What are the radiological and cognitive changes in patients treated with Stereotactic Radiosurgery (SRS) and Fractionated Stereotactic Radiotherapy (FSRT) for central nervous system (CNS) conditions?

From the Guidelines

Your thesis on radiological and cognitive changes in patients treated with stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (FSRT) for CNS conditions requires a comprehensive understanding of radiation biology principles, imaging changes, dosimetry, and cognitive outcomes, with a focus on the most recent and highest quality study, which is the 2022 guideline from the Journal of Clinical Oncology 1. To prepare for your viva, focus on the following key areas:

• Radiation biology principles, particularly the linear-quadratic model that explains why FSRT may spare normal tissue better than single-fraction SRS through repair of sublethal damage between fractions, as discussed in the context of SRS and FSRT for brain metastases 1.
• Imaging changes post-treatment, including pseudoprogression (transient enhancement that mimics tumor progression) versus true progression, radiation necrosis patterns, and white matter changes visible on T2/FLAIR sequences, which are critical for assessing treatment response and potential complications 1.
• Dosimetry, including dose constraints for critical structures like optic nerves, brainstem, and cochlea, as well as dose-volume histograms and their interpretation, which are essential for minimizing toxicity and maximizing treatment efficacy 1.
• Cognitive outcomes, emphasizing neurocognitive domains most affected by radiation (memory, executive function, processing speed), assessment tools like the Mini-Mental State Examination or Montreal Cognitive Assessment, and the relationship between radiation dose to hippocampal regions and memory decline, as highlighted in the 2022 guideline from the Journal of Clinical Oncology 1. Some key points to consider:
• The 2022 guideline from the Journal of Clinical Oncology 1 recommends SRS, WBRT, and the combination of SRS plus WBRT as reasonable options for patients with more than four unresected or more than two resected brain metastases and better performance status.
• The linear-quadratic model explains why FSRT may spare normal tissue better than single-fraction SRS through repair of sublethal damage between fractions, as discussed in the context of SRS and FSRT for brain metastases 1.
• Pseudoprogression and radiation necrosis are potential complications of SRS and FSRT, and can be assessed using imaging techniques such as MRI, as discussed in the 2008 guidelines from the Journal of the National Comprehensive Cancer Network 1.
• Cognitive outcomes are an important consideration in the treatment of brain metastases, and can be affected by radiation dose to hippocampal regions, as highlighted in the 2022 guideline from the Journal of Clinical Oncology 1. For your viva, be prepared to discuss:
• Your methodology and statistical analysis approaches, including any limitations of your retrospective study.
• How your findings compare with existing literature, including the 2022 guideline from the Journal of Clinical Oncology 1 and other relevant studies.
• The implications of your research for clinical practice, including potential changes to treatment protocols or patient management strategies.

From the Research

Radiological Changes

• Radiological changes in patients treated with Stereotactic Radiosurgery (SRS) and Fractionated Stereotactic Radiotherapy (FSRT) for central nervous system (CNS) tumors have been studied in various research papers 2, 3, 4.
• A study published in 2021 found that SRS leads to a decline in cognitive performance, which stabilizes or returns to baseline in patients with survival of at least 9-15 months 2.
• Another study published in 2012 compared the efficacy and toxicity of SRS and FSRT in 260 patients with brain metastases, and found that SRS was associated with a higher toxicity rate, but FSRT presented low toxicity and was an effective and safe treatment for brain metastases not amenable to SRS 3.

Cognitive Changes

• Cognitive changes in patients treated with SRS and FSRT have also been studied, with a focus on the impact of radiation on neurocognitive functioning 2, 5.
• A study published in 2011 reviewed clinical studies investigating central nervous system dose tolerances after cranial or spinal SRS/SRT, and discussed the impact of dose, volume, fractionation, and other relevant clinic-pathologic variables on cognitive changes 5.
• A study published in 2019 discussed the principles and applications of SRS and SBRT, and outlined the accepted appropriate clinical indications for stereotactic RT, including the potential role of stereotactic treatment in future oncologic management 4.

Dosimetry

• Dosimetry is an important aspect of SRS and FSRT, with a focus on delivering high doses of radiation to small tumors while minimizing damage to surrounding healthy tissue 4, 6.
• A study published in 2018 documented the 5- and 10-year rates of late toxicity and vertebral compression fracture (VCF) in long-term survivors after SRS for spine metastases, and found that the risk of late toxicity significantly increases with cumulative biologically effective dose (BED3) > 200 Gy 6.
• Another study published in 2011 reviewed clinical studies investigating central nervous system dose tolerances after cranial or spinal SRS/SRT, and discussed the impact of dose, volume, fractionation, and other relevant clinic-pathologic variables on dosimetry 5.