Focal boosted IMRT treatment of prostate cancer to 84 Gy in 28 fractions: Preliminary clinical outcomes, toxicity, and dosimetry

Jacob Michael Hands^1,2Michael Whalen¹Harold Frazier¹Shawn Haji-Momenian¹Ramez Andrawis¹Destie Provenzano¹Julie E Bauman^1,2Fayez Estephan²Hamid Aghdam²Dongjun Chen¹Sharad Goyal²Martin Ojong-Ntui²Yuan Rao^1*

• ¹School of Medicine and Health Sciences, George Washington University, Washington, D.C., United States
• ²George Washington University Hospital, Washington, D.C., District of Columbia, United States

The FLAME trial reported that focal boosting of prostate tumors up to 95 Gy in 35 fractions improves biochemical control (disease free survival). However, this treatment (regimen) is not commonly used in the United States. Methods: We investigated a focally boosted treatment of 84 Gy in 28 fractions (EQD2 108 Gy, BED 252 Gy). We retrospectively evaluated men with unfavorable-intermediate risk (uIR) and high risk (HR) prostate cancer treated with focal boost IMRT between 2019-2022. Results: Twenty men were included in the analysis, 2 (10%) uIR and 18 (90%) HR. 6 (30%) GG2, 3 (15% ) GG3, 7 (30%) GG4, and 4 (20%) GG5. There were 13 (65%) stage cT1, 4 (20%) cT2 and 3 (15%) cT3. One (5%) patient received short term ADT, 18 (95%) long term ADT, and 1 (5%) refused ADT. 18 (90%) men received elective pelvic nodal radiation. The mean baseline PSA was 25.1 ng/mL (range 4.2-73.4). The median baseline IPSS score was 11.1 . 4 patients had severe baseline urinary symptoms (IPSS ≥20). The mean baseline prostate volume was 57.4 cc (range 26.8-198.3). The mean volume of the 84 Gy boost target was 7.1 cc (range 2.3-15.0) and the mean proportion of the prostate boosted was 14.8% (range 2% -47%). Patients met all per-protocol normal tissue criteria of NRG-GU005, except for bladder D0.03cc with mean reported 79.2 (<73.5 Gy). At a median follow up of 42 months (range 18-63)), no patients have developed recurrence, metastasis, or death from prostate cancer. One patient died at 18 months from unrelated metastatic colorectal cancer. Acute grade 1-2 GU toxicity occurred in 13 (65%) patients, and acute grade 1-2 GI toxicity occurred in 4 (20%) patients. No patients developed grade 3+ acute or late GU or GI toxicity.A novel 28-fraction focal boosted IMRT treatment is feasible and has an acceptable preliminary toxicity profile. Oncologic results are promising but require longer follow up and prospective study.