3D-printed bolus ensures the precise postmastectomy chest wall radiation therapy for breast cancer

PURPOSE: To investigate the values of a 3D-printed bolus ensuring the precise postmastectomy chest wall radiation therapy for breast cancer. METHODS AND MATERIALS: In the preclinical study on the anthropomorphic phantom, the 3D-printed bolus was used for dosimetry and fitness evaluation. The dosimetric parameters of planning target volume (PTV) were assessed, including D(min), D(max), D(mean), D(95%), homogeneity index (HI), conformity index (CI), and organs at risk (OARs). The absolute percentage differences (|%diff|) between the theory and fact skin dose were also estimated, and the follow-up was conducted for potential skin side effects. RESULTS: In preclinical studies, a 3D-printed bolus can better ensure the radiation coverage of PTV (HI 0.05, CI 99.91%), the dose accuracy (|%diff| 0.99%), and skin fitness (mean air gap 1.01 mm). Of the 27 eligible patients, we evaluated the radiation dose parameter (median(min–max): D(min) 4967(4789–5099) cGy, D(max) 5447(5369–5589) cGy, D(mean) 5236(5171–5323) cGy, D(95%) 5053(4936–5156) cGy, HI 0.07 (0.06–0.17), and CI 99.94% (97.41%–100%)) and assessed the dose of OARs (ipsilateral lung: D(mean) 1341(1208–1385) cGy, V(5) 48.06%(39.75%–48.97%), V(20) 24.55%(21.58%–26.93%), V(30) 18.40%(15.96%–19.16%); heart: D(mean) 339(138–640) cGy, V(30) 1.10%(0%–6.14%), V(40) 0.38%(0%–4.39%); spinal cord PRV: D(max) 639(389–898) cGy). The skin doses in vivo were D(theory) 208.85(203.16–212.53) cGy, D(fact) 209.53(204.14–214.42) cGy, and |%diff| 1.77% (0.89–2.94%). Of the 360 patients enrolled in the skin side effect follow-up study (including the above 27 patients), grade 1 was the most common toxicity (321, 89.2%), some of which progressing to grade 2 or grade 3 (32, 8.9% or 7, 1.9%); the radiotherapy interruption rate was 1.1%. CONCLUSION: A 3D-printed bolus can guarantee the precise radiation dose on skin surface, good fitness to skin, and controllable acute skin toxicity, which possesses a great clinical application value in postmastectomy chest call radiation therapy for breast cancer.