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Enhancing benefits of bolus use through minimising the effect of air-gaps on dose distribution in photon beam radiotherapy

Published online by Cambridge University Press:  12 May 2020

Karim Bahhous Open the ORCID record for Karim Bahhous [Opens in a new window] ,
Mustapha Zerfaoui ,
Abdelaali Rahmouni  and
Naima El Khayati
Karim Bahhous*
Affiliation:
Department of Physics, Faculty of Science, Mohammed V University in Rabat, Rabat, Morocco Hassan II Oncology Center, University Hospital Mohammed VI, Oujda, Morocco
Mustapha Zerfaoui
Affiliation:
Department of Physics, Faculty of Science, University Mohamed 1st, Oujda, Morocco
Abdelaali Rahmouni
Affiliation:
Department of Physics, Faculty of Science Dhar El Mahraz, Sidi Mohamed Ben Abdellah University, Fez, Morocco
Naima El Khayati
Affiliation:
Department of Physics, Faculty of Science, Mohammed V University in Rabat, Rabat, Morocco
*
Author for correspondence: Karim Bahhous, Department of Physics, Faculty of Science, Mohammed V University in Rabat, Rabat, Morocco. E-mail: bahhouskarim@gmail.com
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Abstract

Introduction:

Bolus material is frequently used on patient’s skin during radiation therapy to reduce or remove build-up effect for high-energy beams. However, the air-gaps formed between the bolus and the skin’s irregular surface reduce the accuracy of treatment planning. To achieve a good treatment outcome using bolus, experimental investigations are required to choose its thickness and to quantify the air-gap effect.

Material and methods:

Measurements for a 6 MV photon beam with a fixed source surface distance were carried out using the 31021 Semiflex 3D chamber into the water phantom. Firstly, the depth of maximum dose (R100) and the dose value at surface (Ds) were evaluated as a function of bolus thickness for some square fields. Secondly, to test the effect of the air-gaps ranged from 5 to 30 mm with a step of 5 mm between the bolus and the phantom surface, a water-equivalent RW3 (Goettingen White Water) slab form of 10 mm thickness was considered as a bolus.

Results:

We observed that the linear behaviour of R100 in terms of the bolus thickness makes the choice of this parameter more convenient depending on field size. In addition, increasing the air-gaps widens the penumbra and created electrons that have a greater probability to quit the radiation field borders before reaching the surface. The dose spread of the off-field area could have a significant influence on the patient treatment.

Conclusion:

Based on dose distribution comparisons between the measurements with and without air-gaps for the field size of 100 mm × 100 mm, it has been demonstrated that a maximum air-gap value lower than 5 mm would be desirable for an efficient use of the bolus technique.

Keywords

air-gaps effectbolusdose distribution analysisout-of-field dosepenumbra
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 20 , Issue 2 , June 2021 , pp. 210 - 216
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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