Effect on therapeutic ratio of planning a boosted radiotherapy dose to the dominant intraprostatic tumour lesion within the prostate based on multifunctional MR parameters

• Published in: British journal of radiology Vol. 87; no. 1037; p. 20130813
• Main Authors: Riches, S F, Payne, G S, Desouza, N M, Dearnaley, D, Morgan, V A, Morgan, S C, Partridge, M
• Format: Journal Article
• Language: English
• Published: England The British Institute of Radiology 01-05-2014
• Subjects: Aged; Aged, 80 and over; Androgen Antagonists - therapeutic use; Contrast Media; Feasibility Studies; Fiducial Markers; Humans; Imaging, Three-Dimensional - methods; Magnetic Resonance Spectroscopy - methods; Male; Middle Aged; Prostatic Neoplasms - radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Intensity-Modulated - methods; Rectum - radiation effects; Tomography, X-Ray Computed - methods; Urinary Bladder - radiation effects
• ISSN: 0007-1285; 1748-880X
• DOI: 10.1259/bjr.20130813

To demonstrate the feasibility of an 8-Gy focal radiation boost to a dominant intraprostatic lesion (DIL), identified using multiparametric MRI (mpMRI), and to assess the potential outcome compared with a uniform 74-Gy prostate dose.
The DIL location was predicted in 23 patients using a histopathologically verified model combining diffusion-weighted imaging, dynamic contrast-enhanced imaging, T2 maps and three-dimensional MR spectroscopic imaging. The DIL defined prior to neoadjuvant hormone downregulation was firstly registered to MRI-acquired post-hormone therapy and subsequently to CT radiotherapy scans. Intensity-modulated radiotherapy (IMRT) treatment was planned for an 8-Gy focal boost with 74-Gy dose to the remaining prostate. Areas under the dose-volume histograms (DVHs) for prostate, bladder and rectum, the tumour control probability (TCP) and normal tissue complication probabilities (NTCPs) were compared with those of the uniform 74-Gy IMRT plan.
Deliverable IMRT plans were feasible for all patients with identifiable DILs (20/23). Areas under the DVHs were increased for the prostate (75.1 ± 0.6 vs 72.7 ± 0.3 Gy; p < 0.001) and decreased for the rectum (38.2 ± 2.5 vs 43.5 ± 2.5 Gy; p < 0.001) and the bladder (29.1 ± 9.0 vs 36.9 ± 9.3 Gy; p < 0.001) for the boosted plan. The prostate TCP was increased (80.1 ± 1.3 vs 75.3 ± 0.9 Gy; p < 0.001) and rectal NTCP lowered (3.84 ± 3.65 vs 9.70 ± 5.68 Gy; p = 0.04) in the boosted plan. The bladder NTCP was negligible for both plans.
Delivery of a focal boost to an mpMRI-defined DIL is feasible, and significant increases in TCP and therapeutic ratio were found.
The delivery of a focal boost to an mpMRI-defined DIL demonstrates statistically significant increases in TCP and therapeutic ratio.