Background: High dose rate remote after loading brachytherapy machines have seen tremendous advancement both technologically and their clinical applications during the last 25 years. With the introduction of computerized remote after loading machines and computerized planning system, stepping source dosimetry system (SSDS) has become the system of choice making almost all traditional dosimetry systems obsolete. In this study we evaluated the impact of source step size on dosimetry of interstitial implant using parameters of ICRU-58 and various quality indices (QI).Material & Methods: For this study, 10 implant cases which have 3-D CT image based planning were selected. Contouring of clinical target volume and various organs were done following standard guidelines for the same. Plans were optimized to achieve the desired clinical outcome using different source step sizes of 2.5, 5 and 10 mm respectively. Cumulative DVH’s were calculated for the estimation of various ICRU-58 parameters and quality indices.Results and Conclusion: The mean values of the target volumes, minimum target doses, treated volumes, low dose volumes; high dose volumes, overdose volumes, reference volumes, coverage, external volume, relative dose homogeneity, overdose volume and COIN indices have been presented for the source step sizes of 2.5 mm, 5 mm and 10 mm respectively. Among source step sizes used in this study, most favorable clinically acceptable dose distributions & dose homogeneity occurs around step size of 5 mm as predicted by the various parameters of ICRU-58 and dose quality indices. Keywords: Brachytherapy, interstitial implant, source step-size, remote after loading, optimization, quality indices.

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patients in concurrent group developed grade 2 or 3 pneumonitis at some point during crizotinib therapy. Time to onset of pneumonitis ranged from 14 days to 61 days in concurrent group. Imaging analysis was strongly consistent with lung parenchyma changes in the irradiated lung volume receiving a total dose of 15-38 Gy. Pulmonary toxicity was manageable; however, interruption of crizotinib therapy was not necessary. Three (37.5%) experienced development of a grade 2 pneumonitis in sequential group. Pneumonitis in irradiated lungs did not aggravate after crizotinib therapy in sequential group. Conclusion: In conclusion, this is, to our knowledge, the first report of lung toxicity after treatment with crizotinib and TRT. We observed a high incidence of pulmonary toxicity when crizotinib and concurrent TRT were administered in patients with ALK-positive NSCLC. Careful consideration and monitoring for pneumonitis may be warranted in patients treated with crizotinib in concurrent with TRT. In addition, using other schedules (e.g., sequential as opposed to concurrent administration) may be safe and optimal strategies.

the plans for all 5 patients bilaterally. Coverage was acceptable with an average of 45 Gy covering the 90% IDL. Conclusion: This study demonstrates the feasibility of delivering ablative doses of SABR to the medial branch nerves of the lumbar spine below the level of the cord. OARs received acceptable doses, with lower values obtained from the plans with targeted radiation to the nerves when compared with plans involving radiation to the entire facet. PTV coverage was not compromised. Though efficacy would require in vivo testing, with accurate targeting and the assistance of IR in selecting appropriate patients, SABR may provide a noninvasive, reasonable, and effective treatment option for facetogenic low back pain.

and intrafraction imaging. Maximum tolerated misalignment prior to treatment initiation was sub-mm & sub-degree. Following initial setup , 6 intrafraction CBCT's were acquired (1) Pretreatment localization scan (2) post-residual errors correction pretreatment check scan (verification) (3) four Intrafraction scans, each scan after delivery of every 4000 mu. For intrafraction motion analysis, CBCT data scans of same patients with more than 0.5 0 & 0.5mm mm vector shifts was considered. Free form Intensity based deformation algorithm was used to deform structures, dose & plan with intrafraction CBCT scan which revealed > 0.5 0 , o.5mm vector shifts. Intermodality and intramodality deformation errors were quality assured using registration refine tools prior to data collection. Clinical relevance was measured as the Target percent underdosaged & max dose increase to OAR. In brainstem the volume doses D 1% , D 2% were taken for analyzing the higher doses in the brain stem. In addition, max temporal doses and mean cochlear doses analyzed. The p-values were calculated using two tailed Student's Ttest and tabulated in appropriate tables. Statistical comparison was done using SPSS software using paired t test. Results: Mean rotational errors observed between planning CT and CBCT were in Pitch (meane0.4 , SD AE 0.372) , Yaw (meane0.370, SD AE 0.22) and roll (meane0.380, SD AE 0.383) respectively. The mean 3D intrafraction shift was 0.26 mm (SD,0.26 mm) and The max brainstem voxel dose D 1% variation was 3% over planned (range:2-5%).The temporal lobe and cochlear doses were unaffected. A loss of prescribed isodose coverage of 3% (SD, 0.08) was found without 6DOF re-positioning. Conclusion: Using CBCT DIR for intrafraction motion analysis, 0.5 mm vector translation error and 0.5 degree rotation error about each axis should be used as the maximum tolerated misalignment before initiation of frameless functional SRS treatment. We observed that patient compliance is important as few patients fall asleep and move involuntarily during the procedure.