Original Research

Determination of an optimal treatment margin for intracranial tumours treated with radiotherapy at Groote Schuur Hospital

Andre Vos, Thuran Naiker, Hannelie MacGregor
South African Journal of Oncology | Vol 4 | a124 | DOI: https://doi.org/10.4102/sajo.v4i0.124 | © 2020 Andre Vos, Thuran Naiker, Hannelie MacGregor | This work is licensed under CC Attribution 4.0
Submitted: 22 February 2020 | Published: 18 June 2020

About the author(s)

Andre Vos, Department of Radiation Oncology, Faculty of Medicine, University of Cape Town, Cape Town, South Africa
Thuran Naiker, Department of Radiation Oncology, Faculty of Medicine, University of Cape Town, Cape Town, South Africa
Hannelie MacGregor, Department of Radiation Oncology, Faculty of Medicine, University of Cape Town, Cape Town, South Africa


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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% < 3mm; 6.1% > 5mm), followed by the medial/lateral direction (76.2% < 3 mm; 0 > 5 mm) and least in the anterior/posterior direction (91.6% < 3 mm; 0 > 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.


Keywords

Setup margin; random error; systematic error; intracranial tumours; CTV-PTV expansion margin

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