Stereotactic body radiotherapy for primary management of early-stage, low- to intermediate-risk prostate cancer: report of the American Society for Therapeutic Radiology and Oncology Emerging Technology Committee

SBRT for Localized Prostate Cancer: CyberKnife vs. VMAT-FFF, a Dosimetric Study

In recent years, stereotactic body radiation therapy (SBRT) has gained popularity among clinical methods for the treatment of medium and low risk prostate cancer (PCa), mainly as an alternative to surgery. The hypo-fractionated regimen allows the administration of high doses of radiation in a small number of fractions; such a fractionation is possible by exploiting the different intrinsic prostate radiosensitivity compared with the surrounding healthy tissues. In addition, SBRT treatment guaranteed a better quality of life compared with surgery, avoiding risks, aftermaths, and possible complications. At present, most stereotactic prostate treatments are performed with the CyberKnife (CK) system, which is an accelerator exclusively dedicated for stereotaxis and it is not widely spread in every radiotherapy centre like a classic linear accelerator (LINAC). To be fair, a stereotactic treatment is achievable also by using a LINAC through Volumetric Modulated Arc Therapy (VMAT), but some precautions must be taken. The aim of this work is to carry out a dosimetric comparison between these two methodologies. In order to pursue such a goal, two groups of patients were selected at Instituto Nazionale Tumori—IRCCS Fondazione G. Pascale: the first group consisting of ten patients previously treated with a SBRT performed with CK; the second one was composed of ten patients who received a hypo-fractionated VMAT treatment and replanned in VMAT-SBRT flattening filter free mode (FFF). The two SBRT techniques were rescaled at the same target coverage and compared by normal tissue sparing, dose distribution parameters and delivery time. All organs at risk (OAR) constraints were achieved by both platforms. CK exhibits higher performances in terms of dose delivery; nevertheless, the general satisfying dosimetric results and the significantly shorter delivery time make VMAT-FFF an attractive and reasonable alternative SBRT technique for the treatment of localized prostate cancer.

Randomised controlled trial on the effect of simethicone bowel preparation on rectal variability during image-guided radiation therapy for prostate cancer (SPoRT study)

INTRODUCTION

The purpose of this study was to assess whether simethicone reduces the rectal volume (RV) and gas volume (GV), to increase treatment accuracy and to decrease toxicity of prostate radiation therapy.

METHODS

30 patients were randomised to simethicone or no intervention. Cone-beam computed tomography (CBCT) scans were performed on Days 1-3 and weekly until completion of radiation. RV and GV were measured using volume delineation. Toxicity data were collected.

RESULTS

264 CBCTs were analysed. RV and GV were not significantly different in the simethicone group compared with the control group at each time point (P >0.05) after adjusting for Week 0 values as a covariate. The simethicone group showed an average reduction in RV and GV of 10% and 21%, respectively, compared with the control group (P >0.05). Standard deviations were calculated over 10 time points, which were grouped to represent the first 2-3 weeks of radiation therapy versus subsequent weeks. These were not significantly different between the simethicone and control group. However, there was a statistically significant decrease in the variability of RV at time points 6-10 compared with time points 1-5 within the simethicone group (P = 0.012), but no significant difference was found between these grouped time points in the control group (P = 0.581). The toxicity questionnaires showed no significant difference between the groups.

CONCLUSIONS

Simethicone did not decrease the RV or GV overall. However, simethicone appeared to significantly decrease the RV variability from Week three onwards. This suggests that taking simethicone two to three weeks before starting radiation therapy may reduce RV variability, although a larger study is needed to confirm this.

Natural history of lower urinary tract symptoms among men undergoing stereotactic body radiation therapy for prostate cancer with and without a Rectal Hydrogel Spacer

PURPOSE

Stereotactic body radiation therapy (SBRT) is increasingly used for prostate cancer, but has morbidity as both the bladder and rectum are radiated during treatment. Our goal was to document and compare lower urinary tract symptoms (LUTS) among men who underwent SBRT with and without SpaceOAR hydrogel (Augmenix, Inc., Bedford, MA).

METHODS

We performed a retrospective analysis of 87 men (50 SpaceOAR and 37 non-SpaceOAR) who underwent SBRT. Primary outcomes were patient reported symptoms during radiation therapy, pharmacotherapy usage, and urologic and bowel survey scores up to 6-months post-SBRT.

RESULTS

78% of men were on α-inhibitors at the end of SBRT, an increase from 27.6% baseline usage (p < 0.001). Post-SBRT urinary frequency was more common in the non-SpaceOAR group versus the SpaceOAR group (68% versus 38%, p = 0.006), as was nocturia (35% vs. 8%, p = 0.002). Acute gastrointestinal symptoms did not differ. 58.8% of men were on α-inhibitors at 6-months of follow-up post-SBRT, an increase from 27.6% baseline usage (p < 0.001). Importantly, there was a difference of α-inhibitor use between non-SpaceOAR and SpaceOAR groups at the end of SBRT and at 1.5-, 3-, and 6-months follow up (86% vs. 53% [p = 0.002], 83% vs. 53% [p = 0.005], 72% vs. 49% [p = 0.038], respectively).

CONCLUSION

LUTS after SBRT remains a significant problem for men undergoing treatment for prostate cancer. LUTS affects men during and up to 6-months following SBRT. Owing to these increased LUTS, preemptive minimally invasive solutions and their mechanisms of protection, including the SpaceOAR, should be further investigated.

Effects on annual income changes after radical radiotherapy versus after prostatectomy in patients with localized prostate cancer with a specific employment status: A web-based pilot study

Men with localized prostate cancers are insured for undergoing radical radiotherapy or prostatectomy. However, limited information is available on the influence of cancer treatments on patients’ employment status in Japan. Therefore, in this web-based survey, we aimed to compare the effects of post-treatment changes on the annual income of patients with prostate cancer after undergoing radical radiotherapy and prostatectomy and to identify the risk factors associated with the decrease in annual income. We investigated the clinical characteristics and demographics including pre-treatment working status, self-employment, non-regular employment, working for wage or salary, and joblessness of patients with localized prostate cancer. Multivariable logistic regression was performed to analyze the effects of various factors on the change in the annual income of self-employed and non-regularly employed workers. Seventy-eight eligible patients with localized prostate cancer had undergone radiotherapy, and 128 patients had undergone prostatectomy. Among self-employed and non-regularly employed workers, post-treatment income decline rates in those who underwent radiotherapy were smaller but not significant (12% vs. 42%, P = 0.074). Multivariable logistic regression analysis revealed that initial treatment for prostate cancer was the only significant risk factor for the post-treatment income decline among self-employed and non-regularly employed workers. Radiotherapy was associated with a smaller decrease in income (odds ratio, 0.22; 95% confidence interval, 0.052–0.95; P = 0.042). Our novel results implied the effectiveness of radiotherapy in preventing post-treatment income decline among patients with prostate cancer based on specific employment status: self-employed or non-regularly employed.

First experimental evaluation of multi-target multileaf collimator tracking during volumetric modulated arc therapy for locally advanced prostate cancer

PURPOSE

Locally advanced and oligometastatic cancer patients require radiotherapy treatment to multiple independently moving targets. There is no existing commercial solution that can simultaneously track and treat multiple targets. This study experimentally implemented and evaluated a real-time multi-target tracking system for locally advanced prostate cancer.

METHODS

Real-time multi-target MLC tracking was integrated with 3D x-ray image guidance on a standard linac. Three locally advanced prostate cancer treatment plans were delivered to a static lymph node phantom and dynamic prostate phantom that reproduced three prostate trajectories. Treatments were delivered using multi-target MLC tracking, single-target MLC tracking, and no tracking. Doses were measured using Gafchromic film placed in the dynamic and static phantoms. Dosimetric error was quantified by the 2%/2 mm gamma failure rate. Geometric error was evaluated as the misalignment between target and aperture positions. The multi-target tracking system latency was measured.

RESULTS

The mean (range) gamma failure rates for the prostate and lymph nodes, were 18.6% (5.2%, 28.5%) and 7.5% (1.1%, 13.7%) with multi-target tracking, 7.9% (0.7%, 15.4%) and 37.8% (18.0%, 57.9%) with single-target tracking, and 38.1% (0.6%, 75.3%) and 37.2% (29%, 45.3%) without tracking. Multi-target tracking had the lowest geometric error with means and standard deviations within 0.2 ± 1.5 for the prostate and 0.0 ± 0.3 mm for the lymph nodes. The latency was 730 ± 20 ms.

CONCLUSION

This study presented the first experimental implementation of multi-target tracking to independently track prostate and lymph node displacement during VMAT. Multi-target tracking reduced dosimetric and geometric errors compared to single-target tracking and no tracking.

Adapting to the motion of multiple independent targets using multileaf collimator tracking for locally advanced prostate cancer: Proof of principle simulation study

PURPOSE

For patients with locally advanced cancer, multiple targets are treated simultaneously with radiotherapy. Differential motion between targets can compromise the treatment accuracy, yet there are currently no methods able to adapt to independent target motion. This study developed a multileaf collimator (MLC) tracking algorithm for differential motion adaptation and evaluated it in simulated treatments of locally advanced prostate cancer.

METHODS

A multi-target MLC tracking algorithm was developed that consisted of three steps: (a) dividing the MLC aperture into two possibly overlapping sections assigned to the prostate and lymph nodes, (b) calculating the ideally shaped MLC aperture as a union of the individually translated sections, and (c) fitting the MLC positions to the ideal aperture shape within the physical constraints of the MLC leaves. The multi-target tracking method was evaluated and compared with two existing motion management methods: single-target tracking and no tracking. Treatment simulations of six locally advanced prostate cancer patients with three prostate motion traces were performed for all three motion adaptation methods. The geometric error for each motion adaptation method was calculated using the area of overexposure and underexposure of each field. The dosimetric error was estimated by calculating the dose delivered to the prostate, lymph nodes, bladder, rectum, and small bowel using a motion-encoded dose reconstruction method.

RESULTS

Multi-target MLC tracking showed an average improvement in geometric error of 84% compared to single-target tracking, and 83% compared to no tracking. Multi-target tracking maintained dose coverage to the prostate clinical target volume (CTV) D98% and planning target volume (PTV) D95% to within 4.8% and 3.9% of the planned values, compared to 1.4% and 0.7% with single-target tracking, and 20.4% and 31.8% with no tracking. With multi-target tracking, the node CTV D95%, PTV D90%, and gross tumor volume (GTV) D95% were within 0.3%, 0.6%, and 0.3% of the planned values, compared to 9.1%, 11.2%, and 21.1% for single-target tracking, and 0.8%, 2.0%, and 3.2% with no tracking. The small bowel V57% was maintained within 0.2% to the plan using multi-target tracking, compared to 8% and 3.5% for single-target tracking and no tracking, respectively. Meanwhile, the bladder and rectum V50% increased by up to 13.6% and 5.2%, respectively, using multi-target tracking, compared to 2.7% and 1.9% for single-target tracking, and 11.2% and 11.5% for no tracking.

CONCLUSIONS

A multi-target tracking algorithm was developed and tracked the prostate and lymph nodes independently during simulated treatments. As the algorithm optimizes for target coverage, tracking both targets simultaneously may increase the dose delivered to the organs at risk.

A treatment planning study comparing IMRT techniques and cyber knife for stereotactic body radiotherapy of low-risk prostate carcinoma

PURPOSE

Comparing radiation treatment plans by using the same safety margins and dose objectives for all techniques, to ascertain the optimal radiation technique for the stereotactic body radiotherapy (SBRT) of low-risk prostate cancer.

MATERIAL AND METHODS

Treatment plans for 27 randomly selected patients were compared using intensity-modulated (IMRT) techniques as Sliding Window (SW), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT), as well as Cyber Knife (CK) system. The target dose was calculated to 36.25 Gy delivered in five fractions over 1 week. Dosimetric indices for target volume and organs at risk (OAR) as well as normal tissue complication probability (NTCP) of late rectal and urinary bladder toxicities were analyzed.

RESULTS

The CK provided lower homogeneity in the target volume, but higher values for most of the conformity indices compared to the IMRT approaches. The SW demonstrated superior rectum sparing at medium-to-high dose range (V18 Gy - V32.6 Gy) compared to other techniques (p < 0.05). The whole urinary bladder experienced the best shielding by SW and VMAT at the medium dose (V18 Gy, p < 0.05 versus CK), however we obtained no relevant differences between techniques at the high dose. Generally, the CK demonstrated significantly superior rectum and bladder exposure at V18 Gy as compared to HT, SW, and VMAT. For the rectum, mean NTCP values were significantly superior for HT (NTCP = 2.3%, p < 0.05), and for urinary bladder, the NTCP showed no significant advantages for any technique.

CONCLUSION

No absolute dosimetric advantage was revealed to choose between CK or IMRT techniques for the SBRT of low-grade prostate cancer. Using the same safety margins and dose objectives, IMRT techniques demonstrated superior sparing of the rectum and bladder at a medium dose compared to CK. Comparing different IMRT approaches SW displayed superior rectum sparing at a medium-to-high dose range, whereas both SW and RA revealed superior bladder sparing compared to HT. HT demonstrated a significantly lower NTCP outcome compared to CK or IMRT techniques regarding the rectum. Radiation plans can be optimized further by an individual modification of dose objectives independent of the treatment plan strategy.

The Influence of Stereotactic Body Radiation Therapy Adoption on Prostate Cancer Treatment Patterns

PURPOSE

To our knowledge it is unknown whether stereotactic body radiation therapy of prostate cancer is a substitute for other radiation treatments or surgery, or for expanding the pool of patients who undergo treatment instead of active surveillance.

MATERIALS AND METHODS

Using SEER (Surveillance, Epidemiology, and End Results)-Medicare we identified men diagnosed with prostate cancer between 2007 and 2011. We developed physician-hospital networks by identifying the treating physician of each patient based on the primary treatment received and subsequently assigning each physician to a hospital. We examined the relative distribution of prostate cancer treatments stratified by whether stereotactic body radiation therapy was performed in a network by fitting logistic regression models with robust SEs to account for patient clustering in networks.

RESULTS

We identified 344 physician-hospital networks, including 30 (8.7%) and 314 (91.3%) in which stereotactic body radiation therapy was and was not performed, respectively. Networks in which that therapy was and was not done did not differ with time in the performance of robotic and radical prostatectomy, and active surveillance (all p >0.05). The relationship with intensity modulated radiation therapy did not show any consistent temporal pattern. In networks in which it was performed less intensity modulated radiation therapy was initially done but there were similar rates in later years. Brachytherapy trends differed among networks in which stereotactic body radiation therapy was vs was not performed with a lower brachytherapy rate in networks in which stereotactic body radiation therapy was done (p=0.03).

CONCLUSIONS

Surgery and active surveillance rates did not differ in networks in which stereotactic body radiation therapy was vs was not performed but when that therapy was done there was a lower brachytherapy rate. Stereotactic body radiation therapy may represent more of an alternative to brachytherapy than to active surveillance.

Multi-center evaluation of dose conformity in stereotactic body radiotherapy

BACKGROUND AND PURPOSE

Stereotactic body radiotherapy (SBRT) is an emerging technique for treating oligometastases, but limited data is available on what plan quality is achievable for a range of modalities and clinical sites.

METHODS

SBRT plans for lung, spine, bone, adrenal, liver and node sites from 17 participating centers were reviewed. Centers used various delivery techniques including static and rotational intensity-modulation and multiple non-coplanar beams. Plans were split into lung and other body sites and evaluated with different plan quality metrics, including two which are independent of target coverage; "prescription dose spillage" (PDS) and "modified gradient index" (MGI). These were compared to constraints from the ROSEL and RTOG 0813 clinical trials.

RESULTS

Planning target volume (PTV) coverage was compromised (PTV V100% < 90%) in 29% of patient plans in order to meet organ-at-risk (OAR) tolerances, supporting the use of plan quality metrics which are independent of target coverage. Both lung (n = 48) and other body (n = 99) site PDS values agreed well with ROSEL constraints on dose spillage, but RTOG 0813 values were too high to detect sub-optimal plans. MGI values for lung plans were mis-matched to both sets of previous constraints, with ROSEL values too high and RTOG 0813 values too low. MGI values were lower for other body plans as expected, though this was only statistically significant for PTV volumes <20 cm3.

CONCLUSIONS

Updated guidance for lung and other body site SBRT plan quality using the PDS and MGI metrics is presented.

Stereotactic Body Radiotherapy versus Low Dose Rate Brachytherapy for Localised Prostate Cancer: a Cost-Utility Analysis

AIMS

To conduct a cost-utility analysis comparing stereotactic body radiotherapy (SBRT) with low dose rate brachytherapy (LDR-BT) for localised prostate cancer (PCa).

MATERIALS AND METHODS

A decision-analytic Markov model was developed from the healthcare payer perspective to simulate the history of a 66-year-old man with low-risk PCa. The model followed patients yearly over their remaining lifetimes. Health states included 'recurrence-free', 'biochemical recurrence' (BR), 'metastatic' and 'death'. Transition probabilities were based on a retrospective cohort analysis undertaken at our institution. Utilities were derived from the literature. Costs were assigned in 2015 Canadian dollars ($) and reflected Ontario's health system and departmental costs. Outcomes included quality-adjusted life years (QALYs), costs and incremental cost-effectiveness ratios. A willingness-to-pay threshold of $50 000/QALY was used.

RESULTS

SBRT was the dominant strategy with 0.008LYs and 0.029QALYs gained and a reduction in cost of $2615. Under base case conditions, our results were sensitive to the BR probability associated with both strategies. LDR-BT becomes the preferred strategy if the BR with SBRT is 1.3*[baseline BR_SBRT] or if the BR with LDR-BT is 0.76*[baseline BR_LDR-BT]. When assuming the same BR for both strategies, LDR-BT becomes marginally more effective with 0.009QALYs gained at a cost of $272 848/QALY.

CONCLUSIONS

SBRT represents an economically attractive radiation strategy. Further research should be carried out to provide longer-term follow-up and high-quality evidence.

Stereotactic radiotherapy of the prostate: fractionation and utilization in the United States

Purpose

To analyze the utilization and fractionation of extreme hypofractionation via stereotactic body radiotherapy (SBRT) in the treatment of prostate cancer.

Materials and Methods

Data was analyzed on men diagnosed with localized prostate cancer between 2004–2012 and treated with definitive-intent radiation therapy, as captured in the National Cancer Database. This database is a hospital-based registry that collects an estimated 70% of all diagnosed malignancies in the United States.

Results

There were 299,186 patients identified, of which 4,962 (1.7%) were identified as receiving SBRT as primary treatment. Of those men, 2,082 had low risk disease (42.0%), 2,201 had intermediate risk disease (44.4%), and 679 had high risk disease (13.7%). The relative utilization of SBRT increased from 0.1% in 2004 to 4.0% in 2012. Initially SBRT was more commonly used in academic programs, though as time progressed there was a shift to favor an increased absolute number of men treated in the community setting. Delivery of five separate treatments was the most commonly utilized fractionation pattern, with 4,635 patients (91.3%) receiving this number of treatments. The most common dosing pattern was 725 cGy × 5 fractions (49.6%) followed by 700 cGy × 5 fractions (21.3%).

conclusions

Extreme hypofractionation via SBRT is slowly increasing acceptance. Currently 700-725 cGy × 5 fractions appears to be the most commonly employed scheme. As further long-term data regarding the safety and efficacy emerges, the relative utilization of this modality is expected to continue to increase.

The early adoption of intensity-modulated radiotherapy and stereotactic body radiation treatment among older Medicare beneficiaries with prostate cancer

BACKGROUND

Several new prostate cancer treatments have emerged since 2000, including 2 radiotherapies with similar efficacy at the time of their introduction: intensity-modulated radiotherapy (IMRT) and stereotactic body radiation therapy (SBRT). The objectives of this study were to compare their early adoption patterns and identify factors associated with their use.

METHODS

By using the Surveillance, Epidemiology, and End Results (SEER)-Medicare database, patients who received radiation therapy during the 5 years after IMRT introduction (2001-2005) and the 5 years after SBRT introduction (2007-2011) were identified. The outcome of interest was the receipt of new radiation therapy (ie, IMRT or SBRT) compared with the existing standard radiation therapies at that time. The authors fit a series of multivariable, hierarchical logistic regression models accounting for patients nested within health service areas to examine the factors associated with the receipt of new radiation therapy.

RESULTS

During 2001 to 2005, 5680 men (21%) received IMRT compared with standard radiation (n = 21,555). Men who received IMRT were older, had higher grade tumors, and lived in more populated areas (P < .05). During 2007 through 2011, 595 men (2%) received SBRT compared with standard radiation (n = 28,255). Men who received ng SBRT were more likely to be white, had lower grade tumors, lived in more populated areas, and were more likely to live in the Northeast (P < .05). Adjusting for cohort demographic and clinical factors, the early adoption rate for IMRT was substantially higher than that for SBRT (44% vs 4%; P < .01).

CONCLUSIONS

There is a stark contrast in the adoption rates of IMRT and SBRT at the time of their introduction. Further investigation of the nonclinical factors associated with this difference is warranted. Cancer 2017;123:2945-54. © 2017 American Cancer Society.

Salvage Stereotactic Body Radiotherapy for Isolated Lymph Node Recurrent Prostate Cancer: Single Institution Series of 94 Consecutive Patients and 124 Lymph Nodes

BACKGROUND

The purpose of the study was to evaluate the prostate serum antigen (PSA) response, local control, progression-free survival (PFS), and toxicity of stereotactic body radiotherapy (SBRT) for lymph node (LN) oligorecurrent prostate cancer.

PATIENTS AND METHODS

Between May 2012 and October 2015, 124 lesions were treated in 94 patients with a median dose of 24 Gy in 3 fractions. Seventy patients were treated for a single lesion and 25 for > 1 lesion. In 34 patients androgen deprivation (AD) was combined with SBRT. We evaluated biochemical response according to PSA level every 3 months after SBRT: a 3-month PSA decrease from pre-SBRT PSA of more than 10% identified responder patients. In case of PSA level increase, imaging was performed to evaluate clinical progression. Toxicity was assessed every 6 to 9 months after SBRT.

RESULTS

Median follow-up was 18.5 months. In 13 patients (14%) Grade 1 to 2 toxicity was reported without any Grade 3 to 4 toxicity. Biochemical response, stabilization, and progression were observed in 64 (68%), 10 (11%), and 20 (21%) of 94 evaluable patients. Clinical progression was observed in 31 patients (33%) after a median time of 8.1 months. In-field progression occurred in 12 lesions (9.7%). Two-year local control and PFS rates were 84% and 30%, respectively. Age older than 75 years correlated with better biochemical response rate. Age older than 75 years, concomitant AD administered up to 12 months, and pelvic LN involvement correlated with longer PFS.

CONCLUSION

SBRT is safe and offers good in-field control. At 2 years after SBRT, 1 of 3 patients is progression-free. Further investigation is warranted to identify patients who benefit most from SBRT and to define the optimal combination with AD.

Dosimetric Comparison and Evaluation of 4 Stereotactic Body Radiotherapy Techniques for the Treatment of Prostate Cancer

PURPOSE

The aim of this study was to compare dosimetric characteristics, monitor unit, and delivery efficiency of 4 different stereotactic body radiotherapy techniques for the treatment of prostate cancer.

METHODS

This study included 8 patients with localized prostate cancer. Dosimetric assets of 4 delivery techniques for stereotactic body radiotherapy were evaluated: robotic CyberKnife, noncoplanar intensity-modulated radiotherapy, and 2 intensity-modulated arc therapy techniques (RapidArc and Elekta volumetric-modulated arc therapy). All the plans had equal treatment margins and a prescription dose of 35 Gy in 5 fractions.

RESULTS

Statistically significant differences were observed in homogeneity index and mean doses of bladder wall and penile bulb, all of which were highest with CyberKnife. No significant differences were observed in the mean doses of rectum, with values of 15.2 ± 2.6, 13.3 ± 2.6, 13.1 ± 2.8, and 13.8 ± 1.6 Gy with CyberKnife, RapidArc, volumetric-modulated arc therapy, and noncoplanar intensity-modulated radiotherapy, respectively. The highest dose conformity was realized with RapidArc. The dose coverage of the planning target volume was lowest with noncoplanar intensity-modulated radiotherapy. Treatment times and number of monitor units were largest with CyberKnife (on average 34.0 ± 5.0 minutes and 8704 ± 1449 monitor units) and least with intensity-modulated arc therapy techniques (on average 5.1 ± 1.1 minutes and 2270 ± 497 monitor units).

CONCLUSION

Compared to CyberKnife, the RapidArc, volumetric-modulated arc therapy, and noncoplanar intensity-modulated radiotherapy produced treatment plans with similar dosimetric quality, with RapidArc achieving the highest dose conformity. Overall, the dosimetric differences between the studied techniques were marginal, and thus, the choice of the technique should rather focus on the delivery accuracies and dose delivery times.

Hypofractionated image guided radiation therapy followed by prostate seed implant boost for men with newly diagnosed intermediate and high risk adenocarcinoma of the prostate: Preliminary results of a phase 2 prospective study

PURPOSE

A phase 2 protocol was designed and implemented to assess the toxicity and efficacy of hypofractionated image guided intensity modulated radiation therapy (IG-IMRT) combined with low-dose rate 103Pd prostate seed implant for treatment of localized intermediate- and high-risk adenocarcinoma of the prostate.

METHODS AND MATERIALS

This is a report of an interim analysis on 24 patients enrolled on an institutional review board-approved phase 2 single-institution study of patients with intermediate- and high-risk adenocarcinoma of the prostate. The median pretreatment prostate-specific antigen level was 8.15 ng/mL. The median Gleason score was 4 + 3 = 7 (range, 3 + 4 = 7 - 4 + 4 = 8), and the median T stage was T2a. Of the 24 patients, 4 (17%) were high-risk patients as defined by the National Comprehensive Cancer Network criteria, version 2016. The treatment consisted of 2465 cGy in 493 cGy/fraction of IG-IMRT to the prostate and seminal vesicles. This was followed by a 103Pd transperineal prostate implant boost (prescribed dose to 90% of the prostate volume of 100 Gy) using intraoperative planning. Five patients received neoadjuvant, concurrent, and adjuvant androgen deprivation therapy.

RESULTS

The median follow-up was 18 months (range, 1-42 months). The median nadir prostate-specific antigen was 0.5 ng/mL and time to nadir was 16 months. There was 1 biochemical failure associated with distant metastatic disease without local failure. Toxicity (acute or late) higher than grade 3 was not observed. There was a single instance of late grade 3 genitourinary toxicity secondary to hematuria 2 years and 7 months after radiation treatment. There were no other grade 3 gastrointestinal or genitourinary toxicities.

CONCLUSIONS

Early results on the toxicity and efficacy of the combination of hypofractionated IG-IMRT and low-dose-rate brachytherapy boost are favorable. Longer follow-up is needed to confirm safety and effectiveness.

Guidance on patient consultation. Current evidence for prostate-specific antigen screening in healthy men and treatment options for men with proven localised prostate cancer

The main objective of this review is to summarise, for primary and secondary care doctors, the management options and current supporting evidence for clinically localised prostate cancer. We review all aspects of management including current guidelines on early cancer detection and the importance of informed consent on PSA-based screening and assess the most common treatment options and the evidence for managing patients with low-, medium-, and high-risk disease.

Local coverage determination policy and the use of stereotactic body radiation therapy for prostate cancer

INTRODUCTION

Local coverage determinations (LCDs) are local decisions that regulate healthcare coverage. We evaluated the impact of LCDs as well as patient, tumor, and market characteristics on the adoption of stereotactic body radiation therapy (SBRT) for prostate cancer.

METHODS

Using Surveillance, Epidemiology, and End Results (SEER)-Medicare, we identified men treated with SBRT, intensity-modulated radiotherapy (IMRT), and robotic prostatectomy. We compared demographics, clinical characteristics, and market factors among these three treatments. Our primary exposure was LCD policy; using the Medicare Coverage Database, we categorized LCDs as favorable (SBRT covered), neutral (SBRT covered in the context of a clinical trial or registry), unfavorable (SBRT not covered), or absent (i.e., SBRT not governed by an LCD at the time of treatment). We fit a multivariable multinomial logistic regression model and generated predicted probabilities to examine the relation between LCDs and SBRT.

RESULTS

During this early period of SBRT adoption, IMRT was the most common of the three treatments followed by robotic prostatectomy and then SBRT. SBRT use was high when governed by favorable and neutral LCDs and lowest when governed by unfavorable LCDs. Compared with favorable LCDs, areas where LCDs were absent were associated with higher SBRT use compared with IMRT (odds ratio [OR] 1.56; 95%CI, 1.07-2.25) and robotic prostatectomy (OR 1.84; 95%CI, 1.25-2.69).

CONCLUSIONS

When present, LCDs appear to regulate early SBRT adoption, but, when absent, are associated with increased SBRT use. Although SBRT use was uncommon, it varied across a wide range of patient, tumor, and market characteristics.

Ultrasound Imaging in Radiation Therapy: From Interfractional to Intrafractional Guidance

External beam radiation therapy (EBRT) is included in the treatment regimen of the majority of cancer patients. With the proliferation of hypofractionated radiotherapy treatment regimens, such as stereotactic body radiation therapy (SBRT), interfractional and intrafractional imaging technologies are becoming increasingly critical to ensure safe and effective treatment delivery. Ultrasound (US)-based image guidance systems offer real-time, markerless, volumetric imaging with excellent soft tissue contrast, overcoming the limitations of traditional X-ray or computed tomography (CT)-based guidance for abdominal and pelvic cancer sites, such as the liver and prostate. Interfractional US guidance systems have been commercially adopted for patient positioning but suffer from systematic positioning errors induced by probe pressure. More recently, several research groups have introduced concepts for intrafractional US guidance systems leveraging robotic probe placement technology and real-time soft tissue tracking software. This paper reviews various commercial and research-level US guidance systems used in radiation therapy, with an emphasis on hardware and software technologies that enable the deployment of US imaging within the radiotherapy environment and workflow. Previously unpublished material on tissue tracking systems and robotic probe manipulators under development by our group is also included.

Stereotactic Ablative Radiotherapy with CyberKnife in the Treatment of Locally Advanced Prostate Cancer: Preliminary Results

Aims and Background

Recent clinical reports of stereotactic ablative radiotherapy (SABR) in the treatment of low-risk prostate cancer have been encouraging. Our study evaluates the efficacy and safety of SABR using the CyberKnife system for treating intermediate- to very-high-risk prostate cancer.

Methods and Study Design

Between May 2010 and June 2013, 31 patients (15 intermediate risk, 14 high risk, and 2 very high risk) without pelvic lymph node metastasis were enrolled retrospectively. The treatment consisted of 37.5 Gy in 5 fractions over 1-2 weeks using CyberKnife SABR. Twenty-five patients (81%) received androgen deprivation therapy (ADT). Biochemical failure was defined using the nadir + 2 criterion. Toxicity was assessed with the Common Terminology Criteria of Adverse Events (version 4).

Results

The median follow-up was 36 months (range 7-58 months). The median pretreatment prostate-­pecific antigen (PSA) was 13.5 ng/mL (range 4.5-124.0 ng/mL). The median PSA decreased to 0.09 ng/mL (range <0.04-5.38 ng/mL) and 0.12 ng/mL (range <0.04-2.63 ng/mL) at 6 months and 12 months after SABR, respectively. The 3-year biochemical relapse-free survival was 90.2% for all patients, 100% for the intermediate-risk patients, and 82% for the high- and very-high-risk patients (p = 0.186). No patient experienced ≥ grade 3 toxicity. There were 7 acute and 5 late grade 2 genitourinary toxicities and 1 acute and no late grade 2 gastrointestinal toxicity.

Conclusions

Our preliminary results support that CyberKnife SABR with ADT is safe and feasible in patients with intermediate- to high-risk prostate cancer. A further large-scale clinical trial with longer follow-up is warranted.

[Irradiation in stereotactic conditions: prerequisites]

Indications of treatment by stereotactic body radiotherapy are dramatically increasing due to new potential indications. The conditions associated with the treatment delivery are multiple. The first step of the process is crucial. It is related to the validation of the indication proposed during the multidisciplinary meeting as regard the evidence-based proof of the concept. These emerging techniques mainly extracranial stereotactic body irradiation do not benefit from long-term evaluation in terms of efficiency as well as normal tissue late toxicities. Priority should be given to prospective independent clinical trials, validated by an independent scientific committee, performed under a relevant and well dedicated multicentric quality assurance program aiming to improve knowledge and selection of indications. The SFRO is still working with others professionals on the definition of the conditions for the implementation of such treatments and actively collaborates with the authorities to define the appropriate conditions to preserve the quality of the treatment delivery under these specific conditions.

Assessing the dosimetric impact of real-time prostate motion during volumetric modulated arc therapy

PURPOSE

To develop a method for dose reconstruction by incorporating the interplay effect between aperture modulation and target motion, and to assess the dosimetric impact of real-time prostate motion during volumetric modulated arc therapy (VMAT).

METHODS AND MATERIALS

Clinical VMAT plans were delivered with the TrueBeam linac for 8 patients with prostate cancer. The real-time target motion during dose delivery was determined based on the 2-dimensional fiducial localization using an onboard electronic portal imaging device. The target shift in each image was correlated with the control point with the same gantry angle in the VMAT plan. An in-house-developed Monte Carlo simulation tool was used to calculate the 3-dimensional dose distribution for each control point individually, taking into account the corresponding real-time target motion (assuming a nondeformable target with no rotation). The delivered target dose was then estimated by accumulating the dose from all control points in the plan. On the basis of this information, dose-volume histograms and 3-dimensional dose distributions were calculated to assess their degradation from the planned dose caused by target motion. Thirty-two prostate motion trajectories were analyzed.

RESULTS

The minimum dose to 0.03 cm(3) of the gross tumor volume (D0.03cc) was only slightly degraded after taking motion into account, with a minimum value of 94.1% of the planned dose among all patients and fractions. However, the gross tumor volume receiving prescription dose (V100%) could be largely affected by motion, dropping below 60% in 1 trajectory. We did not observe a correlation between motion magnitude and dose degradation.

CONCLUSIONS

Prostate motion degrades the delivered dose to the target in an unpredictable way, although its effect is reduced over multiple fractions, and for most patients the degradation is small. Patients with greater prostate motion or those treated with stereotactic body radiation therapy would benefit from real-time prostate tracking to reduce the margin.

Prostate stereotactic ablative radiation therapy using volumetric modulated arc therapy to dominant intraprostatic lesions

PURPOSE

To investigate boosting dominant intraprostatic lesions (DILs) in the context of stereotactic ablative radiation therapy (SABR) and to examine the impact on tumor control probability (TCP) and normal tissue complication probability (NTCP).

METHODS AND MATERIALS

Ten prostate datasets were selected. DILs were defined using T2-weighted, dynamic contrast-enhanced and diffusion-weighted magnetic resonance imaging. Four plans were produced for each dataset: (1) no boost to DILs; (2) boost to DILs, no seminal vesicles in prescription; (3) boost to DILs, proximal seminal vesicles (proxSV) prescribed intermediate dose; and (4) boost to DILs, proxSV prescribed higher dose. The prostate planning target volume (PTV) prescription was 42.7 Gy in 7 fractions. DILs were initially prescribed 115% of the PTV(Prostate) prescription, and PTV(DIL) prescriptions were increased in 5% increments until organ-at-risk constraints were reached. TCP and NTCP calculations used the LQ-Poisson Marsden, and Lyman-Kutcher-Burman models respectively.

RESULTS

When treating the prostate alone, the median PTV(DIL) prescription was 125% (range: 110%-140%) of the PTV(Prostate) prescription. Median PTV(DIL) D50% was 55.1 Gy (range: 49.6-62.6 Gy). The same PTV(DIL) prescriptions and similar PTV(DIL) median doses were possible when including the proxSV within the prescription. TCP depended on prostate α/β ratio and was highest with an α/β ratio = 1.5 Gy, where the additional TCP benefit of DIL boosting was least. Rectal NTCP increased with DIL boosting and was considered unacceptably high in 5 cases, which, when replanned with an emphasis on reducing maximum dose to 0.5 cm(3) of rectum (Dmax(0.5cc)), as well as meeting existing constraints, resulted in considerable rectal NTCP reductions.

CONCLUSIONS

Boosting DILs in the context of SABR is technically feasible but should be approached with caution. If this therapy is adopted, strict rectal constraints are required including Dmax(0.5cc). If the α/β ratio of prostate cancer is 1.5 Gy or less, then high TCP and low NTCP can be achieved by prescribing SABR to the whole prostate, without the need for DIL boosting.

Survey of stereotactic ablative body radiotherapy in the UK by the QA group on behalf of the UK SABR Consortium

OBJECTIVE

To ascertain the progress being made towards the implementation of stereotactic ablative body radiotherapy (SABR) treatment in the UK, to obtain details of current practice in centres with an active treatment programme and to assess the projected future provision.

METHODS

In August 2012, an online questionnaire was sent to all 65 UK radiotherapy institutions. The included questions covered the current number of patients being treated and the intended number of patients for each clinical site; immobilization and motion management methods; CT scanning protocols; target and organ-at-risk delineation; treatment planning; image-guidance and treatment protocols; and quality assurance methods.

RESULTS

48/65 (74%) institutions responded by the end of November 2012, with 15 indicating an active SABR programme. A further four centres indicated that a SABR protocol had been established but was not yet in clinical use. 14 of the 29 remaining responses stated an intention to develop a SABR programme in the next 2 years.

CONCLUSION

The survey responses confirm that SABR provision in the UK is increasing and that this should be expected to continue in the next 2 years. A projection of the future uptake would suggest that by the end of 2014, UK SABR provision will be broadly in line with international practice.

Stereotactic body radiotherapy: a critical review for nonradiation oncologists

Stereotactic body radiotherapy (SBRT) involves the treatment of extracranial primary tumors or metastases with a few, high doses of ionizing radiation. In SBRT, tumor kill is maximized and dose to surrounding tissue is minimized, by precise and accurate delivery of multiple radiation beams to the target. This is particularly challenging, because extracranial lesions often move with respiration and are irregular in shape, requiring careful treatment planning and continual management of this motion and patient position during irradiation. This review presents the rationale, process workflow, and technology for the safe and effective administration of SBRT, as well as the indications, outcome, and limitations for this technique in the treatment of lung cancer, liver cancer, and metastatic disease.

La Radioterapia Nel Trattamento Del Carcinoma Della Prostata: Indicazioni, Evoluzione Tecnologica e Approcci Integrati

Prostate cancer is a heterogeneous, indolent or sometimes aggressive tumor. Treatment options are various and without proved superiority. Radiotherapy (RT) plays a key role in the disease history. Technological evolution with Intensity Modulate Radiation Therapy (IMRT) and Image Guided Radiation Therapy (IGRT) allowed improvement, with significant results on local control and survival. Hypofractionation, Stereotactic Body RT (SBRT) and new brachytherapy approachs are still under investigation, with promising opportunities. Adjuvant vs salvage postoperative RT, hormone association, prophylactic pelvic irradiation are still under debate, but guidelines express overlapping indications.

Multidisciplinary managements will be the future for care optimization, providing the best tool for holistic and informed patients' choice.

Stereotactic body radiotherapy in prostate cancer: is rapidarc a better solution than cyberknife?

AIMS

There is increasing interest in stereotactic body radiotherapy (SBRT) for the management of prostate adenocarcinoma, with encouraging initial biological progression-free survival results. However, the limited literature is dominated by the use of the Cyberknife platform. This led to an international phase III study comparing outcomes for Cyberknife SBRT with both surgery and conventionally fractionated intensity-modulated radiotherapy (the PACE study). We aim to compare Cyberknife delivery with Rapidarc, a more widely available treatment platform.

MATERIALS AND METHODS

The scans of six previous prostate radiotherapy patients with a range of prostate sizes were chosen. The clinical target volume was defined as the prostate gland, with 3 mm added for the Cyberknife planning target volume (PTV) and 5 mm for the Rapidarc PTV. Accuray multiplan v. 4.5 was used for planning with delivery on a Cyberknife VSI system v9.5; Varian Eclipse v10 was used for Rapidarc planning with delivery using a Varian 21EX linear accelerator. Both systems attempted to deliver at least 35 Gy to the PTV in five fractions with PTV heterogeneity <12%.

RESULTS

All organ at risk (OAR) constraints were achieved by both platforms, whereas the Cyberknife failed to achieve the desired PTV homogeneity constraint in two cases. In other OARs without constraints, Cyberknife delivered higher doses. The volume of the 35 Gy isodose was slightly larger with Rapidarc, but conversely at doses <35 Gy normal tissues received higher doses with Cyberknife. The mean planning and delivery time was in favour of Rapidarc.

CONCLUSIONS

We have shown that there is no discernible dosimetric advantage to choosing Cyberknife over Rapidarc for SBRT delivery in prostate cancer. Given the significant benefits of Rapidarc in terms of availability, planning and delivery time, the authors suggest that phase III trials of SBRT should include Rapidarc or equivalent rotational delivery platforms.

Low rectal toxicity after dose escalated IMRT treatment of prostate cancer using an absorbable hydrogel for increasing and maintaining space between the rectum and prostate: results of a multi-institutional phase II trial

PURPOSE

To evaluate the safety and efficacy of an absorbable hydrogel when injected between the rectum and prostate to reduce rectal radiation toxicity in adult men undergoing Intensity Modulated Radiotherapy (IMRT) for treatment of low and intermediate risk prostate cancer.

METHODS

This prospective, non-randomized, multi-center, single arm, open-label study included 52 men with a confirmed diagnosis of prostate cancer. They received transperineal injection of the hydrogel and 3-5 days after injection the simulation scans. All patients received IMRT (78Gy delivered, 2 Gy per fraction). Space stability was evaluated by using MRI or CT. Gastrointestinal (GI) and genitourinary (GU) toxicity was assessed using RTOG/EORTC scoring system and proctoscopy after 12 months. The median follow up time was 12 months.

RESULTS

Hydrogel application was straight forward using brachytherapy equipment and techniques, with minimal patient discomfort. Six patients (12%) experienced acute GI Grade 2 toxicity, with no patients experiencing Grade 3 or 4 toxicity. In addition, no patients had early late GI toxicity ≥ Grade 2 after 12 months. The gel was stable during the course of radiotherapy and was not detectable in MRI after 9-12 months due to absorption in 42 of 43 patients.

CONCLUSION

These data demonstrated that the hydrogel is a safe method to displace the rectal wall away from the prostate therefore substantially reducing toxicity to the rectum.

Gastrointestinal radiation injury: Prevention and treatment

With the recent advances in detection and treatment of cancer, there is an increasing emphasis on the efficacy and safety aspects of cancer therapy. Radiation therapy is a common treatment for a wide variety of cancers, either alone or in combination with other treatments. Ionising radiation injury to the gastrointestinal tract is a frequent side effect of radiation therapy and a considerable proportion of patients suffer acute or chronic gastrointestinal symptoms as a result. These side effects often cause morbidity and may in some cases lower the efficacy of radiotherapy treatment. Radiation injury to the gastrointestinal tract can be minimised by either of two strategies: technical strategies which aim to physically shift radiation dose away from the normal intestinal tissues, and biological strategies which aim to modulate the normal tissue response to ionising radiation or to increase its resistance to it. Although considerable improvement in the safety of radiotherapy treatment has been achieved through the use of modern optimised planning and delivery techniques, biological techniques may offer additional further promise. Different agents have been used to prevent or minimize the severity of gastrointestinal injury induced by ionising radiation exposure, including biological, chemical and pharmacological agents. In this review we aim to discuss various technical strategies to prevent gastrointestinal injury during cancer radiotherapy, examine the different therapeutic options for acute and chronic gastrointestinal radiation injury and outline some examples of research directions and considerations for prevention at a pre-clinical level.

Prostate alpha/beta revisited -- an analysis of clinical results from 14 168 patients

PURPOSE

To determine the dose response parameters and the fractionation sensitivity of prostate tumours from clinical results of patients treated with external beam radiotherapy.

MATERIAL AND METHODS

The study was based on five-year biochemical results from 14 168 patients treated with external beam radiotherapy. Treatment data from 11 330 patients treated with conventional fractionation have been corrected for overall treatment time and fitted with a logit equation. The results have been used to determine the optimum α/β values that minimise differences in predictions from 2838 patients treated with hypofractionated schedules.

RESULTS

Conventional fractionation data yielded logit dose response parameters for all risk groups and for all definitions of biochemical failures. The analysis of hypofractionation data led to very low α/β values (1-1.7 Gy) in all mentioned cases. Neglecting the correction for overall treatment time has little impact on the derivation of α/β values for prostate cancers.

CONCLUSIONS

These results indicate that the high fractionation sensitivity is an intrinsic property of prostate carcinomas and they support the use of hypofractionation to increase the therapeutic gain for these tumours.

Radiation treatment for patients with intermediate-risk prostate cancer

Around 70% of men presenting with prostate cancer will have organ-confined disease, with the majority presenting with low- or intermediate-risk prostate cancer. This article reviews the evidence supporting the current standard of care in radiation oncology for the evaluation and management of men with intermediate-risk prostate cancer. Dose escalation, hormonal therapy, combined modality therapy, and modern techniques for the delivery of radiation therapy are reviewed.

Stereotactic body radiation therapy for prostate cancer

Stereotactic body radiation therapy (SBRT) is a promising treatment option for prostate cancer. Hypofractionation regimens, such as SBRT, may be more advantageous compared with conventional regimens because low α:β ratio of prostate cancer has high sensitivity to dose per fraction. In addition, a smaller and tighter margin with SBRT is expected to provide a low toxicity rate without reducing tumor control. The purpose of this article is to examine radiobiological, technical and clinical aspects of SBRT for prostate cancer.

A survey of stereotactic body radiotherapy use in the United States

BACKGROUND

Stereotactic body radiotherapy (SBRT) is a technique used to deliver high, ablative doses of radiation in a limited number of fractions to ≥ 1 extracranial target(s). To the authors' knowledge, the prevalence of SBRT use among radiation oncologists in the United States is unknown.

METHODS

A random sample of 1600 American radiation oncologists was surveyed via e-mail and facsimile (fax) regarding SBRT usage, including year of adoption, motivations, disease sites treated, and common prescriptions used.

RESULTS

Of 1373 contactable physicians, 551 responses (40.1%) were received. The percentage of physicians using SBRT was 63.9% (95% confidence interval, 60%-68%), of whom nearly half adopted it in 2008 or later. The most commonly cited reasons for adopting SBRT were to allow the delivery of higher than conventional radiation doses (90.3%) and to allow retreatment (73.9%) in select patients. Academic physicians were more likely to report research as a motivation for SBRT adoption, whereas physicians in private practice were more likely to list competitive reasons. Among SBRT users, the most common disease sites treated were lung (89.3%), spine (67.5%), and liver (54.5%) tumors. Overall, 76.0% of current SBRT users planned to increase their use, whereas 66.5% of nonusers planned to adopt the technology in the future.

CONCLUSIONS

SBRT has rapidly become a widely adopted treatment approach among American radiation oncologists. Further research and prospective trials are necessary to assess the benefits and risks of this novel technology.

Robotic image-guided stereotactic radiotherapy, for isolated recurrent primary, lymph node or metastatic prostate cancer

PURPOSE

To evaluate the outcome of robotic CyberKnife (Accuray, Sunnyvale, CA)-based stereotactic radiotherapy (CBK-SRT) for isolated recurrent primary, lymph node, or metastatic prostate cancer.

METHODS AND MATERIALS

Between May 2007 and December 2009, 34 consecutive patients/38 lesions were treated (15 patients reirradiated for local recurrence [P], 4 patients reirradiated for anastomosis recurrence [A], 16 patients treated for single lymph node recurrence [LN], and 3 patients treated for single metastasis [M]). In all but 4 patients, [(11)C]choline positron emission tomography/computed tomography was performed. CBK-SRT consisted of reirradiation and first radiotherapy in 27 and 11 lesions, respectively. The median CBK-SRT dose was 30 Gy in 4.5 fractions (P, 30 Gy in 5 fractions; A, 30 Gy in 5 fractions; LN, 33 Gy in 3 fractions; and M, 36 Gy in 3 fractions). In 18 patients (21 lesions) androgen deprivation was added to CBK-SRT (median duration, 16.6 months).

RESULTS

The median follow-up was 16.9 months. Acute toxicity included urinary events (3 Grade 1, 2 Grade 2, and 2 Grade 3 events) and rectal events (1 Grade 1 event). Late toxicity included urinary events (3 Grade 1, 2 Grade 2, and 2 Grade 3 events) and rectal events (1 Grade 1 event and 1 Grade 2 event). Biochemical response was observed in 32 of 38 evaluable lesions. Prostate-specific antigen stabilization was seen for 4 lesions, and in 2 cases prostate-specific antigen progression was reported. The 30-month progression-free survival rate was 42.6%. Disease progression was observed for 14 lesions (5, 2, 5, and 2 in Groups P, A, LN, and M respectively). In only 3 cases, in-field progression was seen. At the time of analysis (May 2010), 19 patients are alive with no evidence of disease and 15 are alive with disease.

CONCLUSIONS

CyberKnife-based stereotactic radiotherapy is a feasible approach for isolated recurrent primary, lymph node, or metastatic prostate cancer, offering excellent in-field tumor control and a low toxicity profile. Further investigation is warranted to identify the patients who benefit most from this treatment modality. The optimal combination with androgen deprivation should also be defined.

CyberKnife radiosurgery for prostate cancer

Treatment of prostate cancer with SBRT is an area of significant controversy for many in the radiation oncology community despite radiobiologic data that strongly suggest the prostate would be an excellent SBRT target. Recently, new data have emerged that show promising outcomes with minimal toxicity for CyberKnife SBRT of prostate cancer. In the following we present the motivating factors for prostate cancer SBRT followed by a critical evaluation of the current literature and discussion of the future of prostate cancer treatment with SBRT.