Prostate stereotactic body radiotherapy with simultaneous integrated boost: which is the best planning method?

Abstract

BackgroundThe delivery of a simultaneous integrated boost to the intra-prostatic tumour nodule may improve local control. The ability to deliver such treatments with hypofractionated SBRT was attempted using RapidArc (Varian Medical systems, Palo Alto, CA) and Multiplan (Accuray inc, Sunnyvale, CA).Materials and methods15 patients with dominant prostate nodules had RapidArc and Multiplan plans created using a 5 mm isotropic margin, except 3 mm posteriorly, aiming to deliver 47.5 Gy in 5 fractions to the boost whilst treating the whole prostate to 36.25 Gy in 5 fractions. An additional RapidArc plan was created using an 8 mm isotropic margin, except 5 mm posteriorly, to account for lack of intrafraction tracking.ResultsBoth RapidArc and Multiplan can produce clinically acceptable boost plans to a dose of 47.5 Gy in 5 fractions. The mean rectal doses were lower for RapidArc plans (D50 13.2 Gy vs 15.5 Gy) but the number of missed constraints was the same for both planning methods (11/75). When the margin was increased to 8 mm/5 mm for the RapidArc plans to account for intrafraction motion, 37/75 constraints were missed.ConclusionsRapidArc and Multiplan can produce clinically acceptable simultaneous integrated boost plans, but the mean rectal D50 and D20 with RapidArc are lower. If the margins are increased to account for intrafraction motion, the RapidArc plans exceed at least one dose constraint in 13/15 cases. Delivering a simultaneous boost with hypofractionation appears feasible, but requires small margins needing intrafraction motion tracking.

Cyberknife, Helical Tomotherapy and Rapid Arc SIB-SBRT Treatment Plan Comparison for Carcinoma Prostate

“…Hegazy et al, (2016) found that all dose constraints regarding PTV coverage were similarly achieved by both plans generated by the RA and CK except for the maximal doses generated by the RA plans which were statistically significant lower than those of the CK plans. Tree et al, (2013) have shown that RA and CK can produce clinically acceptable plans. Macdougall et al, (2014) showed no distinct dosimetric advantage to choose CK over RA and also found that CK failed to achieve the desired PTV homogeneity constraint in two cases.…”

Dosimetric impacts of endorectal balloon in CyberKnife stereotactic body radiation therapy (SBRT) for early‐stage prostate cancer

“…The rectum dose reduction we have seen between patients planned with ERB and noERB is a meaningful finding in the context of extreme hypofractionated CyberKnife prostate SBRT of 36.25 Gy in five fractions. These results and the effective plan optimization technique may turn out to be even more important in view of the more recent interests in prostate focal therapy approach by generating a simultaneously integrated dose escalation to 47.5 Gy onto the dominant intra‐prostatic lesion while maintaining the 36.25 Gy to the prostate gland …”

The Delineation of Intraprostatic Boost Regions for Radiotherapy Using Multimodality Imaging

“…Most studies to date have used static field IMRT [14,[19][20][21][22][23]. Planning studies have also assessed VMAT [24][25][26] and SBRT techniques [27,28]. Also unclear is which groups of patients would benefit from an intraprostatic boost.…”

“…Adequate margins must be added to take into account co-registration and delineation errors plus motion during the treatment course (intra-and interfraction motion). Even taking into account the margin required to cover the IPL adequately, given the discrepancy seen with delineation as discussed earlier, the optimal intraprostatic margin for the boost is unclear and is dependent on the mode of delivery with some studies using a 0mm margin and relying on a relatively shallow dose fall off within the prostate CTV [19,23,24,28]. Treatment must be delivered accurately with the use of in-room IGRT, with fiducial markers as the current gold standard.…”