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Comparison Between Small Field Point Dose Measurement and Planar Dose Profile Measurement for Stereo Tactic Radio Therapy and Stereo Tactic Radio Surgery Patients

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U Giri

U Giri*, T Ganesh , K Jassal , K Vittal , S Singh , B Sarkar , Fortis Memorial Research Institute, Gurgaon, Haryana


SU-I-GPD-T-532 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study was performed to assess the relationship between point dose variation and planner dose profile measurement for the stereotype patients

Methods: For the comparison between planar and point dose measurement, 13 stereo tactic radiotherapy and radiosurgery patients, previously treated in our institute were selected for this study. The planar dose was measured with 729 phantom, all detectors in single mid plane and each detector made up of vented to air ionisation chamber with an edge to edge distance of 5 mm each. The acquired mid plane planar dose profile (2-D) on the phantom was compared with the reference 2-D dose profile calculated on computed tomography (CT) data set of the the phantom using Monaco treatment planning system. For the dose profile matching criteria, 2-D gamma indexes were calculated by choosing stringent passing criteria of 2 % dose difference (DD) and 2 mm distance to agreement. For the point dose measurement, 10 cm slab of solid water phantom, having an insertion for the holder o pin point ionisation chamber (0.01 cc) was used

Results: A Pearson correlation coefficient was computed to assess the relationship between Point dose variation and measured planner dose [r = -.309, n=13, p=.305] shown in table-1

Conclusion: Our study concluded that more deviation in point dose corresponds to less passing percentage of 2-D planner dose profile, indicating negative correlation between these two variables

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