Peak Skin and Eye Lens Radiation Dose From Brain Perfusion CT Based on Monte Carlo Simulation

Abstract

OBJECTIVE. The purpose of our study was to accurately estimate the radiation dose to skin and the eye lens from clinical CT brain perfusion studies, investigate how well scanner output (expressed as volume CT dose index [CTDIvol]) matches these estimated doses, and investigate the efficacy of eye lens dose reduction techniques. MATERIALS AND METHODS. Peak skin dose and eye lens dose were estimated using Monte Carlo simulation methods on a voxelized patient model and 64-MDCT scanners from four major manufacturers. A range of clinical protocols was evaluated. CTDIvol for each scanner was obtained from the scanner console. Dose reduction to the eye lens was evaluated for various gantry tilt angles as well as scan locations. RESULTS. Peak skin dose and eye lens dose ranged from 81 mGy to 348 mGy, depending on the scanner and protocol used. Peak skin dose and eye lens dose were observed to be 66–79% and 59–63%, respectively, of the CTDIvol values reported by the scanners. The eye lens dose was significantly reduced when the eye lenses were not directly irradiated. CONCLUSION. CTDIvol should not be interpreted as patient dose; this study has shown it to overestimate dose to the skin or eye lens. These results may be used to provide more accurate estimates of actual dose to ensure that protocols are operated safely below thresholds. Tilting the gantry or moving the scanning region further away from the eyes are effective for reducing lens dose in clinical practice. These actions should be considered when they are consistent with the clinical task and patient anatomy.

Estimating peak skin and eye lens dose from neuroperfusion examinations: Use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM Report No. 111, and ImPACT dosimetry tool values

“…For example, as illustrated in Table II of a previous study, the skin dose from the AAPM posted protocol for the model Irene ranges from 87 to 348 mGy, and the eye lens dose from the AAPM posted protocol for the model Irene ranges from 81 to 279 mGy. 17 The results of this study indicate that the CTDI vol overestimates the peak skin dose by between 26% and 65%, and it overestimates eye lens dose by between 33% and 106%. This is primarily because of the integration of the 100 cm long ion chamber in the CTDI vol measurement.…”

“…30 In summary, radiation dose from CT neuroperfusion examinations should be closely monitored. Factors to be monitored include the accurate estimation of radiation dose (including the prospective prediction of dose and the retrospective evaluation of dose), the reduction of patient dose to specific target organs (for example, tilting the gantry or avoiding direct exposure to eye lenses in order to reduce eye lens dose 17 ), the optimization of the scan protocol, the enforcement of optimized scan protocols, and the elimination of operator errors. The results of this study could be used to facilitate the optimization of scan protocol by providing very detailed dose perspectives across different patients and scanner models.…”

“…As in the previous study, the scan simulations were performed using repeated axial scans at the location where the primary beam covers the eye lens completely, to represent a worst case scenario. 17 The widest collimation and typical bowtie filter for head scans were used for each scanner. It should be noted that although the highest tube voltage setting (140 kV or 135 kV) is not typically used and is not recommended for brain perfusion scans in clinical protocols, they are included in our results for reference.…”

“…Previous work has investigated the peak skin dose and eye lens dose during CT neuroperfusion scans for a range of scanning protocols using one patient model. 17 The purpose of this study is to: (a) expand the scope of the previous work and investigate the effects of patient size on radiation dose from CT neuroperfusion exams using four different adult patient models, and (b) investigate how well these doses can be approximated not only by CTDI vol , which is currently reported on scanner consoles, but also by other current or future CT dosimetry tools, such as values derived from the ImPACT dosimetry spreadsheet tool and measurements based on AAPM Report No. 111.…”

Lateral Decubitus Positioning for Cervical Nerve Root Block Using CT Image Guidance Minimizes Effective Radiation Dose and Procedural Time

“…20 It has been demonstrated that during simulated brain perfusion procedures, the dose to the skin may vary from 53% to 89% of the CTDI vol , while the dose to the eye lens is approximately 62% of the CTDI vol . 21,22 If one assumes an average dose reduction by 75%, the product of this factor by the increase due to the 12-cm neck size results in a net overestimate of the true CTDI vol and DLP of approximately 10%-12%.…”