Dosimetric Impact and Theoretical Clinical Benefits of Fiducial Markers for Dose Escalated Prostate Cancer Radiation Treatment

Purpose

To assess the impact of fiducial markers and daily kilovoltage imaging (FM-kV) on dose–volume histogram (DVH) parameters and normal tissue complication probabilities (NTCPs) for the rectum and bladder during prostate cancer radiotherapy.

Methods and Materials

Two different setup scenarios were compared for 20 patients treated with three-dimensional conformal radiotherapy (3D-CRT) for localized prostate cancer to a total dose of 76 Gy: a traditional setup with planning target volume (PTV) margins associated with skin mark alignment vs. another setup using FM-kV. Various DVH parameters were compared, including Radiation Therapy Oncology Group (RTOG) dose–volume constraints for the rectum and bladder. Analysis of NTCPs was also performed according to the Lyman model.

Results

With the traditional setup, 85% of patients had rectal V70_Gy >25% compared with 45% with FM-kV. Moreover, 30% of patients with traditional setup vs. 5% with FM-kV did not fulfill at least 3 RTOG constraint parameters for the rectum. Mean rectal and bladder dose were 4.7 Gy and 6.7 Gy less, respectively, with FM-kV. The NTCP for the rectum was 11.5% with the traditional setup and 9% with FM-kV. This indicates that with FM-kV, the prescription dose could be increased by 2.1 Gy while keeping the same level of late rectal toxicity as with the traditional setup.

Conclusions

Use of FM-kV is an efficient way of lowering the proportion of patients not fulfilling RTOG rectal and bladder dose–volume constraints. The results of the NTCP analysis suggest that the PTV margin reduction allowed by FM-kV should decrease the rate of late rectal toxicities or may allow moderate dose escalation.

Image-guided radiotherapy, Fiducial markers, Prostate cancer, Dose–volume histograms, Normal tissue complication probability