This study supports the sparse dosimetric data regarding the quantitative tumour volume reduction, re-emphasizing the need for adaptive replanning for minimizing normal tissue toxicity without compromising local control, and adds to the existing body of literature.
Axillary levels I and II (lower axilla) receive substantial amount of incidental radiation doses with all the three techniques; however, conformal techniques (IMRT, 3DCRT) deliver significantly lesser incidental radiation to lower axilla than ST technique.
The purpose of this study was to evaluate quantitatively the patient‐specific 3D dosimetry tool COMPASS with 2D array MatriXX detector for stereotactic volumetric‐modulated arc delivery. Twenty‐five patients CT images and RT structures from different sites (brain, head & neck, thorax, abdomen, and spine) were taken from CyberKnife Multiplan planning system for this study. All these patients underwent radical stereotactic treatment in CyberKnife. For each patient, linac based volumetric‐modulated arc therapy (VMAT) stereotactic plans were generated in Monaco TPS v3.1 using Elekta Beam Modulator MLC. Dose prescription was in the range of 5–20 Gy per fraction. Target prescription and critical organ constraints were tried to match the delivered treatment plans. Each plan quality was analyzed using conformity index (CI), conformity number (CN), gradient Index (GI), target coverage (TC), and dose to 95% of volume (D95). Monaco Monte Carlo (MC)‐calculated treatment plan delivery accuracy was quantitatively evaluated with COMPASS‐calculated (CCA) dose and COMPASS indirectly measured (CME) dose based on dose‐volume histogram metrics. In order to ascertain the potential of COMPASS 3D dosimetry for stereotactic plan delivery, 2D fluence verification was performed with MatriXX using MultiCube phantom. Routine quality assurance of absolute point dose verification was performed to check the overall delivery accuracy. Quantitative analyses of dose delivery verification were compared with pass and fail criteria of 3 mm and 3% distance to agreement and dose differences. Gamma passing rate was compared with 2D fluence verification from MatriXX with MultiCube. Comparison of COMPASS reconstructed dose from measured fluence and COMPASS computed dose has shown a very good agreement with TPS calculated dose. Each plan was evaluated based on dose volume parameters for target volumes such as dose at 95% of volume (D95) and average dose. For critical organs dose at 20% of volume (D20), dose at 50% of volume (D50), and maximum point doses were evaluated. Comparison was carried out using gamma analysis with passing criteria of 3 mm and 3%. Mean deviation of 1.9%±1% was observed for dose at 95% of volume (D95) of target volumes, whereas much less difference was noticed for critical organs. However, significant dose difference was noticed in two cases due to the smaller tumor size. Evaluation of this study revealed that the COMPASS 3D dosimetry is efficient and easy to use for patient‐specific QA of VMAT stereotactic delivery. 3D dosimetric QA with COMPASS provides additional degrees of freedom to check the high‐dose modulated stereotactic delivery with very high precision on patient CT images.PACS numbers: 87.55.Qr, 87.56.Fc
Purpose: To investigate the plan quality and delivery efficiency with different penalty on minimum segment width in volumetric modulated arc delivery for SBRT cases. Methods: Total of eighteen cases with tumors in lung, liver and abdomen were taken for the study. For each case, three VMAT SBRT plans were generated with different penalties on minimum segment width of 0.5, 1.0 and 1.5cm using CMS Monaco v3.1 TPS. Dose prescriptions were in the range of 7 to 20Gy per fraction. Each plan with different penalty was developed in a way to achieve same dose distribution and evaluated with dose indices(DIs), Conformity Index, Conformity Number and Gradient Index. Plan efficiency was analyzed in terms of monitor units(MUs) and delivery accuracy. The plan with 0.5cm of minimum segment width was used as a reference plan. All these plans were delivered using Elekta Beam Modulator having 4mm leaf width. The delivery accuracy was verified by measured fluence and point dose using Matrixx 2D detector array. Results: The difference between the reference and compared plan DIs were achieved within 2%. When compared with reference plan the total MUs was increased on average of 15.04±8.0% and 22.14±10.7% for 1.0cm and 1.5cm of minimum segment width plans respectively. Analysis of measured dose with TPS calculated showed a deviation of 3.1±1.9%, 2.9±1.2% and 2.7±0.8% for point dose verification and 95.9±2.8%, 96.5±2.6% and 97.8±1.6% for planar dose measurements with pass criteria of 2%/2mm for 0.5, 1.0 and 1.5cm of minimum segment width plans respectively. Conclusion: VMAT SBRT plans with increased value of minimum segment width shows a clear merit of better plan quality and delivery efficiency. Reducing the MUs by controlling redundant modulation for VMAT SBRT plans with optimal values of minimum segment width will increase the comfort for the patients with motion management system.
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