Large prostate gland size is not a contraindication to low-dose-rate brachytherapy for prostate adenocarcinoma

Stereotactic Body Radiation Therapy for the Curative Treatment of Prostate Cancer in Ultralarge (≥100 cc) Glands

PURPOSE

Historically, toxicity concerns have existed in patients with large prostate glands treated with radiation therapy, particularly brachytherapy. There are questions whether this risk extends to stereotactic body radiation therapy (SBRT). In this retrospective review, we examine clinical outcomes of patients with prostate glands ≥100 cc treated curatively with SBRT.

METHODS AND MATERIALS

We retrospectively analyzed a large institutional database to identify patients with histologically confirmed localized prostate cancer in glands ≥100 cc, who were treated with definitive-robotic SBRT. Prostate volume (PV) was determined by treatment planning magnetic resonance imaging. Toxicity was measured using Common Terminology Criteria for Adverse Events, version 5.0. Many patients received the Expanded Prostate Cancer Index Composite Quality of Life questionnaires. Minimum follow-up (FU) was 2 years.

RESULTS

Seventy-one patients were identified with PV ≥100 cc. Most had grade group (GG) 1 or 2 (41% and 37%, respectively) disease. All patients received a total dose of 3500 to 3625 cGy in 5 fractions. A minority (27%) received androgen deprivation therapy (ADT), which was used for gland size downsizing in only 10% of cases. Nearly half (45%) were taking GU medications for urinary dysfunction before RT. Median toxicity FU was 4.0 years. Two-year rates of grade 1+ genitourinary (GU), grade 1+ gastrointestinal (GI), and grade 2+ GU toxicity were 43.5%, 15.9%, and 30.4%, respectively. Total grade 3 GU toxicities were very limited (2.8%). There were no grade 3 GI toxicities. On logistic regression analysis, pretreatment use of GU medications was significantly associated with increased rate of grade 2+ GU toxicity (odds ratio, 3.19; P = .024). Furthermore, PV (analyzed as a continuous variable) did not have an effect on toxicity, quality of life, or oncologic outcomes.

CONCLUSIONS

With early FU, ultra large prostate glands do not portend increased risk of high-grade toxicity after SBRT but likely carry an elevated risk of low-grade GU toxicity.

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

Purpose/Objectives

To compare the dose escalation potential of stereotactic body proton therapy (SBPT) versus stereotactic body photon therapy (SBXT) using high-dose rate prostate brachytherapy (HDR-B) dose-prescription metrics.

Patients and Methods

Twenty-five patients previously treated with radiation for prostate cancer were identified and stratified by prostate size (≤ 50cc; n = 13, > 50cc; n = 12). Initial CT simulation scans were re-planned using SBXT and SBPT modalities using a prescription dose of 19Gy in 2 fractions. Target coverage goals were designed to mimic the dose distributions of HDR-B and maximized to the upper limit constraint for the rectum and urethra. Dosimetric parameters between SBPT and SBXT were compared using the signed-rank test and again after stratification for prostate size (≤ 50cm³ and >50cm³) using the Wilcoxon rank test.

Results

Prostate volume receiving 100% of the dose (V100) was significantly greater for SBXT (99%) versus SBPT (96%) (P ≤ 0.01), whereas the median V125 (82% vs. 73%, P < 0.01) and V200 (12% vs. 2%, P < 0.01) was significantly greater for SBPT compared to SBXT. Median V150 was 49% for both cohorts (P = 0.92). V125 and V200 were significantly correlated with prostate size. For prostates > 50cm³, V200 was significantly greater with SBPT compared to SBXT (14.5% vs. 1%, P = 0.005), but not for prostates 50cm³ (9% vs 4%, P = 0.11). Median dose to 2cm³ of the bladder neck was significantly lower with SBPT versus SBXT (9.6 Gy vs. 14 Gy, P < 0.01).

Conclusion

SBPT and SBXT can be used to simulate an HDR-B boost for locally advanced prostate cancer. SBPT demonstrated greater dose escalation potential than SBXT. These results are relevant for future trial design, particularly in patients with high risk prostate cancer who are not amenable to brachytherapy.

Patient-reported health-related quality of life outcomes after HDR brachytherapy between small (<60 cc) and large (≥60 cc) prostate glands

PURPOSE

Patients with large prostate glands are underrepresented in clinical trials incorporating brachytherapy due to concerns for excessive toxicity. We sought to compare health-related quality of life (HRQOL) outcomes between small (<60 cc) and large (≥60 cc) prostates treated with high-dose-rate brachytherapy (HDR-B).

METHODS AND MATERIALS

One hundred thirty patients at Emory University were treated with HDR-B monotherapy (n = 75) or HDR-B in combination with external beam radiation therapy (n = 55). American Urologic Association Symptom Score (AUASS) and expanded prostate cancer index composite for clinical practice (EPIC-CP) scores were recorded. A linear mixed model was performed dichotomizing prostate volume (<60 and ≥ 60 cc) with AUASS, individual EPIC-CP domains (urinary incontinence, urinary irritation/obstruction [UIO], bowel function, sexual function, and vitality/hormonal function), and overall EPIC-CP HRQOL scores.

RESULTS

Median followup was 22.6 months (range 2.2-55.8). The median gland volume for the entire cohort (n = 130), <60 cc cohort (n = 104), and ≥60 cc cohort (n = 26) was 44 cc, 41.1 cc, and 68.0 cc, respectively. There were no baseline differences in HRQOL scores between cohorts. At 2 months, AUASS and UIO scores increased similarly between cohorts (AUASS p = 0.807; UIO p = 0.539), then decreased (longitudinal effect p < 0.001 and p = 0.005, respectively) to remain not significantly different at 12 months (AUASS p = 0.595; UIO p = 0.673). Overall, prostate volume was not significantly associated with change in AUASS (p = 0.403), urinary incontinence (p = 0.322), UIO symptoms (p = 0.779), bowel symptoms (p = 0.757), vitality/hormonal symptoms (p = 0.503), or overall HRQOL (p = 0.382).

CONCLUSIONS

In appropriately selected patients, HDR-B appears well tolerated in patients with ≥60 cc prostate glands without an increase in patient-reported toxicity. Volume should not be a strict contraindication in those with adequate baseline function.

The evolution of brachytherapy for prostate cancer

Brachytherapy (BT), using low-dose-rate (LDR) permanent seed implantation or high-dose-rate (HDR) temporary source implantation, is an acceptable treatment option for select patients with prostate cancer of any risk group. The benefits of HDR-BT over LDR-BT include the ability to use the same source for other cancers, lower operator dependence, and - typically - fewer acute irritative symptoms. By contrast, the benefits of LDR-BT include more favourable scheduling logistics, lower initial capital equipment costs, no need for a shielded room, completion in a single implant, and more robust data from clinical trials. Prospective reports comparing HDR-BT and LDR-BT to each other or to other treatment options (such as external beam radiotherapy (EBRT) or surgery) suggest similar outcomes. The 5-year freedom from biochemical failure rates for patients with low-risk, intermediate-risk, and high-risk disease are >85%, 69-97%, and 63-80%, respectively. Brachytherapy with EBRT (versus brachytherapy alone) is an appropriate approach in select patients with intermediate-risk and high-risk disease. The 10-year rates of overall survival, distant metastasis, and cancer-specific mortality are >85%, <10%, and <5%, respectively. Grade 3-4 toxicities associated with HDR-BT and LDR-BT are rare, at <4% in most series, and quality of life is improved in patients who receive brachytherapy compared with those who undergo surgery.

Comparison of outcomes and toxicities among radiation therapy treatment options for prostate cancer

We review radiation therapy (RT) options available for prostate cancer, including external beam (EBRT; with conventional fractionation, hypofractionation, stereotactic body RT [SBRT]) and brachytherapy (BT), with an emphasis on the outcomes, toxicities, and contraindications for therapies. PICOS/PRISMA methods were used to identify published English-language comparative studies on PubMed (from 1980 to 2015) that included men treated on prospective studies with a primary endpoint of patient outcomes, with ⩾70 patients, and ⩾5year median follow up. Twenty-six studies met inclusion criteria; of these, 16 used EBRT, and 10 used BT. Long-term freedom from biochemical failure (FFBF) rates were roughly equivalent between conventional and hypofractionated RT with intensity modulation (evidence level 1B), with 10-year FFBF rates of 45-90%, 40-60%, and 20-50% (for low-, intermediate-, and high-risk groups, respectively). SBRT had promising rates of BF, with shorter follow-up (5-year FFBF of >90% for low-risk patients). Similarly, BT (5-year FFBF for low-, intermediate-, and high-risk patients have generally been >85%, 69-97%, 63-80%, respectively) and BT+EBRT were appropriate in select patients (evidence level 1B). Differences in overall survival, distant metastasis, and cancer specific mortality (5-year rates: 82-97%, 1-14%, 0-8%, respectively) have not been detected in randomized trials of dose escalation or in studies comparing RT modalities. Studies did not use patient-reported outcomes, through Grade 3-4 toxicities were rare (<5%) among all modalities. There was limited evidence available to compare proton therapy to other modalities. The treatment decision for a man is usually based on his risk group, ability to tolerate the procedure, convenience for the patient, and the anticipated impact on quality of life. To further personalize therapy, future trials should report (1) race; (2) medical comorbidities; (3) psychiatric comorbidities; (4) insurance status; (5) education status; (6) marital status; (7) income; (8) sexual orientation; and (9) facility-related characteristics.