Comparison of the effects of filtered and unfiltered X-RAY beams and ptv size on the treatment plan in volumetric modulated ARC therapy of prostate cancers

This study has two aims. First is to investigate the feasibility of using a flattening filter free (FFF) beams for VMAT of prostate cancer. Second is to investigate the effect of the PTV size on plan quality with the FFF-VMAT plans. This study contains total of 20 prostate cancer patients which divided into two groups of ten named as Group A and Group B. Group A patients have tumors with seminal vesicle and lymph node invasion. Group B patients tumors are constrained with the prostate gland. Two seperate plans, with and without flattening filter, were created for each patient. All plans were normalised for 95% of the PTV to receive 95% of the periscibed dose. For a healty observation same optimization values are used for both plans. When optimizing, it was noted that no plan did exceed 110% of the desired dose to be given the maximum dose. To compare plans, PTV and critical organ doses (which recorded by using DVH), CI and HI values calculated for each PTV and total MU values for each TP were examined. There was no significant difference (p>0,05) in the dose distribution of target volumes in the prepared TPs. In VMAT-FFF (Group B) plans, the D17 of the rectum was 0.4% and the Dmean'i was 0.5% lower, while the right femoral head's Dmean was 2.3% higher. Apart from these, no statistically significant difference were found in dose distributions of critical organs. The most noticeable difference has been in MU values. In VMAT-FFF plans, MU values were 20.3% higher for Group A and 11% for Group B.