Abstract
PurposeWhole lung irradiation (WLI) is indicated for certain pediatric patients with lung metastases. This study investigated whether WLI delivered as intensity-modulated proton therapy (IMPT) could significantly spare the heart and breasts when compared with conventional WLI delivered with anteroposterior/posteroanterior photon fields and with intensity-modulated photon therapy (IMRT) WLI.Materials and MethodsConventional, IMRT, and IMPT plans were generated for 5 patients (aged 5-22 years). The prescription dose was 16.5 GyRBE in 1.5-GyRBE fractions. Conventional plans used 6-MV photons prescribed to the midline and a field-in-field technique to cover the planning target volume (the internal target volume [ITV] + 1 cm). IMRT plans used 6-MV photons with a 7-beam arrangement with dose prescribed to the planning target volume. IMPT plans used scenario-based optimization with 5% range uncertainty and 5-mm positional uncertainty to cover the ITV robustly. Monte Carlo dose calculation was used for all IMPT plans. Doses were compared with paired Student t test.ResultsThe ITV Dmean was similar for the IMPT, conventional, and IMRT plans, but the IMPT plans had a lower Dmin and a higher Dmax at tissue interfaces than conventional plans (Dmean ratio: 0.96, P > .05; Dmin ratio: 0.9, P < .001; Dmax ratio: 1.1, P = .014). Dmeans for breast and heart substructures were lower with IMPT plans than with conventional/IMRT plans (heart ratios, 0.63:0.73; left ventricle ratios, 0.61:0.72; right ventricle ratios, 0.45:0.57; left atrium ratios, 0.79:0.85; right atrium ratios, 0.81:0.86; left breast ratios, 0.40:0.51; right breast ratio, 0.46:0.52; all P < .05).ConclusionsIMPT resulted in comparable ITV coverage and lower mean doses to the heart and breasts when compared with other techniques. Whole lung irradiation delivered as IMPT warrants prospective evaluation in pediatric patients.
Highlights
Contemporary European and North American treatment protocols require whole lung irradiation (WLI) for certain pediatric patients with pulmonary metastases
We investigated the feasibility of reducing the dose to the heart and breasts via intensitymodulated proton therapy (IMPT), using 2 posterior oblique beams to deliver WLI
When Monte Carlo (MC)-calculated intensity-modulated proton therapy (IMPT) plans were compared with conventional photon and intensity-modulated radiation therapy (IMRT) plans, the lung internal target volume (ITV) Dosimetry endpoints were the mean (Dmean) were similar but the IMPT plan doses were more heterogeneous than conventional plan doses (Dmin ratio: 0.87, P, .001; Dmax ratio: 1.12, P 1⁄4 .014)
Summary
Contemporary European and North American treatment protocols require whole lung irradiation (WLI) for certain pediatric patients with pulmonary metastases. Intensity-modulated proton therapy for whole lung irradiation conventionally delivered via opposed anteroposterior-posteroanterior (AP/PA) photon fields, which include nontarget organs such as the mediastinum and breasts. Both the mediastinum and breasts receive the full dose of radiation, which can range from 10.5 to 16.5 Gy. Whole lung irradiation can be delivered via intensity-modulated radiation; breast and cardiac substructures typically fall within the low-dose spill. The long-term effects of cardiac and breast irradiation in this young population are not negligible; they can include potentially fatal cardiac events [5], an overall increase in cardiac comorbidities [6], secondary breast cancers [6, 7], breast hypoplasia [8], and decreased lactation [8]
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