Measurement of the Contralateral Breast Photon and Thermal Neutron Doses in Breast Cancer Radiotherapy: A Comparison Between Physical and Dynamic Wedges

Abstract

This research aimed to measure the received photon and thermal neutron doses to contralateral breast (CB) in breast cancer radiotherapy for various field sizes in presence of physical and dynamic wedges. The measurement of photon and thermal neutron doses was carried out on right breast region of RANDO phantom (as CB) for 18 MV photon beams. The dose measurements were performed by thermoluminescent dosimeter chips. These measurements obtained for various field sizes in presence of physical and dynamic wedges. The findings of this study showed that the received doses (both of the photon and thermal neutron) to CB in presence of physical wedge for 11 × 13, 11 × 17 and 11 × 21 cm2 field sizes were 5.92, 6.36 and 6.77% of the prescribed dose, respectively as well as for dynamic wedge were 2.92, 4.63 and 5.60% of the prescribed dose, respectively. The results showed that the received photon and thermal neutron doses to CB increase with increment of field sizes. The received photon and thermal neutron doses to CB in presence of physical wedge were more than dynamic wedge. According to obtained findings, it is suggested that using a dynamic wedge is preferable than physical wedge, especially for medial tangential field.

Measurement of the photon and thermal neutron doses of contralateral breast surface in breast cancer radiotherapy

“…Finally, a source axis distance technique was used to deliver 200 cGy based on the International Commission on Radiation Units and Measurements. 29 For a possible comparison of the results of the current study (doses received at CB surface) with that of our previous study (doses received to CB), 12 treatment planning in this study was similar to our previous study. Figure 1 shows the anterior view relating to the tangential fields of left breast region of the RANDO phantom.…”

“…The corresponding dose values for the dynamic wedge were 9•18%, 12•92% and 29•26% of the prescribed dose, respectively. In a previous study, 12 we measured photon and thermal neutron dose values received by CB in breast cancer radiation therapy. Table 2 compares the total dose values received at CB surface and CB 12 in the presence of physical and dynamic wedge for 11 × 13, 11 × 17 and 11 × 21 cm 2 filed sizes.…”

“…In a previous study, 12 we measured photon and thermal neutron dose values received by CB in breast cancer radiation therapy. Table 2 compares the total dose values received at CB surface and CB 12 in the presence of physical and dynamic wedge for 11 × 13, 11 × 17 and 11 × 21 cm 2 filed sizes. By comparing the results of both studies (Table 2), it is evident that the received dose at CB surface was more than that of CB, especially for larger field sizes.…”

“…More details on the calibration of 600 TLD and 700 TLD chips are available in our previous study. 12 Furthermore, a pair of TLD chips was applied to measure background dose.…”

“…9,10 Nevertheless, the interaction of high-energy beams (>8 MV) with various high-atomic-number (Z) nuclei of the materials in the components of the linear accelerator (linac) head would produce unavoidable neutrons. [11][12][13] The areas away from the treatment field receive scatter radiation from different sources (such as the linac head, internal patient scatter radiation and unavoidable neutrons). 14,15 Compared to the inside-field dose, the out-of-field region would receive low dose values.…”