PHASE i TRIAL OF MRI-GUIDED Prostate Cancer Lattice Extreme Ablative Dose (LEAD) BOOST Radiotherapy.

A phase I clinical trial was designed to test the feasibility and toxicity of administering high-dose spatially-fractionated radiotherapy to MRI-defined prostate tumor volumes, in addition to standard treatment.

We enrolled 25 men with favorable to high-risk prostate cancer and 1-3 suspicious multiparametric MRI (mpMRI) gross tumor volumes (GTVs). The mpMRI-GTVs were treated on day 1 with 12-14 Gy via dose cylinders using a Lattice Extreme Ablative Dose (LEAD) technique. The entire prostate, along with the proximal seminal vesicles (SVs), was then treated to 76 Gy at 2 Gy/fraction. For some high-risk patients, the distal SVs and pelvic lymph nodes received 56 Gy at 1.47 Gy/fraction concurrently in 38 fractions. The total dose to the LEAD dose cylinder volume(s) was 88-90 Gy (112-123 Gy in 2.0 Gy equivalents, assuming an α/β ratio of 3).

Dosimetric parameters were satisfactorily met. Median follow-up is 66 months. There were no grade 3 acute/subacute genitourinary (GU) or gastrointestinal (GI) adverse events. Maximum late GU toxicity was Grade 1 in 15 (60%), Grade 2 in 4 (16%), and Grade 4 in 1 (4%; sepsis after a post-treatment transurethral resection). Maximum late GI toxicity was Grade 1 in 11 (44%) and Grade 2 in 4 (16%). Two patients experienced biochemical failure.

External beam radiotherapy delivered with an upfront spatially-fractionated, stereotactic high dose mpMRI-GTV boost is feasible and was not associated with any unexpected events. The technique is now part of a follow-up Phase II randomized trial.

International journal of radiation oncology, biology, physics. 2020 Feb 18 [Epub ahead of print]

Alan Pollack, Felix M Chinea, Elizabeth Bossart, Deukwoo Kwon, Matthew Abramowitz, Charles Lynne, Merce Jorda, Brian Marples, Vivek N Patel, Xiaodong Wu, Isildinha Reis, Matthew T Studenski, Javier Casillas, Radka Stoyanova

Department of Radiation Oncology, University of Miami Miller School of Medicine, Sylvester Comprehensive Cancer Center, Miami, FL, USA. Electronic address: ., Department of Radiation Oncology, University of Miami Miller School of Medicine, Sylvester Comprehensive Cancer Center, Miami, FL, USA., Department of Public Health Sciences and Biostatistics and Bioinformatics Shared Resource, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL, USA., Department of Urology, University of Miami Miller School of Medicine, Miami, FL, USA., Department of Pathology, University of Miami Miller School of Medicine, Miami, FL, USA., Biophysics Research Institute of America, Miami, FL, USA., Department of Radiology, University of Miami, Miller School of Medicine, Miami, FL, USA.