A dosimetric comparison of RapidArc and IMRT with hypofractionated simultaneous integrated boost to the prostate for treatment of prostate cancer

Objective: To compare the dosimetric results and treatment delivery efficiency among RapidArc (R) (Varian Medical Systems, Palo Alto, CA), 7-field intensity-modulated radiotherapy (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate. Methods: RapidArc, 7-f IMRT and 9-f IMRT plans were created for 21 consecutive patients treated for high-risk prostate cancer using the Eclipse (TM) treatment planning system (Varian Medical Systems). All plans were designed to deliver 70.0Gy in 28 fractions to the prostate planning target volume (PTV) while simultaneously delivering 50.4Gy in 28 fractions to the pelvic nodal PTV. Target coverage and sparing of organs at risk (OARs) were compared across techniques. The total number of monitor units (MUs) and the treatment time were used to assess treatment delivery efficiency. Results: RapidArc resulted in slightly superior conformity and homogeneity of prostate PTV, whereas all plans were comparable with respect to dose to the nodal PTV. Although OARs sparing for RapidArc and 7-f IMRT plans were almost equivalent, 9-f IMRT achieved better sparing of the rectum and bladder than RapidArc and 7-f IMRT. RapidArc provided the highest treatment delivery efficiency with the lowest MUs and shortest treatment time. Conclusion: RapidArc resulted in similar OAR sparing to 7-f IMRT, whereas 9-f IMRT provided the best OAR sparing. Treatment delivery efficiency is significantly higher for RapidArc. Advances in knowledge: This study validated the feasibility and limitations of RapidArc in the treatment of high-risk prostate cancer with complex pelvic target volumes.