPC patients with the contribution of repeat computed tomography (CT) and magnetic resonance imaging (MRI) scans; to quantify the absorbed dose, effective dose and the estimation of the additional risk of inducing fatal cancers from CBCT for NPC patients undergoing IMRT; and to compare the image quality of different head protocols. Nineteen loco-regionally advanced NPC patients treated with IMRT were recruited prospectively. Repeat CT and MRI were acquired at 30 and 50 Gy intervals. Recontouring of target volumes and OARs was based on the fused CT-MRI images. Hybrid plans with recontouring were generated. The volumetric and dosimetric changes were assessed by comparing the hybrid plans with the original plan. There was volume reduction of target volumes and parotid glands over the course of IMRT. Relative to the original plan, the hybrid plans demonstrated significantly higher dose to the target volumes with greater dose inhomogeneity, higher maximum doses to the spinal cord and brainstem, and higher medium doses to the parotid glands. The image quality and dosimetry on the Varian CBCT system between software Versions 1.4.13 (“new” protocol) and 1.4.11 (“old” protocol) were studied. A calibrated Farmer-type ionization chamber and a standard cylindrical Perspex CT dosimetry head phantom were used to measure the weighted CBCT dose index (CBCTDIw) of the Varian CBCT system. The absorbed dose of different organs was measured in a female anthropomorphic phantom with thermoluminescent dosimeters (TLD) and the total effective dose was estimated according to ICRP Publication 103. The dosimetry and image quality were studied for head-and-neck region and comparison was made between the new and old protocols. The values of the CBCTDIw, absorbed dose, effective dose of the new head protocol were much lower than the old head protocol in each imaging group. The additional fatal cancer risk from daily CBCT might be up to 1.6%. In conclusion, replanning with repeat imaging at 30 Gy is essential to keep a satisfactory dose to the target volumes and avoid overdosing the OARs for NPC patients. The new Varian CBCT provides volumetric information for image guidance with acceptable image quality and lower radiation dose. This CBCT gives a better standard for NPC patient daily setup verification. / published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy

Effects of different radiation therapy techniques on swallowing function in individuals with nasopharyngeal cancer

Fong, Raymond, 方思行 January 2013 (has links)
Nasopharyngeal cancer (NPC) is more common in the Southern China region than the rest of the world. Radiation therapy (RT) is the contemporary and standard treatment for nasopharyngeal cancer. Chronic complications arise from RT including hearing loss, xerostomia, trismus and dysphagia. Previous research has shown that dysphagia is prevalent in irradiated NPC patients. Radiation therapy techniques have improved in the last decade with the emergence of Intensity Modulated Radiation Therapy (IMRT), which allows more precise radiation beams directed at the tumor. In turn, it should also allow greater sparing of surrounding structures that are vital for preservation of swallowing function. This study was designed to investigate the difference in the degree of swallowing function preservation in two groups of irradiated NPC patients: the conventional RT and the IMRT group. Thirty patients with NPC who received RT from 1998 to 2006 in Queen Mary Hospital, Hong Kong were randomly recruited during the period from January to December 2011. Participant’s swallowing competence and its effect on the quality of life was assessed by videofluoroscopic swallowing study (VFSS) and by the MD Anderson Dysphagia Inventory, respectively. In comparison of swallowing performance with VFSS between the two groups, only one measure (Duration of Laryngeal Elevation) out of 13 showed significant difference on thin liquid and congee diet. Results from the MDADI did not show significant difference between the two groups. From the results, it was concluded that IMRT only resulted in subtle improvement in preserving the swallowing function as compared to conventional RT. One possibility is the subject self-compensation of their swallowing impairments that led to functionally similar performance despite their differences in the anatomy and physiology. Swallowing is a highly complex body function and no single parameter can be used to accurately quantify and characterize one’s swallowing function. The interaction between the anatomical and physiological impairments resulted from radiation therapy and the compensatory mechanism could not be clearly explained with this study. Future research could adopt a longitudinal approach such that the changes in NPC patients who received radiation therapy can be better understood. / published_or_final_version / Speech and Hearing Sciences / Master / Master of Philosophy

A search for optimal radiation therapy technique for lung tumours stereotactic body radiation therapy (SBRT) : dosimetric comparison of 3D conformal radiotherapy, static gantry intensity modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) with flattening filter (FF) or flattening filter-free (FFF) beams

Chiu, Siu-hau, 招兆厚 January 2013 (has links)
Materials/Methods: Ten patients who underwent thoracic SBRT with primary stage I (T1/2N0) lung cancer or oligometastatic lung lesion, with PTV diameter ≤ 5cm were selected and were immobilized with Easyfoam or Vac-Lock. Planned/treated with inspiratory breath-hold (25 seconds, 70 to 80% of vital capacity) assisted with Active Breathing Control (ABC). Four treatment plans: non-coplanar 3DCRT, coplanar static gantry IMRT, coplanar VMAT (FF) and VMAT (FFF) were generated. Field arrangements, either static fields or partial arcs (duration=20 sec) were used to avoid direct beam entry to contralateral lung. All plans were compared in terms of dosimetric performance included dose to PTV or organs at risk (OAR), high/low dose spillage, integral dose (body and lungs), dose delivery efficiency (MU/Gy) and estimated beam-on time (BOT) with reference to the RTOG 0813 protocol. Results: All plans complied with RTOG 0813 protocol. VMAT (FF/ FFF) techniques improved target coverage and dose conformity, with the highest conformity number (CN > 0.91), compared to IMRT (0.88) and 3DCRT (0.85). The control of high dose spillage (NT>105% and CI) for IMRT (3.04% and 1.08) and VMAT (FF/ FFF) (1.08/ 1.06% and 1.03/ 1.04) techniques were comparable (p > 0.05) and significantly better than 3DCRT (4.22% and 1.11, p < 0.005) technique. In addition, VMAT (FF/ FFF) techniques performed the best in controlling low dose spillage (D2cm and R50%) compared with IMRT (reduction: 4.7%, p=0.036 and >5.9%, p = 0.009) and 3DCRT (reduction: > 16.3%, p < 0.001 and > 10%, p = 0.002). Benefits of rapid and isotropic dose fall-off were shown from superior tissue sparing (reduction ranges from 3.2% up to 67%) of ipsilateral brachial plexus, skin (0-5mm), great vessels and ribs. Also lung V10, V12.5, esophagus and heart tend to receive lower dose with VMAT technique. The relatively lower integral dose to whole body (> 3Gy∙L reduction, p < 0.013) and ipsilateral lung (0.65Gy∙L reduction, p = 0.025) compared with 3DCRT, were associated with lower risk of radiation induced cancers. The MU/Gy and BOT were substantial lower for VMAT (FF) (22.4% and 32.4%) compared with IMRT. Apart from higher (7%) maximum skin dose, dosimetric performance for VMAT (FFF) was comparable with VMAT (FF), with advantages of further reduction of MU/Gy (1.8% lesser), partial arc numbers (from 12-14 arcs down to 8 arcs) and BOT (35% shortened), owing to the increased dose output with flattening filter removal. Conclusions: VMAT (FF and FFF) plans maintained IMRT equivalent plan qualities, simultaneously enhanced the delivery efficiency with shortened BOT. VMAT (FFF) further reduced the required arcs number and BOT, significantly minimized the intra-fraction motions and more tolerable to patient with long SBRT treatment duration. / published_or_final_version / Medicine / Master / Master of Medical Sciences

Four-dimensional Monte Carlo stereotactic body radiotherapy for lung cancers using image-guided robotic target tracking

Chan, Ka-heng, 陳加慶 January 2014 (has links)
Stereotactic body radiotherapy (SBRT) is a promising treatment strategy for early–stage lung cancers. Conventional three–dimensional (3D) SBRT based on a static patient geometry is an insufficient model of reality, posing constraints on accurate Monte Carlo (MC) dose calculation and intensity–modulated radiotherapy (IMRT) optimization. Four–dimensional (4D) radiotherapy explicitly considers temporal anatomical changes by characterizing the organ motion and building a 4D patient model, generating a treatment plan that optimizes the doses to moving tissues, i.e., 4D dose (as opposed to the static 3D dose to tissue), and delivering this plan by synchronizing the radiation with the moving tumor. This thesis focuses on 4D robotic tracking lung SBRT. By recalculating the conventional 3D plan on the 4D patient model using MC simulation, it was found that 4D moving dose distributions could detect increase of normal tissue doses and complication probabilities (NTCP), and decrease of tumor dose and control probability. For one patient, the risk of myelopathy was estimated at 8% and 18% from the 3D equivalent path–length corrected (EPL) and the 4D MC doses, respectively. Such increased NTCP suggests that better estimations of different dosimetric quantities using 4D MC dose calculation are crucial to improve the existing dose–response models. Dosimetric error in 4D robotic tracking SBRT was found to be caused predominately by tissue heterogeneities, as assessed by the comparisons of the 4D moving tissue doses calculated using the conventional EPL and MC algorithms. At 3% tolerance level, our results indicated clinically significant dose prediction errors only in tumor but not in other major normal tissues. Furthermore, 4D tracking radiotherapy was found to have greater ability to limit the normal tissue volume receiving high to medium doses than the other advanced SBRT strategy combining volumetric–arc radiotherapy with 4D cone–beam CT verification. Invariant target motion was found to be an unrealistic assumption of 4D radiotherapy from the analysis of probability motion function (pmf) of motion data. Systematic and random variations of motion amplitude, frequency, and baseline were found to reduce the reproducibility of pmfs, on average, to just 30% for the principal motion of 3400 seconds. Experimental evaluations showed that systematic motion change reduced the gamma passing rate of radiochromic film measurements at 3mm distance–to–agreement and 3% dose difference criteria from 91% for 4D dose calculated with MCand EPL algorithms to 47% and 53% in the static object, respectively,. For moving target object, gamma passing rates of the 4D MC doses hardly changed with reproducible and non–reproducible motion (95% vs. 93%), and barely differed between conventional 3D and 4D MC doses (95% vs. 95% with reproducible, and 96% vs. 93% with non–reproducible motions). Distortions due to image artifacts and registration errors were consistently observed in the 4D dose distributions but not the 3D dose distributions. In conclusion, 4D Monte Carlo planning shall be considered for robotic target tracking only if robustness against uncertainties of patient geometry, and accuracy of 4DCT imaging and deformation registration are significantly improved. / published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy

A comparison of contralateral breast dose from primary breast radiotherapy using different treatment techniques

Tse, Ka-ho, 謝家豪 January 2014 (has links)
Breast cancer is the most common cancer among women worldwide. Millions of new breast cancer cases are diagnosed every year, accounting for one-tenth of all new cancer cases. Because of the proof of equivalent efficacy between breast-conserving therapy (BCT) plus radiotherapy and mastectomy, increasing number of patients received breast irradiation during the past three decades, and radiotherapy plays a more and more important role in managing breast cancer. With the advancement of technology, the radiotherapy treatment techniques changed from conventional wedged technique to intensity modulated radiotherapy (IMRT), resulting in an improvement in the dose homogeneity. Regardless of the treatment techniques, peripheral dose to the contralateral breast is inevitable. The possibility of the peripheral dose causing contralateral breast cancer (CBC) has re-attracted the interest. However, the variation of the peripheral dose with different treatment techniques has not been well identified. Thus this study aims to compare the contralateral breast dose from the primary breast irradiation using various radiotherapy treatment techniques and types of shielding. Six treatment plans by different treatment techniques, including paired physical wedges (PW-P), a lateral physical wedge only(PW-L), paired enhanced dynamic wedges (EDW-P), a lateral enhanced dynamic wedge only(EDW-L), field-in-field tangential opposing (TO-FiF), and inverse-planned intensity modulated radiotherapy (IMRT-IP), were generated using a female Rando phantom. The phantom was treated by all plans, and 15 metal oxide semiconductor field effect transistor(MOSFET)detectors on the surface and inside the contralateral breast were utilized for measuring the contralateral breast dose for each plan. Measurement was repeated with the application of 0.2, 0.3 and 0.5cm lead sheets or 0.5 and 1cm superflab (SF) on the TO-FiF to demonstrate the effect of shielding on the contralateral breast dose. The measured contralateral breast doses were: 2.05Gy for PW-P, 1.44Gyfor PW-L, 1.51Gyfor EDW-P, 1.52Gyfor EDW-L, 1.25Gyfor TO-FiF, and 1.17Gyfor IMRT-IP, corresponding to 2.35% to 4.11% of total dose. PW-P producedthe highest contralateral breast dose while IMRT-IP producedthe lowest. For the addition of shielding, the doses were: 1.25Gy for no shielding, 0.65Gy for 0.2cm lead, 0.61Gy for 0.3cm lead, 0.49Gy for 0.5cm lead, 0.76Gy for 0.5cm SF, and 0.72Gy for 1cm SF. Lead sheet with 0.5cm thickness most effectively reduced the contralateral breast dose by 60%.All techniques showed that the surface dose was much higher than the dose at depth, and the dose dropped exponentially from the surface to the internal. Low energy radiation constitutes a large portion of the contralateral breast dose, so all types of shielding could decrease the surface dose effectively, but not the internal dose. The radiation-induced CBC risks were estimated to be about 0.77% to 1.36%. To conclude, it is important that the contralateral breast dose to patients, especially those under 45, is maintained minimal. Therefore, TO-FiF or IMRT-IP are recommended to be the treatment of choices. The used of shielding, either lead or SF, is also advisable. / published_or_final_version / Diagnostic Radiology / Master / Master of Medical Sciences

Evaluation of verification accuracy of two different immobilization methods in stereotactic body radiotherapy of early stage non-small cell lung carcinoma and pulmonary oligometastases

Ho, Lok-man, 何樂文 January 2014 (has links)
Purpose: The aim of the study is to compare the positioning accuracy of two immobilization systems commonly used in stereotactic body radiation therapy (SBRT) of non–small cell lung carcinoma (NSCLC) and lung oligometastases, Polyurethane Foam Cradles (PFC) and the BodyFIX System (BFS) with 2D and 3D image guidance. Both the interfraction and intrafractional positional errors were analyzed. Methods and Materials: 189 CBCT scans from 44 patients with NSCLC or lung oligometastases who received SBRT between August 2008 and April 2014 were analyzed retrospectively. Of these, 20 and 24 patients were immobilized with a Polyurethane Foam Cradle (PFC) and the BodyFIX System (BFS) respectively. The results of on board imaging (OBI) and pre-treatment cone-beam computed tomography (CBCT) at initial setup and after correction were registered to planning CT for online matching. The positional errors in anteroposterior (AP), superior-inferior (SI) and medial-lateral (ML) directions were analyzed. Post-treatment CBCT were used to assess intrafraction tumour displacement for 19 patients. The planning target volume margins were calculated using the van Herk’s formula. Other possible factors contributing to setup uncertainty were also analyzed. Result: By using skin mark as a reference, the mean setup errors were 0.09, -0.10 and 0.02 cm for PFC and 0.04, -0.19 and -0.10 cm for BFS in AP, SI and ML directions respectively. The mean setup errors were decreased to 0.04, 0.02 and 0.04 cm for PFC; and -0.04, -0.04 and -0.02 cm for BFS after the application of OBI. The errors were further decreased to below 0.02 cm in all directions after the application of first pre-treatment CBCT in both immobilization methods. Statistically significant difference (p < 0.05 ) was only found in the comparison of AP error between the two devices, when OBI was used as the verification method. For PFC, the 3D vector errors of skin mark, OBI and first pre-treatment CBCT were 6.4 mm, 2.9 mm and 0.5 mm, respectively cases. For BFS, the errors were 7.1 mm, 3.0 mm and 0.4 mm, respectively. Smaller PTV margins in various directions were needed in BFS when using CBCT as the verification method. Positioning errors of skin mark setup in AP and SI directions had major contributions to all the setup errors; gender and tumour location might significantly affect the setup uncertainties. Comparatively large intrafractional errors were found in the post-treatment CBCT results of PFC. Conclusion: When employing the CBCT-based final couch position as the benchmark, the setup errors of skin mark, OBI and first CBCT results were compared relatively. The positioning accuracies of PFC and BFS were similar. Apart from the vertical error (AP direction) found in the OBI verification, there was no significant difference between the positioning accuracy of both immobilization devices. Both imaging guided RT techniques were superior to skin mark. OBI and CBCT online correction improved the positioning accuracy of lung SBRT and substantially reduces required target margins and normal tissue irradiation. / published_or_final_version / Diagnostic Radiology / Master / Master of Medical Sciences

Dose analysis of 2-dimensional and 3-dimensional radiotherapy techniques in the treatment of nasopharyngeal carcinoma

Wu, Wing-cheung, Vincent, 胡永祥 January 1997 (has links)
published_or_final_version / Radiation Oncology / Master / Master of Philosophy

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