Why is Volumetric Modulated Arc Therapy Better Than Three Dimensional Conformal Radiotherapy in Prostate Cancer? Dosimetric Analysis from a Tertiary Care Hospital in Saudi Arabia | ||
| SECI Oncology Journal | ||
| Volume 12, Issue 1, January 2024, Pages 106-111 | ||
| Abstract | ||
| Background: Prostate cancer is one of the most common cancers among older men. It is ranked as the third most common cancer among Saudi men. (As per the last Saudi cancer registry,2016) Current protocols for prostate cancer external beam radiation therapy (EBRT) commonly use two main techniques for treatment planning, including three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) including volumetric modulated arc therapy (VMAT). Objectives: The goal of this study is to compare target volumes and organ at risk (OAR) for VMAT versus 3D-CRT plans. Materials and methods: Forty patients with localized prostate cancer, diagnosed and treated at King Fahad Medical City (KFMC), Riyadh, Saudi Arabia were selected retrospectively for this planning study. Patients were treated with radical definitive external beam radiation therapy (EBRT) using the VMAT technique with a prescribed dose of 78Gy in 39 daily fractions over about 8 weeks. Elective pelvic nodal irradiation was not performed. All patients were re-planned with six fields of 3D-CRT for study purposes. Treatments were delivered using the Trilogy VARIAN Linear Accelerator. Treatment plans were done by Eclipse Varian treatment planning system (TPS) version 10, dose calculations were performed using Analytical Anisotropic Algorithm (AAA) for both VMAT and 3D-CRT techniques. Plans were evaluated using the conformity index (CI) and homogeneity index (HI) for target volumes. Mean, maximum, and OAR dose volumes were compared between both techniques based on QUANTEC normal tissue tolerance doses. Data was analyzed using SPSS-23. Results: Planning Target Volume (PTV) received a significantly higher maximum dose in VMAT than 3D-CRT plans (p=0.000). The HI for PTV was better in 3D-CRT compared to VMAT plans (p = 0.010). However, CI was significantly better in VMAT vs. 3D-CRT plans (p = 0.002). As expected, 3D- CRT plans required a smaller number of monitor units (MU) than VMAT plans to deliver the same prescribed dose (p = 0.000). VMAT technique resulted in the delivery of lower OAR mean doses to the rectum, penile bulb, bone marrow, and femoral heads compared to the 3D-CRT technique (p < 0.05); however, there was no significant difference between the two techniques for small bowel (p=0.234) and bladder (p=0.509). On the other hand, the mean dose was lower in 3D than the VMAT plan for testis (p = 0.000). VMAT delivered significantly higher maximum doses than 3D-CRT to the bladder and rectum while 3D-CRT delivered higher maximum doses to the femoral heads and small bowel. VMAT plans resulted in the delivery of significantly lower OAR dose volumes for all dosimetric endpoints, except for small bowel (V45) and bone marrow (V5), for which there was no significant difference. Conclusion: VMAT generated more favorable treatment plans compared to 3D- CRT, however, 3-D CRT can also achieve QUANTEC goals with required PTV coverage. VMAT requires more MU than 3 D-CRT, raising the issue of possible second malignancies that need to be clarified by further clinical trials. | ||
| Keywords | ||
| prostate cancer; radiation therapy; VMAT; 3D-CRT | ||
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