Abstract
PurposeWe aimed to evaluate the magnetic resonance imaging (MRI) appearance changes during stereotactic radiotherapy (SRT) for large sized brain metastases, and analyze the lesions necessitating treatment plan modification.Materials and methodsA total of 23 patients (27 lesions, >2 cm in tumor diameter) underwent SRT and all lesions were evaluated the appearance changes which had the necessity of the treatment plan modification. The appearance change of tumor during SRT was evaluated using gadolinium-enhanced MRI. The reasons of the modification were classified into tumor reduction, tumor enlargement, displacement, and shape change.ResultsAmong the 27 lesions, 55.6% required the treatment plan modification. The reasons were tumor reduction in six lesions, tumor enlargement in three lesions, displacement in three lesions, and shape change in three lesions. The planning target volume (PTV) size changed up to 43.0% and the shift of center of PTV was a maximum of 1.7 mm. The pathological status (adenocarcinoma vs others) and timing of steroid administration (prior vs after SRT start) were the predictive factors of tumor changes required the modification.ConclusionsAs tumor changes might occur even during short period of SRT, the treatment plan evaluation and modification were important in SRT for large brain metastases.
Highlights
Stereotactic irradiation (STI) for brain metastasis, including stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT), is a well-established treatment option [1, 2]
SRS administered in a single fraction using gamma knife or linac has been a standard treatment for small brain metastasis, and SRT administered in multiple fractions using gamma knife or linac has been considered for patients with large brain metastasis to reduce the risk of radiation necrosis while
Recursive partitioning analysis (RPA) class I was observed in three patients, and RPA class II was in 20 patients, respectively [11]
Summary
Stereotactic irradiation (STI) for brain metastasis, including stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT), is a well-established treatment option [1, 2]. In the case of linac-based SRT for large brain metastasis, there is a concern about the tumor changes during the treatment period, such as tumor size, shape, and geometry. The changes in tumor size, shape, and geometry during SRT could affect the treatment, such as insufficient target coverage and unnecessary irradiation to normal tissue. There were few studies that have assessed the need for treatment plan evaluation and modification during the treatment period of SRT [9, 10], and the specific cases requiring attention remain unclear. This study aimed to evaluate the magnetic resonance imaging (MRI) appearance changes during SRT for large brain metastases, and analyze the lesions necessitating treatment plan modification
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