Razi Journal of Medical Sciences

    Background & Aim: Genitalia system cancers are the third most common cancers. In females, surgery and/or radiotherapy±chemotherapy are treatments of choice for cervical, endometrial or vaginal cancers. Brachytherapy is a complementary part of External Beam Radiotherapy(EBRT). MDR(Medium Dose Rate) brachytherapy in female genitalia cancers is founded on two bases: high and appropriate dose distribution in tumor area as well as dose reduction beyond tumor area especially in sensitive organs such as rectum and bladder. Use of treatment-planning system is a contemporary part of treatment in brachytherapy. This presentation introduces a quality control way for dose distribution in normal adjustment tissues (rectum/bladder) by TLD(Thermoilluminecent Dosimeter) in-vivo dosimetry. Patients & Method: In the present study, 33 patients with cervical and endometrial cancers staged 1-3 were evaluated for rectal dose specifications as per ICRU-38(International Committee of Radiological Protection and Unit) recommendations. Each TLD was placed in one sheet and each sheet was separated 1 centimeter from the other and fixed on rectal applicator and named as R3,R1,R2,R4. Then, the applicator was totally inserted in the rectum of the patients who were candidates for brachytherapy and fixed. The TLDs were read out at the end of the treatment course by using calibration and correction factor. Rectal doses from R1 to R4 (in-vivo doses) were evaluated by TLD reading and compared with treatment–planning doses calculated at the same points. This descriptive study involved statistical methods including regression, t-test, X2,and paired t-test. Results: Mean TLD reading was 579.8 cGy(SD=213.7) and mean planning dose was 654cGy(SD=245), suggesting that the difference between these two was meaningful and planning dose on average was 75.4cGy more than the dose of TLDs(P-value<0.001,CI=50.5-100.2). Conclusion: According to the obtained results within the studied range of 300-1200cGy, the real dose received by rectal area can be calculated by the following formula: Y=0.7X + 118.5 (R2=66%)(X=planning dose). Parameters such as mean rectal points distances (LR=Length from Reference point), age, dose rate, total dose, anterior-posterior diameter of the patient, and stage had no effect on the model of correlation between TLD mean dose and planning dose. Only applicator type (cylinder) affected this model and had positive effect on formula confidence(P-value<0.002,R2=0.99).