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Modulation Complexity Score Evaluation for Multitarget Site Planning Using VMAT and IMRT Technique

Gopishankar Natanasabapathi*, Dhanabalan Rajasekharan, Surendra Kumar Saini, Vellaiyan Subramani, Laviraj Macherla, Rajkishor Bisht, Dayanand Sharma, Subash Chander, Gourakishor Rath, All India Institute of Medical Sciences, New Delhi, India

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To evaluate modulation complexity score for multitarget site planning with single-arc-VMAT, double-arc-VMAT, 7-field-IMRT and 9-field-IMRT techniques.

Methods:
An in-house developed human head mimicking phantom (PMMA Material) was used for planning which simulated multiple metastasis brain lesion case. Four PTV cylinders of each size 3cm diameter, 5cm length and HU values 290,70,50,-35 were delineated on the X-Ray CT images of the plan. A critical organ of 1cm diameter and 5cm length was delineated in-between four PTV. The Synergy-S Linac (Elekta) with 6MV Photons, field size 16x21cm2 and MLC (Beam modulator) machine parameters were used for generating plan. The Monaco TPS (Version 5.11) was used for generating single-arc-VMAT (sVMAT), double-arc-VMAT (dVMAT), 7-Field-IMRT and 9-Field-IMRT plan. The calculation grid size was of 3mm resolution. The dose prescription was 66Gy/33 fractions for each PTV. All four plans underwent two-stage optimization for dose calculation with same physical and biological objectives and constraints. An in-house developed MATLAB program computed the leaf sequence variability (LSV), aperture area variability (AAV), modulation complexity score (MCS) score for VMAT and IMRT by acquiring following plan information (i) jaws position, (ii) number of control points, (iii) MLC leaf positions per control point, (iv) cumulative MU weights per control point and (v) MU per arc/field. The routine planning parameters such as DVH analysis, minimum, maximum, mean dose were generated for PTV, critical organ and body.

Results:
Following are the values for sVMAT, dVMAT, 7-Field-IMRT and 9-Field-IMRT plans : number of control points-98,217,262,350;LSV-0.7659,0.7312,0.6976,0.7180;AAV-0.1733,0.1437,0.1756,0.1639;MCS-0.1504,0.1295,0.1385,0.1299;MU-738.2,798.25,940.46,1029.05. The sVMAT showed higher MCS value among four plans. The MCS of dVMAT was nearly equal to that of 9-Field-IMRT. The mean dose to critical organ and body was lowest in dVMAT plan.

Conclusion:
MCS analysis performs quantitative assessment of plan complexity and provides comprehensive information on dose delivery than simple beam parameters such as monitor units.

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Keywords

MLC, Treatment Techniques, Beam Shaping

Taxonomy

TH- External Beam- Photons: Quality Assurance - IMRT/VMAT

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