Evaluation of stereotactic body radiation therapy planning and dosimetry in modern radiotherapy for improved clinical practice

Abstract

Stereotactic body radiation therapy (SBRT) entails focused radiation dose delivery in a few fractions with a high degree of accuracy and precision. With the advancement in imaging and delivery technologies, the usage of SBRT is increasing, and the clinical implication of SBRT is extended to various sites such as lung, liver, prostate, pancreas, head, and neck cancers. Generally, in SBRT, the number of fractions delivered in 5 but sometimes 6-9 fractions are also considered for it. The important characteristics of SBRT are accurately and precisely target localization and target tracking using external and internal markers, usage of adequate imaging modalities, stringent patient immobilization, and instruments to limit the organ movement, advancement in the treatment planning system with adequate optimization and dose calculation algorithm and treatment dose delivery with 1mm accuracy. The SBRT delivery in moving tumors is a challenging task, there could be variation in the dose due to the interplay effect. The number of dependent parameters like fraction dose, patient amplitude, breath per minute, plan complexity, energy, and dose rate can affect the tumors dose because of the relative movement of the target to the linear accelerator parameters. Modeling of the interplay effect can be done which facilitates reducing the dose variation using optimized and appropriate values of the parameters. One of the most important tasks of a medical physicist to validate treatment planning is a patient-specific quality assurance test. Conventional QA test fails to predict the true results in high dose gradient regions which is predominate in SBRT. The spatial change in dose in SBRT is high, so the new stringent QA test was developed which is a derivative-based gamma-index. Derivative-based gamma-index facilitates the prediction of the true result in high dose gradient region. newline