PO-0692: 18F-FDG PET/CT-based treatment response evaluation in locally advanced rectal cancer
Radiotherapy and Oncology
S262 2nd ESTRO Forum 2013 adjuvant intent. We compared plans with Foward Planning -IMRT (FP-IMRT) adjusted to the delineated breast volume with two other plans without the breast delineated (one with standard tangential beams with wedges and another with FP-IMRT). The ACOSOG Z0011 trial showed the non inferiority of the irradiation of axillary levels I and II (included in the irradiated volume when using standard tangential beam radiotherapy to the breast) when compared with axillary dissection
... axillary dissection of the same levels, in selected patients with breast cancer. Materials and Methods: We analyzed data from 40 patients undergoing radiotherapy after breast conserving surgery, with a negative sentinel node biopsy. The patients were submitted to a CT for virtual simulation with 3mm slice. The data from the CT were doubled. In one CT, 2 dosimetry plans were done: one with conventional RT with tangential beams with wedges (2-3 segments were added if necessary to achieve dose homogeneity) and another with FP-IMRT. On the other CT data, target volumes were delineated: breast CTV and PTV (expansions of 10 mm were made for all directions except for the posterior one, which was 7 mm), and a plan was calculated using the FP-IMRT technique, adjusted to the PTV. We then outlined the axillary levels I and II, for analysis, on one CT data and copied it to the other. Mean dose (Dmean) and V95 were evaluated for axillary levels I and II. The Conformity Index (CI) of the PTV was also analysed. Results: Both V95 and Dmean for axillary level I were higher in the standard tangential beams with wedges technique and in the FP-IMRT technique without the breast volume delineated. When compared with these plans, the plan adjusted to the breast PTV achieved an inferior V95 value to axillary level I. When evaluating the axillary level II, these differences were more pronounced. We found a higher CI value in the plan adjusted to the breast target volume. Conclusions: We found a higher conformity index to the breast target volume using the FP-IMRT technique with the breast target volumes delineated, and a lower V95 for the axillary levels evaluated. This shows that when conforming the dose to the breast alone the unintended irradiation of the axilla is lower. Although a higher V95 was achieved with the standard tangential breast irradiation with wedges, it happens at the expenses of a lower conformity index to the breast volume, and this technique has shown a higher rate of skin toxicity, which lead to being less used. We conclude that the delineation of axillary levels I and II is mandatory when there is the need to irradiate them, and the information obtained by the sentinel node biopsy is therefore important to the radiotherapy treatment.