Radiation and Cancer Physics

SS 15 - Physics 3 - Treatment Planning

115 - Feasibility of Noninvasive Cardiac Ablation Utilizing Intensity Modulated Proton Therapy to Treat Ventricular Tachycardia

Monday, October 22
5:35 PM - 5:45 PM
Location: Room 006

Feasibility of Noninvasive Cardiac Ablation Utilizing Intensity Modulated Proton Therapy to Treat Ventricular Tachycardia
S. M. Goddu1, J. Hilliard2, N. Knutson3, T. Zhao4, G. D. Hugo1, S. Mutic1, J. D. Bradley1, P. Cuculich1, and C. G. Robinson4; 1Washington University School of Medicine, St. Louis, MO, 2Washington University in St. Louis, St. Louis, MO, 3Washington University, St. Louis, MO, 4Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO

Purpose/Objective(s): We have recently demonstrated safety and feasibility (Cuculich et al, NEJM-2017) of using noninvasive single-fraction photon based SBRT to treat patients with refractory, life-threatening, ventricular tachycardia (VT). Intensity Modulated Proton Therapy (IMPT) has the potential to reduce dose to non-target heart tissue (NTHT). In this study we evaluated the feasibility and potential dosimetric improvements using IMPT for noninvasive treatment of VT.

Materials/Methods: Sixteen patients who underwent single fraction VMAT-SBRT, using 3-5 non-coplanar 6 MV arcs, to arrhythmogenic focus on a prospective phase I/II trial were selected for this study. Patients were retrospectively re-planned using a Varian’s ProBeam IMPT using Eclipse Treatment Planning System. Four non-coplanar beams were selected by minimizing the irradiated volumes of the surrounding NTHT, stomach, esophagus and bowel while maximizing plan robustness. A single fraction dose of 35 Gy to ITV and 25 Gy to PTV were prescribed to match their respective clinical plans. Optimization goals were to keep 0.035 cc of esophagus, stomach and bowel receiving doses no more than 15 Gy, 22 Gy and 29 Gy, respectively. Varian pencil beam model was used to optimize the plans to maximize the NTHT sparing and meeting the OAR constraints.

Results: Esophagus and/or stomach were adjacent to PTVs in 25% of patients, which limited the PTV coverage. However, all IMPT plans showed adequate target coverage (V95%Rx=>99%) while meeting the OAR constraints. IMPT plans showed comparable high dose conformity with large reduction in V50%Rx /VRx. Excellent NTHT sparing is achieved in IMPT plans. Average reduction in mean dose by 4.3 Gy and V15Gy and V10Gy volumes by 95 cc and 199 cc, respectively. Results are summarized in Table 1.

Conclusion: NTHT sparing in IMPT plans due to lower entrance dose and sharp distal dose fall off by protons is highly promising for this group of patients where cardiac toxicity may play a vital role in long-term survivors. However, delivery errors caused by target-motion due to interplay-effects need to be evaluated before using this technique. Furthermore, this may open doors to a new set of patients otherwise treated using catheter ablation.
Table 1: Plan quality metrics along with DVH parameters (Mean ± SD) of the targets and Non-target Heart-Tissue. Last row shows the NTHT volume (in cc) sparing at different dose levels.
Targets Coverage Conformity
Volume (cc) Plan Type Mean D (Gy) %VRx %V95%Rx VRx/VPTV V50%Rx /VRx
ITV 48.1 ± 29 IMPT 38.4 ± 0.9 98.3 ± 1.8 99.6 ± 0.7
VMAT_Clin 38.2 ± 1.1 97.3 ± 2.3 99.5 ± 0.8
PTV 138.9 ± 67.8 IMPT 34.1 ± 0.8 98.4 ± 1.3 99.1 ± 1.0 1.21 ± 0.08 2.80 ± 0.36
VAMT_Clin 33.6 ± 1.0 98.7 ± 1.3 99.4 ± 1.1 1.15 ± 0.12 4.82 ± 1.04
Non-Target Heat Tissue
MeanD (Gy) %V25Gy %V20Gy %V15Gy %V10Gy %V5Gy %V2Gy
IMPT 1.9 ± 0.8 0.7 ± 0.4 2.6 ± 1.0 4.8 ± 1.8 7.8 ± 3.1 12.8 ± 5.6 16.9 ± 7.4
VMAT_Clin 6.2 ± 2.0 1.0 ± 0.8 5.1 ± 2.6 11.5 ± 5.5 21.9 ± 8.9 40.7 ± 13.3 65.3 ± 17.5
Volume (cc) spared by IMPT 4.8 ±11.3 35.4 ±31.7 94.7 ± 71.2 199.1 ± 125.0 390.7 ± 218.3 670.2 ± 314.2

Author Disclosure: S.M. Goddu: None. J. Hilliard: None. T. Zhao: None. G.D. Hugo: Research Grant; National Institutes of Health. Royalty; Varian Medical Systems. Patent/License Fees/Copyright; Varian Medical Systems. Vice-chair, Therapy Imaging Subcommittee; American Association of Physicists in Medicine. Editorial Board Member; Practical Radiation Oncology. International Advisory Board member; Physics In Medicine and Biology. S. Mutic: Honoraria; ViewRay Inc, Varian Medical Systems, Inc, American Society for Radiation Oncology (ASTRO). Advisory Board; ViewRay Inc. Travel Expenses; ViewRay Inc, Varian Medical Systems, Inc, American Society for Radiation Oncology (ASTRO). Stock; Radialogica. Partnership; TreatSafely. Chief Technical Officer; Radialogica, LLC. J.D. Bradley: None. C.G. Robinson: Research Grant; Varian Medical Systems, Elekta. Speaker's Bureau; Varian Medical Systems, DFINE. Advisory Board; Radialogica. Stock Options; Radialogica.

Sreekrishna Goddu, PhD

Disclosure:
Employment
Washington University: Associate Professor: Employee

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