Effect of melatonin on low and high dose radiotherapy induced thyroid injury

We investigated the radioprotective effect of melatonin (MEL) against thyroid gland damage in rats caused by flattening filter (FF) and flattening filter free (FFF) single dose X-ray beams. We used 48 female rats divided into six groups of eight: group 1, untreated control group; group 2, MEL treated group; group 3, FF-low dose rate radiotherapy (FF-LDR) group; group 4, FF-LDR + MEL group; group 5, FFF-high dose rate radiotherapy (FFF-HDR) group; group 6, FFF-HDR + MEL group. Groups 2, 4 and 6 rats were injected intraperitoneally (i.p.) with 10 mg/kg MEL 15 min before exposure to radiation. The head and neck regions of each rat in groups 3 and 5 and groups 4 and 6 were irradiated with 16 Gy at 6 MV X-ray in FF and FFF beam modes. The histopathology of the thyroid gland and salient biochemical parameters were assessed in all rats 10 days after radiotherapy. We found increased inflammation, vacuolization, degradation, swelling and necrosis, and M30 apoptosis and M65 necrosis indicators in groups 3 and 5 compared to group 1; however, we found significant reductions in histopathological and biochemical parameters following application of MEL. MEL treatment before FF-LDR and FFF-HDR radiotherapy minimized thyroid gland injury due to irradiation.

Evaluation of bone dose arising from skin cancer brachytherapy: A comparison between 192Ir and 60Co sources through Monte Carlo simulations

PURPOSE

This study aimed to calculate and compare absorbed dose to bone following exposure to ¹⁹²Ir and ⁶⁰Co sources in high dose rate (HDR) skin brachytherapy. Moreover, effects of the bone thickness and soft tissue thickness before the bone on absorbed dose to the bone are evaluated .

MATERIALS AND METHODS

¹⁹²Ir and ⁶⁰Co sources inserted in Leipzig applicators with internal diameters of 1, 2 and 3 cm with/without their optimal flattening filters were simulated by MCNPX Monte Carlo code. Then, heterogeneous phantoms (including skin, soft tissue before and after the bone, cortical bone and bone marrow) were defined. Finally, relative depth dose values for the bone and other tissues in the heterogeneous phantoms were obtained and compared.

RESULTS

The average relative depth dose values of the skin, soft tissue before and after bone and bone marrow were almost similar for both ¹⁹²Ir and ⁶⁰Co sources, with a maximum difference less than 2%. However, a 0.1-6.8% difference was observed between average relative depth dose values of these two sources for the cortical bone. The results showed that with increasing the bone thickness and bone distance from the skin surface, the average relative depth dose values of the bone marrow and cortical bone decreased for both ¹⁹²Ir and ⁶⁰Co sources inserted in the applicators without/with their optimal flattening filters. For most of evaluated the applicators without/with their flattening filters, the average relative depth dose values of the bone marrow arisen from the ⁶⁰Co source were higher than those obtained from the ¹⁹²Ir source, while an opposite trend was observed for the cortical bone .

CONCLUSION

The obtained findings showed that the average relative depth dose values of ¹⁹²Ir and ⁶⁰Co sources at the corresponding depths of the designed heterogeneous phantoms were almost similar (expect for the cortical bone). Hence, it is concluded that ⁶⁰Co source can be used instead of ¹⁹²Ir source in HDR skin brachytherapy, particularly in developing countries.

Design and characterization of flattening filter for high dose rate 192Ir and 60Co Leipzig applicators used in skin cancer brachytherapy: A Monte Carlo study

PURPOSE

This study aimed to design optimal flattening filters for high dose rate (HDR) ¹⁹²Ir and ⁶⁰Co Leipzig applicators which are used to treat skin cancer.

MATERIALS AND METHODS

MCNPX Monte Carlo code was used to design flattening filters for Leipzig applicators with inner diameters of 1, 2 and 3 cm. Then, their dosimetric characterizations such as dose distribution, dose profile, percentage depth dose, flatness, symmetry and homogeneity were evaluated in a 20 × 20 × 20 cm³ water phantom and compared with those without the flattening filter.

RESULTS

The flattening filter thickness varied from 0 mm (at the edge) to the maximum values of 0.30, 1.18, and 2.41 mm for the ¹⁹²Ir Leipzig applicators of H1, H2, and H3 type, respectively. This quantity has maximum values of 0.96, 6.27, and 12.31 mm for the ⁶⁰Co double wall applicators of D1, D2, and D3 type, respectively. The dose profile flatness values for the H1, H2, and H3 ¹⁹²Ir Leipzig applicators with the optimal flattening filters were 0.76, 1.26, and 1.85%, respectively. Furthermore, the dose profile flatness values for the D1, D2, and D3 ⁶⁰Co double wall applicators with the optimal flattening filters were 1.11, 2.10 and 3.12%, respectively. The dose profile symmetry values obtained from various source-applicator combinations were less than 1.02. Compared to the applicators without flattening filter, the homogeneity values for the H1, H2, and H3 ¹⁹²Ir Leipzig applicators with the optimal flattening filters were improved 1.68, 6.51, and 13.17 times, respectively, and for the D1, D2, and D3 ⁶⁰Co double wall applicators were improved 1.23, 6.21 and 9.54 times, respectively.

CONCLUSION

The findings revealed that the inhomogeneous dose distribution resulted from the Leipzig applicators without the optimal flattening filter at the treatment surface could be improved by insertion of optimal lead flattening filters between the sources and treatment surface.

Structural Shielding Design of a 6 MV Flattening Filter Free Linear Accelerator: Indian Scenario

Detailed structural shielding of primary and secondary barriers for a 6 MV medical linear accelerator (LINAC) operated with flattening filter (FF) and flattening filter free (FFF) modes are calculated. The calculations have been carried out by two methods, one using the approach given in National Council on Radiation Protection (NCRP) Report No. 151 and the other based on the monitor units (MUs) delivered in clinical practice. Radiation survey of the installations was also carried out. NCRP approach suggests that the primary and secondary barrier thicknesses are higher by 24% and 26%. respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes with an assumption that only 20% of the workload is shared in FFF mode. Primary and secondary barrier thicknesses calculated from MUs delivered on clinical practice method also show the same trend and are higher by 20% and 19%, respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes. Overall, the barrier thickness for a LINAC operated in FF mode is higher about 20% to that of a LINAC operated in both FF and FFF modes.

Patient-specific compensation for Co-60 TBI treatments based on Monte Carlo design: A feasibility study

PURPOSE

To develop an AP-PA treatment technique for the delivery of total body irradiation (TBI) at extended SSD using a modified Co-60 unit equipped with flattening filter and patient-specific compensators supported by Monte Carlo (MC) simulations and measurements.

METHODS

An existing Eldorado-78 Co-60 teletherapy unit was stripped of its original collimator and equipped with two beam-defining cerrobend blocks. An acrylic flattening filter was numerically designed based on detailed mapping of the dose distribution of the large open field at a 10 cm depth in water using a primary radiation attenuation calculation. An EGSnrc/BEAMnrc MC model of the resulting unit was developed and experimentally validated and was used to calculate MC dose distributions in whole-body supine and prone CT images of a patient. AP-PA patient-specific compensators were designed based on the supine and prone mid-plane dose distributions.

RESULTS

The designed flattening filter flattens the beam to within ±2% over a 200 cm × 70 cm area at 10 cm depth in water. Experimental validation of the calculated dose profiles in the open and flattened beams shows agreement of better than 2% and 1%, respectively. Patient MC dose calculations in the flattened, uncompensated beam showed dose deviations from prescription dose most notably in lung, neck and extremities ranging from -5% to +25%. The use of patient-specific compensators reduced inhomogeneities to within -5% to +10%.

CONCLUSIONS

This work demonstrates that a Co-60 TBI setup upgraded with patient-specific compensators, numerically designed using MC patient dose calculations, is feasible and considerably improves the dose homogeneity.

Comparison of Head Scatter Factor for 6MV and 10MV flattened (FB) and Unflattened (FFF) Photon Beam using indigenously Designed Columnar Mini Phantom

To measure and compare the head scatter factor for flattened (FB) and unflattened (FFF) of 6MV and 10MV photon beam using indigenously designed mini phantom. A columnar mini phantom was designed as recommended by AAPM Task Group 74 with low and high atomic number materials at 10 cm (mini phantom) and at approximately twice the depth of maximum dose water equivalent thickness (brass build-up cap). Scatter in the accelerator (Sc) values of 6MV-FFF photon beams are lesser than that of the 6MV-FB photon beams (0.66-2.8%; Clinac iX, 2300CD) and (0.47-1.74%; True beam) for field sizes ranging from 10 × 10 cm² to 40 × 40 cm². Sc values of 10MV-FFF photon beams are lesser (0.61-2.19%; True beam) than that of the 10MV-FB photons beams for field sizes ranging from 10 × 10 cm² to 40 × 40 cm². The SSD had no influence on head scatter for both flattened and unflattened beams and irrespective of head design of the different linear accelerators. The presence of field shaping device influences the Sc values. The collimator exchange effect reveals that the opening of the upper jaw increases Sc irrespective of FB or FFF photon beams and different linear accelerators, and it is less significant in FFF beams. Sc values of 6MV-FB square field were in good agreement with that of AAPM, TG-74 published data for Varian (Clinac iX, 2300CD) accelerator. Our results confirm that the removal of flattening filter decreases in the head scatter factor compared to flattened beam. This could reduce the out-of-field dose in advanced treatment delivery techniques.