Dose-Escalated Robotic SBRT for Stage I-II Prostate Cancer

Biologically effective doses of 60-70Gy versus >70Gy of stereotactic body radiotherapy (SBRT) combined with chemotherapy in locally advanced pancreatic cancer: protocol of a single-centre, phase II clinical trial

INTRODUCTION

There is a paucity of studies about whether dose escalation of stereotactic body radiation therapy (SBRT) prolongs survival compared with de-escalation for patients with locally advanced pancreatic cancer (LAPC). Therefore, the aim of the study is to compare the survival benefits of biologically effective dose (BED₁₀, α/β=10) of 60-70 Gy with those of BED₁₀ >70 Gy.

METHODS AND ANALYSIS

This study is a single-centre, phase II trial. Patients with LAPC are randomly allocated to receive SBRT with BED₁₀ of 60-70 Gy or >70 Gy in 5-6 fractions combined with gemcitabine plus albumin-bound paclitaxel. The primary outcome is progression-free survival. The secondary outcomes are adverse events, local control and overall survival.

ETHICS AND DISSEMINATION

The trial protocol has been approved by the Ethics committee of Shanghai Changhai Hospital. The ethics number is CHEC2020-100. Study results will be disseminated through peer-reviewed journals and released in related medical conferences.

TRIAL REGISTRATION NUMBERS

NCT04603586.

Plan comparison of prostate stereotactic radiotherapy in spacer implant patients

In prostate stereotactic body radiation therapy (SBRT), hydrogel spacers are increasingly used. This study aimed to perform a dosimetry comparison of treatment plans using CyberKnife (CK), commonly used for prostate SBRT, Helical TomoTherapy (HT), and TrueBeam (TB) in patients with hydrogel spacer implantations. The data of 20 patients who received hydrogel spacer implantation for prostate SBRT were retrospectively analyzed. The prescription dose was 36.25 Gy in five fractions to 95% of the planning target volume (PTV; D95). The conformity index (CI), gradient index (GI), homogeneity index (HI), and dose‐volume histogram (DVH) were analyzed for the three modalities, using the same PTV margins. The monitor unit (MU) and the beam‐on‐time (BOT) values were subsequently compared. The CI of TB (0.93 ± 0.02) was significantly superior to those of CK (0.82 ± 0.03, p < 0.01) and HT (0.86 ± 0.03, p < 0.01). Similarly, the GI value of TB (3.59 ± 0.12) was significantly better than those of CK (4.31 ± 0.43, p < 0.01) and HT (4.52 ± 0.24, p < 0.01). The median doses to the bladder did not differ between the CK and TB (V18.1 Gy: 16.5% ± 4.5% vs. 15.8% ± 4.4%, p = 1.00), but were significantly higher for HT (V18.1 Gy: 33.2% ± 7.3%, p < 0.01 vs. CK, p < 0.01 vs. TB). The median rectal dose was significantly lower for TB (V18.1 Gy: 5.6% ± 4.5%) than for CK (V18.1 Gy: 11.2% ± 6.7%, p < 0.01) and HT (20.2% ± 8.3%, p < 0.01). TB had the shortest BOT (2.6 min; CK: 17.4 min, HT: 6.9 min). TB could create treatment plans dosimetrically comparable to those of CK when using the same margins, in patients with hydrogel spacers.

Management of Lower Urinary Tract Symptoms after Prostate Radiation

PURPOSE OF REVIEW

To present urologists with guidance on how to approach and manage lower urinary tract symptoms (LUTS) in patients who have undergone radiation therapy (RT) for prostate cancer.

RECENT FINDINGS

There are few studies that specifically examine treatment approaches for LUTS in patients who have undergone prostate cancer RT. LUTS after prostate RT are unique when compared to de novo LUTS. Understanding these distinctions is important for urologists' practice as well as patients' quality of life. Discussion of the risks and management of post-RT LUTS should be included in the shared decision-making process when counseling patients on various treatment options for prostate cancer. Further studies evaluating treatments for storage and voiding symptoms after RT are needed to help guide future care.

Stereotactic body radiotherapy with periprostatic hydrogel spacer for localized prostate cancer: toxicity profile and early oncologic outcomes

Background

Multiple phase I-II clinical trials have reported on the efficacy and safety of prostate stereotactic body radiotherapy (SBRT) for the treatment of prostate cancer. However, few have reported outcomes for prostate SBRT using periprostatic hydrogel spacer (SpaceOAR; Augmenix). Herein, we report safety and efficacy outcomes from our institutional prostate SBRT experience with SpaceOAR placement.

Methods

Fifty men with low- or intermediate-risk prostate cancer treated at a single institution with linear accelerator-based SBRT to 3625 cGy in 5 fractions, with or without androgen deprivation therapy (ADT) were included. All patients underwent SpaceOAR and fiducial marker placement followed by pre-treatment MRI. Toxicity assessments were conducted at least weekly while on treatment, 1 month after treatment, and every follow-up visit thereafter. Post-treatment PSA measurements were obtained 4 months after SBRT, followed by every 3–6 months thereafter. Acute toxicity was documented per RTOG criteria.

Results

Median follow up time was 20 (range 4–44) months. Median PSA at time of diagnosis was 7.4 (2.7–19.5) ng/ml. Eighteen men received 6 months of ADT for unfavorable intermediate risk disease. No PSA failures were recorded. Median PSA was 0.9 ng/mL at 20 months; 0.08 and 1.32 ng/mL in men who did and did not receive ADT, respectively. Mean prostate-rectum separation achieved with SpaceOAR was 9.6 ± 4 mm at the prostate midgland.

No grade ≥ 3 GU or GI toxicity was recorded. During treatment, 30% of men developed new grade 2 GU toxicity (urgency or dysuria). These symptoms were present in 30% of men at 1 month and in 12% of men at 1 year post-treatment. During treatment, GI toxicity was limited to grade 1 symptoms (16%), although 4% of men developed grade 2 symptoms during the first 4 weeks after SBRT. All GI symptoms were resolving by the 1 month post-treatment assessment and no acute or late rectal toxicity was reported > 1 month after treatment.

Conclusions

Periprostatic hydrogel placement followed by prostate SBRT resulted in minimal GI toxicity, and favorable early oncologic outcomes. These results indicate that SBRT with periprostatic spacer is a well-tolerated, safe, and convenient treatment option for localized prostate cancer.

Electronic supplementary material

The online version of this article (10.1186/s13014-019-1346-5) contains supplementary material, which is available to authorized users.

Reirradiation for isolated local recurrence of prostate cancer: Mono-institutional series of 64 patients treated with salvage stereotactic body radiotherapy (SBRT)

OBJECTIVE:

To evaluate high-precision external beam reirradiation (re-EBRT) for local relapse of prostate cancer (PCa) after radiotherapy.

METHODS:

This retrospective study included patients with biochemical failure and evidence of isolated local recurrence of PCa after radical/salvage EBRT or brachytherapy that received salvage stereotactic body radiation therapy (SBRT, re-EBRT). Biopsy was not mandatory if all diagnostic elements were univocal (prostate specific antigen evolution, choline-positron emission tomography or magnetic resonance imaging). Salvage SBRT (re-EBRT) was delivered with image-guided radiation therapy (RapidArc®, VERO® and CyberKnife®).

RESULTS:

Data of 64 patients were included, median age at salvage SBRT was 73.2 years, median pre-salvage SBRT prostate specific antigen was 3.89  ng ml-1 . Median total dose was 30  Gy in five fractions, biologically effective dose (BED) of 150  Gy. One acute G3 genitourinary event and one late G3 genitourinary event were observed. No G ≥ 3 bowel toxicity was registered. At the median follow-up of 26.1 months, tumor progression was observed in 41 patients (64%). 18 patients (28%) experienced local relapse. 2-year local control, biochemical and clinical relapse free survival rates were 75, 40 and 53%, respectively. With BED ≥130  Gy 1-year biochemical and clinical progression-free survival rate were 85 and 90%, respectively.

CONCLUSIONS:

Salvage SBRT (re-EBRT) for isolated local PCa recurrence is a safe, feasible and noninvasive salvage treatment. Further investigation is warranted to define the optimal patient selection, dose and volume parameters.

ADVANCES IN KNOWLEDGE:

Salvage SBRT reirradiation for the locally recurrent PCa offer a satisfactory tumor control and excellent toxicity profile, if BED ≥130 Gy is administered.

Dose escalation for prostate stereotactic ablative radiotherapy (SABR): Late outcomes from two prospective clinical trials

PURPOSE

Optimal prostate SABR dose-fractionation is unknown. This study compares long-term outcomes from two prospective trials.

METHODS

Study1 patients had low-risk PCa and received 35 Gy/5. Study2 patients had low/intermediate-risk PCa and received 40 Gy/5. Biochemical failure (BF) was defined as nadir + 2.

RESULTS

114 patients were included (study1, n = 84; study2, n = 30). Median follow-up was 9.6 years and 6.9 years. Median nPSA was 0.4 and 0.1 ng/ml. Nine patients had BF (8 in study1, 1 in study2); two were managed with ADT and four had local salvage. The BF rate was 2.5% and 12.8% at 5 and 10 years for study1 and 3.3% at 5 years for study 2. BF probability was 0% if PSA <0.4 at 4 years, and 20.5% at 10 years if PSA ≥0.4 (p = 0.02). Nine patients died, none of PCa. No patient has metastases or castrate-resistance. At 10 years, OS and CSS were 90.4% (p = 0.25) and 100%.

CONCLUSIONS

Dose-escalated prostate SABR was associated with lower nPSAs but no difference in BF, OS, CSS or MFS. PSA <0.4 at 4 years was a predictor of biochemical control. Half of patients with BF were successfully salvaged. Given that this is a favorable-risk cohort, longer follow-up will be needed to see if the lower nPSA translates into lower BF rates.

Comparison of multileaf collimator and conventional circular collimator systems in Cyberknife stereotactic radiotherapy

Multileaf collimator (MLC) technology has been newly introduced with the Cyberknife system. This study investigated the advantages of this system compared with the conventional circular collimator (CC) system. Dosimetric comparisons of MLC and CC plans were carried out. First, to investigate suitable target sizes for the MLC mode, MLC and CC plans were generated using computed tomography (CT) images from 5 patients for 1, 3, 5 and 7 cm diameter targets. Second, MLC and CC plans were compared in 10 patients, each with liver and prostate targets. For brain targets, doses to the brain could be spared in MLC plans better than in CC plans (P ≤ 0.02). The MLC mode also achieved more uniform dose delivery to the targets. The conformity index in MLC plans was stable, irrespective of the target size (P = 0.5). For patients with liver tumors, the MLC mode achieved higher target coverage than the CC mode (P = 0.04). For prostate tumors, doses to the rectum and the conformity index were lowered in MLC plans compared with in CC plans (P ≤ 0.04). In all target plans, treatment times in MLC plans were shorter than those in CC plans (P < 0.001). The newly introduced MLC technology can reduce treatment time and provide favorable or comparable dose distribution for 1-7 cm targets. In particular, the MLC mode has dosimetric advantage for targets near organs at risk. Therefore, the MLC mode is recommended as the first option in stereotactic body radiotherapy.

The Role of Hypofractionated Radiotherapy in Prostate Cancer

PURPOSE OF REVIEW

It is now accepted that prostate cancer has a low alpha/beta ratio, establishing a strong basis for hypofractionation of prostate radiotherapy. This review focuses on the rationale for hypofractionation and presents the evidence base for establishing moderate hypofractionation for localised disease as the new standard of care. The emerging evidence for extreme hypofractionation in managing localized and oligometastatic prostate cancer is reviewed.

RECENT FINDINGS

The 5-year efficacy and toxicity outcomes from four phase III studies have been published within the last 12 months. These studies randomizing over 6000 patients to conventional fractionation (1.8-2.0 Gy per fraction) or moderate hypofractionation (3.0-3.4 Gy per fraction). They demonstrate hypofractionation to be non-inferior to conventional fractionation. Moderate hypofractionation for localized prostate cancer is safe and effective. There is a growing body of evidence in support of extreme hypofractionation for localized prostate cancer. Extreme hypofractionation may have a role in managing prostate oligometastases, but further studies are needed.

Exploring Value From the Patient's Perspective Between Modern Radiation Therapy Modalities for Localized Prostate Cancer

PURPOSE

Patients' perspectives on their treatment experiences have not been compared between modern radiation modalities for localized prostate cancer. We evaluated treatment regret and patients' perceptions of their treatment experiences to better inform our understanding of a treatment's value.

METHODS AND MATERIALS

Patients with localized prostate cancer treated with stereotactic body radiation therapy (SBRT), intensity modulated radiation therapy (IMRT), or high-dose-rate (HDR) brachytherapy between 2008 and 2014 with at least 1 year of follow-up were surveyed. The questionnaire explored the decision-making experience, expectations of toxicities versus the reality, and treatment regret by means of a validated tool.

RESULTS

Three hundred twenty-nine consecutive patients were surveyed, with an 86% response rate (IMRT, n=74; SBRT, n=108; HDR, n=94). The median patient age and posttreatment follow-up time were 68 years and 47 months, respectively. Eighty-two percent of patients had T1c disease with either Gleason 6 (42%) or Gleason 7 (58%) pathologic features and a median initial prostate-specific antigen of 5.8 ng/mL. Thirteen percent expressed regret with their treatment. Among patients with regret, 71% now wish they had elected for active surveillance. The incidence of regret was significantly different between treatment modalities: 5% of patients treated with SBRT expressed regret versus 18% with HDR and 19% with IMRT (P<.01). On multivariable logistic regression, patients treated with HDR versus SBRT were 7.42 times more likely to have regret, and patients treated with IMRT versus SBRT were 11.11 times more likely to have regret (P<.01 and P<.01, respectively). Significantly more patients treated with SBRT selected that their actual long-term toxicities were significantly less than originally expected, compared with IMRT and HDR patients (SBRT 43% vs IMRT 20% vs HDR 10%, P<.01).

CONCLUSIONS

We found significant differences in patients' experiences between SBRT, IMRT, and HDR, with significantly less treatment regret and less toxicity than expected among SBRT patients. The majority of patients with regret would now opt for active surveillance; therefore, pretreatment counseling is essential.

VERO® radiotherapy for low burden cancer: 789 patients with 957 lesions

Purpose

The aim of this retrospective study is to evaluate patient profile, feasibility, and acute toxicity of RadioTherapy (RT) delivered by VERO® in the first 20 months of clinical activity.

Methods

Inclusion criteria: 1) adult patients; 2) limited volume cancer (M0 or oligometastatic); 3) small extracranial lesions; 4) treatment between April 2012 and December 2013 and 5) written informed consent. Two techniques were employed: intensity modulated radiotherapy (IMRT) and stereotactic body radiotherapy (SBRT). Toxicity was evaluated using Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer (RTOG/EORTC) criteria.

Results

Between April 2012 and December 2013, 789 consecutive patients (957 lesions) were treated. In 84% of them one lesion was treated and in 16% more than one lesion were treated synchronously/metachronously; first radiotherapy course in 85%, re-irradiation in 13%, and boost in 2% of cases. The treated region included pelvis 46%, thorax 38%, upper abdomen 15%, and neck 1%. Radiotherapy schedules included <5 and >5 fractions in 75% and 25% respectively. All patients completed the planned treatment and an acceptable acute toxicity was observed.

Conclusions

RT delivered by VERO® was administrated predominantly to thoracic and pelvic lesions (lung and urologic tumours) using hypofractionation. It is a feasible approach for limited burden cancer offering short and well accepted treatment with favourable acute toxicity profile. Further investigation including dose escalation and other available VERO® functionalities such as real-time dynamic tumour tracking is warranted in order to fully evaluate this innovative radiotherapy system.

High-quality Linac-based Stereotactic Body Radiation Therapy with Flattening Filter Free Beams and Volumetric Modulated Arc Therapy for Low-Intermediate Risk Prostate Cancer. A Mono-institutional Experience with 90 Patients

AIMS

The aim of this phase II study was to evaluate the efficacy and toxicity of stereotactic body radiotherapy in patients with low or intermediate risk prostate cancer.

MATERIALS AND METHODS

Biopsy-confirmed prostate cancer patients were enrolled, provided that they had the following characteristics: initial prostate-specific antigen (PSA) ≤ 20 ng/ml, Gleason Score < 7, International Prostate Symptom Score < 7. The treatment schedule was 35 Gy in five fractions, delivered with volumetric modulated arcs with flattening filter free beams. Toxicity was recorded according to CTCAE criteria v4.0. Biochemical failure was calculated according to the Phoenix definition. The Expanded Prostate Cancer Index Composite questionnaire was used to record health-related quality of life.

RESULTS

Between December 2011 and March 2015, 90 patients were enrolled (53 low risk, 37 intermediate risk). The median age was 71 years (range 48-82). In total, 58 (64.5%) of the patients had Gleason Score=6, the remaining had Gleason Score=7.The median initial PSA was 6.9 ng/ml (range 2.7-17.0). Acute toxicity was mild, with 32.2 patients presenting grade 1 urinary toxicity and 32.2% of patients presenting grade 2 urinary toxicity, mainly represented by urgency, dysuria and stranguria. Rectal grade 1 toxicity was found in 15.5% of patients, whereas grade 2 toxicity was recorded in 6.6% of patients. Regarding late toxicity, grade 1 proctitis was recorded in 11.1% of patients and grade 1 urinary in 38.8%; only two events of grade 2 urinary toxicity were observed (transient urethral stenosis, resolved by a 24 h catheterisation). At a median follow-up of 27 months (6-62 months) only two intermediate risk patients experienced a biochemical failure. Health-related quality of life revealed a slight worsening in all the domains during treatment, with a return to baseline 3 months after treatment.

CONCLUSIONS

Stereotactic body radiotherapy delivered using linac-based flattening filter free volumetric modulated arc radiotherapy in low and intermediate risk prostate cancer patients is associated with mild toxicity profiles and good patient-reported quality of life.

Use, complications, and costs of stereotactic body radiotherapy for localized prostate cancer

BACKGROUND

Stereotactic body radiotherapy (SBRT) for localized prostate cancer has potential advantages over traditional radiotherapies. Herein, the authors compared national trends in use, complications, and costs of SBRT with those of traditional radiotherapies.

METHODS

The authors identified men who underwent SBRT, intensity-modulated radiotherapy (IMRT), brachytherapy, and proton beam therapy as primary treatment of prostate cancer between 2004 and 2011 from Surveillance, Epidemiology, and End Results Program (SEER)-Medicare linked data. Temporal trend of therapy use was assessed using the Cochran-Armitage test. Two-year outcomes were compared using the chi-square test. Median treatment costs were compared using the Kruskal-Wallis test.

RESULTS

A total of 542 men received SBRT, 9647 received brachytherapy, 23,408 received IMRT, and 800 men were treated with proton beam therapy. There was a significant increase in the use of SBRT and proton beam therapy (P<.001), whereas brachytherapy use decreased (P<.001). A higher percentage of patients treated with SBRT and brachytherapy had low-grade cancer (Gleason score ≤ 6 vs ≥ 7) compared with individuals treated with IMRT and proton beam therapy (54.0% and 64.2% vs 35.2% and 49.6%, respectively; P<.001). SBRT compared with brachytherapy and IMRT was associated with equivalent gastrointestinal toxicity but more erectile dysfunction at 2-year follow-up (P<.001). SBRT was associated with more urinary incontinence compared with IMRT and proton beam therapy but less compared with brachytherapy (P<.001, respectively). The median cost of SBRT was $27,145 compared with $17,183 for brachytherapy, $37,090 for IMRT, and $54,706 for proton beam therapy (P<.001).

CONCLUSIONS

The use of SBRT and proton beam therapy for localized prostate cancer has increased over time. Despite men of lower disease stage undergoing SBRT, SBRT was found to be associated with greater toxicity but lower health care costs compared with IMRT and proton beam therapy. Cancer 2016;122:2496-504. © 2016 American Cancer Society.

Use of stereotactic body radiotherapy for prostate cancer in the United States from 2004 through 2012

BACKGROUND

Stereotactic body radiotherapy (SBRT) is a newer treatment option for patients with localized prostate cancer. The rates of diffusion of this technology across the United States are unknown. The goal of the current study was to describe the use of SBRT among patients with prostate cancer based on different risk groups (low, intermediate, or high risk) and by type of facility (community cancer program, comprehensive community cancer program, or academic program) in which patients were treated.

METHODS

Using the National Cancer Data Base, a national registry that contains approximately 70% of patients with cancer in the United States, the authors identified 274,466 men between the ages of 40 to 80 years who were diagnosed from 2004 to 2012 with localized prostate cancer and received radiation therapy (RT) as their initial treatment. The authors described the prevalence of SBRT use each year, and multivariable analysis was used to examine factors associated with the receipt of SBRT.

RESULTS

In 2004, SBRT use was low (<1% in all patient groups), and was observed to increase steadily each year. By 2012, 8.8% of low-risk patients treated at academic centers with RT received SBRT. Uptake of SBRT was highest in patients with low-risk or intermediate-risk disease. Multivariable analysis demonstrated that year of diagnosis, type of center, risk group, and race were all significantly associated with the use of SBRT.

CONCLUSIONS

To the authors' knowledge, the current study is the first report of the adoption of SBRT for localized prostate cancer across the United States. Diffusion was noted to be slowest at community cancer programs, reflecting potential barriers of cost or expertise for this new technology. Adoption of SBRT was found to be highest among patients with low-risk or intermediate-risk disease, in accordance with the bulk of patients included in published SBRT studies. Cancer 2016;122:2234-41. © 2016 American Cancer Society.

[Localized prostate cancer: Radiotherapeutic concepts]

BACKGROUND

Radiation therapy is an established cornerstone in the treatment of prostate cancer. Significant advances in the techniques and therapeutic concepts have been made in recent decades.

OBJECTIVES

The objective of this article is to provide an overview of current standards of care and recent technical and conceptional developments.

CONCLUSIONS

Three-dimensional conformal radiotherapy has long been the standard of care for percutaneous radiotherapy. The development of intensity-modulated radiation therapy (IMRT) and image-guided radiation therapy (IGRT) have increased the precision of treatment, thus, reducing side effects and allowing dose escalation. LDR (low dose rate) and HDR (high dose rate) brachytherapy alone or in combination are a treatment option in localized prostate cancer with a distinct side effect profile. The roles of proton therapy and stereotactic radiotherapy should be further investigated in prospective trials.

Dose-escalation of five-fraction SABR in prostate cancer: Toxicity comparison of two prospective trials

PURPOSE

To compare biochemical outcome and toxicities of two prospective 5-fraction stereotactic ablative radiotherapy (SABR) studies in prostate cancer.

MATERIALS AND METHODS

84 patients in pHART3 received 35 Gy, 30 patients in pHART6 received 40 Gy in 5-fractions to the prostate alone, once weekly. 4mm and 5mm PTV margins were used, respectively. Biochemical outcome, acute, late and cumulative genitourinary (GU)/gastrointestinal (GI) toxicities were compared.

RESULTS

Median follow-up was 74 and 36 months, respectively. Median prostate specific antigen nadir was 0.4 ng/ml and 0.3 ng/ml. 2-, 4- and 6-year biochemical relapse-free survival (bRFS-2+nadir) was 100%, 98.7% and 95.9% in pHART3; 100%, 100% and not reached in pHART6 (p=0.91). There was one acute grade 3 GU (retention) and late grade 4 GI (fistula) toxicity in pHART3, none in pHART6. One patient in each study had persisting grade 2+ toxicity at the last follow-up. pHART6 patients had a greater grade 2+ cumulative GU (5% versus 24.2%) and GI (7.6% versus 26.2%) toxicities.

CONCLUSIONS

Patients receiving dose-escalated SABR had slightly lower PSA nadir and similar bRFS, longer follow-up is needed to better estimate biochemical outcomes. There was a greater risk of grade 2 toxicity in pHART6 but not grade 3+ toxicities. Persisting toxicity at the last follow-up is similar.

Dosimetric benefits of hemigland stereotactic body radiotherapy for prostate cancer: implications for focal therapy

OBJECTIVE

Compared with standard, whole-gland (WG) therapies for prostate cancer, focal approaches may provide equivalent oncologic outcomes with fewer adverse effects. The purpose of this study was to compare organ-at-risk (OAR) dosimetry between hemigland (HG) and WG stereotactic body radiotherapy (SBRT) plans.

METHODS

Volumetric-modulated arc radiotherapy-based SBRT plans were designed to treat the left HG, right HG and WG in eight patients, using five fractions of 8 Gy. OARs of interest included the contralateral HG, rectum, urinary bladder, urethra, penile bulb and contralateral neurovascular bundle.

RESULTS

Rectal V80% (the percentage of a normal structure receiving a dose of 80%) and V90% were significantly lower with HG plans than with WG plans (median values of 4.4 vs 2.5 cm(3) and 2.1 vs 1.1 cm(3), respectively, p < 0.05 by Student's t-test). Bladder V50% was also reduced significantly in HG plans (32.3 vs 17.4 cm(3), p < 0.05), with a trend towards reduction of V100% (3.4 vs 1.3 cm(3), p = 0.09). Urethral maximum dose and mean doses to the penile bulb and contralateral neurovascular bundle were also reduced significantly (42.0 vs 39.7 Gy, p < 0.00001; 13.3 vs 9.2 Gy, p < 0.05; and 40.2 vs 19.3 Gy, p < 0.00001, respectively).

CONCLUSION

Targeting an HG volume rather than a WG volume when delivering SBRT can offer statistically significant reductions for all OARs. Given the large magnitude of the reduction in dose to these OARs, it is anticipated that HG SBRT could offer a superior toxicity profile when compared with WG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.

ADVANCES IN KNOWLEDGE

The dosimetric feasibility of HG SBRT is demonstrated. When compared with WG SBRT plans, the HG plans demonstrate statistically significant and large magnitude reduction in doses to the rectum, bladder, urethra, penile bulb and contralateral neurovascular bundle, suggesting the possibility of improved toxicity outcomes with HG SBRT. This is likely to be most relevant in the context of salvaging a local failure after radiation therapy.