Dosimetry Study of Radiation Toxicity in Young Patients with Mediastinal Lymphoma by the Use of an Inclined Board and Deep Inspiration Breath-Holding, under the Guidance of an Optical Surface Management System

Abstract

<h3>Purpose/Objective(s)</h3> Survivors of mediastinal lymphoma are at increased risk of lung cancer, breast cancer, and cardiovascular disease after radiotherapy. We compared treatment plans for patients in one of two positions while using one of two breathing techniques: supine on an inclined board (IB) or flat; and using deep inspiration breath-hold (DIBH) or free-breathing. <h3>Materials/Methods</h3> Ten young patients with mediastinal lymphoma were eligible for the study. Sets of intensity-modulated radiation therapy (IMRT) treatment plans were created for each of 10 patients with mediastinal lymphoma (6 women, 4 men): DIBH-IB (for women); FB-IB (for women); DIBH-flat (for men); and FB-flat (for men and women). During DIBH, an optical surface management system (OSMS) was used to monitor breathing rate and magnitude, track respiratory status in real time. Tumor target volumes and organs at risk (OARs; lungs, breasts [in women], thyroid, and heart and its substructures) were compared in all four conditions. <h3>Results</h3> A total of 26 plans were created for all 10 patients. The DIBH-IB plan (for women) and the DIBH-flat plan (for men) was used for actual patient treatment. Daily pre-RT cone beam CT (CBCT) was used before treatment to adjust for set-up errors. Daily post-RT CBCT was used after treatment to assess intra-fractional variability. Registration of post-RT CBCT with the planning CT showed that both tumor and OARs matched well, with rather small intra-fractional variability. The planning target volume (PTV) was considerably smaller in the DIBH plans (380.0 cm³ for DIBH vs 527 cm³ for FB, <i>P</i><0.001), because of the smaller clinical target volume-to-PTV margins in the DIBH plans and the compression of the CTV due to the deep inspiration and breath hold. Plans for DIBH-IB for women and DIBH-flat for men produced lower mean lung dose (6.1 vs 8.1 Gy; <i>P</i><0.001), lung V5 (36.1% vs 47.9%; <i>P</i>=0.001), and lung V20 (7.9% vs 11.7%; <i>P</i><0.001) compared with FB-IB and FB-flat plans. Plans for FB-IB also resulted in smaller mean breast dose and breast V5 than FB-flat (3.4 vs 4.0 Gy, 16.3% vs 20.4%, <i>P</i>=0.018 and 0.008). Use of DIBH-IB reduced both measures still further relative to FB-flat (2.6 vs 4.0 Gy, 13.8% vs 20.4%, <i>P</i>=0.015 and 0.013). Plans for DIBH produced lower mean heart dose (8.7 vs 10.4Gy; <i>P</i>=0.048) and heart V5 (40.6% vs 55.4%; <i>P</i>=0.023) compared with FB plans. Use of DIBH brought more dosimetric benefits of mean dose, V5 and V20 to the right heart substructures including right ventricle, right atrium and right coronary artery. <h3>Conclusion</h3> In this small group of patients with mediastinal lymphoma, use of DIBH (with an OSMS) and an IB resulted in lower estimated doses to lungs, breasts and heart, especially the right heart, than did FB; these reduced doses may reduce the probability of pulmonary, breast and cardiac radiation toxicity.