Program Information
The Influence of Different Beamlet Width On Volumetric Modulated Arc Therapy Plan Quality and Delivery for Glioblastoma Brain Tumor Patients
P Mohandass1,2*, D Khanna2 , D Manigandan1 , M Kumar1 , A Puri1 , N Bhalla1 , (1) Fortis Cancer Institute, Fortis Hospital, Mohali, Punjab, (2) Karunya University, Coimbatore, Tamilnadu,
Presentations
SU-I-GPD-T-401 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To evaluate the influence of different beamlet width (BW) on volumetric modulated arc therapy (VMAT) plan quality and deliverability for glioblastoma brain tumor patients.
Methods: Five glioblastoma brain tumor patients treated with 6000cGy/30fractions were chosen for this study. All plans were generated with VMAT (6MV, Dual arc) in Monaco™ treatment planning system (TPS) (V5.10). Plans were generated for Elekta Synergy™ linear accelerator with leaf width of 1cm and plan verification was performed using PTW-729 ion-chamber array. Initial VMAT plan was made using 0.3cm beamlet width. Similarly, plans were generated by changing different beamlet width to 0.1, 0.5, 0.7 and 1.0cm. For plan comparison, conformity index (CI), homogeneity index (HI), integral dose (ID) were used. For planning target volume (PTV), dose covered by 98% of PTV, mean dose (Dmean), and max dose (Dmax) were compared. The mean and max dose to brain stem, optical structures, and PTV–brain were analyzed. Normal tissue integral dose (NTID) (body volume–PTV) was also compared. Total number of segments, total monitor unit (MU) required to deliver a plan and gamma pass rate (<1.00) (3%/2mm) was analyzed.
Results: Dose coverage to D98% of PTV was 5723.88±68.82cGy, 5800.90±141.30cGy, 5825.94±72.64cGy, 5781.14±98.96cGy and 5675.62±121.92cGy for BW 0.1, 0.3, 0.5, 0.7 and 1.0cm, respectively. Similarly, critical organ doses were stable between 0.3–0.5cm BW and showed random effect for other beamlet widths. For example, brainstem maximum doses were 5605.64±269.84, 5630.80±290.50, 5610.94±270.14, 5565.52±237.38 and 5585.62±293.38cGy. NTID were 145.38±33.05, 151.27±23.60, 153.78±24.09, 159.68±25.81 and 167.028±20.30Litre/Gy. Gamma pass rates were 98.04±3.4%, 97.50±2.5%, 97.10±2.8%, 96.90±3.1% and 96.64±2.0%.
Conclusion: The target coverage, CI, HI and critical organ doses were stable between 0.3–0.5cm BW and showed random effect for other beamlet sizes. Gamma pass rates decreased and integral dose increased with increase of BW. The optimal BW during VMAT optimization can be chosen between 0.3–0.5cm, preferably 0.3cm.
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