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Utilising virtual bolus in superficial planning target volume dose optimisation (TomoTherapy): a phantom study

Published online by Cambridge University Press:  20 June 2019

Gim Chee Ooi Open the ORCID record for Gim Chee Ooi [Opens in a new window]  and
Iskandar Shahrim Bin Mustafa Open the ORCID record for Iskandar Shahrim Bin Mustafa [Opens in a new window]
Gim Chee Ooi*
Affiliation:
Mount Miriam Cancer Hospital, Penang, Malaysia School of Physics, University Sains Malaysia, Penang, Malaysia
Iskandar Shahrim Bin Mustafa
Affiliation:
School of Physics, University Sains Malaysia, Penang, Malaysia
*
Author for correspondence: Gim Chee Ooi, Sri Kota Specialist Medical Centre, Jalan Mohet, Kawasan 1, 41000 Klang, Selangor, Malaysia. Tel. +6016-5022673. E-mail: [email protected]
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Abstract

Aim:

This is a phantom study to evaluate the dosimetry effects of using virtual bolus (VB) in TomoTherapy Treatment Planning System (TPS) optimisation for superficial planning target volume (PTV) that extends to the body surface. Without VB, the inverse-planning TPS will continuously boost the photon fluence at the surface of the superficial PTV due to lack of build-up region. VB is used during TPS optimisation only and will not be present in actual treatment delivery.

Materials and methods:

In this study, a dummy planning target was contoured on a cylindrical phantom which extends to the phantom surface, and VB of various combinations of thickness and density was used in treatment planning optimisation with TomoTherapy TPS. The plans were then delivered with the treatment modality TomoTherapy. Radiochromic films (Gafchromic EBT3) were calibrated and used for dose profiles measurements. TomoTherapy Planned-Adaptive software was used to analyse the delivered Dose-Volume Histograms (DVHs).

Results:

The use of 2 mm VB was not providing adequate build-up area and was unable to reduce the hot spots during treatment planning and actual delivery. The use of 4 mm VB was able to negate the photon fluence boosting effect by the TPS, and the actual delivery showed relatively small deviations from the treatment plan. The use of 6 mm VB caused significant dose overestimation by the TPS in the superficial regions resulting in insufficient dose coverage delivered.

Findings:

VB with the combination of 4 mm thickness and 1·0 g/cc density provides the most robust solution for the TomoTherapy TPS optimisation of superficial PTV.

Keywords

IMRTSuperficial TargetSuperficial PTVTomoTherapyVirtual Bolus
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 19 , Issue 1 , March 2020 , pp. 65 - 70
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Copyright
© Cambridge University Press 2019 

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