Dosimetric comparison of intensity modulated radiotherapy isocentric field plans and field in field (FIF) forward plans in the treatment of breast cancer

Abstract

The present study is aimed at comparing the planning and delivery efficiency between three-dimensional conformal radiotherapy (3D-CRT), field-in-field, forward planned, intensity modulated radiotherapy (FIF-FP-IMRT), and inverse planned intensity modulated radiotherapy (IP-IMRT). Treatment plans of 20 patients with left-sided breast cancer, 10 post-mastectomy treated to a prescribed dose of 45 Gy to the chest wall in 20 fractions, and 10 post-breast-conserving surgery to a prescribed dose of 50 Gy to the whole breast in 25 fractions, with 3D-CRT were selected. The FiF-FP-IMRT plans were created by combining two open fields with three to four segments in two tangential beam directions. Eight different beam directions were chosen to create IP-IMRT plans and were inversely optimized. The homogeneity of dose to planning target volume (PTV) and the dose delivered to heart and contralateral breast were compared among the techniques in all the 20 patients. All the three radiotherapy techniques achieved comparable radiation dose delivery to PTV-95% of the prescribed dose covering > 95% of the breast PTV. The mean volume of PTV receiving 105% (V105) of the prescribed dose was 1.7% (range 0-6.8%) for IP-IMRT, 1.9% for FP-IMRT, and 3.7% for 3D-CRT. The homogeneity and conformity indices (HI and CI) were similar for 3D-CRT and FP-IMRT, whereas the IP-IMRT plans had better conformity index at the cost of less homogeneity. The 3D-CRT and FiF-FP-IMRT plans achieved similar sparing of critical organs. The low-dose volumes (V5Gy) in the heart and lungs were larger in IP-IMRT than in the other techniques. The value of the mean dose to the ipsilateral lung was higher for IP-IMRT than the values for with FiF-FP-IMRT and 3D-CRT. In the current study, the relative volume of contralateral breast receiving low doses (0.01, 0.6, 1, and 2Gy) was significantly lower for the FiF-FP-IMRT and 3D-CRT plans than for the IP-IMRT plan. Compared with 3D-CRT and IP-IMRT, FiF-FP-IMRT proved to be a simple and efficient planning technique for breast irradiation. It provided dosimetric advantages, significantly reducing the size of the hot spot and minimally improving the coverage of the target volume. In addition, it was felt that FiF-FP-IMRT required less planning time and easy field placements.

Intensity-modulated radiation therapy for early-stage breast cancer: is it ready for prime time?

“…A possible explanation of why the planning timings of 3D CRT and IMRT in Al-Rahbi et al15 study is substantially less than the Cambridge Breast IMRT Trial is that breast IMRT planning in the Cambridge Breast IMRT Trial was at its infancy 17. As technology and planning experience matures, planning timings may consequentially be shortened.…”

“…IP is an IMRT technique that requires contouring of target volumes and OARs 15. This way, a homogenous dose distribution can be achieved and controlled by applying constraints to the target volume and OAR.…”

“…Al-Rahbi et al15 compared the planning times of 3D CRT, FP FIF IMRT, and IP IMRT 15. The planning times were 20–30 minutes, 15–20 minutes, and 50–60 minutes, respectively.…”

“…However, IMRT is more complex as deliberate attempts must be made to reduce dose homogeneity and lower the maximum dose 15,16…”

“…In terms of MUs, Al-Rahbi et al15 demonstrated that IP IMRT technique required more MUs compared to 3D CRT and FP FIF IMRT techniques 15. The number of MUs for the FP FIF IMRT technique was four times lesser than that for the IP IMRT technique (293 MU vs 1160 MU), whereas those for the 3D CRT technique was three times lesser (443 MU vs 1160 MU).…”