Background: Aim is to find correlation between 2D-gamma passing rate and 3D-DVHbased pre-treatment patient-specific quality assurance. Materials and Methods: 21 head and neck and 21 pelvis patients, treated with volumetric modulated arc therapy (VMAT) were selected for this study. All patients were planned with Elekta VersaHD linear accelerator using Monaco (5.11) treatment planning system. 2D-planar dose measurements were performed with IBA-I'matriXX evolution detector-array using MyQA-Patients software. For 2D-Gamma index evaluation, 3%/3mm and 2%/2mm criteria were used. 3D-dose measurements were performed using the IBA-COMPASS system. For 3D measurement, Monaco and COMPASS doses were compared in terms of percentage dose differences to PTV and organs at risk. For PTV D95, D2, and D50 (dose received by 95%, 2%, and 50% volume), similarly for OARs D2 and D50 were noted. 3D Gamma index was also noted. Correlation coefficient and its corresponding two-tailed p-value (<= 0.05, for statistically significant) were calculated for 2D-gamma passing rate and 3D Gamma index & percentage dose differences of 3D-DVH based metrics (Monaco calculated versus COMPASS measured). Strength of correlation will be considered weak or strong based on the r -value. Results: 2D-Gamma index passing rate was 98.6 +/- 1.8%, 92.1 +/- 7.1% and 98.5 +/- 1.3%, 93.5 +/- 4.4% for head-neck and pelvis patients (3%/3mm, 2%/2mm criteria) respectively. Percentage dose-differences for PTV D95, D2, D50 for head-neck and pelvis were: 4.22 +/- 2.09%, 4.25 +/- 2.23%, 3.93 +/- 1.59 & 0.60 +/- 1.96%, 1.53 +/- 1.64%, 1.59 +/- 1.20% respectively. Spine and brainstem D2 were 0.84 +/- 6.10%, 0.77 +/- 2.70%, bladder and rectum D50 were 3.75 +/- 3.31%, -2.19 +/- 3.60%. Conclusion: No strong correlation was observed between the 2D Gamma passing rate and 3D measurements.

Purpose: The aim of this study is to evaluate influence of statistical uncertainty on Monte-Carlo dose calculation of Monaco 5.11 treatment planning system (TPS). Methods: Phantom with contoured C-Shape structure set was downloaded from AAPM website provided with TG119 report. VMAT plan was created for C-Shape test case using Monaco TPS for 6 MV Elekta Versa-HD linear-accelerator. Dose prescription and constraints were as per TG119. After optimizations, C-Shape plan was calculated with different statistical-uncertainty (i) 0.5%, 1.0%, 3.0% and 5.0% per control point and (ii) 0.5%, 1.0%, 3.0% and 5.0% per calculation. Base plan was calculated with 0.5% per control point. Results: Variations in PTV doses for different statistical-uncertainties with respect to 0.5% per control point were within PTV-D95: 82 cGy(1.64%); PTV-D10: 14.8 cGy(0.28%); Core-D10: 3.7 cGy(0.15%). MU required to deliver a plan (920 MU) were observed same with different statistical-uncertainty. Calculation time increases with decrease in statistical-uncertainty due to more number of histories. 2D-Gamma pass rate was ranging from 98.1% to 98.9% for analyzed statistical-uncertainties. Statistical-uncertainty 0.5% per control point showed higher Gamma pass-rate (98.9%). Conclusion: Minor variation (<1.64%) in dose volume parameters was observed with different statistical-uncertainties, whereas Monitor unit remain same. 3.0% per control point and 0.5% per calculation resulted in almost similar results and found optimal with reasonable calculation time in terms of plan quality and delivery accuracy (gamma pass-rate).

Purpose: The purpose of this study is to estimate technical treatment accuracy in fractionated stereotactic radiosurgery (fSRS) using extend system (ES) of Gamma Knife (GK). Methods: The fSRS with GK relies on a patient specific re-locatable immobilization system. The reference treatment position is estimated using a digital probe and a repositioning check tool (RCT). The “calibration values” of RCT apertures were compared with measured values on RCT-QA tool to evaluate the standard error (SE) associated with RCT measurements. A treatment plan with single “4 mm collimator shot” was created to deliver a radiation dose of 5 Gy at the predefined plane of a newly designed in-house head-neck phantom. The plan was investigated using radiochromic EBT3 films. The stereotactic CT imaging of a designed mini CT phantom and distortion study of MR imaging, were combined to calculate imaging SE. The focal precision check for GK machine tolerance was performed using a central diode test tool. Results: Twenty observations of RCT and digital probe, shown the SE of +/−0.0186mm and +/−0.0002mm respectively. A mean positional shift of 0.2752mm (σ=0.0696mm) was observed for twenty similar treatment settings of head-neck phantom. The difference between radiological and predefined exposure point was 0.4650mm and 0.4270mm; for two independent experiments. The imaging studies showed a combined SE of +/− 0.1055mm. Twenty frequent runs of a diode test tool showed the tolerance SE of +/−0.0096mm. If, the measurements are considered to be at 95% of confidence level, an expanded uncertainty was evaluated as +/− 0.2371mm with our system. The positional shift, when combined with an expanded uncertainty, a trivial variation of 0.07mm (max) was observed in comparing resultant radiological precision through film investigations. Conclusion: The study proposes an expression of “technical treatment accuracy” within “known uncertainties” is rational in the estimation of routine fSRS quality. The research work is supported by the research section of “All India Institute of Medical Sciences” - New Delhi, India under project no A-247.

Purpose:Aim of the study is to evaluate mechanical and radiological accuracy of multi‐fraction regimen and validate Gamma knife based fractionation using newly developed patient simulating multipurpose phantom.Methods:A patient simulating phantom was designed to verify fractionated treatments with extend system (ES) of Gamma Knife however it could be used to validate other radiotherapy procedures as well. The phantom has options to insert various density material plugs and mini CT/MR distortion phantoms to analyze the quality of stereotactic imaging. An additional thorax part designed to predict surface doses at various organ sites. The phantom was positioned using vacuum head cushion and patient control unit for imaging and treatment. The repositioning check tool (RCT) was used to predict phantom positioning under ES assembly. The phantom with special inserts for film in axial, coronal and sagittal plane were scanned with X‐Ray CT and the acquired images were transferred to treatment planning system (LGP 10.1). The focal precession test was performed with 4mm collimator and an experimental plan of four 16mm collimator shots was prepared for treatment verification of multi‐fraction regimen. The prescription dose of 5Gy per fraction was delivered in four fractions. Each fraction was analyzed using EBT3 films scanned with EPSON 10000XL Scanner.Results:The measurement of 38 RCT points showed an overall positional accuracy of 0.28mm. The mean deviation of 0.28% and 0.31 % were calculated as CT and MR image distortion respectively. The radiological focus accuracy test showed its deviation from mechanical center point of 0.22mm. The profile measurement showed close agreement between TPS planned and film measured dose. At tolerance criteria of 1%/1mm gamma index analysis showed a pass rate of > 95%.Conclusion:Our results show that the newly developed multipurpose patient simulating phantom is highly suitable for the verification of fractionated stereotactic radiosurgery using ES of Gamma knife.The study is a part of intramural research project of Research Section, All India Institute of Medical Sciences New Delhi India (A 247).

PURPOSE:To study the impact of different smoothing parameters on IMRT plan quality and deliverabilityMethods: Five previously treated patients of carcinoma cervix were chosen. Planning target volume (PTV) and organ at risk (OAR) i.e. bladder and rectum were contoured. In each case, five different dynamic IMRT plans with 6MV photon beam were created in eclipse TPS for Varian 2300C/D linear accelerator. During optimization, dose volume constraints and priorities were kept constant and smoothing parameters were varied as follows: 10/5, 40/30 (TPS default value), 80/60, 100/80 and 200/150 in x/y direction. Total dose was 5040cGy in 28 fractions and prescribed at 95% isodose. Plan quality was analyzed by means of coverage index (CI=PTV covered by prescription dose/PTV), OAR mean doses and total monitor units (MUs) required to deliver a plan. In each case, deliverability of treatment plans were verified with I'matriXX ion-chamber array and compared with TPS dose-plane using gamma index of 3% dose difference and 3mm distance to agreement criteria.RESULTS:The CI values were 0.9435±0.032, 0.9418±0.034, 0.9380±0.041, 0.9330±0.047 and 0.8681±0.072 for 10/5, 40/30, 80/60, 100/80 and 200/150 in x/y direction. PTV dose maximum decreases with the increase of smoothing parameters and values were 5724.38±106.08 5723.30±131.60, 5708.44±1 16.74, 5697.92±116.82 and 5587.50±189.50cGy. The bladder mean doses were 4027.46±630.40, 3821.62±420.62, 3819.58±427.08, 3813.42±435.02 and 3814.78±438.0cGy. Rectum mean doses were 3839.88±466.02, 3835.52±473.18, 3837.52±472.88, 3839.10±471.20 and 3918.94±469.76cGy. Similarly, Total MUs were 1588±205, 1573±214, 1513±274, 1456±335 and 1219±68. Gamma pass rate increases with the increase of smoothing parameters and values were 99.16±0.21%, 99.07±0.19%, 99.24±0.28%, 99.29±0.29% and 99.75±0.15%.CONCLUSIONS:When smoothing parameters decreased below TPS default value, plan quality increases, but deliverability decreases. If smoothing parameters increased above TPS default value, deliverability increases but plan quality decreases. Total MU decreases with the increase of smoothing parameters. Therefore, it's a trade-off between plan quality and deliverability which needs to be justified clinically.

PURPOSE:To dosimetrically compare the whole-IMRT, hybrid-IMRT (combination of IMRT and 3D-CRT) and 3D-conformal radiotherapy (3D- CRT) plans for larger targets.METHODS:Five previously treated patients of carcinoma cervix with para-aortic lymph-nodes (target length 33-34cm) were selected. PTV-P (PTV-Primary), PTV-PA (PTV-para-aortic) and organ at risks (OARs) were defined. Three plans were generated using Eclipse TPS for Varian CL2300C/D linear accelerator using 6MV photon beam. Three plans were: (i) Whole-IMRT: IMRT for both PTV-P and PTV-PA (ii) Hybrid-IMRT: IMRT for PTV-P and 3D-CRT for PTV-PA (iii) 3D-CRT: 3D-CRT for both PTV-P and PTV-PA. Prescription dose for PTV-P is 50.4Gy and PTV-PA is 45Gy in 28 fractions. Coverage index (CI=Target volume covered by prescription dose/Target volume), mean doses to bladder, rectum and bowel were used for plan comparison by using DVH. Integral dose (liter-Gray) to normal tissue (i.e., patient volume minus PTV-P and PTV-PA) and total monitor units (MUs) required to deliver a plan was also noted.RESULTS:The CI for PTV-P is 0.98±0.20, 0.96±0.09, and 0.95±0.01 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan and for PTV- PA is 0.98±0.01, 0.98±0.01, and 0.97±0.20. Maximum doses to PTV-P are 5660.85±90.85cGy, 5640.35±70.35cGy and 5813.80±97.40cGy. Maximum doses to PTV-PA are 5000.60±109.10cGy, 5079.85±20.25cGy and 5092.25±19.75cGy. Mean doses to the bladder are 3810±225.80cGy, 3842.10±182.70cGy and 5204±98.25cGy for Whole-IMRT, Hybrid-IMRT and 3D-CRT plan, respectively. Mean doses to rectum are 3955.35±324.95cGy, 3971.15±354.15cGy and 4741.20±371.60cGy. Mean doses to bowel are 2623.35±320.85cGy, 2855.30±371.05cGy and 3011.7±433.80cGy. Average MUs required to deliver one fraction is 1285±87, 1585±186, 485±46 for Whole-IMRT, Hybrid-IMRT and 3D-CRT plans, respectively. Higher integral doses to normal tissue were observed for whole-IMRT (267.60±76 liter-Gy) followed by hybrid-IMRT (259.20±53 liter-Gy) and 3D-CRT (186.30±33 liter-Gy).CONCLUSIONS:Whole-IMRT is useful for larger targets compared to hybrid-IMRT in terms of dose conformity, lesser MUs and reduced critical organ doses with little compromise on integral dose, where 3D-CRT sacrificed the OAR sparing.