Dosimetric comparison of target volume and critical organs by conventional and 3d treatment planning methods in high dose rate (HDR) brachytherapy of cervical cancer

Several treatment planning techniques are used in brachytherapy of locally advanced cervical cancer. In this study we aimed to compare 2-dimensional conventional(CONV), 3-dimensional conformal(CONF) and 3-dimensional volumetric optimized(VOL) treatment plans of patients treated with tandem-ovoid applicators. Plans are compared in terms of target and critical organ doses. In 25 locally advanced cervical cancer patients doses were prescribed to the A point for CONV plans according to ICRU-38 report. D90HR-CTV doses were calculated therafter. The D90HR-CTV doses for target volume and D2cc doses for rectal and bladder was calculated according to GEC-ESTRO recommendations. We calculated HR-CTV doses for CONV plans and relation between the target volume and HR-CTV dose was investigated. When the prescribed dose was set to be 7Gy, we found that D90HR-CTV dose ranged between 623,6 – 1389,7cGy. Exclusively, for tumors less than 21cc during brachytherapy, unncessary high doses were given to the HR-CTV. We have also evaluated rectal and bladder doses as well as analysed relation between target doses and critical organ volumes for CONF and VOL plans. We could not find any relation between 3-dimensional treatment technique and critical organ volumes in terms of rectal and bladder doses for CONF and VOL treatment plans. We could not find any relation between bladder doses and bladder volume in terms of type of 3-dimensional plans(p=0.68). When we evaluated the relation between rectal doses and rectal volume, we observed a staistically signicicant difference for patients with rectal volume more than 60cc(p=0.007). We found CONF technique more succesful compared to VOL plans in terms of rectal protection. As a conclusion, the main reason for unnecessarily high doses for HR-CTV in patients treated with CONV plans is the location of A point much far away from the tumor. It is much more healtier and safer to prescribe the dose according to the tumor volume instead of A point in terms of target and crtical organ doses. Exclusively, for tumors less than 21cc, during brachytherapy, there is a high risk of unncessary dose exposure to the crticial structers like bladder and rectum which may cause late complications.