External-beam partial breast irradiation in a supine versus prone position after breast-conserving surgery for Chinese breast cancer patients.

To investigate the differences in target volumes and dosimetric parameters between the supine and prone positions for external-beam partial breast irradiation (EB-PBI) after breast-conserving surgery (BCS) for Chinese breast cancer patients, thirty breast cancer patients who underwent three-dimensional conformal radiation therapy (3DCRT) EB-PBI after BCS were enrolled. Supine and prone scan sets were acquired during free breathing for all patients. Target volumes and organs at risk (OARs) including the heart, ipsilateral lung and bilateral breast were contoured by the same radiation oncologist. For each patient, supine and prone EB-PBI plans were generated based on the same planning criteria. The clinical target volume (CTV) and planning target volume (PTV) in the prone position were significantly greater than those in the supine position (P = 0.003, 0.004, respectively). A 0.95 Gy reduction in the mean dose (Dmean) to the heart (P = 0.000) was apparent in the supine position compared to the prone position. The Dmean to the ipsilateral lung was significantly lower in the prone position than in the supine position (1.59 Gy vs. 1.72 Gy, P = 0.029). Therefore, for Chinese breast cancer patients, carrying out 3DCRT EB-PBI in the prone position during free breathing is feasible.

Evaluation of dosimetric variance in whole breast forward-planned intensity-modulated radiotherapy based on 4DCT and 3DCT.

This study was performed to explore and compare the dosimetric variance caused by respiratory movement in the breast during forward-planned IMRT after breast-conserving surgery. A total of 17 enrolled patients underwent the 3DCT simulation scans followed by 4DCT simulation scans during free breathing. The treatment planning constructed using the 3DCT images was copied and applied to the end expiration (EE) and end inspiration (EI) scans and the dose distributions were calculated separately. CTV volume variance amplitude was very small (11.93 ± 28.64 cm(3)), and the percentage change of CTV volumes receiving 50 Gy and 55 Gy between different scans were all less than 0.8%. There was no statistically significant difference between EI and EE scans (Z =-0.26, P = 0.795). However, significant differences were found when comparing the Dmean at 3DCT planning with the EI and EE planning (P = 0.010 and 0.019, respectively). The homogeneity index at EI, EE and 3D plannings were 0.139, 0.141 and 0.127, respectively, and significant differences existed between 3D and EI, and between 3D and EE (P = 0.001 and 0.006, respectively). The conformal index (CI) increased significantly in 3D treatment planning (0.74 ± 0.07) compared with the EI and EE phase plannings (P = 0.005 and 0.005, respectively). The V30, V40, V50 and Dmean of the ipsilateral lung for EE phase planning were significantly lower than for EI (P = 0.001-0.042). There were no significant differences in all the DVH parameters for the heart among these plannings (P = 0.128-0.866). The breast deformation during respiration can be disregarded in whole breast IMRT. 3D treatment planning is sufficient for whole breast forward-planned IMRT on the basis of our DVH analysis, but 4D treatment planning, breath-hold, or respiratory gate may ensure precise delivery of radiation dose.