Proton range uncertainty due to bone cement injected into the vertebra in radiation therapy planning.
We wanted to evaluate the influence of bone cement on the proton range and to derive a conversion factor predicting the range shift by correcting distorted computed tomography (CT) data as a reference to determine whether the correction is needed. Two CT datasets were obtained with and without a bone cement disk placed in a water phantom. Treatment planning was performed on a set of uncorrected CT images with the bone cement disk, and the verification plan was applied to the same set of CT images with an effective CT number for the bone cement disk. The effective CT number was determined by measuring the actual proton range with the bone cement disk. The effects of CT number, thicknesses, and position of bone cement on the proton range were evaluated in the treatment planning system (TPS) to draw a conversion factor predicting the range shift by correcting the CT number of bone cement. The effective CT number of bone cement was 260 Hounsfield units (HU). The calculated proton range for native CT data was significantly shorter than the measured proton range. However, the calculated range for the corrected CT data with the effective CT number coincided exactly with the measured range. The conversion factor was 209.6 [HU · cm/mm] for bone cement and predicted the range shift by approximately correcting the CT number. We found that the heterogeneity of bone cement could cause incorrect proton ranges in treatment plans using CT images. With an effective CT number of bone cement derived from the proton range and relative stopping power, a more actual proton range could be calculated in the TPS. The conversion factor could predict the necessity for CT data correction with sufficient accuracy.
Department of Radiation Oncology, Institute of Health Sciences, Gyeongsang National University, Jinju, Korea.
Young Kyung
YK
Lim
Ui-Jung
UJ
Hwang
Dongho
D
Shin
Dong Wook
DW
Kim
Jungwon
J
Kwak
Myonggeun
M
Yoon
Doo Hyun
DH
Lee
Se Byeong
SB
Lee
Sang-Yeob
SY
Lee
Sung Yong
SY
Park
Hong Ryeol
HR
Pyo
D001843:Bone Cements; D003287:Contrast Media / Q000008:administration & dosage*; D006801:Humans; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013131:Spine; D014057:Tomography, X-Ray Computed / Q000379:methods*; D035501:Uncertainty
D001843:Bone Cements; D003287:Contrast Media