A case study of IMRT planning (Plan B) subsequent to a previously treated IMRT plan (Plan A)

17th International Conference on the Use of Computers in Radiation Therapy

物理学;计算机科学

Cao, F.^1 ; Leong, C.^2 ; Schroeder, J.^2 ; Lee, B.^2

Department of Medical Physics, Fraser Valley Centre, BC Cancer Agency, Surrey, BC, Canada^1

Department of Radiation Oncology, Fraser Valley Centre, BC Cancer Agency, Surrey, BC, Canada^2

关键词: Brainstem;    Fluences;    Head-and-neck cancer;    Intensity-modulated radiation therapy;    Neck dissections;    Planning target volumes;    Spinal cords;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/489/1/012046/pdf
DOI  :  10.1088/1742-6596/489/1/012046

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

Background and purpose: Treatment of the contralateral neck after previous ipsilateral intensity modulated radiation therapy (IMRT) for head and neck cancer is a challenging problem. We have developed a technique that limits the cumulative dose to the spinal cord and brainstem while maximizing coverage of a planning target volume (PTV) in the contralateral neck. Our case involves a patient with right tonsil carcinoma who was given ipsilateral IMRT with 70Gy in 35 fractions (Plan A). A left neck recurrence was detected 14 months later. The patient underwent a neck dissection followed by postoperative left neck radiation to a dose of 66 Gy in 33 fractions (Plan B). Materials and Methods: The spinal cord-brainstem margin (SCBM) was defined as the spinal cord and brainstem with a 1.0 cm margin. Plan A was recalculated on the postoperative CT scan but the fluence outside of SCBM was deleted. A further modification of Plan A resulted in a base plan that was summed with Plan B to evaluate the cumulative dose received by the spinal cord and brainstem. Plan B alone was used to evaluate for coverage of the contralateral neck PTV. Results: The maximum cumulative doses to the spinal cord with 0.5cm margin and brainstem with 0.5cm margin were 51.96 Gy and 45.60 Gy respectively. For Plan B, 100% of the prescribed dose covered 95% of PTVb1. Conclusion: The use of a modified ipsilateral IMRT plan as a base plan is an effective way to limit the cumulative dose to the spinal cord and brainstem while enabling coverage of a PTV in the contralateral neck.