SU-E-T-594: Dosimetric Evaluation of Different Treatment Techniques for Prostate Cancer

To evaluate the Volumetric Modulated Arc Therapy (VMAT, RapidArc) and IMRT plan quality for prostate deliveries conducted by two different treatment planning systems: Oncentra Masterplan (Nucletron inc.) and Eclipse (Varian inc.).

We investigated ten prostate treatment delivery plans. For a given case studied we created a RapidArc plan (Eclipse), a VMAT and an IMRT plan (Oncentra) by using both treatment planning systems. The rotational therapy plans consisted of 2 to 3 arcs and the IMRT fields consisted of 7 to 9 fields. The prescription dose was 200 cGy X 40 fx using a Varian Trilogy with 10 MV beams. The treatment parameters were used to evaluate the plan quality: the minimal, mean and maximal doses to the target (PTV) and the volumes received 65Gy and 40 Gy, respectively, for the rectum and bladder, V65 and V40. In addition, we calculated the conformity index (CI) and the heterogeneity index (HI) for each delivery type.

No significant difference was found between RapidArc, VMAT and IMRT, regarding the minimal and average PTV dose value. The rectum and bladder constraints showed no significant variation as well. The PTV hot spot was significantly higher for the VMAT plan compared to the RapidArc plan (p=0.007). The target CI for VMAT (0.55±0.05) and IMRT (0.71±0.08) was found to be smaller than the RapidArc (0.82±0.04) and the difference is statistically significant (p=0). The HI, value was found to have no significant difference between RapidArc, VMAT and IMRT plan deliveries.

Two TPS are capable of producing high-quality treatment plans for prostate cancer. The quality is associated with the degree of intensity modulation and the number of incident angles. Overall, the RapidArc plans with 2-3 arcs showed better dosimetric qualities than the VMAT and IMRT plans.