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Purpose: Apply gel dosimetry to evaluate the dose‐increase dependency with nanoparticle concentration in a tissue‐simulator dosimeter irradiated with 250kV Radiotherapy beam. Quantify the components of dose contribution by Monte Carlo spectrometry. Material and Methods: Gold nanoparticles (AuNP) were embedded in MAGIC‐f gel in different biocompatible concentrations: 0.11mM(A), 0.06mM(B) and 0.03mM(C). Dosimetric control measures with gel without AuNP were made in the 250kV x‐ray beam studied. An acrylic box was positioned behind the gel samples to guarantee backscattered conditions similar to clinical situations accessed with the beam studied. A dose of 5Gy was delivered to all samples. Polymer gel readings were proffered in a 3Tesla nuclear‐magnetic‐resonance by relaxometry: 5 echoes; Echo‐time=20ms; Repetition‐time=4000ms; Pixel‐size=250μm; Time‐delay‐to‐reading: 12h. Monte Carlo simulations were performed in PENELOPE code precisely reproducing all experimental conditions. Results: Signal of non‐irradiated gel samples (with and without AuNP) presents no significant variation (<0.5%), evidencing no influences of AuNP in MRI reading. Concentrations A, B and C presents a 106%, 90% and 77% of signal increase, respectively. Comparing with the dose calibration curve of gel, the signal growth represents dose enhancements of 5.3Gy, 4.5Gy and 3.9Gy to concentrations A, B and C respectively. Monte Carlo shows a dose increase of 10.2keV/g, 9.1eV/g and 7.3eV/g, representing 105%, 93% and 75% of perceptual dose growth to concentrations A, B and C respectively. Spectrometry analysis revel a fluorescence dose fraction that contributes to dose increase of 0.98, 0.89 and 0.73 and low‐energy Compton events that contributes to local dose increase in fractions of 0.66, 0.38 and 0.12 to concentrations A, B and C respectively. Conclusions: Dose increase in Radiotherapy due to AuNP presence has a non‐linear dependency with the concentration. The growth of local doses may be high expressed indicating possible clinical benefits of using AuNP added Radiotherapy.

Purpose: Evaluate the volume fraction enclosed by maximum isodose (isodosemax) within a structure as a quantitative criterion for assessing the benefits of using nanoparticles in Radiotherapy. Material and Methods: Dose enhancement can be evaluated in a volume with and without nanoparticles by the ratio between mean doses, defining an average‐dose‐enhancement‐factor (DEF). Decompounding DEF in multiplicative terms is possible to define a maximum‐dose‐enhancement‐factor(DEFmax) and a dose‐gradient‐factor(GF). GF express what fraction of volume is enclosed by the isodosemax present in the analyzed structure. GF close to 1 express that the isodosemax present in the analyzed volume increase its value. GF close to 0 indicates that the isodosemax decrease its value. Soft and lung targets with 3×3×1cm3 containing and not containing 0.11mM concentration of gold nanoparticles (AuNP) were considered to Monte Carlo simulations, performed with PENELOPE‐2008. Adjacent‐volumes were delimited as tissues 1cm far from the target in all directions. A 120kV x‐ray beam was considered to simulate Intra‐Operative‐Radiotherapy situations. Results: Dose distributions visually revels changes in dose‐gradient and depth dose curves presents it quantitatively. In target soft tissue: To adjacent‐volume It indicates that in target isodose max changes not so much, presenting almost the same values in situations with and without AuNP; However in adjacent‐volume isodosemax had its value increased. In target lung tissue: These parameters indicate that the isodosemax changes its value not so much in lung‐target but radically in lung‐adjacent‐tissue. This behavior is expressed in each corresponding GF of these structures: Coclusions: AuNP increase the mean dose in target and decrease radically the maximum isodose in adjacent tissues. The GF express quantitatively how attenuation and dose‐contribution effects are balanced providing information to guide clinical cases of nanoparticle added to Radiotherapy.

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