Hypofractionated Boost With High-Dose-Rate Brachytherapy and Open Magnetic Resonance Imaging–Guided Implants for Locally Aggressive Prostate Cancer: A Sequential Dose-Escalation Pilot Study

Brachytherapy based microboosting to the dominant intraprostatic lesion in prostate cancer: A systematic review on treatment outcomes and toxicities

PURPOSE

Whether brachytherapy based microboosting of the dominant intraprostatic lesion (DIL) improves outcomes over standard approaches is not known. The purpose of this study is to perform a systematic review on brachytherapy microboosting of the DIL to evaluate clinical outcomes and toxicities with this treatment approach.

MATERIALS AND METHODS

This review was performed according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Databases including Pubmed, Embase, and Google Scholar were queried. About 16 studies met our inclusion criteria. These studies reported PSA control and/or toxicities based on standardized scales.

RESULTS

There were 10 studies (two monotherapy, eight combination) that used HDR microboosting on a total of 516 patients. HDR dose (EQD2 assuming alpha/beta of 1.5) to the DIL ranged from 90 to 180 Gy. Most patients were low/intermediate risk. PSA control rates at 5-8 years ranged from 69% to 100%. Acute/late G3-G4 GU/GI toxicities ranged from 0% to 12%. There were six studies (five monotherapy, one combination) that used LDR microboosting on a total of 1041 patients. Studies performed a microboost of 130-150% of the whole gland prescription to the DIL. Most patients were low/intermediate risk. PSA control rates at 5 years ranged from 69% to 98%. Acute/late G3-4 GU/GI toxicities ranged from 0% to 4%.

CONCLUSIONS

Over 1000 patients have been treated with a brachytherapy based microboost in published series. Severe acute/late toxicities appear limited. PSA control rates with more than 5 years of follow-up are limited. Longer-term follow-up is needed to determine ideal utilization of this approach.

MRI-guided focal boost to dominant intraprostatic lesion using volumetric modulated arc therapy in prostate cancer. Results of a phase II trial

OBJECTIVE

To determine morphological and biological control as well as toxicity and quality of life (QoL) of men with localized prostate cancer (PCa) treated with MRI-guided focal boost radiotherapy.

MATERIAL AND METHODS

30 patients with PCa and a visible dominant intraprostatic lesion (DIL) identified on mpMRI were included in a prospective Phase II trial. Matching point registration of planning CT and T2W, diffusion-weighted and a gradient-recalled echo (GRE) MRI images made in treatment position was used for prostate and tumour delineation. Treatment consisted on 35 daily fractions of 2.17 Gy with a concomitant focal boost to the DIL of 2.43 Gy using volumetric modulated arc therapy (VMAT) and image-guided radiation therapy (IGRT) with intraprostatic fiducial markers. Biochemical failure was analysed using PSA nadir +2 ng/mL criteria and local control using mpMRI evaluation at 6-9 months following RT. Acute and late toxicity were defined according to CTCAE v.4.0 and RTOG/EORTC scales and QoL was assessed using IPSS, EPIC short-form and UCLA-PCI questionnaires.

RESULTS

The median radiation dose to the prostate was 77.6 Gy (IQR 77.3-78.1), and to the DIL was 85.5 Gy (IQR 85.0-86.0). With a median follow up of 30.0 months (IQR 25.5-40.27), all patients remain free of biochemical relapse. An mpMRI complete response was observed in 25 patients during the first post-treatment evaluation at 6 months. The remaining five patients achieved a complete disappearance of the DIL both on T2 and DWI on the second mpMRI performed at 9 months following treatment. Six out of 30 (20%) patients presented acute Grade 2 urinary toxicity with no Grade 3 acute complications. Acute rectal toxicity was only found in 2 (6.6%) patients (both Grade 1). Only late Grade 1 urinary and rectal complications were observed in 3/30 patients, respectively, with no Grade 2 or more late toxicity. The urinary, bowel and sexual bother EPIC scores were slightly and insignificantly increased in the first 3 months post-treatment, returning to normal afterwards.

CONCLUSIONS

mpMRI-guided focal boost using VMAT hypofractionated technique is associated with an excellent morphological and functional response control and a safe toxicity profile.

ADVANCES IN KNOWLEDGE

In the present trial, we examined the potential role of mpMRI for radiological assessment (functional and morphological) of treatment response in high-risk prostate cancer patients treated with MRI-guided focal radiotherapy dose intensification to dominant Intraprostatic lesion.

The Journey of Radiotherapy Dose Escalation in High Risk Prostate Cancer; Conventional Dose Escalation to Stereotactic Body Radiotherapy (SBRT) Boost Treatments

High risk prostate cancer (HR-PrCa) is a subset of localized PrCa with significant potential for morbidity and mortality associated with disease recurrence and metastasis. Radiotherapy combined with Androgen Deprivation Therapy has been the standard of care for many years in HR-PrCa. In recent years, dose escalation, hypo-fractionation and high precision delivery with immobilization and image-guidance have substantially changed the face of modern PrCa radiotherapy, improving treatment convenience and outcomes. Ultra-hypo-fractionated radiotherapy delivered with high precision in the form of stereotactic body radiation therapy (SBRT) combines delivery of high biologically equivalent dose radiotherapy with the convenience of a shorter treatment schedule, as well as the promise of similar efficacy and reduced toxicity compared to conventional radiotherapy. However, rigorous investigation of SBRT in HR-PrCa remains limited. Here, we review the changes in HR-PrCa radiotherapy through dose escalation, hypo- and ultra-hypo-fractionated radiotherapy boost treatments, and the radiobiological basis of these treatments. We focus on completed and on-going trials in this disease utilizing SBRT as a sole radiation modality or as boost therapy following pelvic radiation.

Brachytherapy boost (BT-boost) or stereotactic body radiation therapy boost (SBRT-boost) for high-risk prostate cancer (HR-PCa)

Systematic review for the treatment of high-risk prostate cancer (HR-PCa, D'Amico classification risk system) with external body radiation therapy (EBRT)+brachytherapy-boost (BT-boost) or with EBRT+stereotactic body RT-boost (SBRT-boost). In March 2020, 391 English citations on PubMed matched with search terms "high risk prostate cancer boost". Respectively 9 and 48 prospective and retrospective studies were on BT-boost and 7 retrospective studies were on SBRT-boost. Two SBRT-boost trials were prospective. Only one study (ASCENDE-RT) directly compared the gold standard treatment [dose-escalation (DE)-EBRT+androgen deprivation treatment (ADT)] versus EBRT+ADT+BT-boost. Biochemical control rates at 9 years were 83% in the experimental arm versus 63% in the standard arm. Cumulative incidence of late grade 3 urinary toxicity in the experimental arm and in the standard arm was respectively 18% and 5%. Two recent studies with HR-PCa (National Cancer Database) demonstrated better overall survival with BT-boost (low dose rate LDR or high dose rate HDR) compared with DE-EBRT. These recent findings demonstrate the superiority of EBRT+BT-boost+ADT versus DE-EBRT+ADT for HR-PCa. It seems that EBRT+BT-boost+ADT could now be considered as a gold standard treatment for HR-PCa. HDR or LDR are options. SBRT-boost represents an attractive alternative, but the absence of randomised trials does not allow us to conclude for HR-PCa. Prospective randomised international phase III trials or meta-analyses could improve the level of evidence of SBRT-boost for HR-PCa.

Tumor-targeted dose escalation for localized prostate cancer using MR-guided HDR brachytherapy (HDR) or integrated VMAT (IB-VMAT) boost: Dosimetry, toxicity and health related quality of life

PURPOSE

To report dosimetry, preliminary toxicity and health-related quality of life (HRQoL) outcomes of tumor-targeted dose-escalation delivered by integrated boost volumetric arc therapy (IB-VMAT) or MR-guided HDR brachytherapy (HDR) boost for prostate cancer.

MATERIALS AND METHODS

Patients diagnosed with localized prostate cancer, with at least 1 identifiable intraprostatic lesion on multiparametric MRI (mpMRI) were enrolled in a prospective non-randomized phase II study. All patients received VMAT to the prostate alone (76 Gy in 38 fractions) plus a GTV boost: IB-VMAT (95 Gy in 38 fractions) or MR-guided HDR (10 Gy single fraction). GTV was delineated on mpMRI and deformably registered to planning CT scans. Comparative dosimetry using EQD2 assuming α/β 3 Gy was performed. Toxicity and health-related quality of life data (HRQoL) data were collected using CTCAE v.4.0, International Prostate Symptom Score (IPSS) and the Expanded Prostate Index Composite (EPIC).

RESULTS

Forty patients received IB-VMAT and 40 HDR boost. Organs at risk and target minimal doses were comparable between the two arms. HDR achieved higher mean and maximal tumor doses (p < 0.05). Median follow-up was 31 months (range 25-48); Acute grade G2 genitourinary (GU) toxicity was 30% and 37.5% in IB-VMAT and HDR boost, while gastrointestinal (GI) toxicity was 7.5% and 10%, respectively. Three patients developed acute G3 events, two GU toxicity (one IB-VMAT and one HDR boost) and one GI (IB-VMAT). Late G2 GU toxicity was 25% and 17.5% in the IB-VMAT and HDR boost arm and G2 GI was 5% and 7.5%, respectively. Two patients, both on the IB-VMAT arm, developed late G3 toxicity: one GI and one GU. No statistically significant difference was found in HRQoL between radiotherapy techniques (p > 0.2). Urinary and bowel HRQoL domains in both groups declined significantly by week 6 of treatment in both arms (p < 0.05) and recovered baseline scores at 6 months.

CONCLUSION

Intraprostatic tumor dose escalation using IB-VMAT or MR-guided HDR boost achieved comparable OAR dosimetry, toxicity and HRQOL outcomes, but higher mean and maximal tumor dose were achieved with the HDR technique. Further follow-up will determine long-term outcomes including disease control.

Salvage reirradiation for local failure of prostate cancer after curative radiation therapy: Association of rectal toxicity with dose distribution and normal-tissue complication probability models

PURPOSE

This study aimed to assess the impact of radiation dose on rectal toxicity after salvage external beam radiation therapy (EBRT) with or without a brachytherapy boost for exclusive local failures after the primary EBRT for prostate cancer.

METHODS AND MATERIALS

Fourteen patients with no severe residual late toxicity after primary EBRT ± brachytherapy were reirradiated after a median time interval of 6.1 years. The median normalized total dose in 2 Gy fractions (NTD2Gy, α/β ratio = 1.5 Gy for prostate cancer cells) was 74 Gy at primary EBRT and 85.1 Gy at reirradiation. Rectal dose-volume histograms (converted to NTD2Gy_alpha/beta = 3 Gy) and the corresponding normal-tissue complication probability (NTCP) values for gastrointestinal (GI) toxicity were evaluated for 2 groups: High GI toxicity (grade ≥3) and low GI toxicity (grade ≤2).

RESULTS

The 5-year grade ≥3 GI toxicity-free survival rate was 57.1%. The median rectal V70Gy and maximum dose to 1 cm3 (D1ccrect) at primary EBRT were both predictive for grade ≥3 GI toxicity (9% vs 0%; P = .04 and 72.2 Gy vs 66.8 Gy; P < .01, respectively). When adding primary radiation therapy (RT) and reirradiation plans, the median D1ccrect was 139.8 Gy versus 126.7 Gy (P < .01) for high and low GI toxicity groups. NTCP >10% at primary RT was predictive for high GI toxicity at reirradiation (P < .05).

CONCLUSIONS

Even in the absence of residual toxicity after primary RT, rectal doses >70 Gy and NTCP >10% calculated for a first irradiation may be associated with a higher risk of developing high GI toxicity at reirradiation with a possible D1ccrect threshold of 130 Gy.

Prostate irradiation with focal dose escalation to the intraprostatic dominant nodule: a systematic review

Radiation therapy (RT) is a curative treatment option for localized prostate cancer. Prostate irradiation with focal dose escalation to the intraprostatic dominant nodule (IDN) is an emerging treatment option that involves the prophylactic irradiation of the whole prostate while increasing RT doses to the visible prostatic tumor. Because of the lack of large multicentre trials, a systematic review was performed in an attempt to get an overview on the feasibility and efficacy of focal dose escalation to the IDN.

A bibliographic search for articles in English, which were listed in MEDLINE from 2000 to 2016 to identify publications on RT with focal directed boost to the IDN, was performed. The review was completed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

Twenty-two articles describing 1,378 patients treated with RT using focal boost were identified and fulfilled the selection criteria. Intensity-modulated radiation therapy (IMRT) was used in 720 patients (52.3%), volumetric modulated arc therapy was used in 45 patients (3.3%), stereotactic body radiation therapy (SBRT) in 113 patients (8.2%), and low–dose rate and high–dose rate brachytherapy (BT) were used in 305 patients (22.1%) and 195 patients (14.1%), respectively. Use of androgen deprivation therapy varied substantially among series. Biochemical disease-free survival at 5 years was reported for a cohort of 812 (58.9%) patients. The combined median biochemical disease-free survival for this group of patients was 85% (range: 78.8–100%; 95% confidence interval: 77.1–82.7%).

The average occurrence of grade III or worse gastrointestinal and genitourinary late toxicity was, respectively, 2.5% and 3.1% for intensity-modulated RT boost, 10% and 6% for stereotactic body RT, 6% and 2% for low–dose rate BT, and 4% and 4.3% for high–dose rate BT.

This review shows encouraging results for focal dose escalation to the IDN with acceptable short- to medium-term side effects and biochemical disease control rates. However, owing to the heterogeneity of patient population and the short follow-up, the results should be interpreted with caution. Considering that the clinical endpoint in the studies was biochemical recurrence, the use and duration of androgen deprivation therapy administration should be carefully considered before driving definitive conclusions. Randomized trials with long-term follow-up are needed before this technique can be generally recommended.

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.

Simultaneous automatic segmentation of multiple needles using 3D ultrasound for high-dose-rate prostate brachytherapy

PURPOSE

Sagittally reconstructed 3D (SR3D) ultrasound imaging shows promise for improved needle localization for high-dose-rate prostate brachytherapy (HDR-BT); however, needles must be manually segmented intraoperatively while the patient is anesthetized to create a treatment plan. The purpose of this article was to describe and validate an automatic needle segmentation algorithm designed for HDR-BT, specifically capable of simultaneously segmenting all needles in an HDR-BT implant using a single SR3D image with ~5 mm interneedle spacing.

MATERIALS AND METHODS

The segmentation algorithm involves regularized feature point classification and line trajectory identification based on the randomized 3D Hough transform modified to handle multiple straight needles in a single image simultaneously. Needle tips are identified based on peaks in the derivative of the signal intensity profile along the needle trajectory. For algorithm validation, 12 prostate cancer patients underwent HDR-BT during which SR3D images were acquired with all needles in place. Needles present in each of the 12 images were segmented manually, providing a gold standard for comparison, and using the algorithm. Tip errors were assessed in terms of the 3D Euclidean distance between needle tips, and trajectory error was assessed in terms of 2D distance in the axial plane and angular deviation between trajectories.

RESULTS

In total, 190 needles were investigated. Mean execution time of the algorithm was 11.0 s per patient, or 0.7 s per needle. The algorithm identified 82% and 85% of needle tips with 3D errors ≤3 mm and ≤5 mm, respectively, 91% of needle trajectories with 2D errors in the axial plane ≤3 mm, and 83% of needle trajectories with angular errors ≤3°. The largest tip error component was in the needle insertion direction.

CONCLUSIONS

Previous work has indicated HDR-BT needles may be manually segmented using SR3D images with insertion depth errors ≤3 mm and ≤5 mm for 83% and 92% of needles, respectively. The algorithm shows promise for reducing the time required for the segmentation of straight HDR-BT needles, and future work involves improving needle tip localization performance through improved image quality and modeling curvilinear trajectories.

Brachytherapy boost for prostate cancer: Trends in care and survival outcomes

PURPOSE

Androgen suppression combined with elective nodal and dose-escalated radiation therapy recently demonstrated an improved biochemical failure-free survival in men who received external beam radiation therapy (EBRT) plus a brachytherapy boost (BB) compared with dose-escalated external beam radiotherapy (DE-EBRT). We sought to analyze the factors predictive for use of EBRT + BB as compared with DE-EBRT and report resulting survival outcomes on a national level using a hospital-based registry.

METHODS AND MATERIALS

We identified 113,719 men from the National Cancer Database from 2004 to 2013 with intermediate- or high-risk prostate cancer who were treated with EBRT + BB or DE-EBRT. We performed univariate and multivariate analyses of all available factors potentially predictive of receipt of treatment selection. Survival was evaluated in a multivariable model with propensity adjustment.

RESULTS

For intermediate-risk patients, utilization of BB decreased from 33.1% (n = 1742) in 2004 to 12.5% (n = 766) in 2013 and for high-risk patients, utilization dropped from 27.6% (n = 879) to 10.8% (n = 479). Numerous factors predictive for use of BB were identified. Cox proportional hazards analysis was performed-adjusting for age, Charlson-Deyo comorbidity score, T stage, prostate-specific antigen, Gleason score, and sociodemographic factors-and demonstrated BB use was associated with a hazard ratio of 0.71 (95% confidence interval, 0.67-0.75; p < 0.0005) and 0.73 (95% confidence interval, 0.68-0.78; p < 0.0005) for intermediate- and high-risk patients, respectively.

CONCLUSIONS

There has been a concerning decline in the utilization of BB for intermediate- and high-risk prostate cancer patients despite an association with improved on overall survival. Numerous factors predictive for use of BB have been identified.

Clinical use of magnetic resonance imaging across the prostate brachytherapy workflow

MRI produces better soft tissue contrast than does ultrasonography or computed tomography for visualizing male pelvic anatomy and prostate cancer. Better visualization of the tumor and organs at risk could allow better conformation of the dose to the target volumes while at the same time minimizing the dose to critical structures and the associated toxicity. Although the use of MRI for prostate brachytherapy would theoretically result in an improved therapeutic ratio, its implementation been slow, mostly because of technical challenges. In this review, we describe the potential role of MRI at different steps in the treatment workflow for prostate brachytherapy: for patient selection, treatment planning, in the operating room, or for postimplant assessment. We further present the current clinical experience with MRI-guided prostate brachytherapy, both for permanent seed implantation and high-dose-rate brachytherapy.

Trends in targeted prostate brachytherapy: from multiparametric MRI to nanomolecular radiosensitizers

The treatment of localized prostate cancer is expected to become a significant problem in the next decade as an increasingly aging population becomes prone to developing the disease. Recent research into the biological nature of prostate cancer has shown that large localized doses of radiation to the cancer offer excellent long-term disease control. Brachytherapy, a form of localized radiation therapy, has been shown to be one of the most effective methods for delivering high radiation doses to the cancer; however, recent evidence suggests that increasing the localized radiation dose without bound may cause unacceptable increases in long-term side effects. This review focuses on methods that have been proposed, or are already in clinical use, to safely escalate the dose of radiation within the prostate. The advent of multiparametric magnetic resonance imaging (mpMRI) to better identify and localize intraprostatic tumors, and nanomolecular radiosensitizers such as gold nanoparticles (GNPs), may be used synergistically to increase doses to cancerous tissue without the requisite hazard of increased side effects.

In-bore MRI interventions: current status and future applications

PURPOSE OF REVIEW

This review discusses the feasibility, recent advances and current status of in-bore MRI-guided interventional techniques for diagnosis and treatment of focal prostate cancer (PCa) and also explores the future applications, highlighting the emerging strategies for the treatment of PCa.

RECENT FINDINGS

Multiparametric MRI has opened up opportunities for diagnosis and targeted therapeutics to the site of disease within the organ wherein minimizing the incidence of treatment-related toxicity of whole gland therapy. MRI-guided targeted biopsy has a higher detection rate for significant cancer and lower rate of detection of insignificant cancer. In comparison to ultrasound-guided focal therapy, in-bore treatment provides the advantage of real time thermal monitoring during treatment and assessment of treatment coverage by an enhanced scan immediately post-treatment. Preliminary results of ongoing phase I and II in-bore focal PCa treatment trials via transperineal, transrectal and transurethral routes, using different energy modalities for the ablation, have shown promising results.

SUMMARY

Advances in multiparametric-MRI has opened up opportunities for in-bore targeted focal treatment of PCa in the correctly selected patient.

Moderate Hypofractionated Protracted Radiation Therapy and Dose Escalation for Prostate Cancer: Do Dose and Overall Treatment Time Matter?

PURPOSE

This was a retrospective study of 2 sequential dose escalation regimens of twice-weekly 4 Gy/fractions hypofractionated intensity modulated radiation therapy (IMRT): 56 Gy and 60 Gy delivered within a protracted overall treatment time (OTT) of 6.5 and 7 weeks, respectively.

METHODS AND MATERIALS

163 prostate cancer patients with cT1c-T3a disease and nodal involvement risk ≤20% (Roach index) were treated twice weekly to the prostate ± seminal vesicles with 2 sequential dose-escalated IMRT schedules: 56 Gy (14 × 4 Gy, n=81) from 2003 to 2007 and 60 Gy (15 × 4 Gy, n=82) from 2006 to 2010. Patient repositioning was made with bone matching on portal images. Gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to the Common Terminology Criteria for Adverse Events version 3.0 grading scale.

RESULTS

There were no significant differences regarding the acute GU and GI toxicities in the 2 dose groups. The median follow-up times were 80.2 months (range, 4.5-121 months) and 56.5 months (range, 1.4-91.2 months) for patients treated to 56 and 60 Gy, respectively. The 5-year grade ≥2 late GU toxicity-free survivals with 56 Gy and 60 Gy were 96 ± 2.3% and 78.2 ± 5.1% (P=.001), respectively. The 5-year grade ≥2 late GI toxicity-free survivals with 56 Gy and 60 Gy were 98.6 ± 1.3% and 85.1 ± 4.5% (P=.005), respectively. Patients treated with 56 Gy showed a 5-year biochemical progression-free survival (bPFS) of 80.8 ± 4.7%, worse than patients treated with 60 Gy (93.2 ± 3.9%, P=.007). A trend for a better 5-year distant metastasis-free survival was observed among patients treated in the high-dose group (95.3 ± 2.7% vs 100%, P=.073, respectively). On multivariate analysis, only the 60-Gy group predicted for a better bPFS (P=.016, hazard ratio = 4.58).

CONCLUSIONS

A single 4-Gy additional fraction in patients treated with a hypofractionated protracted IMRT schedule of 14 × 4 Gy resulted in a similar and minimal acute toxicity, in worse moderate to severe urinary and GI late effects, but a significantly better biochemical control.

Magnetic resonance image guided brachytherapy

The application of magnetic resonance image (MRI)-guided brachytherapy has demonstrated significant growth during the past 2 decades. Clinical improvements in cervix cancer outcomes have been linked to the application of repeated MRI for identification of residual tumor volumes during radiotherapy. This has changed clinical practice in the direction of individualized dose administration, and resulted in mounting evidence of improved clinical outcome regarding local control, overall survival as well as morbidity. MRI-guided prostate high-dose-rate and low-dose-rate brachytherapies have improved the accuracy of target and organs-at-risk delineation, and the potential exists for improved dose prescription and reporting for the prostate gland and organs at risk. Furthermore, MRI-guided prostate brachytherapy has significant potential to identify prostate subvolumes and dominant lesions to allow for dose administration reflecting the differential risk of recurrence. MRI-guided brachytherapy involves advanced imaging, target concepts, and dose planning. The key issue for safe dissemination and implementation of high-quality MRI-guided brachytherapy is establishment of qualified multidisciplinary teams and strategies for training and education.

Potential applications of image-guided radiotherapy for radiation dose escalation in patients with early stage high-risk prostate cancer

Patients with early stage high-risk prostate cancer (prostate specific antigen > 20, Gleason score > 7) are at high risk of recurrence following prostate cancer irradiation. Radiation dose escalation to the prostate may improve biochemical-free survival for these patients. However, high rectal and bladder dose with conventional three-dimensional conformal radiotherapy may lead to excessive gastrointestinal and genitourinary toxicity. Image-guided radiotherapy (IGRT), by virtue of combining the steep dose gradient of intensity-modulated radiotherapy and daily pretreatment imaging, may allow for radiation dose escalation and decreased treatment morbidity. Reduced treatment time is feasible with hypo-fractionated IGRT and it may improve patient quality of life.

Multi-parametric MRI-guided focal tumor boost using HDR prostate brachytherapy: a feasibility study

PURPOSE

This study investigates the feasibility of delivering focal boost dose to tumor regions, identified with multi-parametric MRI, in high-dose-rate prostate brachytherapy.

METHODS AND MATERIALS

T2-weighted, diffusion-weighted, and dynamic-contrast-enhanced MRI were acquired the day before treatment and analyzed retrospectively for 15 patients. Twelve patients had hormone therapy before the MRI scan. The tumor was delineated on MRI by a radiologist and registered to treatment planning transrectal ultrasound images. A margin based on analysis of delineation and registration uncertainties was applied to create a focal boost planning target volume (F-PTV). Delivered treatment plans were compared with focal boost plans optimized to increase F-PTV dose as much as allowed by urethral and rectal dose constraints.

RESULTS

Tumors were delineated in all patients with volumes 0.4-23.0cc. The margin for tumor delineation and image registration uncertainties was estimated to be 4.5 mm. For F-PTV, the focal boost treatment plans increased median D90 from 17.6 to 20.9 Gy and median V150 from 27.3% to 75.9%.

CONCLUSIONS

MRI-guided high-dose-rate prostate brachytherapy focal tumor boost is feasible-tumor regions can be identified even after hormone therapy, and focal boost dose can be delivered without violating urethral and rectal dose constraints.

A gEUD-based inverse planning technique for HDR prostate brachytherapy: feasibility study

PURPOSE

The purpose of this work was to study the feasibility of a new inverse planning technique based on the generalized equivalent uniform dose for image-guided high dose rate (HDR) prostate cancer brachytherapy in comparison to conventional dose-volume based optimization.

METHODS

The quality of 12 clinical HDR brachytherapy implants for prostate utilizing HIPO (Hybrid Inverse Planning Optimization) is compared with alternative plans, which were produced through inverse planning using the generalized equivalent uniform dose (gEUD). All the common dose-volume indices for the prostate and the organs at risk were considered together with radiobiological measures. The clinical effectiveness of the different dose distributions was investigated by comparing dose volume histogram and gEUD evaluators.

RESULTS

Our results demonstrate the feasibility of gEUD-based inverse planning in HDR brachytherapy implants for prostate. A statistically significant decrease in D10 or/and final gEUD values for the organs at risk (urethra, bladder, and rectum) was found while improving dose homogeneity or dose conformity of the target volume.

CONCLUSIONS

Following the promising results of gEUD-based optimization in intensity modulated radiation therapy treatment optimization, as reported in the literature, the implementation of a similar model in HDR brachytherapy treatment plan optimization is suggested by this study. The potential of improved sparing of organs at risk was shown for various gEUD-based optimization parameter protocols, which indicates the ability of this method to adapt to the user's preferences.

Focal therapy for prostate cancer: rationale and treatment opportunities

Focal therapy is an emerging treatment modality for localised prostate cancer that aims to reduce the morbidity seen with radical therapy, while maintaining cancer control. Focal therapy treatment strategies minimise damage to non-cancerous tissue, with priority given to the sparing of key structures such as the neurovascular bundles, external sphincter, bladder neck and rectum. There are a number of ablative technologies that can deliver energy to destroy cancer cells as part of a focal therapy strategy. The most widely investigated are cryotherapy and high-intensity focussed ultrasound. Existing radical therapies, such as brachytherapy and external beam radiotherapy, also have the potential to be applied in a focal manner. The functional outcomes of focal therapy from several phase I and II trials have been encouraging, with low rates of urinary incontinence and erectile dysfunction. Robust medium- and long-term cancer control outcomes are currently lacking. Controversies in focal therapy remain, notably treatment paradigms based on the index lesion hypothesis, appropriate patient selection for focal therapy and how the efficacy of focal therapy should be assessed. This review articles discusses the current status of focal therapy, highlighting controversies and emerging strategies that can influence treatment outcomes for the future.

MRI-guided interventions for the treatment of prostate cancer

OBJECTIVE

The purpose of this article is to evaluate MRI-guided therapies and to investigate their feasibility for focal therapy in prostate cancer patients. Relevant articles were retrieved using the PubMed online search engine.

CONCLUSION

Currently, MRI-guided laser ablation and MRI-guided focused ultrasound are the most promising options for focal treatment of the prostate in patients with prostate cancer. Other techniques-that is, cryosurgery, microwave ablation, and radiofrequency ablation-are, for several and different reasons, less suitable for MRI-guided focal therapy of the prostate.

Basics of particle therapy I: physics

With the advance of modern radiation therapy technique, radiation dose conformation and dose distribution have improved dramatically. However, the progress does not completely fulfill the goal of cancer treatment such as improved local control or survival. The discordances with the clinical results are from the biophysical nature of photon, which is the main source of radiation therapy in current field, with the lower linear energy transfer to the target. As part of a natural progression, there recently has been a resurgence of interest in particle therapy, specifically using heavy charged particles, because these kinds of radiations serve theoretical advantages in both biological and physical aspects. The Korean government is to set up a heavy charged particle facility in Korea Institute of Radiological & Medical Sciences. This review introduces some of the elementary physics of the various particles for the sake of Korean radiation oncologists' interest.

High-dose-rate brachytherapy boost to the dominant intra-prostatic tumor region: hemi-irradiation of prostate cancer

BACKGROUND

To assess the feasibility, toxicity, and outcome of prostate hemi-irradiation with a high-dose-rate brachytherapy (HDR-BT) boost for patients presumed to harbor dominant intra-prostatic tumors in a single lobe.

METHODS

After 3D conformal external radiotherapy (3DCRT) to 64-64.4 Gy, 77 patients with non-metastatic locally aggressive prostate cancer have been treated from 2000 to 2004, with HDR-BT using temporary open MRI-guided (192) Ir implants, to escalate the dose in the boost region. Twenty patients (26%) had one lobe involvement (i.e., one sided endorectal MRI, rectal examination, and biopsies) and were boosted to one side of the gland only. A dose of 12, 14, and 16 Gy in two fractions was delivered to 5, 6, and 9 patients, respectively.

RESULTS

After a median follow-up 69 months, no differences in late rectal toxicity were observed between the unilaterally and bilaterally irradiated cohorts. Although, grade 2 late urinary toxicity was worse in the hemi-irradiated group (P = 0.03), severe grade ≥3 late urinary toxicity at 5 years was not different: 10% versus 8.8% in the unilaterally and bilaterally irradiated cohorts, respectively. Grade 4 late urinary toxicity, however, was exclusively observed in patients boosted to both lobes (5/57, 8.8%). Five-year biochemical relapse-free survival was 79.7% versus 70.5% for the unilateral and bilateral boost groups, respectively (P = 0.99).

CONCLUSION

Prostate hemi-irradiation with a HDR-BT boost to the dominant tumor region may be considered when rectal examination, MRI, and biopsies suggest one lobe involvement. Nevertheless, strict dosimetric optimization is needed in order to further reduce the risk of late severe toxicity.

[SFRO 2010: congress highlights]

The 21st SFRO Congress during October 2010 focused on three main topics: prostate, radiotherapy technical innovations (including reirradiation) and quality of life. The pitfalls of IMRT (treatment time, number of monitor unit, low doses) are in competition with arctherapy dynamic techniques that offer reduction treatment time for an equivalent ballistic. These techniques with high dose gradient should be coupled with the better imagery of repositioning (IGRT) to ensure benefice. A prospective evaluation of toxicity, clinical benefit on tumor control but also on quality of life of patients is necessary. In many current and future clinical trials, quality of life related to health will be a relevant outcome measurement to secure the importance of treatment for the patient and the health system.

Stereotactic body radiotherapy as boost for organ-confined prostate cancer

Stereotactic body radiotherapy (SBRT) boost following external beam radiation therapy (EBRT) for advanced localized prostate cancer may reduce toxicity while escalating the dose. We present preliminary biochemical control and urinary, rectal and sexual toxicities for 73 patients treated with SBRT as a boost to EBRT. Forty-one intermediate- and 32 high-risk localized prostate cancer patients received 45 Gy EBRT with SBRT boost. Twenty-eight patients (38.3%) received a total SBRT boost dose of 18 Gy (3 fractions of 6 Gy), 28 patients (38.3%) received 19.5 Gy (3 fractions of 6.5 Gy), and 17 patients (23.2%) received 21 Gy (3 fractions of 7 Gy). Toxicity was assessed using the Radiation Therapy Oncology Group urinary and rectal toxicity scale. Biochemical failure was assessed using the Phoenix definition. The median follow-up was 33 months (range, 22 - 43 months). Less than 7% Grade II and no higher grade acute toxicities occurred. To date, one Grade III and no Grade IV late toxicities occurred. For the 97% of patients with 24 months minimum follow-up, 71.8% achieved a PSA nadir threshold of 0.5 ng/mL. Three intermediate-risk and seven high-risk biochemical failures occurred; one high-risk patient died of his cancer. Three-year actuarial biochemical control rates were 89.5% and 77.7% for intermediate- and high-risk patients, respectively. SBRT boost for prostate cancer treatment is safe and feasible with minimal acute toxicity. At 33 months late toxicity and biochemical control are promising. Long-term durability of these findings remains to be established.

Dose-fractionation sensitivity of prostate cancer deduced from radiotherapy outcomes of 5,969 patients in seven international institutional datasets: α/β = 1.4 (0.9-2.2) Gy

PURPOSE

There are reports of a high sensitivity of prostate cancer to radiotherapy dose fractionation, and this has prompted several trials of hypofractionation schedules. It remains unclear whether hypofractionation will provide a significant therapeutic benefit in the treatment of prostate cancer, and whether there are different fractionation sensitivities for different stages of disease. In order to address this, multiple primary datasets have been collected for analysis.

METHODS AND MATERIALS

Seven datasets were assembled from institutions worldwide. A total of 5969 patients were treated using external beams with or without androgen deprivation (AD). Standard fractionation (1.8-2.0 Gy per fraction) was used for 40% of the patients, and hypofractionation (2.5-6.7 Gy per fraction) for the remainder. The overall treatment time ranged from 1 to 8 weeks. Low-risk patients comprised 23% of the total, intermediate-risk 44%, and high-risk 33%. Direct analysis of the primary data for tumor control at 5 years was undertaken, using the Phoenix criterion of biochemical relapse-free survival, in order to calculate values in the linear-quadratic equation of k (natural log of the effective target cell number), α (dose-response slope using very low doses per fraction), and the ratio α/β that characterizes dose-fractionation sensitivity.

RESULTS

There was no significant difference between the α/β value for the three risk groups, and the value of α/β for the pooled data was 1.4 (95% CI = 0.9-2.2) Gy. Androgen deprivation improved the bNED outcome index by about 5% for all risk groups, but did not affect the α/β value.

CONCLUSIONS

The overall α/β value was consistently low, unaffected by AD deprivation, and lower than the appropriate values for late normal-tissue morbidity. Hence the fractionation sensitivity differential (tumor/normal tissue) favors the use of hypofractionated radiotherapy schedules for all risk groups, which is also very beneficial logistically in limited-resource settings.

Feasibility of safe ultra-high (EQD(2)>100 Gy) dose escalation on dominant intra-prostatic lesions (DILs) by Helical Tomotheraphy

PURPOSE

to verify the possibility of using Helical Tomotherapy to safely escalate dose to single or multiple highly radioresistant dominant intra-prostatic lesions (DILs) as assessed by functional magnetic resonance imaging (MRI).

MATERIAL

in seven intermediate/high risk patients, T2WI, T1WI and DWI MRI imaging showed evidence of one DIL in four patients and two DILs in three patients in the peripheral zone of the prostate. The planning strategy was to deliver median doses of 80, 90, 100 and 120 Gy to PTVDIL while delivering 71.4 Gy/28 fractions (EQD(2)=75 Gy) to the remaining portion of PTV. A higher priority was assigned to rectal constraints relative to DIL coverage. Rectal NTCP calculations were performed using the most recently available model data.

RESULTS

the median dose to DIL could safely be escalated to at least 100 Gy (EQD(2,α/β=10)=113 Gy) without violating safe constraints for the organs at risk. Typical rectal NTCP values were around or below 1-3% for G3 toxicity and 5-7% for G2-G3 toxicity. For the 100 Gy DIL dose boost strategy, mean D95% of DIL and PTVDIL were 98.8 Gy and 86.7 Gy, respectively. The constraints for bladder, urethra and femoral heads were always respected.

CONCLUSIONS

IGRT by Helical Tomotherapy may permit the safe escalation of EQD(2,α/β=10) to at least 113 Gy to DILs without significantly increasing rectal NTCP compared to plans without dose escalation. A Phase I-II clinical study is warranted.

Three-dimensional dose addition of external beam radiotherapy and brachytherapy for oropharyngeal patients using nonrigid registration

PURPOSE

To develop and evaluate a method for adding dose distributions of combined external beam radiotherapy (EBRT) and brachytherapy (BT) for oropharyngeal patients.

METHODS AND MATERIALS

Two computed tomography (CT) scans were used for 5 patients: the EBRT CT, used for EBRT planning, and the BT CT, acquired after catheter implantation. For each scan, the salivary glands and the chewing and swallowing muscles were contoured, and a dose distribution was calculated. A nonrigid transformation was obtained by registering the organs' surfaces. Then the BT dose distribution was mapped onto the EBRT dose distribution by applying the transformation obtained. To account for differences in fractionation, the physical doses were converted to equivalent dose in 2 Gy (EQD(2)), and the total dose was found by adding dose voxel by voxel. The robustness of the dose addition was investigated by varying delineations and input parameters of the registration method and by varying the α/β parameter for EQD(2). The effect of the perturbations was quantified using dose-volume histograms (DVH) and gamma analyses (distance-to-agreement/dose-difference = 1 mm/1 Gy).

RESULTS

The variations in input parameters and delineations caused only small perturbations in the DVH of the added dose distributions. For most organs the gamma index was low, and it was moderately elevated for organs lying in areas with a steep gradient (median gamma index ≤ 2.3 for constrictor muscles, ≤ 0.7 for all other organs).

CONCLUSIONS

The presented method allows adding dose distributions of combined EBRT and BT for oropharyngeal patients. In general, the method is reliable and robust with respect to uncertainties in organ delineation, perturbations in input parameters of the method, and α/β values.

["Dose-painting": myth or reality?]

"Dose-painting" radiotherapy allows for a heterogeneous delivery of radiation within the tumour volume by targeting radioresistant areas defined by functional imaging. Within gross tumour volume, it is possible to define one or more target volumes based on biology (biological target volume [BTV]) and to apply a strategy of intensity modulated radiation therapy (IMRT) that will deliver a higher dose to these regions. In this review of the literature, we will highlight the biological elements responsible for radioresistance, and how to image them, then we will detail the radiotherapy techniques necessary for this approach, before presenting clinical results in various situations (head and neck tumours, prostate, brain tumours, etc.). Despite many difficulties that make dose-painting IMRT unusable in routine nowadays, biology-guided radiation therapy represents one of the major pathways of development of radiotherapy in the coming years.