Results of a Prospective Dose Escalation Study of Linear Accelerator–Based Virtual Brachytherapy (BOOSTER) for Prostate Cancer; Virtual HDR Brachytherapy for Prostate Cancer

Abstract

PurposeTo demonstrate feasibility and toxicity of linear accelerator–based stereotactic radiation therapy boost (SBRT) for prostate cancer, mimicking a high-dose-rate brachytherapy boost.Methods and MaterialsA phase 1 sequential dose escalation study of SBRT compared 20 Gy, 22 Gy, and 24 Gy to the prostate and 25 Gy, 27.5 Gy, and 30 Gy to the gross tumor volume in 2 fractions, combined with 46 Gy in 23 fractions of external beam radiation. Feasibility of dose escalation (volume receiving 125% and 150% of the dose) while meeting organ-at-risk dose constraints, grade 2 acute and late gastrointestinal and genitourinary toxicity, and freedom from biochemical failure were secondary endpoints.ResultsThirty-six men with intermediate- and high-risk prostate cancer were enrolled with a median follow-up of 24 months. Sixty-four percent of patients had high-risk features. Nine men were enrolled to dose level 1, 6 to level 2, and 6 to level 3. Another 15 patients were treated at dose level 3 on the continuation study. Dose level 3 achieved superior 125% (23.75 Gy) and 150% (28.5 Gy) dose compared to dose levels 1 and 2, with minimal differences in organ-at-risk doses. Kaplan-Meier estimate of freedom from biochemical failure at 3 years was 93.3%. There were no late grade 2 or 3 gastrointestinal events. The late grade 2 genitourinary toxicity at 2 years was 19.3%. Prostate-specific membrane antigen positron emission tomography was performed at 2 years with no local recurrences.ConclusionsWe have shown that a linear accelerator–based SBRT boost for prostate cancer is feasible and can achieve doses comparable to high-dose-rate boost up to the 150% isodose volumes. Rectal, bladder, and urethral doses remained low, and long-term toxicity was the same as or better than previous reports from high-dose-rate or low-dose-rate boost protocols.

Simulation of an HDR “Boost” with Stereotactic Proton versus Photon Therapy in Prostate Cancer: A Dosimetric Feasibility Study

“…After a median follow-up of 3.5 years, they reported a 3-year biochemical control rate of 95%. Similarly, a group from Australia [20] recently reported a Figure 2. Target coverage parameters (V100, V125, V150, V200) between SBPT and SBXT stratified by prostate size 50 cm 3 (n ¼ 13) and prostate size .50 cm 3 (n ¼ 12).…”

“…Many institutions have reported on their experience using SBXT as a boost for intermediate-to high-risk prostate cancer, summarized in Table 3 [15][16][17][18][19][20][21][22][23][24]. These studies vary widely in terms of boost dose, CTV definition, PTV margins, presence of a prostatic urethra avoidance structure, and use of a rectal balloon.…”

“…Advancements in imaging and treatment techniques including the use of magnetic resonance imaging (MRI), spacer gel to move the rectum away from the prostate [13], prostate fiducials for target localization, and intrafraction image guidance [14] have all paved the way for ultrahypofractionated SBXT. Several single-institution experiences using SBXT as a boost for intermediate-and high-risk prostate cancer have demonstrated favorable biochemical control [15][16][17][18][19][20][21][22][23][24]. However, the differences in dose distribution, compared to PB, and its radiobiological impact raise concern regarding the long-term efficacy of this approach.…”

AAPM Task Group 264: The safe clinical implementation of MLC tracking in radiotherapy

“…The dose per fraction ranged from 2 Gy (conventional treatments) to 13.75 Gy (SBRT boost for locally advanced prostate cancer patients). 81 All patients were treated using VMAT, typically with 2 arcs. This trial has completed accrual and the initial findings have been published.…”

Radiation-induced erectile dysfunction in patients with prostate cancer: current methods of radiotherapy

“…В последнее время все большую популярность приобретает так называемая «виртуальная», или HDR-like, БТ [47]. В ее основе лежит возможность современных планирующих систем формировать неоднородное распределение дозовой нагрузки в пределах клинического объема облучения (boost), подобно высокомощностной БТ [48]. При этом отсутствует основная характеристика БТ -введение источника облучения непосредственно в ткань ПЖ, что и определяет «виртуальный» характер метода.…”