Dose accumulation for personalized stereotactic MR-guided adaptive radiation therapy in prostate cancer.

BACKGROUND AND PURPOSE

Adaptive MR-guided radiotherapy (MRgRT) is an innovative approach for delivering stereotactic body radiotherapy (SBRT) in prostate cancer (PC). Despite the increased clinical use of SBRT for PC, there is limited data on the relation between the actual delivered dose and toxicity. We aimed to identify dose parameters based on the total accumulated delivered bladder dose (DOSE). Furthermore, for future personalization, we studied whether prospective accumulation of the first 3 of 5 fractions (DOSE) could be used as a representative of DOSE.

MATERIALS AND METHODS

We deployed a recently validated deformable image registration-based dose accumulation strategy to reconstruct DOSE and DOSE in 101 PC patients treated with stereotactic MRgRT. IPSS scores at baseline, end of MRgRT, at 6 and 12 weeks after treatment were analyzed to identify a clinically relevant increase of acute urinary symptoms. A receiver operator characteristic curve analysis was used to investigate the correlation of an increase in IPSS and bladder DOSE (range V-V D, D) and DOSE (range V-V D D) parameters.

RESULTS

A clinically relevant increase in IPSS in the three months following MRgRT was observed in 25 patients. The V from DOSE and V from DOSE showed good correlation with IPSS increase with area under the curve (AUC) values ranging from 0.71 to 0.75. In contrast, baseline dosimetry showed a poor correlation with AUC values between 0.53 and 0.62.

CONCLUSION

DOSE was superior to baseline dosimetry in predicting acute urinary symptoms. Because DOSE also showed good correlation, this can potentially be used to optimize MRgRT for the remaining fractions.