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KMID : 1164220210330010089
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Journal of Korean Society for Radiotherapeutic Technology
2021 Volume.33 No. 1 p.89 ~ p.97
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Comparative evaluation of dose according to changes in rectal gas volume during radiation therapy for cervical cancer : Phantom Study
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Choi So-Young
Kim Tae-Won
Kim Min-Su
Song Heung-Kwon
Yoon In-Ha
Back Geum-Mun
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Abstract
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Purpose: The purpose of this study is to compare and evaluate the dose change according to the gas volume variations in the rectum, which was not included in the treatment plan during radiation therapy for cervical cancer.
Materials and methods: Static Intensity Modulated Radiation Therapy (S-IMRT) using a 9-field and Volumetric Modulated Arc Therapy (VMAT) using 2 full-arcs were established with treatment planning system on Computed Tomography images of a human phantom. Random gas parameters were included in the Planning Target Volume(PTV) with a maximum change of 2.0 cm in increments of 0.5 cm. Then, the Conformity Index (CI), Homogeneity Index (HI) and PTV Dmax for the target volume were calculated, and the minimum dose (Dmin), mean dose (Dmean) and Maximum Dose (Dmax) were calculated and compared for OAR(organs at risk). For statistical analysis, T-test was performed to obtain a p-value, where the significance level was set to 0.05.
Result: The HI coefficients of determination(R2) of S-IMRT and VMAT were 0.9423 and 0.8223, respectively, indicating a relatively clear correlation, and PTV Dmax was found to increase up to 2.8% as the volume of a given gas parameter increased. In case of OAR evaluation, the dose in the bladder did not change with gas volume while a significant dose difference of more than Dmean 700 cGy was confirmed in rectum using both treatment plans at gas volumes of 1.0 cm or more. In all values except for Dmean of bladder, p-value was less than 0.05, confirming a statistically significant difference.
Conclusion: In the case of gas generation not considered in the reference treatment plan, as the amount of gas increased, the dose difference at PTV and the dose delivered to the rectum increased. Therefore, during radiation therapy, it is necessary to make efforts to minimize the dose transmission error caused by a large amount of gas volumes in the rectum. Further studies will be necessary to evaluate dose transmission by not only varying the gas volume but also where the gas was located in the treatment field.
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KEYWORD
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Cervical cancer, Rectal gas volume, Intensity Modulated Radiation Therapy, Volumetric Modulated Arc Therapy
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