Evaluation of dosage effect of position numbers in IMRT for breast cancer

Abstract

Objective To evaluate the dosage effect of position numbers in intensity-modulated radiotherapy plan (IMRT) for breast cancer. Method A 56 year old patient with breast cancer was selected and treated by IMRT in this study. According to the images of the position verification, the target dosage and organ at risk (OAR) were calculated and verified in detail. Results When the position number was 5, the doses of the target and OARs were CTV 48.8Gy, PTV 48.2Gy, spinal cord 27.5Gy, lung 5.5Gy with V20<11.5%, heart 16.0Gy with V10<33.7%, femoral head 38.2Gy. Although all the doses met the prescription of radiotherapeutic physicist, however, the doses of OAR closed to the dosage limitation. In order the decrease the doses of OAR, the number of position verification increased to 7. Therefore the doses of OAR decreased significantly. Conclusion The positioning error can be decreased by increasing the number of position verification.