Room: Exhibit Hall
Purpose: For proton therapy, cardiac and pulmonary dose sparing is superior to photon therapy, but the skin dose can be high because of the absence of the skin sparing effect in the proton depth dose. The purpose of this study was to develop an optimization technique to reduce skin dose for intensity modulated proton therapy (IMPT) for patients with intact breast and chest wall with breast implant.
Methods: IMPT plans with single en-face beams were generated for an intact breast and a chest wall patient with silicone implant. Dose of 50.4 Gy (RBE) was prescribed to breast/chest wall CTV and regional nodes, which excluded 3 mm skin anteriorly. For the intact breast patient, two plans were created with the skin structure used for optimization, skin_opt, defined as 3 mm and 10 mm thickness above the breast, respectively. For the chest wall patient, three plans were created. Two of the plans were created with the same skin_opt as the breast patient, and the 3rd plan was created by using a CTV_opt structure for optimization. The CTV_opt was the chest wall CTV excluding the implant with 5 mm contraction. For dosimetric evaluation, breast CTV was used for the breast patient. Chest wall CTV and CW CTV_opt were used for the chest wall patient. For the evaluation of skin dose, 3 mm skin above the breast/chest wall CTV, skin_eval, was used.
Results: The coverage of breast/chest wall CTV and CW CTV_opt were similar for all plans. Skin_eval, heart and lung dose were reported in the supporting material.
Conclusion: By using the skin_opt of 10 mm thickness for IMPT optimization, the volumetric dose to the skin (3mm) was significantly reduced without compromising the target coverage. For the patient with implant, avoid treating the implant, however, was less effective to reduce the skin dose.