Feasibility Study of 3D CT Based Brachytherapy Planning for Accelerated Partial Breast Irradiation With Intraoperative Interstitial Implants (original) (raw)

Purpose/Objective(s): To study the feasibility of 3D CT based brachytherapy planning for accelerated partial breast irradiation using intraoperative interstitial implants. Materials/Methods: During October 2005 to March 2007, 26 women participated in the ongoing prospective study of APBI using interstitial brachytherapy as the sole modality of radiation for early breast cancer. Tumor bed demarcation was done intraoperatively during the breast conserving surgery with radiopaque clips and 2-4 plane implant was done with free hand placement of needles which were then replaced with plastic tube catheters. Axial CT scan with 3 mm spacing were obtained for all the patients on postoperative 2-3 day. Catheter reconstruction and delineation of lumpectomy cavity, planning target volume (PTV) and ipsilateral breast was carried out. Cavity with 1 cm margin was considered as PTV and was edited for chest wall and skin. Loading of the catheters was done based on the 3DCT image. Final plan was obtained by interactively optimizing using graphical optimization tool over the geometrically optimized plan and was evaluated on each axial slices and also based on the dosimetric outcomes such as coverage index (CI), and dose homogeneity index (DHI). In first 18 patients this plan was compared with plan extrapolated from Xray based planning. Immediate clinical outcome with respect to healing and early cosmetic outcome were studied. The dose of 34 Gy in 10 fractions over 1 week was delivered with twice daily fractionation using high dose rate iridium source. Results: Mean age of the patients was 54 years. Mean number of needles was 15 and the average number of planes were 3. The Median CI of lumpectomy cavity for the final plan was 0.87 (Range: 0.74-0.99). The corresponding value for PTV was 0.76 (Range: 0.66-0.86). Underdosage of the cavity and PTV if observed at the site of air below the staples was accepted by us so as to avoid the skin toxicity. The median DHI was 0.79 (0.62-0.85). In the X-ray based plan the CI cavity, CI PTV and DHI were 0.80, 0.70 and 0.81 respectively. There was statistically significant improvement in the CI of cavity and PTV with 3DCT based planning with graphical optimization. The treatment was tolerated well in all the patients. Two patients developed wound infection immediately after RT which led to delayed wound healing. In all other patients the skin healed without any complications. The immediate cosmetic outcome was good to excellent in 85% patients. Conclusions: 3D CT based brachytherapy along with graphical optimization allows better visualization of the target which leads to significant improvement in the CI when compared with X ray based plan and appears feasible in patients undergoing APBI using intraoperative implants.