Effects of error on dose of target region and organs at risk in treating nasopharynx cancer with intensity modulated radiation therapy.

Guangsheng Liu,Sumei Zhang,Lingling Zhang,Qing Yuan Wang,Yuzhuo Ma,Fengmei Ma,Xingxiu Chen

doi:10.12669/pjms.321.9218

Guangsheng Liu, Sumei Zhang + Show 5 more

Open Access

https://doi.org/10.12669/pjms.321.9218

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Abstract

Objective:To measure setup error of head and neck neoplasm in radiotherapy and discuss over effects of error on physical dose acting on target region and organs at risk of nasopharynx cancer (NPC) patients treated with intensity modulated radiation therapy (IMRT).Methods:A total of 152 patients who developed head and neck neoplasm and received IMRT were randomly selected. Through comparing digital portal image and digital reconstruction image, we measured setup error, calculated expanding margin from clinical target volume (CTV) to planning target volume (PTV) and analyzed whether there was rules between setup error and treatment time. Additionally, 20 cases of NPC were selected. Three-dimensional error was simulated in planning system. Dose distribution was recalculated and a series of dose parameters of target volume and OAR were analyzed.Results:Setup error in left-right, head-feet and ventral-dorsal direction was (-0.62±1.46) mm, (-0.41±1.54) mm and (-0.31±1.67) mm respectively. Regarding limit value, the maximum and minimum value in left-right direction, head-feet direction and ventral-dorsal direction was 2.70 mm and -6.00 mm; 3.00 mm and -5.00 mm, 5.00 mm and -7.50 mm. Expanding margin from CTV to PTV was 2.26 mm, 1.88 mm and 1.97 mm in left-right direction, head-feet direction and ventral-dorsal direction.Conclusion:During IMRT, only when setup error is controlled below 3 mm can sharply reduce the damage caused by radiation to normal tissue; therefore, quality security and control of electronic portal imaging device need (EPID) to be improved.

Highlights

Nasopharynx cancer (NPC), the most common head and neck malignant tumor, is usually treated by radiotherapy as anatomic sites are close to multiple vital organs.[1]
When intensity modulated radiation therapy (IMRT) is applied in treating NPC, radiation dose can concentrate on target region extremely, which can ensure less radiation on organs beside target region, improve efficiency in killing tumor cells and enhance local control rate of tumor and survival rate.[3]
This study explored setup error of head and neck neoplasm in IMRT, simulated position difference with error value in planning system and analyzed setup error on target region and OAR

Summary

Introduction

Nasopharynx cancer (NPC), the most common head and neck malignant tumor, is usually treated by radiotherapy as anatomic sites are close to multiple vital organs.[1] On this account, cure rate and survival rate are directly determined by radiation technology. Differing from conventional radiotherapy, IMRT is able to provide radiation on different target tissue regions as required by altering radiation technology.[2] When IMRT is applied in treating NPC, radiation dose can concentrate on target region extremely, which can ensure less radiation on organs beside target region, improve efficiency in killing tumor cells and enhance local control rate of tumor and survival rate.[3]. Setup error plays a key role in IMRT.[4] IMRT as a kind of the most advanced technologies can improve local control rate of tumor and survival rate. Xia TY reported that, average error of fixed setup of head and neck neoplasm was (2.47±0.96) mm.[7]

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