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3D DVH Based Patient Specific Quality Assurance Using COMPASS

S Chander*, S SHARMA , V SUBRAMANI , P KUMAR , S BHASKAR , S PATHY , N GOPISHANKAR , S THULKAR , M SINGH , A BINJOLA , P KUMAR , N DHAYANETHI , All India Institute of Medical Sciences, New Delhi, Delhi


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Aim is to evaluate 3D dose-volume-histogram (DVH) based pre-treatment plan verification results along with conventional 2D planar quality assurance.

Methods: Twenty one pelvis patients were treated with volumetric modulated arc therapy (VMAT) were selected for this study. All patients were planned with 6MV X-rays using Elekta VersaHD linear-accelerator. Prescription dose was ranging from 1.8Gy to 3.0Gy per-fraction. Treatment planning was done using Elekta Monaco(5.11) treatment planning system (TPS) having Monte-Carlo dose calculation algorithm. 2D-planar dose measurements were performed with IBA I'matriXX evolution detector array using My-QA Patients software. For 2D-Gamma index evaluation 3%/3mm and 2%/2mm criteria was used and threshold was set as 20%. 3D dose measurements were performed using IBA-COMPASS system. COMPASS software, is used in combination with I’matriXX evolution detector. COMPASS uses collapsed cone convolution algorithm for calculation. Monaco and COMPASS doses were compared using DVH, in terms of doses to planning target volume (PTV) and organ at risks. For PTV D95, D2 and D50 (dose received by 95%, 2% and 50% volume), similarly for OARs D2 and D50 was noted.

Results: 2D-Gamma pass rate for Monaco calculated and I’matriXX measured 2D fluence were 98.5±1.3%, 93.5±4.4% for 3%/3mm and 2%/2mm criteria respectively. Monaco versus COMPASS computed variations (cGy) were as: PTV: D95(-73.62±65.32cGy),D2(-51.00±69.88cGy),D50(-36.17±32.87cGy) respectively. Bladder:D2(-113.32±66.04cGy),D50(-79.47±66.95cGy); Rectum:D2(-68.18±51.69cGy), D50(70.77±61.18cGy); Bowel:D2(-45.69±59.32cGy),D50(-1.77±28.12cGy); RT-Femur: D2(-20.63±39.90cGy),D50(-6.28±24.65cGy); LT-Femur:D2(-21.20±44.71cGy),D50(-2.09±19.02cGy).Monaco computed versus COMPASS measured variations (cGy) were as: PTV: D95(30.69±88.01cGy),D2(81.98±85.05cGy),D50(80.03±60.42cGy); Bladder: D2(87.38±79.33cGy),D50(134.79±153.13cGy); Rectum:D2(10.79±85.38cGy),D50(-66.90±133.86cGy); Bowel:D2(119.28±100.06cGy), D50(37.61±83.96cGy); RT-Femur: D2(50.34±49.19cGy),D50(-18.67±52.51cGy); LT-Femur:D2(40.76±83.44cGy),D50(-22.33±35.15cGy).COMPASS computed versus COMPASS measured variations (cGy) were as: PTV: D95(106.38±92.91cGy),D2(151.99±111.21cGy),D50(116.19±81.03cGy); Bladder: D2(200.70±122.36cGy),D50(214.25±211.68cGy); Rectum:D2(79.00±100.80cGy),D50(3.87±98.49cGy); Bowel:D2(164.97±123.29cGy), D50(39.37±99.74cGy); RT-Femur: D2(55.28±75.65cGy),D50(-12.40±48.03cGy); LT-Femur:D2(61.97±67.46Gy),D50(-18.82±41.01cGy).

Conclusion: 2D-Gamma pass rate was 98.5±1.3% for 3%/3mm. COMPASS 3D-measurement gives direct comparison with Monaco calculation in terms of DVH, which is clinically relevant and easy to explain in patient. COMPASS computed and measured results showed good agreement (<2Gy) with Monaco calculated plan, therefore can be used in clinic.


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TH- External beam- photons: Quality Assurance - VMAT

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