Program Information
Trajectory Modulated Arc Therapy for Delivery of Total Marrow and Total Lymphatic Irradiation
J Liang*, C Han , A Liu , T Schultheiss , J Wong , City of Hope National Medical Center, Duarte, CA
Presentations
MO-F-CAMPUS-TT-5 (Monday, July 31, 2017) 4:30 PM - 5:30 PM Room: Therapy ePoster Theater
Purpose: Trajectory modulated arc therapy (TMAT) is a generalization of VMAT progressive sampling approach that allows concurrent couch and gantry motions with continuous beam modulation. This study is to evaluate the feasibility of TMAT for targeted total marrow and total lymphatic irradiation (TMLI).
Methods: TMLI previously performed with helical tomotherapy (HT) was replanned using TMAT (n=4, 12Gy/8fractions). The GTV was defined as skeletal bone, major lymph node chains and spleen. The OARs included over 20 normal organs. To mimic HT delivery (field width 5cm, pitch 0.287), a TMAT trajectory was generated with longitudinal jaw width 7.5cm, couch travel ~90cm, 9 gantry rotations (5CW and 4CCW) giving a pitch of 1.333. The longitudinal dimension of bone PTV (range 89.5cm-95.3cm) allowed continuous patient translation without violating couch extension limit. TMAT plans were evaluated with TBI and HT TMLI for dosimetric comparison and delivery efficiency.
Results: 30%-50% OARs median dose reductions were observed in TMAT TMLI plans relative to TBI. D50 in lungs, kidney, heart and liver were decreased by 36.1%, 42.6%, 45.8% and 38.5%, respectively. Compared with 30 HT TMLIs treated in our institution, TMAT had similar plan quality. Average lung D80, D50 and D10 were 4.5Gy, 5.8Gy and 9.2Gy respectively in TMAT versus 5.0Gy (range 4.3Gy-6.1Gy), 5.7Gy (range 4.9Gy-6.8Gy) and 8.8Gy (range 7.5Gy-10.4Gy) with HT. Average kidney D80, D50 and D10 were 4.7Gy, 5.9Gy and 9.9Gy respectively using TMAT versus 6.1Gy (range 5.0Gy-7.3Gy), 6.8Gy (range 5.0Gy-8.1Gy) and 10.2Gy (range 8.9Gy-11.3Gy) using HT. A representative TMAT TMLI plan was implemented in developer mode via XML script. The MU from TMAT was 4869 corresponding to a beam-on time of 10.8mins. HT plan had significantly higher MU and longer treatment time (17811MU, 20.4mins).
Conclusion: TMAT provided improved OARs sparing compared with TBI and significant treatment time and MU reductions compared with HT TMLI.
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