Measurement of the contralateral breast photon and neutron dose in breast cancer radiotherapy: A Monte Carlo study

Introduction: This study aimed to calculate the photon and neutron doses received to the contralateral breast (CB) during breast cancer radiotherapy for various field sizes in the presence of a physical wedge. Materials and Methods: Varian 2100 C/D linear accelerator was simulated using a MCNP4C Monte Carlo code. Then, a phantom of real female chest was simulated and the treatment planning was carried out on tumoral breast (left breast). Finally, the received photon and neutron doses to CB (right breast) were calculated in the presence of a physical wedge for 18 MV photon beam energy. These calculations were performed for different field sizes including 11 cm × 13 cm, 11 cm × 17 cm, and 11 cm × 21 cm. Results: The findings showed that the received doses (both of the photon and neutron) to CB in the presence of a physical wedge for 11 cm × 13 cm, 11 cm × 17 cm, and 11 cm × 21 cm field sizes were 9.87%, 12.91%, and 27.37% of the prescribed dose, respectively. In addition, the results showed that the received photon and neutron doses to CB increased with increment in the field size. Conclusion: From the results of this study, it is concluded that the received photon and neutron doses to CB in the presence of a physical wedge is relatively more, and therefore, they should be reduced to as low as possible. Therefore, using a dynamic wedge instead of a physical wedge or field-in-field technique is suggested

A Comparison of Peripheral Doses Scattered from a Physical Wedge and an Enhanced Dynamic Wedge / 의학물리

In order to evaluate the radio-protective advantage of an enhanced dynamic wedge (EDW) over a physical wedge (PW), we measured peripheral doses scattered from both types of wedges using a 2D array of ion-chambers. A 2D array of ion-chambers was used for this purpose. In order to confirm the accuracy of the device, we first compared measured profiles of open fields with the profiles calculated by our commissioned treatment planning system. Then, we measured peripheral doses for the wedge angles of 15 degrees, 30 degrees, 45 degrees, and 60 degrees at source to surface distances (SSD) of 80 cm and 90 cm. The measured points were located at 0.5 cm depth from 1 cm to 5 cm outside of the field edge. In addition, the measurements were repeated by using thermoluminescence dosimeters (TLD). The peripheral doses of EDW were (1.4% to 11.9%) lower than those of PW (2.5% to 12.4%). At 15 MV energy, the average peripheral doses of both wedges were 2.9% higher than those at 6MV energy. At a small SSD (80 cm vs. 90 cm), peripheral dose differences were more recognizable. The average peripheral doses to the heel direction were 0.9% lower than those to the toe direction. The results from the TLD measurements confirmed these findings with similar tendency. Dynamic wedges can reduce unnecessary scattered doses to normal tissues outside of the field edge in many clinical situations. Such an advantage is more profound in the treatment of steeper wedge angles, and shorter SSD.

Comparison of Virtual Wedge versus Physical Wedge Affecting on Dose Distribution of Treated Breast and Adjacent Normal Tissue for Tangential Breast Irradiation / 대한방사선종양학회지

PURPOSE: The ideal breast irradiation method should provide an optimal dose distribution in the treated breast volume and a minimum scatter dose to the nearby normal tissue. Physical wedges have been used to improve the dose distribution in the treated breast, but unfortunately introduce an increased scatter dose outside the treatment field, particularly to the contralateral breast. The typical physical wedge (PW) was compared with the virtual wedge (VW) to determine the difference in the dose distribution affecting on the treated breast and the contralateral breast, lung, heart and surrounding peripheral soft tissue. METHODS AND MATERIALS: The data collected consisted of a measurement taken with solid water, a Humanoid Alderson Rando phantom and patients. The radiation doses at the ipsilateral breast and skin, contralateral breast and skin, surrounding peripheral soft tissue, and ipsilateral lung and heart were compared using the physical wedge and virtual wedge and the radiation dose distribution and DVH of the treated breast were compared. The beam-on time of each treatment technique was also compared. Furthermore, the doses at treated breast skin, contralateral breast skin and skin 1.5 cm away from the field margin were also measured using TLD in 7 patients of tangential breast irradiation and compared the results with phantom measurements. RESULTS: The virtual wedge showed a decreased peripheral dose than those of a typical physical wedge at 15degrees, 30degrees, 45degrees, and 60degrees. According to the TLD measurements with 15degrees and 30degrees virtual wedge, the irradiation dose decreased by 1.35% and 2.55% in the contralateral breast and by 0.87% and 1.9% in the skin of the contralateral breast respectively. Furthermore, the irradiation dose decreased by 2.7% and 6.0% in the ipsilateral lung and by 0.96% and 2.5% in the heart. The VW fields had lower peripheral doses than those of the PW fields by 1.8% and 2.33%. However the skin dose increased by 2.4% and 4.58% in the ipsilateral breast. VW fields, in general, use less monitor units than PW fields and shortened beam-on time about half of PW. The DVH analysis showed that each delivery technique results in comparable dose distribution in treated breast. CONCLUSIONS: A modest dose reduction to the surrounding normal tissue and uniform target homogeneity were observed using the VW technique compare to the PW beam in tangential breast irradiation The VW field is dosimetrically superior to the PW beam and can be an efficient method for minimizing acute, late radiation morbidity and reduce the linear accelerator loading by decreasing the radiation delivery time.

Physical Characteristics Comparison of Virtual Wedge Device With Physical Wedge / 대한방사선종양학회지

PURPOSE: We have compared the characteristics of Siemens virtual wedge device with physical wedges for clinical application. MATERIALS AND METHODS: We investigated the characteristics and physical wedges for various wedge angles (15,30,45,and 60 degrees)using 6- and 15MV photon beams. Wedge factors were measured in water using an ion chamber for various field sizes and depths. In case of virtual wedge device, as upper jaw moves during irradiation, wedge angles were estimated by accumulated doses. These measurements were performed at off-axis points perpendicular to beam central axis in water for a 15Cm x20Cm radiation field size at the depth of 10Cm. Surface doses without and with virtual or physical wedges were measured using a parallel plate ion chamber at surface. Field size was15Cmx20Cm and a polystyrene phantom was used. RESULT: For various field sizes, virtual and physical wedge factors were changed by maximum 2.1%and 3.9%, respectively. For various depths, virtual and physical wedge factors were changed by maximum 1.9% and 2.9%, respectively. No major difference was found between the virtual and physical wedge angles and the difference was within 0.5 degrees. Surface dose with physical wedge was reduced by maximum 20% (x-ray beam : 6 MV, Wedge angle: 45 degrees, SSD; 80 Cm) relative to one with virtual wedge or without wedge. CONCLUSION: comparison of the characteristics of Siemens virtual wedge device with physical wedges was performed.Depth dependence of virtual wedge factor was smaller than of physical wedge factor. Virtual and physical wedge factors were nearly independent of field size. The accuracy of virtual and physical wedge angles was excellent. Surface dose was found to be reduced using physical wedge.

Comparison between dynamic wedge and physical wedge in the influence of dose to the contralateral breast and lung in radiotherapy for primary breast cancer / 中华放射肿瘤学杂志

Objective To compare the dose to the contralateral breast, ipsilateral lung, and the whole lung in the tangential field radiotherapy for primary breast cancer using the dynamic wedge or physical wedge. Methods With thirteen breast cancer patients chosen, the dose distribution was computed for the plan used in practical treatment with the dynamic wedge and physical wedge. Plans were compared using dose volume histograms for the contralateral breast, ipsilateral lung and the whole lung. As for the contralateral breast, the dose distributions were not computed for the whole breast but computed for the two regions similar to a rectangular area in the axial slice and parts of the whole breast. The mean dose was used to evaluate CB1, CB2 and ipsilateral lung, and V_ 20 was used to evaluate the whole lung. The treatment planning system used was Varian CadPlan. An ionization chamber in a water phantom was used to measure some point doses to simulate the dose to the contralateral breast. Results When using the 30? dynamic wedge, the mean dose to CB1 and CB2 was 1.5%-3.9% and 1.1%- 2.6% , and the mean dose to the ipsilateral lung was 4.1%-14.7%. When using the 30? physical wedge, the mean dose to CB1 and CB2 were 1.5%-4.4% and 1.2%-3.0%, respectively, and the mean dose to the ipsilateral lung was 4.4%-15.2%. The values of V_ 20 were equal. When using the 15? dynamic wedge, the mean dose to CB1 and CB2 decreased compared to 15? physical wedge, but the value reduced was smaller than when using 30? wedge. Also, the measured results verified that the dose to the normal tissue is reduced using the dynamic wedge. Conclusions The mean dose to the contralateral breast was reduced by using the dynamic wedge instead of the physical wedge, and the mean dose to the ipsilateral lung or V_ 20 is reduced or equal to each other. So the probability of normal tissue complication such as a second breast malignancy or pneumonitis associated with radiotherapy are likely to be reduced.