ESTRO-ACROP guidelines in postmastectomy radiation after immediate reconstruction: Dosimetric Comparison of 3D-CRT versus VMAT planning.

Purpose: To evaluate target volume coverage and organs at risk (OARs) sparing comparing 3D-Conformal Radiation (3D-CRT) vs. Volumetric Arc Treatme nt (VMAT) planning based on contouring guidelines of European Society for Therapeutic Radiology and Oncology Advisory Committee in Radiation Oncology Practice (ESTRO-ACROP) for implant sparing and target volume delineation in postmastectomy radiation therapy (PMRT) after immediate breast reconstruction (IBR).

Materials and methods: Ten eligible patients were identified via a retrospective chart review. The CTsimulation scans were used to contour target volumes applying ESTRO-ACROP guidelines and OARs. For each case, 3D-CRT and VMAT plans were generated to evaluate the best achievement of target volume coverage and minimal dose to OARs.

Results: There was a significant difference towards VMAT for PTV coverage by 90% and 95% isodose line. The VMAT, compared to 3D-CRT, showed a lower mean (PTV-105%) (8.1 vs. 17.8), (p-value 0.000034). The OARs sparing showed a significant difference in favor of VMAT for ipsilateral lateral lung V20 (p-value 0.007048), both lungs' mean dose (p-value 0.019021), and heart mean dose (p-value 0.000076). The 3D-CRT plan showed lower thyroid mean dose (19.27 vs 23cc), (p-value 0.0235), and contralateral breast Dmax, D5 and D10, p-values (0.04088, < 0.00001 and < 0.00001), respectively. In the implant doses, there was no statistical difference between Dmax (54.59Gy vs. 54.14Gy), while there was a statistically significantly lower mean implant dose for VMAT (43.83Gy) vs. 3D-CRT (50.81Gy), (p-value < 0.00001).

Conclusion: Our study showed an advantage of VMAT compared to 3D-CRT following ESTRO-ACROP consensus for implant sparing in PMRT.