A simple technique to improve calculated skin dose accuracy in a commercial treatment planning system.

Lilie Wang,George X Ding,Anthony J Cmelak

doi:10.1002/acm2.12275

Lilie Wang, George X Ding + Show 1 more

Open Access

https://doi.org/10.1002/acm2.12275

Copy DOI

Abstract

Radiation dermatitis during radiotherapy is correlated with skin dose and is a common clinical problem for head and neck and thoracic cancer patients. Therefore, accurate prediction of skin dose during treatment planning is clinically important. The objective of this study is to evaluate the accuracy of skin dose calculated by a commercial treatment planning system (TPS). We evaluated the accuracy of skin dose calculations by the anisotropic analytical algorithm (AAA) implemented in Varian Eclipse (V.11) system. Skin dose is calculated as mean dose to a contoured structure of 0.5 cm thickness from the surface. The EGSnrc Monte Carlo (MC) simulations are utilized for the evaluation. The 6, 10 and 15 MV photon beams investigated are from a Varian TrueBeam linear accelerator. The accuracy of the MC dose calculations was validated by phantom measurements with optically stimulated luminescence detectors. The calculation accuracy of patient skin doses is studied by using CT based radiotherapy treatment plans including 3D conformal, static gantry IMRT, and VMAT treatment techniques. Results show the Varian Eclipse system underestimates skin doses by up to 14% of prescription dose for the patients studied when external body contour starts at the patient's skin. The external body contour is used in a treatment planning system to calculate dose distributions. The calculation accuracy of skin dose with Eclipse can be considerably improved to within 4% of target dose by extending the external body contour by 1 to 2 cm from the patient's skin. Dose delivered to deeper target volumes or organs at risk are not affected. Although Eclipse treatment planning system has its limitations in predicting patient skin dose, this study shows the calculation accuracy can be considerably improved to an acceptable level by extending the external body contour without affecting the dose calculation accuracy to the treatment target and internal organs at risk. This is achieved by moving the calculation entry point away from the skin.

Highlights

Skin dose and its resultant toxicity, radiation dermatitis, has long been a concern of the radiation oncologist and is often a dose limiting toxicity of high-dose treatments, in head-and-neck and thoracic cancer patients.[1–5] Improvements in radiation therapy treatment technique and immobilization devices reduce patient setup uncertainty but have exacerbated this clinical dilemma
For analytical algorithm (AAA), the default body contour, 2 cm-enlarged body contour, and body contour including head mask are used in the calculations
This study has shown that Eclipse treatment planning systems (TPS) generally underestimated skin doses by up to 14% of prescription dose depending on how external body is contoured

Summary

Introduction

Skin dose and its resultant toxicity, radiation dermatitis, has long been a concern of the radiation oncologist and is often a dose limiting toxicity of high-dose treatments, in head-and-neck and thoracic cancer patients.[1–5] Improvements in radiation therapy treatment technique and immobilization devices reduce patient setup uncertainty but have exacerbated this clinical dilemma. Skin dose and its resultant toxicity, radiation dermatitis, has long been a concern of the radiation oncologist and is often a dose limiting toxicity of high-dose treatments, in head-and-neck and thoracic cancer patients.[1–5]. Improvements in radiation therapy treatment technique and immobilization devices reduce patient setup uncertainty but have exacerbated this clinical dilemma. It is well known that immobilization devices have a noteworthy deleterious effect on patient skin dose.[6–9]. Accuracy of predicting skin dose by commercial treatment planning systems (TPS) is critical, as skin dose toxicity has a major impact on how well a patient tolerates treatment. Accurate skin dose calculations would greatly help clinicians make appropriate treatment plan decisions for these patients where skin toxicity has historically been an issue.[10]

Objectives

Methods

Results

Conclusion