Determining the contralateral breast dose during radiotherapy of breast cancer using rainbow dosimeter

Radiation dose to the heart with hypofractionation in patients with left breast cancer

Introduction

In this study we compared radiation dose received by organs at risk (OARs) after breast conservation surgery(BCS) and mastectomy in patients with left breast cancer.

Materials and methods

Total 30 patients, 15 each of BCS and mastectomy were included in this study. Planning Computerised Tomography (CT) was done for each patient. Chest wall, whole breast, heart, lungs, LAD, proximal and distal LAD, and contra lateral breast was contoured for each patient. Radiotherapy plans were made by standard tangent field. Dose prescribed was 40Gy/16#/3 weeks. Mean heart dose, LAD, proximal and distal LAD, mean and V5 of right lung, and mean, V5, V10 and V20 of left lung, mean dose and V2 of contra lateral breast were calculated for each patient and compared between BCS and mastectomy patients using student’s T test.

Results

Mean doses to the heart, LAD, proximal LAD and distal LAD were 3.364Gy, 16.06Gy, 2.7Gy, 27.5Gy; and 4.219Gy, 14.653Gy, 4.306Gy, 24.6Gy, respectively for mastectomy and BCS patients. Left lung mean dose, V5, V10 and V20 were 5.96Gy, 16%, 14%, 12.4%; and 7.69Gy, 21%, 18% and 16% in mastectomy and BCS patients, respectively. There was no statistical significant difference in the doses to the heart and left lung between mastectomy and BCS. Mean dose to the right lung was significantly less in mastectomy as compared to BCS, 0.29Gy vs. 0.51Gy, respectively (p = 0.007). Mean dose to the opposite breast was significantly lower in patients with mastectomy than BCS (0.54Gy Vs 0.37Gy, p = 0.007). The dose to the distal LAD was significantly higher than proximal LAD both in BCS (24.6Gy Vs 4.3Gy, p = <0.0001) and mastectomy (27.5Gy Vs 2.7Gy, p = <0.0001) patients.

Conclusion

There was no difference in doses received by heart and left lung between BCS and mastectomy patients. Mean doses to the right lung and breast were significantly less in mastectomy patients.

Contralateral breast dose with electronic compensators and conventional tangential fields - A clinical dosimetric study

Dose to the contralateral breast (CLB) from radiotherapy treatment has the potential to induce secondary breast cancer. Electronic tissue compensation (eComp) for breast cancer patients is one of the alternative methods to conventional 3D-conformal radiotherapy that eliminates the use of wedges. Several studies have investigated dose to the CLB using tangential fields involving wedges, intensity-modulated radiation therapy and volumetric modulated arc radiation therapy and various other techniques via treatment planning system calculations, Monte Carlo methods and phantoms. However, there are limited data published in assessing the actual dose received by the CLB from treatment with eComp-based tangential fields. In this study, the CLB dose for patients undergoing tangential field radiotherapy with eComp and enhanced dynamic wedged (standard) tangential fields was measured and compared to assess the CLB dose between the two methods. Measurements were conducted on a randomised trial of 40 patients, 20 of them had undergone standard planning, and the remaining 20 were treated with eComp. The mean surface dose measured with TLDs at 3cm from the medial tangential border for eComp and standard techniques was 10.04±1.37% and 10.14±2.05%, respectively for a prescription dose of 2.65Gy/fraction. The estimated dose at 1cm depth in tissue, measured with the use of perspex domes placed over the TLD at the same location, was 5.12±0.87% and 6.29±2.01% for eComp and standard, respectively. The CLB dose is dependent on the proximity of the medial tangential field edge to the contralateral breast and is patient-specific. The results of this study show that at 1cm depth, eComp technique delivers significantly less dose (p<0.05) to the CLB as compared to standard tangential fields. Furthermore, the surface dose measured for both eComp and standard are comparable indicating that the eComp-based tangential field technique does not contribute any excess dose to CLB when compared to standard tangential fields. The excess relative risk (ERR) for radiation-induced cancers for eComp was found to be 0.08, compared to 0.11 for standard tangential fields.