pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2019.30.1.1 pmp-30-1 Original Article Skin Dose Comparison of CyberKnife and Helical Tomotherapy for Head-and-Neck Stereotactic Body Radiotherapy YoonJeongmin 1 ParkKwangwoo 2 KimJin Sung 2 KimYong Bae 2 LeeHo 3 Department of Radiation Oncology, Seoul National University Hospital Department of Radiation Oncology, Yonsei Cancer Center, Yonsei University College of Medicine Department of Radiation Oncology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea Corresponding author Ho Lee (holee@yuhs.ac) Tel: 82-2-2228-4363 Fax: 82-2-2227-7823 032019 19032019 3011 6 03122018 30122018 07012019 Copyright © 2019 Korean Society of Medical Physics 2019 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Purpose:

This study conducts a comparative evaluation of the skin dose in CyberKnife (CK) and Helical Tomotherapy (HT) to predict the accurate dose of radiation and minimize skin burns in head-and-neck stereotactic body radiotherapy.

 Materials and Methods:

Arbitrarily-defined planning target volume (PTV) close to the skin was drawn on the planning computed tomography acquired from a head-and-neck phantom with 19 optically stimulated luminescent dosimeters (OSLDs) attached to the surface (3 OSLDs were positioned at the skin close to PTV and 16 OSLDs were near sideburns and forehead, away from PTV). The calculation doses were obtained from the MultiPlan 5.1.2 treatment planning system using raytracing (RT), finite size pencil beam (FSPB), and Monte Carlo (MC) algorithms for CK. For HT, the skin dose was estimated via convolution superposition (CS) algorithm from the Tomotherapy planning station 5.0.2.5. The prescribed dose was 8 Gy for 95% coverage of the PTV.

 Results and Conclusions:

The mean differences between calculation and measurement values were −1.2±3.1%, 2.5±7.9%, −2.8±3.8%, −6.6±8.8%, and −1.4±1.8% in CS, RT, RT with contour correction (CC), FSPB, and MC, respectively. FSPB showed a dose error comparable to RT. CS and RT with CC led to a small error as compared to FSPB and RT. Considering OSLDs close to PTV, MC minimized the uncertainty of skin dose as compared to other algorithms.

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Nineteen OSLDs attached on the surface of a head-and-neck phantom.

Comparison of the dose difference between calculated and measured values in 19 OSLDs using RT with and without CC.

Comparison of the dose difference between calculated and measured values in 19 OSLDs using CS and RT with CC.

Comparison of the dose difference between calculated and measured values in 19 OSLDs using MC and CS.

Comparison of the dose difference between calculated and measured values in 19 OSLDs using FSPB and RT.

Comparison of dose calculated by five dose calculation algorithms and measured dose.

Modality Dose calculation algorithms All (19 OSLDs) [%] Near PTV (3 OSLDs) [%]
Helical TomoTherapy CS with VoLO −1.2±3.1 −6.8±3.6
CyberKnife RT for fixed cone 2.5±7.9 17.9±9.4
RT with CC for fixed cone −2.8±3.8 −0.7±6.8
MC for fixed cone −1.4±1.8 −2.7±2.2
FSPB for MLC −6.6±8.8 −24.3±5.7