Investigating VMAT planning technique to reduce rectal and bladder dose in prostate cancer treatment plans

Background: RapidArc is a volumetric modulated arc therapy (VMAT) technique that can deliver conformal dose distribution to the target while minimizing dose to critical structures. The main purpose of this study was to compare dosimetric quality of full double arc (full DA), full single arc (full SA), and partial double arc (partial DA) techniques in RapidArc planning of prostate cancer. Materials and Methods: Twelve cases of prostate cancer involving seminal vesicles were selected for this retrospective study. For each case, RapidArc plans were created using full DA (two full arcs), full SA (one full arc), and partial DA (two partial arcs with anterior and posterior avoidance sectors) techniques. For planning target volume (PTV), the maximum and mean doses, conformity, and inhomogeneity indices were evaluated. For bladder and rectum, volumes that received 70, 50, 40, and 20 Gy (V 70Gy , V 50Gy , V 40Gy and V 20Gy , respectively), and mean dose were compared. For femoral heads, V 40Gy , V 20Gy , and mean dose were evaluated. Additionally, an integral dose and monitor units (MUs) were compared for each treatment plan. Results: In comparison to full DA and full SA techniques, the partial DA technique was better in sparing of rectum and bladder but delivered higher femoral head dose, which was nonetheless within the planning criteria. No clear dosimetric differences were found between full DA and partial DA plans for dose conformity and target homogeneity. The number of MUs and integral dose were largest with the partial DA technique and lowest with the full SA technique. Conclusion: The partial DA technique provides an alternative RapidArc planning approach for low risk prostate cancer.