In Reply to Kishan et al

Abstract

To the Editor: We thank Dr Kishan and colleagues for their interest in our FASTR trial, and they highlight many of the issues addressed in our article ( 1 Kishan A.U. Steinberg M.L. Kupelian P.A. King C.R. In regard to Bauman et al. Int J Radiat Oncol Biol Phys. 2015; 93: 1162-1163 Abstract Full Text Full Text PDF Scopus (5) Google Scholar , 2 Bauman G. Ferguson M. Lock M. et al. A phase 1/2 trial of brief androgen suppression and stereotactic radiation therapy (FASTR) for high-risk prostate cancer. Int J Radiat Oncol Biol Phys. 2015; 92: 856-862 Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar ). Indeed our conclusion, “Use of alternative planning constraints, tighter CTV and PTV margins using MRI for prostate target definition, and implanted fiducials combined with CBCT might improve the tolerance of this extreme hypofractionated treatment of regional nodes” ( 2 Bauman G. Ferguson M. Lock M. et al. A phase 1/2 trial of brief androgen suppression and stereotactic radiation therapy (FASTR) for high-risk prostate cancer. Int J Radiat Oncol Biol Phys. 2015; 92: 856-862 Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar ), is consistent with the letter and results from by Dr Kishan and colleagues. Preliminary dosimetric analysis of FASTR suggests that rectal dose may have been a key driver of toxicity, and FASTR-2 planning target volume margins have been reduced to 4 mm posteriorly. We have also added an intermediate dose volume constraint for planning ( 3 Elias E. Helou J. Zhang L. et al. Dosimetric and patient correlates of quality of life after prostate stereotactic ablative radiotherapy. Radiother Oncol. 2014; 112: 83-88 Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar ). Our decision to omit nodal volumes in addition to these changes is conservative; however, our revised FASTR-2 dose has a biologically equivalent dose (BED) similar to conventional high-dose radiation (assuming α/β of 1.5-3 Gy), and our decision to include the proximal seminal vesicles is consistent with established guidelines ( 4 Qi X. Gao X.S. Asaumi J. et al. Optimal contouring of seminal vesicle for definitive radiotherapy of localized prostate cancer. Radiat Oncol. 2014; 9: 288 Crossref PubMed Scopus (11) Google Scholar ). We look forward to the final results of other prospective studies: the exploration of a range of treatment approaches and prescriptions will help better define the safety and efficacy of hypofractionated nodal irradiation in the setting of high-risk prostate cancer. For example, the completed SATURN phase 2 trial (NCT01953055) used a prescription similar to FASTR and found lower toxicity than FASTR. We are completing dosimetric comparisons of these trials. In addition we are running deformable dose accumulation studies based on the daily cone-beam computed tomography scans for patients treated on FASTR, to better understand any potential contributions of interfraction variations in anatomy to the observed toxicity. In Regard to Bauman et alInternational Journal of Radiation Oncology, Biology, PhysicsVol. 93Issue 5PreviewTo the Editor: We read with interest the results of the Phase 1/2 Trial of Brief Androgen Suppression and Stereotactic Radiation Therapy (FASTR) study (1). In that study, 15 men with high-risk prostate cancer underwent stereotactic body radiation therapy (SBRT), prescribed as 40 Gy to the prostate and seminal vesicles (SVs) and 25 Gy in the same 5 fractions to the pelvic lymph nodes (PLNs), with 12 months of androgen deprivation therapy (ADT). At the interim toxicity analysis, 8 patients (53%) had experienced late grade ≥2 gastrointestinal toxicity, with 4 (27%) experiencing grade ≥3. Full-Text PDF