Dosimetric Analysis of Proton Beam Therapy vs. Photon Radiotherapy for Cardiac Tumors with or without Deep Inspiratory Breath Holding: A Case Report

Abstract

Proton beam therapy (PBT) has been demonstrated to deliver equivalent dosimetric radiation with the benefit of improved sparing of organs at risk (OAR). Deep inspiration breath holding (DIBH) is a commonly used method for reducing the radiation dose to the heart and lungs. However, few studies have ever reported the usage of DIBH combined with proton beam therapy in cardiac tumors. The purpose of this case report is to compare the dosimetric differences between photon radiotherapy and proton radiation therapy (PBT) with or without deep inspiration breath holding. A 66-year-old female patient with cardiac tumors was recruited, and the prescribed dose of radiotherapy for cardiac tumors was 95%PGTV 50Gy/2.5Gy/20f. Two simulation CT scans were collected during free breath (FB) and DIBH. And the target area was delineated on deep inspiratory breath holding image (DIBH-CT) and free breathing image (FB-CT). The target area of FB-CT was modified by referring to the ten-time phases of 4D-CT. Finally, IMRT, VMAT and PBT plans (DIBH-IMRT, DIBH-VAMT, DIBH-PBT, FB-IMRT, FB-VAMT, FB-PBT) were generated on the above images, and the organs at risk were limited as follows: lungs V20 ≤20%, lungs mean ≤11 Gy, heart V30 ≤40%, coronary artery mean ≤26 Gy, spinal cord ≤30 Gy, and left breast mean ≤5 Gy. All of the six plans satisfied most of the treatment planning goals. DIBH resulted in a dose reduction in all organs at risk including the heart, lungs, coronary artery (CA), spinal cord and breasts, when compared with FB using IMRT, VMAT, or PBT. Compared with the FB, DIBH provided a significant reduction in the mean dose of coronary artery (CA mean for DIBH-IMRT vs FB-IMRT = 28.32 Gy vs 42.66 Gy, CA mean for DIBH-VMAT vs FB-VAMT = 26.44Gy vs 40.85Gy, CA mean for DIBH-PBT vs FB-PBT = 27.71Gy vs 39.51Gy). Similarly, when compared with IMRT or VMAT in either FB or DIBH, PBT reduced radiation doses for all of the OAR. In comparison, the difference was less significant between IMRT and VMAT technique. Pitmen compared with IMRT and VMAT, reduced significantly the max dose of spinal cord, lungs V5, breast-L/R mean. Totally, DIBH-PBT was observed sufficient dose coverage and better sparing of organs at risk. PBT combined with DIBH technique gained an advantage in the sparing of OAR for cardiac tumors, especially in coronary protection. The possibility of broader application of PBT with DIBH in clinical practice is currently being evaluated and further studies are needed.