Room: Exhibit Hall
Purpose: RapidArc is a newer technique used widely today, for some tumor sites like breast, to make an acceptable plan, it would not be as straight forward as it is for centralized tumors. Therefore, we decided to investigate the differences of the intensity modulated radiation therapy (IMRT) with RapidArc while the patient undergoes whole breast irradiation including axillary nodes.
Methods: We randomly selected 10 patient plans previously treated to make alternative plans for each of them and then compare the dose and TCP/NTCP results for each. Eclipse was used to create the alternative plans for each case using the same structures, energy, Linac and normalization. Prescription to the planning target volume (left breast) involves treatment of the whole breast at 1.8-2Gy daily for 46-50.4Gy, followed by a sequential boost to the tumor bed for 10-18Gy. All plans were normalized covering 97 5 of PTV with 100% of the dose.
Results: V5, V10 and Dmean of the left lung differ significantly between the two plans (p-value <0.0001). V20 Gy does not (p-value 0.53). V5, V10, and Dmean of heart differ significantly between the two plans (p-values: <0.0001, =0.004, <0.0001 and respectively). However, D33 does not (p-value 0.048). V5 and Dmean of contralateral lung differ significantly between the two plans (p-value <0.0001 for both). Dmean of spinal cord is significantly different between the two plans (p-value <0.0001).The mean conformity index did not differ significantly, p-value 0.12
Conclusion: Dose-volumetric results of IMRT and RapidArc were significantly different for most of the constraints although all plans were made within the threshold values recommended by RTOGs. Mean doses to cord, ipsilateral lung, heart, contralateral lung were significantly different in RapidArc from IMRT plans.If both plans have the same mean conformity index, IMRT will have some advantages in dose sparing on OARs especially in low doses.