Ensuring the intended volume is given the intended absorbed dose in radiotherapy: Managing geometric variations and treatment hazards

Abstract

Methods for ensuring that the intended volume receives the intended absorbed dose in radiotherapy have been investigated. In order to optimise radiation treatment of cancer, geometric variations in the treatment chain need to be controlled. Furthermore, hazards potentially leading to unintended irradiation need to be controlled. While the required methods for optimisation of irradiation are diverse, advances in technology leading to more distinctly defined high dose volumes make the implementation of these methods crucial.



Geometric variations are controlled by (a) knowledge of types and magnitude of variations; (b) minimisation of variations; (c) taking into account remaining variations by creating margins around volumes. Set-up variations have been quantified for lung cancer and breast cancer irradiation. Organ motion has also been measured in connection with treatment of lung tumours. While set-up variations are characterised for groups of patients within individual clinics, it is shown that lung tumour motion needs to be measured for the individual patient due to the range of organ positional variation and corresponding impact. Another parameter that has a high impact on the overall accuracy is the delineation variation in the definition of volumes. It is shown that various methods impact on the minimisation of this variation to different degrees. It is also shown that the delineation of clinical target volume (CTV), being different from gross tumour volume (GTV) delineation in that it also can reflect non-biological parameters such as treatment strategy, will call for the recording of CTV delineation strategy in order to capture the required information. Margins should be based on measured values of variations that are combined according to a documented model. A method of enhancing the potential for dose escalation through stratification of margins based on tumour cell density is suggested and analysed.



Hazards in the treatment preparation chain are controlled by (a) identification of hazards in combination with frequency and consequence analysis, leading to (b) a risk estimation and (c) reducing these risks by introducing a multilayered system of preventive measures. Hazards in radiotherapy preparation have been identified together with corresponding frequencies. Mistakes in the calculation and creation of information were found with a frequency of 1-3% of treatment courses, while the corresponding numbers for information transfer was found to be 1-2%. Layers of preventive measures include (1) actions where potential deviations from intended dose and geometry can be found before the first irradiation-fraction of the patient; (2) actions where deviations can be found during or after the treatment course; (3) application of safety-technology; (4) application of safety procedures; and (5) actions where contributing factors such as staffing-levels and structure, training and communication are addressed. A method for monitoring workload in treatment preparation is explored in this context.

Abstract (Swedish)

Popular Abstract in Swedish

Strålbehandling har sedan länge visat sig vara en bra metod för att behandla patienter med cancer. Den nya teknik som har introducerats under de senaste åren har möjliggjort ökade stråldoser till än mer begränsade volymer. Samtidigt innebär detta att ökade krav ställs på att man försäkrar sig om att den volym man bestrålar är den volym som innehåller tumörceller och att inga misstag görs när man förbereder behandlingen.



I denna avhandling undersöks hur man praktiskt skall gå tillväga för att försäkra sig om:



(1) en stor sannolikhet för att tumören befinner sig i strålfältet vid varje behandlingstillfälle



(2) en liten sannolikhet för att man ska göra något fel då man förbereder behandlingen



Inom strålterapi förekommer ett antal geometriska variationer i tumörposition i förhållande till strålfält. Dessa variationer är en del av terapin och kommer sig av att man behandlar en patient dagligen i flera veckor. Vid varje behandlingstillfälle försöker man positionera patienten med hög noggrannhet för att vara säker på att tumören befinner sig inom strålfältet, men det är alltid en viss variation i positioneringen. Dessutom gör fysiologiska processer som andning och mag- och tarmfunktioner att tumören rör sig. Dessa processer, tillsammans med svårigheten att vara helt säker på vilken som är den korrekta volym som innehåller alla tumörceller, gör att man måste ha vissa marginaler i sitt strålfält. I avhandlingen undersöks geometriska variationer och metoder för att minimera dessa samt återstående marginaler.



I relation till hur man minskar risken för fel vid förberedande av strålbehandling, har förekommande faror kartlagts och kvantifierats. I 3.5% av förberedda behandlingar har fel hittats och åtgärdats innan behandling har påbörjats. Olika metoder som kan kombineras för att få en säker strålbehandling har undersökts.

• author: Holmberg, Ola
• supervisor: [unknown] [unknown]
• opponent: Olsen, Dag Rune, Professor, Det Norske Radiumhospital, Oslo, Norge
• organization: Medical Radiation Physics, Malmö (research group)
• publishing date: 2004
• type: Thesis
• publication status: published
• subject: Radiology, Nuclear Medicine and Medical Imaging
• keywords: medical instrumentation, tomography, radiology, Clinical physics, safety, risk, hazard, organ motion, set-up, margins, volume definition, radiotherapy, accuracy, Klinisk fysiologi, radiologi, tomografi, medicinsk instrumentering, Radiopharmaceutical technology, Radiofarmaceutisk teknik
• pages: 168 pages
• defense location: Diagnostiskt centrums föreläsningssal, plan 2, ingång 44, Universitetssjukhuset MAS, Malmö
• defense date: 2004-04-28 10:15:00
• ISBN: 91-628-6002-X
• language: English
• LU publication?: yes
• additional info: Article: Ekberg L, Holmberg O, Wittgren L, Bjelkengren G, Landberg T. What margins should be added to the clinical target volume in radiotherapy treatment planning for lung cancer? Radiother Oncol 48: 71-77, 1998 Article: Holmberg O, Coffey M, Armstrong J. Geometric uncertainties in radiotherapy of the lung. In: McKenzie et al. (editors). Geometric uncertainties in radiotherapy - defining the planning target volume. British Institute of Radiology, London, United Kingdom, 77-87, 2003 Article: McGibney C, Holmberg O, McClean B, Armstrong J. Analysis of dose distribution in the “Rind” - a volume outside the PTV - in 3-dimensional conformal radiation therapy of non small cell lung cancer. Radiother Oncol 66: 87-93, 2003 Article: Holmberg O, Huizenga H, Idzes M H M, Lebesque J V, Vijlbrief R E, Mijnheer B J. In vivo determination of the accuracy of field matching in breast cancer irradiation using an electronic portal imaging device. Radiother Oncol 33: 157-166, 1994 Article: Holmberg O, McClean B. Preventing treatment errors in radiotherapy by identifying and evaluating near misses and actual incidents. Journal of Radiotherapy in Practice 3: 13-25, 2002 Article: Holmberg O, McClean B. A method of predicting workload and staffing level for radiotherapy treatment planning as plan complexity changes. Clin Onc 15: 359-363, 2003
• id: 2b099f43-7523-4bde-b547-2fa8fe77d993 (old id 466920)
• date added to LUP: 2016-04-04 10:13:57
• date last changed: 2018-11-21 20:57:33