Imaging radiation dose in breast radiotherapy by X-ray CT calibration of Cherenkov light

Abstract

Imaging Cherenkov emission during radiation therapy cancer treatments can provide a realtime, non-contact sampling of the entire dose field. The emitted Cherenkov signal generated is proportional to deposited dose, however, it is affected by attenuation from the intrinsic tissue optical properties of the patient, which in breast, ranges from primarily adipose to fibroglandular tissue. Patients being treated with whole-breast X-ray radiotherapy (n = 13) were imaged for 108 total fractions, to establish correction factors from the linear relationships between Cherenkov light and CT number (HU). This study elucidates this relationship in vivo, and a correction factor approach is used to scale each image to improve the linear correlation between Cherenkov emission intensity and dose (R 2 6X ¼ 0:85; R 2 10X ¼ 0:95). This study provides a major step towards direct quantitative radiation dose imaging in humans by utilizing non-contact camera sensing of Cherenkov emission during the radiation therapy treatment.

Estimation of diffuse Cherenkov optical emission from external beam radiation build-up in tissue

“… Comparison of cumulative Cherenkov images taken during whole-breast radiation therapy at 6 versus 10 MV x-rays for a single patient. 6 The observed Cherenkov intensity remains approximately constant, even at higher x-ray energies. …”

“… 1 – 4 The ability to visualize the beam shape is well documented, although the interpretation of the emitted intensity is much more complex because of the range of factors that influence the observed signal intensity. 5 , 6 While several studies have examined the influence of tissue optical properties, few have systematically examined the nature of the radiation beam itself in affecting the observed emitted Cherenkov signal intensity. In particular, there has always been a mystery about why the intensity of Cherenkov light emitted from patients undergoing radiation therapy does not appear to be a strong function of beam energy, despite the fact that it is well known that the basic production of Cherenkov light is a strong function of particle energy 7 ( Fig.…”

“…In particular, blood attenuation is quite visible, as major blood vessels are highly attenuating and alterations in subcutaneous layer composition can change the radiant emission drastically. 6 This optical attenuation effect has been examined in a number of theoretical, 5 , 7 – 10 as well as experimental, 6 studies. The competing effects of radiation build-up combined with optical attenuation must be grappled with and are folded into the theoretical analysis here, based upon diffusion theory modeling.…”

Measuring Tumor Microenvironment pH During Radiotherapy Using a Novel Cerenkov Emission Multispectral Optical Probe Based on Silicon Photomultipliers

“…Since CE is generated in any region that is receiving radiation dose, it has become an emerging modality for imaging radiation during RT and is also used as a quality assurance tool for its safe delivery. The intensity of CE is proportional to radiation dose [13][14][15] and has been used to measure superficial skin dose as well as to visualize radiation beam coverage, for example, in breast treatments and total skin electron therapy [16][17][18][19][20]. Additionally, CE has also become a useful tool for RT quality assurance by, for example, verifying radiation dose distribution in a water tank for treatment planning [21][22][23].…”

“…More recently, since CE peaks in the blue, it can be used as an optical excitation source for fluorescence with recent work showing how CE can be used to excite various fluorophores to measure tissue oxygenation in rodents [27][28][29]. Additionally, there has also been work using CE specific contrast agents for in vivo pH detection based on fluorinated ( 18 F) pH indicator dyes (phenol red, cresol purple, and phenolphthalein), where the CE generated from the 18 F component is optically quenched by the absorption from the functional dyes [30]. Other work has even shown the feasibility of using CE to image apoptosis to evaluate chemotherapy response of drug-resistant gastric cancers [31] as well as the use of CE to stimulate nanoparticles, such as europium oxide, to generate optical signals that can be used for image guidance during surgery [32].…”