Delivered dose to scrotum in rectal cancer radiotherapy by thermoluminescence dosimetry comparing to dose calculated by planning software

Background: Colorectal carcinoma is a common malignancy, in treatment of which pelvic radiotherapy plays an important role. But this may lead to azospermia. We designed a study to determine the delivered dose to the testis with thermoluminescence dosimetry (TLD) and compare it to the dose calculated by the Three-dimensional planning software. Methods: We measured the testicular doses by TLD; the TLDs were fixed to the scrotum in six points anteriorly and posteriorly in two random fractions of the radiation course. All patients received a 50-50.4 Gy radiation dose to the pelvis in a prone position with standard fractionation and 3-dimensional planning, through three or four fields. The average dose of the TLD measurements was compared to the average of 6 relevant point doses calculated by the planning software. Results: In 33 patients with a mean age of 56 years, the mean testis dose of radiation measured by TLD was 3.77 Gy, equal to 7.5% of the total prescribed dose. The mean of point doses calculated by the 3-dimensional planning software was 4.11 Gy, equal to 8.1% of the total prescribed dose. A significant relationship was seen between the position of the inferior edge of the fields and the mean testis dose (P= 0.04). Also body mass index (BMI) was inversely related with the testicular dose (P= 0.049). Conclusion: In this study, the mean testis dose of radiation was 3.77 Gy, similar to the dose calculated by the planning software (4.11 Gy). This dose could be significantly harmful for spermatogenesis, though low doses of scattered radiation to the testis in fractionated radiotherapy might be followed with better recovery. Based on above findings, careful attention to testicular dose in radiotherapy of rectal cancer for the males desiring continued fertility seems to be required