Penumbra Measurements and Comparison of In-House and Standard Circular Cones by the Gafchoromic Film, Pinpoint Ion Chamber, and MCNPX Monte Carlo Simulation

Introduction: Penumbra is an important property of the radiation beam to obtain a suitable margin surrounding the target volume. Therefore, the precise penumbra width determination in stereotactic radiotherapy is necessary for treatment planning. This study aimed to compare the obtained results of penumbra width by in-house and standard circular cones by different dosimeters, as well as evaluating the function of EBT3 for dosimetric properties of the small field radiation. Material and Methods: Different circular cones were mounted on the head of the accelerator to produce 12, 20, and 40 mm field sizes at isocenter. Dosimetric measurements were performed with the EBT3 film, PinPoint ion chamber. Afterwards, MCNPX Monte Carlo simulation was used to evaluate the dosimetric parameters. Results: According to the obtained results, the penumbra width was increased by larger diameters of circular cones. The obtained measured data by PinPoint ion chamber showed a larger penumbra width compared to those calculated by Monte Carlo at all field sizes. The gamma index analysis revealed  distance-to-agreement and dose-difference of 2 mm /2%/ at all points. The results of this study showed that source to diaphragm distance had a major role in penumbra size determination of small field dosimetry with PinPoint ion chamber, EBT3 film, and Monte Carlo simulation. Conclusion: As findings of this study reported, EBT3 films are reliable detectors for relative dosimetry due to high spatial resolution for small field sizes. Furthermore, they can be used for measuring beam profile and percentage depth dose curves

Dosimetry and verification of ⁶⁰Co total body irradiation with human phantom and semiconductor diodes

Total Body Irradiation (TBI) is a form of radiotherapy used for patients prior to bone marrow or stem cell transplant to destroy any undetectable cancer cells. The dosimetry characteristics of a 60 Co unit for TBI were studied and a simple method for the calculation of the prescribed dose for TBI is presented. Dose homogeneity was verified in a human phantom. Dose measurements were made in water phantom (30 x 30 x 30 cm 3 ), using farmer ionization chamber (0.6 cc, TM30010, PTW) and a parallel plate ionization chamber (TM23343, PTW). Point dose measurements for AP/PA irradiation were measured in a human phantom using silicon diodes (T60010L, PTW). The lung dose was measured with an ionization chamber (0.3 cc, TM31013). The validity of the proposed algorithm was checked at TBI distance using the human phantom. The accuracy of the proposed algorithm was within 3.5%. The dose delivered to the mid-lobe of the lung was 14.14 Gy and it has been reduced to 8.16 Gy by applying the proper shield. Dose homogeneity was within ±7% for all measured points. The results indicate that a good agreement between the total prescribed and calculated midplane doses can be achieved using this method. Therefore, it could be possible to use calculated data for TBI treatments

Dosimetry and verification of 60Co total body irradiation with human phantom and semiconductor diodes

Total Body Irradiation (TBI) is a form of radiotherapy used for patients prior to bone marrow or stem cell transplant to destroy any undetectable cancer cells. The dosimetry characteristics of a 60Co unit for TBI were studied and a simple method for the calculation of the prescribed dose for TBI is presented. Dose homogeneity was verified in a human phantom. Dose measurements were made in water phantom (30 × 30 × 30 cm3), using farmer ionization chamber (0.6 cc, TM30010, PTW) and a parallel plate ionization chamber (TM23343, PTW). Point dose measurements for AP/PA irradiation were measured in a human phantom using silicon diodes (T60010L, PTW). The lung dose was measured with an ionization chamber (0.3 cc, TM31013). The validity of the proposed algorithm was checked at TBI distance using the human phantom. The accuracy of the proposed algorithm was within 3.5%. The dose delivered to the mid-lobe of the lung was 14.14 Gy and it has been reduced to 8.16 Gy by applying the proper shield. Dose homogeneity was within ±7% for all measured points. The results indicate that a good agreement between the total prescribed and calculated midplane doses can be achieved using this method. Therefore, it could be possible to use calculated data for TBI treatments

Optimization of three dimensional planning dosimetric in breast phantom for match region of supraclavicular and tangential fields

Aim: Complex geometry of breast tissue causes perturbation in dose distribution. This problem can beget overdose or under-dose points in match region of three fields. The aim of this study is to create dose homogeneity distribution in match region between tangential and supraclavicular fields (SCF) with Gafchromic external beam therapy (EBT) film. Materials and Methods: In this study, an anatomical slab phantom was designed with cork lung inhomogeneity and plexiy colored heart part. Conventional and three dimensional (3D) methods were utilized along with Gafchromic EBT film. Results: In asymmetric fields (3D method) much better results in match region were observed (i.e., maximum amount overlap area of 0.43 cm 2 , overlap depth of 3.55 cm and an average overlap width of 0.75 cm). Conclusion: This study revealed that EBT film is a proper tool for two dimensional (2D) relative-dose measurements. The study showed difficulties in achieving homogenous dose distribution in match region of tangential and supraclavicular

Comparison of dosimetric characteristics of physical wedge and enhanced dynamic wedge in inhomogeneous medium using Monte Carlo simulations

Background: Widely used physical wedges in clinical radiotherapy lead to beam intensity attenuation as well as the beam hardening effect, which must be considered. Dynamic wedges devised to overcome the physical wedges (PWs) problems result in dosimetry complications due to jaw movement while the beam is on. This study was aimed to investigate the usability of physical wedge data instead of enhanced dynamic wedge due to the enhanced dynamic wedge (EDW) dosimetry measurement hardships of Varian 2100CD in inhomogeneous phantom by Monte Carlo code as a reliable method in radiation dosimetry. Materials and methods: A PW and EDW-equipped-linac head was simulated using BEAMnrc code. DOSXYZnrc was used for three-dimensional dosimetry calculation in the CIRS phantom. Results: Based on the isodose curves, EDW generated a less scattered as well as lower penumbra width compared to the PW. The depth dose variations of PWs and EDWs were more in soft tissue than the lung tissue. Beam profiles of PW and EDW indicated good coincidence in all points, except for the heel area. Conclusion: Results demonstrated that it is possible to apply PW data instead of EDW due to the dosimetry and commissioning hardships caused by EDW in inhomogeneous media

Dosimetry of small photon fields in the presence of bone heterogeneity using MAGIC polymer gel, Gafchromic film, and Monte Carlo simulation

Background: The presence of heterogeneity within the radiation field increases the challenges of small field dosimetry. In this study, the performance of MAGIC polymer gel was evaluated in the dosimetry of small fields beyond bone heterogeneity. Materials and methods: Circular field sizes of 5, 10, 20 and 30 mm were used and Polytetrafluoroethylene with density of 2.2 g/cm3 was used as the bone equivalent material. The PDD curves, beam profiles, and penumbra widths were measured using MAGIC polymer gel, EBT2 film, and Monte Carlo simulation. Results: The maximum differences between MAGIC and EBT2 are 6.1, 4.7, 2.4, and 2.2 for PDD curves at 5, 10, 20, and 30 mm circular fields, respectively. The dose differences and distance to agreement between MAGIC and MC were within 1.89%/0.46 mm, 1.66%/0.43 mm, 1.28%/0.77 mm, and 1.31%/0.81 mm for beam profile values behind bone heterogeneity at 5, 10, 20, and 30 mm field sizes, respectively. Conclusion: The results presented that the MAGIC polymer gel dosimeter is a proper instrument for dosimetry beyond high density heterogeneity