Effect of prescription isodose line on tissue sparing in linear accelerator-based stereotactic radiosurgery treating multiple brain metastases using dynamic conformal arcs.

PURPOSE: Linear accelerator-based stereotactic radiosurgery (SRS) has become a mainstay for simultaneous management of multiple intracranial targets. Recent improvements in treatment planning systems (TPS) have enabled treatment of multiple brain metastases using dynamic conformal arcs (DCA) and a single treatment isocenter. However, as the volume of healthy tissue receiving at least 12 Gy (V12) is linked to the probability of developing radionecrosis, balancing target coverage while minimizing V12 is a critical factor affecting SRS plan quality. Current TPS allow users to adjust various parameters influencing plan optimization. The purpose of this work is to quantify the effect of negative margins on V12 for cranial SRS plans managing multiple brain metastases. METHODS: Using the Brainlab Elements v3.0 TPS (Brainlab, Munich, Germany), we calculated V10, V12, V15, monitor units, and conformity index for seventeen SRS plans treating 2-10 metastases on our Elekta Versa HD (Elekta, Stockholm, Sweden) linear accelerator. We compared plans optimized using 70%-90% prescription isodose lines (IDL) in 5% increments. RESULTS: Irrespective of the number of treated metastases, optimization at a lower prescription IDL reduced V10, V12, and V15 and increased MU compared to the 90% IDL (p < 0.01). However, comparing the 70% and 75% IDL optimizations, there was little difference in tissue sparing. The conformity index showed no consistent trends at different IDLs due to a significant spread in case data. CONCLUSION: For our plans treating up to 10 metastases, diminishing returns for tissue sparing at IDLs below 80% paired with increasing treatment MU and dosimetric hot spot made optimization at lower IDLs less favorable. In our clinic, after consulting with a physician, it was determined that optimization at the 80% IDL achieved the best balance of V12, treatment MU, and maximum dose. Clinics implementing LINAC-based SRS programs may consider using similar evaluations to develop their own clinical protocols.

AERO: An Objective Peripheral Edema Measurement Device.

Peripheral edema is of ten assessed by medical prof essionals to gain insights about development of many patient conditions. Currently, doctors assess edema by pushing on the swollen area of a patient. The difficulty with this method is the inconsistency assessment results between different physicians due to the subjective nature of the practice. The proposed solution uses AERO (or Air Edema RepOrting), a mobile, handheld device consisting of a high-speed camera with a macro lens, LED light, and compressed air to create edema indentation and capture images of the skin /tissue response. A MATLAB program analyzes these images and determines the correct level of edema. AERO was tested with a LifeformOR pitting edema trainer (four pieces of skin sample that represent the four edema levels). Various system configurations, such as the air pressure, camera to sample distance, and air incidence angle, were examined and optimal parameters were identified. Results demonstrated that AERO was able to distinguish the four levels of edema sample pads. This solution can potentially provide a quantified, standard evaluation of peripheral edema for both home and health care environments.