Abstract
Background: Accurate delivery of radiotherapy is a paramount component of providing safe oncological care. Margins are applied when planning radiotherapy to account for subclinical tumour spread, physiological movement and setup error. Setup error is unique to each radiotherapy institution and should be calculated for each organ site to ensure safe delivery of treatment. Aim: The aim of this study is to calculate the random and systematic setup error for a cohort of patients with intracranial tumours treated with 3D Conformal Radiotherapy. Setting: The Department of Radiation Oncology, Groote Schuur Hospital, South Africa. Method: After obtaining above mentioned data, the ideal Clinical Target Volume (CTV)-Planning Target Volume (PTV) expansion margin was calculated using published CTV-PTV expansion margin recipes. The electronic portal images of 20 patients who met the inclusion criteria were compared to their digitally reconstructed radiograph. The setup error for each patient was measured after which the random (σ) and systematic (Σ) setup error for the study group could be calculated. With both these values known, the CTV-PTV expansion margin could be determined. Results: The largest error was in the superior/inferior direction (87.7% 5mm), followed by the medial/lateral direction (76.2% 5 mm) and least in the anterior/posterior direction (91.6% 5 mm). The random and systematic errors in all three directions for this patient cohort were less than 2 mm, conforming to acceptable standards of delivering safe radiotherapy. Using Stroom’s margin recipe (2Σ + 0.7σ) a CTV-PTV expansion margin of 5 mm can safely be applied for this patient cohort. Conclusion: When treating patients with intracranial tumours at Groote Schuur Hospital the CTV-PTV expansion margin can safely be reduced from 1 cm to 5 mm.
Highlights
Accuracy of radiation delivery in radiotherapy is critical to ensure adequate coverage of a tumour and minimisation of normal tissue dose
The largest error was in the Superior/Inferior (SI) direction, followed by the Medial/Lateral (ML) direction and least in the Anterior/Posterior (AP) direction with 87.7%, 76.2% and 91.6% of the errors in the ML, SI and AP directions respectively being less than 3mm
The random and systematic error in all three directions for this patient cohort were less than 2mm conforming to acceptable standards of delivering safe radiotherapy
Summary
Accuracy of radiation delivery in radiotherapy is critical to ensure adequate coverage of a tumour and minimisation of normal tissue dose. The International Commission on Radiation Units and Measurements (ICRU) report 50 introduced the concept of a gross tumour volume (GTV), a clinical target volume (CTV) and a planning target volume (PTV) in radiotherapy. The PTV is a geometrical concept used for treatment planning and it is defined to select appropriate beam sizes and beam arrangements to ensure that the prescribed dose is delivered to the CTV.. The Introduction should put the focus of the manuscript into a broader context and explain its social and scientific value. Address this to readers who are not experts in this field and include a brief review of the key literature. Set-up error is unique to each radiotherapy institution and should be calculated for each organ site to ensure safe delivery of treatment
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