Dosimetric Comparison of Four Different Techniques for Supraclavicular Irradiation in 3D-conformal Radiotherapy of Breast Cancer

Estimating the skin dose near to the applicator and acute toxicity in breast cancer patients: An intraoperative electron radiotherapy technique

Introduction

Intraoperative electron radiation therapy (IOERT) is one of the most recently popular therapeutic methods for breast cancer. This study aimed to measure the skin dose near the applicator during IOERT of breast cancer patients, as well as, the incidence of acute toxicity after surgery.

Materials and Methods

Thirty-six female patients participated in the current study with the prescribed dose of 21 and 12 Gy for IOERT as full and boost, respectively. The skin dose was investigated based on different applicator sizes, tumor bed thicknesses, and monitor units (MUs). The energy was chosen 8 MeV, and EBT3 film was used for the dosimetric process. In addition, the acute toxicity included healing time for the surgical wound, scaling of the skin, itching, necrosis, redness as well as seroma formation for 1 week and 1 month were recorded. The results were compared to those of 22 patients who underwent the surgery without IOERT.

Results

The highest skin dose for the patients was obtained 2.09 Gy, which is lower than the threshold dose (6 Gy). Furthermore, the findings showed that the average skin dose was higher in bigger applicator sizes and MU and lower tumor bed thicknesses. The average of wound healing for the patient underwent IOERT and without the use of IOERT (as the control group) was 19.32 and 11.67 days, respectively. One month after surgery, the volume of aspirated seroma was higher in the patients who performed IOERT compared to the control group (250 ml vs. 200 ml). It is notable that there were not observed any redness, itching, scaling, and necrosis in both investigated groups.

Conclusion

Owing to the results, the skin dose during IOERT was lower than the recommended level. The dose of IOERT as a full was higher than boost which can be related to the lower number of the patients in full method; however, there was a well-tolerated without severe acute complication, especially seroma formation and wound healing time in both full and boost methods.

Assessing the Effect of Directional Bremsstrahlung Splitting on the Output Spectra and Parameters Using BEAMnrc Monte Carlo Simulation Package

Introduction:

EGSnrc software package is one of the computational packages for Monte Carlo simulation in radiation therapy and has several subset codes. Directional bremsstrahlung splitting (DBS) is a technique that applies braking radiations in interactions in this software. This study aimed to evaluate the effect of this technique on the simulation time, uncertainty, particle number of phase-space data, and photon beam spectrum resulting from a medical linear accelerator (LINAC).

Materials and methods:

The gantry of the accelerator, including the materials and geometries of different parts, was simulated using the BEAMnrc code (a subset code in the EGSnrc package). The phase-space data were recorded in different parts of the LINAC. The DBS values (1, 10, 100, and 1000) were changed, and their effects were evaluated on the simulation parameters and output spectra.

Results:

Increasing the DBS value from 1 to 1000 resulted in an increase in the simulation time from 1.778 to 11.310 hours, and increasing the number of particles in the phase-space plane (5 590 732-180 328 382). When the DBS had been picked up from 1 to 100, the simulation uncertainty decreased by about 1.29%. In addition, the DBS increment value from 100 to 1000 leads to an increase in uncertainty and simulation time of about 0.71% and 315%, respectively.

Conclusion:

Although using the DBS technique reduces the simulation time or uncertainty, increasing the DBS from a specific value, equal to 100 in our study, increases simulation uncertainties and times. Therefore, we propose considering a specific DBS value as we obtained for the Monte Carlo simulation of photon beams produced by linear accelerators.

Auxiliary Structures-Assisted Radiotherapy Improvement for Advanced Left Breast Cancer

Background

To improve the quality of plan for the radiation treatment of advanced left breast cancer by introducing the auxiliary structures (ASs) which are used to spare the regions with no intact delineated structures adjacent to the target volume.

Methods

CT data from 20 patients with left-sided advanced breast cancer were selected. An AS designated as A1 was created to spare the regions of the aorta, pulmonary artery, superior vena ava, and contralateral tissue of the upper chest and neck, and another, designated as A2, was created in the regions of the cardia and fundus of the stomach, left liver lobe, and splenic flexure of the colon. IMRT and VMAT plans were created for cases with and without the use of the AS dose constraints in plan optimization. Dosimetric parameters of the target and organs at risk (OARs) were compared between the separated groups.

Results

With the use of AS dose constraints, both the IMRT and VMAT plans were clinically acceptable and deliverable, even showing a slight improvement in dose distribution of both the target and OARs compared with the AS-unused plans. The ASs significantly realized the dose sparing for the regions and brought a better conformity index (p < 0.05) and homogeneity index (p < 0.05) in VMAT plans. In addition, the volume receiving at least 20 Gy (V₂₀) for the heart (p < 0.05), V₄₀ for the left lung (p < 0.05), and V₄₀ for the axillary-lateral thoracic vessel juncture region (p < 0.05) were all lower in VMAT plans.

Conclusion

The use of the defined AS dose constraints in plan optimization was effective in sparing the indicated regions, improving the target dose distribution, and sparing OARs for advanced left breast cancer radiotherapy, especially those that utilize VMAT plans.

The Measurement of Thyroid Absorbed dose by Gafchromic™ EBT2 Film and Changes in Thyroid Hormone Levels Following Radiotherapy in Patients with Breast Cancer

Background:

Radiotherapy is a main method for the treatment of breast cancer. This study aimed to measure the absorbed dose of thyroid gland using Gafchromic EBT2 film during breast cancer radiotherapy. In addition, the relationship between the absorbed dose and thyroid hormone levels was evaluated.

Methods:

Forty-six breast cancer patients, with the age ranged between 25 and 35 years, undergoing external radiotherapy were studied. The patients were treated with 6 and 18 MV X-ray beams, and the absorbed thyroid dose was measured by EBT2 film. Thyroid hormone levels, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxin (T4), were measured before and after the radiotherapy. Pearson's, Spearman's, and Chi-square tests were performed to evaluate the correlation between the thyroid dose and hormone levels.

Results:

The mean thyroid dose was 26 ± 9.45 cGy with the range of 7.85–48.35 cGy. There were not any significant differences at thyroid hormone levels between preradiotherapy and postradiotherapy (P > 0.05). There was a significant relationship between increased thyroid absorbed dose and changes in TSH and T4 levels (P < 0.05), but it was not significant in T3 level (P = 0.1).

Conclusion:

Regarding the results, the thyroid absorbed dose can have an effect on its function. Therefore, the thyroid gland should be considered as an organ at risk in breast cancer radiotherapy.

Radioprotective Effect of Arbutin in Megavoltage Therapeutic X-irradiated Mice using Liver Enzymes Assessment

Background

Medical use of ionizing radiation has direct/indirect undesirable effects on normal tissues. In this study, the radioprotective effect of arbutin in megavoltage therapeutic x-irradiated mice was investigated using serum alkaline phosphatase (ALP), alanine aminotransferase (ALT), and asparate amniotransferase (AST) activity measurements.

Material and Methods

In this analytical and experimental lab study, sixty mice (12 identical groups) were irradiated with 6 MV x-ray beam (2 and 4 Gy in one fraction). Arbutin concentrations were chosen 50, 100, and 200 mg/kg and injected intraperitoneal 2 hours before irradiation. Samples of peripheral blood cells were collected and serum was separated on the 1, 3, and 7 days post-x-radiation; in addition, the level of ALP, ALT, and AST were measured. Data were analyzed using one-way ANOVA, and Tukey HSD test.

Results

X-radiation (2 and 4 Gy) increased the ALT and AST activity levels on the 1, 3, and 7 days post- irradiation, but the ALP level significantly increased on the 1 and 7 days and decreased on the third day compared to the control group (P< 0.001). ALP, ALT and AST activity levels in "2 and 4 Gy x irradiation + distilled water" groups were significantly higher than "2 and 4 Gy irradiation + 50, 100, and 200 mg/kg arbutin" groups on the first and seventh day post-irradiation (P< 0.001).

Conclusion

Arbutin is a strong radioprotector for reducing the radiation effect on the whole-body tissues by measuring ALP, ALT and AST enzyme activity levels. Furthermore, the concentration of 50 mg/kg arbutin showed higher radioprotective effect.

Dosimetric comparison of level II lymph nodes between mono-isocentric and dual-isocentric approaches in 3D-CRT and IMRT techniques in breast radiotherapy of mastectomy patients

Aim:

To evaluate the dosimetric parameters of level II lymph nodes in chest wall three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) of mastectomy patients using dual-isocentric (DIT) and mono-isocentric techniques (MIT).

Materials and methods:

Computed tomography (CT) images of 20 mastectomy patients undergoing chest wall external radiotherapy were used as the input data for the abovementioned techniques. Selected dosimetric parameters were calculated for the axillary level I–III lymph nodes, chest wall, heart and lung. Paired t-test statistical analysis was used for comparing the results of MIT and DIT in both 3D-CRT and IMRT methods.

Results:

There were significant differences in Dmin (minimum dose), Dmax (maximum dose) and maximum–minimum dose between MIT and DIT techniques (13, −8·6, −52·2% differences for Dmin, Dmax and maximum–minimum, respectively) in IMRT. There were also significant differences for Dmean (mean dose), Dmax and maximum–minimum dose (7·8, −11·4, −44·6% differences in Dmean, Dmax and maximum–minimum, respectively) in 3D-CRT (p < 0·05). In addition, there were not any differences in the dosimetric parameters for heart, lung and level I and III lymph nodes.

Conclusion:

In both 3D-CRT and IMRT methods, level II lymph node dose distribution in MIT was closer to the prescribed dose compared with DIT due to the position of these nodes in the field junction area. To achieve a better dose homogeneity, it could be recommended to use MIT instead of DIT in 3D-CRT and IMRT for mastectomy patients.