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Impact of Photon Energy On Volumetric Modulated Radiotherapy Plans for the Hodgkin's Lymphoma Patients Under Deep Inspiration Breath-Hold

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D Manigandan

D Manigandan*, M Kumar , P Mohandass , A Puri , P Kumar , N Bhalla , Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab


SU-I-GPD-T-408 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To find the suitability of different photon energies for mediastinal lymphoma patients during volumetric modulated arc therapy (VMAT) planning under deep inspiration breath-hold (DIBH).

Methods: Three patients with proven Hodgkin’s lymphoma with mediastinal involvement were chosen for the study. Planning target volume (PTV) was prescribed to 36Gy/20fractions. Elekta™ active breathing co-ordinator™ (ABC) system was used for deep inspiration breath hold (DIBH) to halt the breathing. Breath hold duration varied between 20–25s. Simulation CT scans were performed under DIBH and VMAT plans (dual Arc) were created for 4MV, 6MV and 6MV-4MV combination by using Monaco treatment planning system (TPS-V5.11.01) for Elekta Synergy™ linear accelerator with 1cm leaf width. For consistency, all plans were generated by the same planner. For plan comparison, PTV covered by 95% of isodose line, conformity index, homogeneity index were analyzed. Mean doses of lungs, heart, esophagus, maximum dose spinal cord, integral dose(liter/Gray) to normal tissue (patient volume-PTV), total monitor unit(MU) required to deliver a plan was analyzed.

Results: 6MV showed better plan quality in most of the cases, including target coverage, homogeneity, critical organ doses and integral dose, compared to both 4MV & 4MV-6MV plans. 4MV-6MV consistently showed poor plan quality followed by 4MV. 4MV was advantageous only in heart mean dose, showed 10.8% lesser with 6MV. Similarly, 6MV showed lesser MU of 15.92% compared to 4MV and 12.92% to 6MV, which may reduce the intra-fraction motions under beam interrupted delivery in DIBH. Availability of higher dose rate at 6MV compared to 4MV also advantageous for shorter treatment time and patient comfort under DIBH.

Conclusion: 6MV was found to be more suitable photon energy for the optimization and delivery of VMAT for mediastinal lymphoma patients under DIBH with shorter treatment time, lesser MU and higher dose rate, which may reduce intra-fraction motions with better patient comfort.

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