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.