TO ASSESS THE DOSIMETRIC IMPACT ON PROSTATE, BLADDER AND RECTUM IN CARCINOMA PROSTATE DUE TO INTERFRACTIONALANATOMICAL VARIATION IN IMAGE GUIDED RADIATION THERAPY.

ABTRACT- Prostate cancer is second most frequent cancer in men and fifth leading cause of death worldwide. Most radiotherapy patients with prostate cancer are treated with intensity modulated radiotherapy. IMRT requires high spatial accuracy in localizing the target volume and high precision in treatment delivery, because even a small geographic miss can have a large dosimetric effect. However, the patient setup position and anatomy changes daily, particularly in the prostate region, due to rectum and bladder filling. Materials Methods: We analyzed 30 patients with prostate cancer patient treated with IMRT kV CBCT was performed for each patient twice per week during the entire course of treatment. The bladder, rectum, prostate and PTV were contoured on each CBCT scan. Results: Delivered dose of prostate D95% and prostate D100% was 99.15% and 93.66% respectively and mean value of V70 for bladder was 16% and delivered value was 16.45%. Whereas the mean value of V70 of plan for rectum was 18.12% and delivered value was 27.58%. Conclusion: Interfractional variation during prostate radiotherapy can results in substantial difference between planned and delivered doses, particularly in critical structure. IG-IMRT is useful tool in assessing dosimetric changes in critical structure due to interfractional anatomical interfractional anatomical variation in prostate radiotherapy.