Study of polymer gel for dose imaging in radiotherapy

Fluorescent organic particle doped polymer-based gel dosimeter for neutron detection

The purpose of this work is to develop a material capable of detecting neutrons produced by photodisintegration in a linear accelerator for its medical use. In this study, we have developed a gel-like material doped with fluorescent organic particles. PPO at 1 wt% is used as primary dopant and POPOP as secondary one at 0.03 wt%. A set of four samples is produced, with boric acid concentrations of 0, 400, 800 and 1200 ppm. The viscoelastic properties of the material are characterized with rheological measurements, finding a gel-like behavior, i.e., a material that can keep its original shape if no stresses are applied, but can also be deformed by applying a moderate shear rate. Furthermore, the material was irradiated with gamma, electron, and neutron emission sources from ¹³⁷Cs, ²²Na, ⁶⁰Co, ²¹⁰Po, ⁹⁰Sr and ²⁴¹AmBe, and its response was measured in two different experimental settings, in two different institutions, for comparative purposes. From these measurements, one can clearly establish that the new material detects neutrons, electrons, and gammas within the MeV regions and below. Thus, our findings show that the developed material and its properties make it a promising technology for its use in a neutron detector.

Polymer gel dosimeter based on itaconic acid

A new polymeric dosimeter based on itaconic acid and N, N'-methylenebisacrylamide was studied. The preparation method, compositions of monomer and crosslinking agent and the presence of oxygen in the dosimetric system were analyzed. The resulting materials were irradiated with an X-ray tube at 158cGy/min, 226cGymin and 298cGy/min with doses up to 1000Gy. The dosimeters presented a linear response in the dose range 75-1000Gy, sensitivities of 0.037 1/Gyat 298cGy/min and an increase in the sensitivity with lower dose rates. One of the most relevant outcomes in this study was obtaining different monomer to crosslinker inclusion in the formed gel for the dosimeters where oxygen was purged during the preparation method. This effect has not been reported in other typical dosimeters and could be attributed to the large differences in the reactivity among these species.

Role of gel dosimeters in boron neutron capture therapy

Gel dosimeters have acquired a unique status in radiotherapy, especially with the advent of the new techniques in which there is a need for three-dimensional dose measurement with high spatial resolution. One of the techniques in which the use of gel dosimeters has drawn the attention of the researchers is the boron neutron capture therapy. Exploring the history of gel dosimeters, this paper sets out to study their role in the boron neutron capture therapy dosimetric process.

Optical and NMR dose response of N-isopropylacrylamide normoxic polymer gel for radiation therapy dosimetry

BACKGROUND

Application of less toxic normoxic polymer gel of N-isopropyl acrylamide (NIPAM) for radiation therapy has been studied in recent years.

AIM

In the current study the optical and NMR properties of NIPAM were studied for radiation therapy dosimetry application.

MATERIALS AND METHODS

NIPAM normoxic polymer gel was prepared and irradiated by 9 MV photon beam of a medical linac. The optical absorbance was measured using a conventional laboratory spectrophotometer in different wavelengths ranging from 390 to 860 nm. R 2 measurements of NIPAM gels were performed using a 1.5 T scanner and R 2-dose curve was obtained.

RESULTS

Our results showed R 2 dose sensitivity of 0.193 ± 0.01 s(-1) Gy(-1) for NIPAM gel. Both R 2 and optical absorbance showed a linear relationship with dose from 1.5 to 11 Gy for NIPAM gel dosimeter. Moreover, absorbance-dose response varied considerably with light wavelength and highest sensitivity was seen for the blue part of the spectrum.

CONCLUSION

Our results showed that both optical and NMR approaches have acceptable sensitivity and accuracy for dose determination with NIPAM gel. However, for optical reading of the gel, utilization of an optimum optical wavelength is recommended.

Normoxic polymer gel dosimetry using less toxic monomer of N-isopropyl acrylamide and X-ray computed tomography for radiation therapy applications

BACKGROUND

Polymer gel dosimetry has been used extensively in radiation therapy for its capability in depicting a three dimensional view of absorbed dose distribution. However, more studies are required to find less toxic and more efficient polymers for application in radiotherapy dosimetry.

AIM

The purpose of this work was to evaluate the N-isopropyl acrylamide (NIPAM) gel dosimetric characteristics and optimize the protocol for X-ray computed tomography (CT) imaging of gel dosimeters for radiation therapy application.

MATERIAL AND METHODS

A polymer gel dosimeter based on NIPAM monomer was prepared and irradiated with (60)Co photons. The CT number changes following irradiation were extracted from CT images obtained with different sets of imaging parameters.

RESULTS

The results showed the dose sensitivity of ΔN CT (H) = 0.282 ± 0.018 (H Gy(-1)) for NIPAM gel dosimeter. The optimized set of imaging exposure parameters was 120 kVp and 200 mA with the 10 mm slice thickness. Results of the depth dose measurement with gel dosimeter showed a great discrepancy with the actual depth dose data.

CONCLUSION

According to the current study, NIPAM-based gel dosimetry with X-ray CT imaging needs more technical development and formulation refinement to be used for radiation therapy application.

Polymer gels for in-phantom dose imaging in radiotherapy

Normoxic polymer gel dosimeters are studied, with the aim of achieving a valid and advantageous method for in-phantom 3D dose determinations. Developments were carried out in the application of such dosimetric material to the method based on dosimeter gel layers that has shown good reliability for absorbed dose imaging in radiotherapy. The technique has been improved, in particular taking care of minimizing the oxygen infiltration into the gel matrix in order to suitably avoid its effect of inhibiting the polymerization process after exposure. A suitable choice of the material of dosimeter walls has brought to achieve good steadiness in time of dosimeter sensitivity and satisfactory results in dose imaging and depth-dose profiling.