Dosimetric analysis of intensity-modulated radiation therapy and volumetric-modulated arc therapy in comparison with conventional box technique in the treatment of carcinoma cervix: An impact of prosthetic implant.

Introduction: The number of patients for carcinoma cervix with implanted hip prostheses has been increasing worldwide during the past several decades. Technological advancements are useful for delivering higher doses, i.e., dose escalation to the target, but the presence of high-density implanted hip prosthesis creates challenges for the planner.
Materials and Methods: A population of 25 patients was selected for the study. Plans were generated using the MONACO treatment planning system keeping the isocenter same. The parameters evaluated for planning target volume (PTV) were D _98% , D _50% , D _2% , D _max , D _mean , V _107%, and V _110% . Similarly, the parameters D _max , D _mean , and D _2cc were evaluated for the delineated critical organs. Average monitor units (TMU _mean ) were also assessed.
Results: D _98% of PTV was 44.51 (standard deviation [SD]: 0.13) Gy, 44.41 (SD: 0.38) Gy, 44.58 (SD: 0.14) Gy, 44.08 (SD: 0.41) Gy and 44.46 (SD: 0.32) Gy for 4F, intensity-modulated radiation therapy (IMRT), IMRT_WP, volumetric-modulated arc therapy (VMAT), and VMAT_WP techniques, respectively, where WP stands for "without prosthesis". Volume of bowel receiving 45 Gy was 86.82 (SD: 66.38) cm ³ , 6.97 (SD: 5.77) cm ³ , 14.11 (SD: 14.29) cm ³ , 13.31 (SD: 6.57) cm ³ , and 10.31 (SD: 10.94) cm ³ for 4F, IMRT, IMRT_WP, VMAT and VMAT_WP techniques, respectively.
Discussion: Radiotherapy is standard care of practice for known cases of cervical malignancies. As per our investigations, VMAT has generated comparable plans in terms of target coverage (D _98% ) as compared to IMRT and 4F techniques (P = 0.015 and P = 0.002) and with prosthesis also (P = 0.024). The mean dose to the bladder was significantly lesser with IMRT and VMAT. Our results highlight that VMAT has reduced the mean dose to the rectum (P = 0.001) in presence of high-density implant. The mean dose to femoral heads was also reduced when compared with the 4-field technique.
Conclusion: VMAT has an edge over other techniques in terms of target coverage and sparing of critical organs in the presence of metallic prosthesis. Information about the geometry and density of prosthesis will be beneficial for treatment planning.
Competing Interests: None