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. 2018 Apr 12;13(1):64.
doi: 10.1186/s13014-018-0978-1.

Image-guided radiotherapy reduces the risk of under-dosing high-risk prostate cancer extra-capsular disease and improves biochemical control

Per Munck Af Rosenschold  1   2 , Michael J Zelefsky  3 , Aditya P Apte  1 , Andrew Jackson  1 , Jung Hun Oh  1 , Elliot Shulman  4 , Neil Desai  4   5 , Margie Hunt  1 , Pirus Ghadjar  4 , Ellen Yorke  1 , Joseph O Deasy  1
Affiliations

Image-guided radiotherapy reduces the risk of under-dosing high-risk prostate cancer extra-capsular disease and improves biochemical control

Per Munck Af Rosenschold et al. Radiat Oncol. .

Abstract

Background: To determine if reduced dose delivery uncertainty is associated with daily image-guidance (IG) and Prostate Specific Antigen Relapse Free Survival (PRFS) in intensity-modulated radiotherapy (IMRT) of high-risk prostate cancer (PCa).

Methods: Planning data for consecutive PCa patients treated with IMRT (n = 67) and IG-IMRT (n = 35) was retrieved. Using computer simulations of setup errors, we estimated the patient-specific uncertainty in accumulated treatment dose distributions for the prostate and for posterolateral aspects of the gland that are at highest risk for extra-capsular disease. Multivariate Cox regression for PRFS considering Gleason score, T-stage, pre-treatment PSA, number of elevated clinical risk factors (T2c+, GS7+ and PSA10+), nomogram-predicted risk of extra-capsular disease (ECD), and dose metrics was performed.

Results: For IMRT vs. IG-IMRT, plan dosimetry values were similar, but simulations revealed uncertainty in delivered dose external to the prostate was significantly different, due to positioning uncertainties. A patient-specific interaction term of the risk of ECD and risk of low dose to the ECD (p = 0.005), and the number of elevated clinical risk factors (p = 0.008), correlate with reduced PRFS.

Conclusions: Improvements in PSA outcomes for high-risk PCa using IG-IMRT vs. IMRT without IG may be due to improved dosimetry for ECD.

Keywords: High risk disease; IMRT; Image-guided; Prostate cancer; Radiotherapy; Tumor control probability.

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Conflict of interest statement

Ethics approval and consent to participate

Data collection was approved by the local IRB.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1
Fig. 1
Transversal cross section (left) and sagittal plan (right) through the PTV of an example patient treated on the IMRT protocol with the bootstrap variance of the dose within the CTV shown in color-wash. It is apparent that the variance was larger within the CTV close to the rectum, which stems from a steep dose-gradient in that region as well as the magnitude of the positioning uncertainty in this direction
Fig. 2
Fig. 2
PSA relapse-free survival for high-risk prostate cancer patients for the whole cohort (left) and the IMRT cohort only (right). The respective Cox models were used to select the patients with favorable and unfavorable outcome, respectively
Fig. 3
Fig. 3
Dose fall-off in the posterolateral direction, averaged over all patients for all treatment plans. This is also averaged between the left and right regions for each patient. The 0 cm distance point is the average of the whole CTV. The probability of the existence of extra-capsular disease for the whole cohort of high-risk patients is plotted onto the secondary axis
See this image and copyright information in PMC

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