The emerging role of high-dose-rate (HDR) brachytherapy as monotherapy for prostate cancer

AAPM Task Group Report 267: A joint AAPM GEC-ESTRO report on biophysical models and tools for the planning and evaluation of brachytherapy

Brachytherapy utilizes a multitude of radioactive sources and treatment techniques that often exhibit widely different spatial and temporal dose delivery patterns. Biophysical models, capable of modeling the key interacting effects of dose delivery patterns with the underlying cellular processes of the irradiated tissues, can be a potentially useful tool for elucidating the radiobiological effects of complex brachytherapy dose delivery patterns and for comparing their relative clinical effectiveness. While the biophysical models have been used largely in research settings by experts, it has also been used increasingly by clinical medical physicists over the last two decades. A good understanding of the potentials and limitations of the biophysical models and their intended use is critically important in the widespread use of these models. To facilitate meaningful and consistent use of biophysical models in brachytherapy, Task Group 267 (TG-267) was formed jointly with the American Association of Physics in Medicine (AAPM) and The Groupe Européen de Curiethérapie and the European Society for Radiotherapy & Oncology (GEC-ESTRO) to review the existing biophysical models, model parameters, and their use in selected brachytherapy modalities and to develop practice guidelines for clinical medical physicists regarding the selection, use, and interpretation of biophysical models. The report provides an overview of the clinical background and the rationale for the development of biophysical models in radiation oncology and, particularly, in brachytherapy; a summary of the results of literature review of the existing biophysical models that have been used in brachytherapy; a focused discussion of the applications of relevant biophysical models for five selected brachytherapy modalities; and the task group recommendations on the use, reporting, and implementation of biophysical models for brachytherapy treatment planning and evaluation. The report concludes with discussions on the challenges and opportunities in using biophysical models for brachytherapy and with an outlook for future developments.

Functional imaging-guided carbon ion irradiation with simultaneous integrated boost for localized prostate cancer: study protocol for a phase II randomized controlled clinical trial

Background

Due to the physical dose distribution characteristic of “Bragg peak” and the biological effect as a kind of high linear energy transfer ray, heavy ion therapy has advantages over conventional photon therapy in both efficacy and safety. Based on the evidence that prostate cancer lesions before treatment are the most common sites of tumor residual or recurrence after treatment, simultaneous integrated boost radiation therapy for prostate cancer has been proven to have the advantage of improving efficacy without increasing toxicities.

Methods

This study is a prospective phase II randomized controlled clinical trial evaluating the efficacy and safety of functional imaging-guided carbon ion irradiation with simultaneous integrated boost for localized prostate cancer. One hundred and forty patients with localized prostate cancer will be randomized into carbon ion radiotherapy group and simultaneous integrated boost carbon ion radiotherapy group at a 1:1 ratio. The primary endpoint is to compare the incidence of treatment-related grade 2 and higher acute toxicities between the two groups according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) version 4.03. Secondary endpoints are late toxicities, biochemical relapse-free survival, overall survival, progression-free survival, and quality of life.

Discussion

This study adopts functional imaging-guided simultaneous integrated boost of carbon ion radiotherapy for localized prostate cancer, aiming to evaluate the differences in the severity and incidence of acute toxicities in patients with localized prostate cancer treated with carbon ion radiotherapy and simultaneous integrated boost carbon ion radiotherapy, in order to optimize the carbon ion treatment strategy for localized prostate cancer.

Trial registration

ClinicalTrials.gov NCT05010343. Retrospectively registered on 18 August 2021

Targeting prostate lesions on multiparametric MRI with HDR brachytherapy: Optimal planning margins determined using whole-mount digital histology

PURPOSE

Multiparametric magnetic resonance imaging (mpMRI) has demonstrated the ability to localize intraprostatic lesions. It is our goal to determine how to optimally target the underlying histopathological cancer within the setting of high-dose-rate brachytherapy (HDR-BT).

METHODS AND MATERIALS

Ten prostatectomy patients had pathologist-annotated mid-gland histology registered to pre-procedural mpMRI, which were interpreted by four different observers. Simulated HDR-BT plans with realistic catheter placements were generated by registering the mpMRI lesions and corresponding histology annotations to previously performed clinical HDR-BT implants. Inverse treatment planning was used to generate treatment plans that treated the entire gland to a single dose of 15 Gy, as well as focally targeted plans that aimed to escalate dose to the mpMRI lesions to 20.25 Gy. Three margins to the lesion were explored: 0 mm, 1 mm, and 2 mm. The analysis compared the dose that would have been delivered to the corresponding histologically-defined cancer with the different treatment planning techniques.

RESULTS

mpMRI-targeted plans delivered a significantly higher dose to the histologically-defined cancer (p < 0.001), in comparison to the standard treatment plans. Additionally, adding a 1 mm margin resulted in significantly higher D98, and D90 to the histologically-defined cancer in comparison to the 0 mm margin targeted plans (p = 0.019 & p = 0.0026). There was no significant difference between plans using 1 mm and 2 mm margins.

CONCLUSIONS

Adding a 1 mm margin to intraprostatic mpMRI lesions significantly increased the dose to histologically-defined cancer, in comparison applying no margin. No significant effect was observed by further expanding the margins.

Axially rigid steerable needle with compliant active tip control

Steerable instruments allow for precise access to deeply-seated targets while sparing sensitive tissues and avoiding anatomical structures. In this study we present a novel omnidirectional steerable instrument for prostate high-dose-rate (HDR) brachytherapy (BT). The instrument utilizes a needle with internal compliant mechanism, which enables distal tip steering through proximal instrument bending while retaining high axial and flexural rigidity. Finite element analysis evaluated the design and the prototype was validated in experiments involving tissue simulants and ex-vivo bovine tissue. Ultrasound (US) images were used to provide visualization and shape-reconstruction of the instrument during the insertions. In the experiments lateral tip steering up to 20 mm was found. Manually controlled active needle tip steering in inhomogeneous tissue simulants and ex-vivo tissue resulted in mean targeting errors of 1.4 mm and 2 mm in 3D position, respectively. The experiments show that steering response of the instrument is history-independent. The results indicate that the endpoint accuracy of the steerable instrument is similar to that of the conventional rigid HDR BT needle while adding the ability to steer along curved paths. Due to the design of the steerable needle sufficient axial and flexural rigidity is preserved to enable puncturing and path control within various heterogeneous tissues. The developed instrument has the potential to overcome problems currently unavoidable with conventional instruments, such as pubic arch interference in HDR BT, without major changes to the clinical workflow.

Catheter position prediction using deep-learning-based multi-atlas registration for high-dose rate prostate brachytherapy

PURPOSE

High-dose-rate (HDR) prostate brachytherapy involves treatment catheter placement, which is currently empirical and physician dependent. The lack of proper catheter placement guidance during the procedure has left the physicians to rely on a heuristic thinking-while-doing technique, which may cause large catheter placement variation and increased plan quality uncertainty. Therefore, the achievable dose distribution could not be quantified prior to the catheter placement. To overcome this challenge, we proposed a learning-based method to provide HDR catheter placement guidance for prostate cancer patients undergoing HDR brachytherapy.

METHODS

The proposed framework consists of deformable registration via registration network (Reg-Net), multi-atlas ranking, and catheter regression. To model the global spatial relationship among multiple organs, binary masks of the prostate and organs-at-risk are transformed into distance maps, which describe the distance of each local voxel to the organ surfaces. For a new patient, the generated distance map is used as fixed image. Reg-Net is utilized to deformably register the distance maps from multi-atlas set to match this patient's distance map and then bring catheter maps from multi-atlas to this patient via spatial transformation. Several criteria, namely prostate volume similarity, multi-organ semantic image similarity, and catheter position criteria (far from the urethra and within the partial prostate), are used for multi-atlas ranking. The top-ranked atlas' deformed catheter positions are selected as the predicted catheter positions for this patient. Finally, catheter regression is used to refine the final catheter positions. A retrospective study on 90 patients with a fivefold cross-validation scheme was used to evaluate the proposed method's feasibility. In order to investigate the impact of plan quality from the predicted catheter pattern, we optimized the source dwell position and time for both the clinical catheter pattern and predicted catheter pattern with the same optimization settings. Comparisons of clinically relevant dose volume histogram (DVH) metrics were completed.

RESULTS

For all patients, on average, both the clinical plan dose and predicted plan dose meet the common dose constraints when prostate dose coverage is kept at V100 = 95%. The plans from the predicted catheter pattern have slightly higher hotspot in terms of V150 by 5.0% and V200 by 2.9% on average. For bladder V75, rectum V75, and urethra V125, the average difference is close to zero, and the range of most patients is within ±1 cc.

CONCLUSION

We developed a new catheter placement prediction method for HDR prostate brachytherapy based on a deep-learning-based multi-atlas registration algorithm. It has great clinical potential since it can provide catheter location estimation prior to catheter placement, which could reduce the dependence on physicians' experience in catheter implantation and improve the quality of prostate HDR treatment plans. This approach merits further clinical evaluation and validation as a method of quality control for HDR prostate brachytherapy.

High-dose-rate brachytherapy for prostate cancer: Rationale, current applications, and clinical outcome

Background

High‐dose‐rate brachytherapy (HDR BRT) has been enjoying rapid acceptance as a treatment modality offered to selected prostate cancer patients devoid of risk group, employed either in monotherapy setting or combined with external beam radiation therapy (EBRT) and is currently one of the most active clinical research areas.

Recent findings

This review encompasses all the current evidence to support the use of HDR BRT in various clinical scenario and shines light to the HDR BRT rationale, as an ultimately conformal dose delivery method enabling safe dose escalation to the prostate.

Conclusion

Valid long‐term data, both in regard to the oncologic outcomes and toxicity profile, support the current clinical indication spectrum of HDR BRT. At the same time, this serves as solid, rigid ground for emerging therapeutic applications, allowing the technique to remain in the spotlight alongside stereotactic radiosurgery.

Radiotherapy for Clinically Localized T3b or T4 Very-High-Risk Prostate Cancer-Role of Dose Escalation Using High-Dose-Rate Brachytherapy Boost or High Dose Intensity Modulated Radiotherapy

Simple Summary

Recently, high-risk prostate cancer was subdivided to a very-high-risk group considered to have the worst prognosis, including clinical stage T3b–T4, primary Gleason pattern 5, or more than four biopsy cores with Gleason score 8–10. Among these, T3b–T4 stage is a special interest in radiotherapy because of their wider target volume outside the prostate. We examined this subgroup and found that dose escalation in radiotherapy both with brachytherapy or intensity modulated radiotherapy (IMRT) improved biochemical free survival rate but not in prostate cancer specific survival rate and overall survival rate.

Abstract

To examine the efficacy of dose escalating radiotherapy into patients with cT3b or T4 localized prostate cancer, we compared Group A (86 conventional dose external beam radiotherapy: EBRT group, treated with 70–72 Gy) and group B (39 high dose EBRT group (HDEBRT group, 74–80 Gy) and 124 high-dose-rate brachytherapy (HDR) + EBRT (HDR boost)) using multi-institutional retrospective data. The actuarial 5-year biochemical disease-free survival (bDFS) rate, prostate cancer specific survival rate (PSS), and overall survival rate (OS) were 75.8%, 96.8%, and 93.5%. Group B showed superior 5-year bDFS rate (81.2%) as compared to the group A (66.5%) (p < 0.0001) with a hazard ratio of 0.397. Equivocal 5-year PSS (98.3% and 94.8% in group B and group A) and OS (both 93.7%) were found between those groups. Accumulated late grade ≥ 2 toxicities in gastrointestinal and genitourinary tracts were similar among those three groups. Therefore, both HDEBRT and HDR boost could be good options for improving the bDFS rate in cT3–T4 localized prostate cancer without affecting PSS and OS.

A multiobserver study investigating the effectiveness of prostatic multiparametric magnetic resonance imaging to dose escalate corresponding histologic lesions using high-dose-rate brachytherapy

PURPOSE

Using multiparametric MRI data and the pathologic data from radical prostatectomy specimens, we simulated the treatment planning of dose-escalated high-dose-rate brachytherapy (HDR-BT) to the Multiparametric MRI dominant intraprostatic lesion (mpMRI-DIL) to compare the dose potentially delivered to the pathologically confirmed locations of the high-grade component of the cancer.

METHODS AND MATERIALS

Pathologist-annotated prostatectomy midgland histology sections from 12 patients were registered to preprostatectomy mpMRI scans that were interpreted by four radiologists. To simulate realistic HDR-BT, we registered each observer's mpMRI-DILs and corresponding histology to two transrectal ultrasound images of other HDR-BT patients with a 15-Gy whole-gland prescription. We used clinical inverse planning to escalate the mpMRI-DILs to 20.25 Gy. We compared the dose that the histopathology would have received if treated with standard treatment plans to the dose mpMRI-targeting would have achieved. The histopathology was grouped as high-grade cancer (any Gleason Grade 4 or 5) and low-grade cancer (only Gleason Grade 3).

RESULTS

212 mpMRI-targeted HDR-BT plans were analyzed. For high-grade histology, the mpMRI-targeted plans achieved significantly higher median [IQR] D98 and D90 values of 18.2 [16.7-19.5] Gy and 19.4 [17.8-20.9] Gy, respectively, in comparison with the standard plans (p = 0.01 and p = 0.003). For low-grade histology, the targeted treatment plans would have resulted in a significantly higher median D90 of 17.0 [16.1-18.4] Gy in comparison with standard plans (p = 0.015); the median D98 was not significantly higher (p = 0.2).

CONCLUSIONS

In this retrospective pilot study of 12 patients, mpMRI-based dose escalation led to increased dose to high-grade, but not low-grade, cancer. In our data set, different observers and mpMRI sequences had no substantial effect on dose to histologic cancer.

Dosimetry of local failure with single dose 19 Gy high-dose-rate brachytherapy for prostate cancer

PURPOSE/OBJECTIVE

Long-term follow up of single dose high-dose rate brachytherapy (HDR BT) for localised prostate cancer has revealed higher than expected rates of biochemical and local failure. This study aimed (i) to investigate the pattern of relapse within the prostate with reference to the initial site of disease in those patients; and (ii) to examine if there were any relationships between the HDR BT dosimetric parameters to these areas of recurrence.

MATERIALS/METHODS

A retrospective review of treatment records of patients who received 19 Gy single fraction of HDR BT was carried out. A matched pair analysis used one control for each biochemical recurrence case matched with pre-treatment Clinical target volume (CTV) size, Gleason score, T stage, risk category and presence of an identifiable dominant intraprostatic nodule (DIL) for each biochemical recurrence case identified. For all datasets, the pre HDR BT DILs were delineated on the diagnostic pre-treatment T2-weighted MRI and planning CT images. For patients with local recurrence post HDR BT, the recurrent nodules were contoured on the diagnostic T2-weighted MRI and choline PET which were registered to the original HDR BT planning CT. Dosimetric parameters of CTV, planning target volume (PTV), DIL and organs at risk (OARs) were evaluated. Wilcoxon signed-rank test was performed to investigate if there were any significant differences in dosimetric parameters between cases and controls. Cox regression analysis was performed to explore if there were any clinical and dosimetric parameters predicting for biochemical progression free survival (bPFS), local recurrence free survival (LR-PFS) and DIL recurrence free survival (DIL-PFS).

RESULTS

Between 2013 and 2018, 180 patients received 19 Gy HDR-BT monotherapy. With a median follow up of 36 months, 19 (10.6%) patients developed biochemical recurrence. Of the 19 patients with biochemical failure, 13 had a local recurrence, including 7 who occurred at the site of DIL. Thirty-eight intermediate/high risk patients were included in the matched pair analysis. No statistically significant differences were found in all CTV, PTV, DIL and OAR dosimetric parameters between cases and controls (p > 0.05). For the Cox regression analysis, none of the covariates investigated were found to be statistically significant factors to predict for bPFS, LC-PFS and DIL-PFS.

CONCLUSION

No associations between biochemical recurrences and HDR BT dosimetry were identified in our cohort of patients receiving 19 Gy single fraction HDR BT. A large proportion of recurrences occurred at the site of original disease. HDR BT for intermediate/high risk prostate cancer should be undertaken using a minimum of two fractions.

Accuracy of dwell position detection with a combined electromagnetic tracking brachytherapy system for treatment verification in pelvic brachytherapy

BACKGROUND AND PURPOSE

To investigate the accuracy of dwell position detection with a combined electromagnetic tracking (EMT) brachytherapy (BT) system for treatment verification, by quantifying positional errors due to EM field interference in typical pelvic BT clinical settings.

MATERIALS AND METHODS

Dedicated prostate and cervix BT phantoms were imaged with CT. For the cervix phantom, the Utrecht applicator + interstitial catheters were used. The implants were reconstructed and treatment plans were created with 270/65 dwell positions for the prostate/cervix phantom. Next, EMT experiments were performed in clinical BT settings using a prototype of a combined EMT/BT system. We quantified positional errors due to EM field interference from surrounding equipment by comparing planned and EMT-measured dwell positions. The mean residual error between planned and EMT-measured dwell positions was calculated in the prostate interstitial catheters and in the whole cervix implant including the applicator. For the cervix phantom, the analysis was repeated for only the interstitial catheters.

RESULTS

Mean residual errors of less than 0.5/0.4 mm in the prostate/cervix catheters were found. For the whole cervix implant including the applicator, large deviations up to 2.4 mm were found. Compared to the interference free set-up, the CT and patient bed environments showed larger residual errors in the interstitial catheters, but residual errors remained <1 mm in all cases.

CONCLUSION

Dwell position detection with the combined system in interstitial catheters is sufficiently accurate to perform EMT-based treatment verification. The effect of EM interference from the surrounding equipment was limited.

A planning study of focal dose escalations to multiparametric MRI-defined dominant intraprostatic lesions in prostate proton radiation therapy

OBJECTIVES

The purpose of this study is to investigate the dosimetric effect and clinical impact of delivering a focal radiotherapy boost dose to multiparametric MRI (mp-MRI)-defined dominant intraprostatic lesions (DILs) in prostate cancer using proton therapy.

METHODS

We retrospectively investigated 36 patients with pre-treatment mp-MRI and CT images who were treated using pencil beam scanning (PBS) proton radiation therapy to the whole prostate. DILs were contoured on co-registered mp-MRIs. Simultaneous integrated boost (SIB) plans using intensity-modulated proton therapy (IMPT) were created based on conventional whole-prostate-irradiation for each patient and optimized with additional DIL coverage goals and urethral constraints. DIL dose coverage and organ-at-risk (OAR) sparing were compared between conventional and SIB plans. Tumor control probability (TCP) and normal tissue complication probability (NTCP) were estimated to evaluate the clinical impact of the SIB plans.

RESULTS

Optimized SIB plans significantly escalated the dose to DILs while meeting OAR constraints. SIB plans were able to achieve 125, 150 and 175% of prescription dose coverage in 74, 54 and 17% of 36 patients, respectively. This was modeled to result in an increase in DIL TCP by 7.3-13.3% depending on α / β and DIL risk level.

CONCLUSION

The proposed mp-MRI-guided DIL boost using proton radiation therapy is feasible without violating OAR constraints and demonstrates a potential clinical benefit by improving DIL TCP. This retrospective study suggested the use of IMPT-based DIL SIB may represent a strategy to improve tumor control.

ADVANCES IN KNOWLEDGE

This study investigated the planning of mp-MRI-guided DIL boost in prostate proton radiation therapy and estimated its clinical impact with respect to TCP and NTCP.

High-dose-rate brachytherapy as monotherapy for prostate cancer: The impact of cellular repair and source decay

PURPOSE

This work quantifies the influence of intrafraction DNA damage repair and cellular repopulation on biologically effective dose (BED) in Ir-192 high-dose-rate brachytherapy for prostate cancer. In addition, it examines the effect of source-decay-induced BED variation for patients treated at different time points in a source exchange cycle.

MATERIALS AND METHODS

Current fractionation schemes are based on simplified-form BED = nd(1 + d/(α/β)), which assumes that intrafraction repair, interfraction repair, and repopulation are negligible. We took accepted radiobiological parameters of T_k, T_p, and α from the recommendations of the AAPM TG-137, and recalculated the full-form BED. Fraction times were normalized to require 15 min for 20 Gy at 10 Ci. Calculations were carried out for both α/β = 1.5 and 3 Gy.

RESULTS

After accounting for intrafraction repair, interfraction repair, and/or repopulation, full-form BED calculations showed significant values, as compared with simplified-form BED. For 1-fraction 20 Gy fractionation, the full-form BED was only 64-82% of the simplified-form BED. Dose protraction effects were milder for smaller prescriptions (6 Gy/Fx), where full form was 87-94%. With regard to source decay, BED varied >20% for patients treated at the beginning and the end of a source exchange cycle for 20 Gy single-fraction prescription.

CONCLUSIONS

Repair and repopulation can be significant in monotherapy high-dose-rate for prostate cancer. As fractionation schemes are established, the simplified BED calculation may not be appropriate. Investigators should consider evaluating BED as a range rather than a discrete value when presenting results unless source activity is explicitly incorporated as well.

Multiparametric MRI-guided dose boost to dominant intraprostatic lesions in CT-based High-dose-rate prostate brachytherapy

OBJECTIVE

The purpose of this study is to investigate the dosimetric feasibility of delivering focal dose to multiparametric (mp) MRI-defined DILs in CT-based high-dose-rate (HDR) prostate brachytherapy with MR/CT registration and estimate its clinical benefit.

METHODS

We retrospectively investigated a total of 17 patients with mp-MRI and CT images acquired pre-treatment and treated by HDR prostate brachytherapy. 21 dominant intraprostatic lesions (DILs) were contoured on mp-MRI and propagated to CT images using a deformable image registration method. A boost plan was created for each patient and optimized on the original needle pattern. In addition, separate plans were generated using a virtually implanted needle around the DIL to mimic mp-MRI guided needle placement. DIL dose coverage and organ-at-rick (OAR) sparing were compared with original plan results. Tumor control probability (TCP) was estimated to further evaluate the clinical impact on the boost plans.

RESULTS

Overall, optimized boost plans significantly escalated dose to DILs while meeting OAR constraints. The addition of mp-MRI guided virtual needles facilitate increased coverage of DIL volumes, achieving a V150 > 90% in 85 % of DILs compared with 57 % of boost plan without an additional needle. Compared with original plan, TCP models estimated improvement in DIL control by 28 % for patients with external-beam treatment and by 8 % for monotherapy patients.

CONCLUSION

With MR/CT registration, the proposed mp-MRI guided DIL boost in CT-based HDR brachytherapy is feasible without violating OAR constraints, and indicates significant clinical benefit in improving TCP of DIL. It may represent a strategy to personalize treatment delivery and improve tumor control.

ADVANCES IN KNOWLEDGE

This study investigated the feasibility of mp-MRI guided DIL boost in HDR prostate brachytherapy with CT-based treatment planning, and estimated its clinical impact by TCP and NTCP estimation.

Clinical outcome of high dose rate brachytherapy with external beam radiotherapy for high-risk prostate cancer: a single institutional retrospective study

Objectives

: This study investigated the clinical outcome of neoadjuvant androgen deprivation therapy followed by high dose rate brachytherapy (HDR-BT, called NEH) with external beam radiotherapy (EBRT) in high-risk prostate cancer (PCa) patients in our institution. : From 2007 to 2012, 192 high-risk PCa patients underwent neoadjuvant treatment-EBRT-NEH ( n = 192). Relations between clinical factors (prostate-specific antigen; PSA, cT stage, Gleason score) and biochemical recurrence were retrospectively analyzed. : The 5- and 7-year overall survival rates were 97.9 and 91.1%. By PSA levels (PSA 20 ng/ml, 20 ng/ml < PSA≤50 ng/ml and PSA > 50 ng/ml), 5-year biochemical recurrence-free survival rates were 85.7, 84.7 and 54.5%, respectively. There were no significant differences between biochemical recurrence and cT stage or Gleason score. : We found that NEH can contribute to better biochemical recurrence free survival of high-risk PCa patients with PSA below 50 ng/ml. High-risk PCa patients with PSA over 50 ng/ml may require more aggressive local or systemic treatment.

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.

Five-year quality of life assessment after carbon ion radiotherapy for prostate cancer

The aim of this study was to prospectively assess 5-year health-related quality of life (HRQOL) of patients treated with carbon ion radiotherapy (C-ion RT) for clinically localized prostate cancer. A total of 417 patients received carbon ion radiotherapy at a total dose of 63-66 Gray-equivalents (GyE) in 20 fractions over 5 weeks, and neoadjuvant and adjuvant androgen deprivation therapy (ADT) were administered for intermediate and high-risk patients. A HRQOL assessment was performed at five time points (immediately before the initiation of C-ion RT, immediately after, and at 12, 36 and 60 months after completion of C-ion RT) using Functional Assessment of Cancer Therapy (FACT) questionnaires. FACT-G and FACT-P scores were significantly decreased; however, the absolute change after 60 months was minimal. The transient decreases in the Trial Outcome Index (TOI) score returned to their baseline levels. Use of ADT, presence of adverse events, and biochemical failure were related to lower scores. Scores of subdomains of FACT instruments indicated characteristic changes. The pattern of HRQOL change after C-ion RT was similar to that of other modalities. Further controlled studies focusing on a HRQOL in patients with prostate cancer are warranted.

Improved prostate delineation in prostate HDR brachytherapy with TRUS-CT deformable registration technology: A pilot study with MRI validation

Accurate prostate delineation is essential to ensure proper target coverage and normal-tissue sparing in prostate HDR brachytherapy. We have developed a prostate HDR brachytherapy technology that integrates intraoperative TRUS-based prostate contour into HDR treatment planning through TRUS-CT deformable registration (TCDR) to improve prostate contour accuracy. In a perspective study of 16 patients, we investigated the clinical feasibility as well as the performance of this TCDR-based HDR approach. We compared the performance of the TCDR-based approach with the conventional CT-based HDR in terms of prostate contour accuracy using MRI as the gold standard. For all patients, the average Dice prostate volume overlap was 91.1 ± 2.3% between the TCDR-based and the MRI-defined prostate volumes. In a subset of eight patients, inter and intro-observer reliability study was conducted among three experienced physicians (two radiation oncologists and one radiologist) for the TCDR-based HDR approach. Overall, a 10 to 40% improvement in prostate volume accuracy can be achieved with the TCDR-based approach as compared with the conventional CT-based prostate volumes. The TCDR-based prostate volumes match closely to the MRI-defined prostate volumes for all 3 observers (mean volume difference: 0.5 ± 7.2%, 1.8 ± 7.2%, and 3.5 ± 5.1%); while CT-based contours overestimated prostate volumes by 10.9 ± 28.7%, 13.7 ± 20.1%, and 44.7 ± 32.1%. This study has shown that the TCDR-based HDR brachytherapy is clinically feasible and can significantly improve prostate contour accuracy over the conventional CT-based prostate contour. We also demonstrated the reliability of the TCDR-based prostate delineation. This TCDR-based HDR approach has the potential to enable accurate dose planning and delivery, and potentially enhance prostate HDR treatment outcome.

Nationwide, Multicenter, Retrospective Study on High-Dose-Rate Brachytherapy as Monotherapy for Prostate Cancer

PURPOSE

To present, analyze, and discuss results of a nationwide, multicenter, retrospective study on high-dose-rate brachytherapy (HDR-BT) as monotherapy for low-, intermediate-, and high-risk prostate cancer.

METHODS AND MATERIALS

From 1995 through 2013, 524 patients, 73 (14%) with low-risk, 207 (40%) with intermediate-risk, and 244 (47%) with high-risk prostate cancer, were treated with HDR-BT as monotherapy at 5 institutions in Japan. Dose fractionations were 27 Gy/2 fractions for 69 patients (13%), 45.5 Gy/7 fractions for 168 (32%), 49 Gy/7 fractions for 149 (28%), 54 Gy/9 fractions for 130 (25%), and others for 8 (2%). Of these patients, 156 (30%) did not receive androgen deprivation therapy, and 202 patients (39%) did receive androgen deprivation therapy <1 year, 112 (21%) for 1-3 years, and 54 (10%) for >3 years. Median follow-up time was 5.9 years (range, 0.4-18.1 years), with a minimum of 2 years for surviving patients.

RESULTS

After 5 years, respective actuarial rates of no biochemical evidence of disease, overall survival, cause-specific survival, and metastasis-free survival for all patients were 92%, 97%, 99%, and 94%. For low/intermediate/high-risk patients, the 5-year no biochemical evidence of disease rates were 95%/94%/89%, the 5-year overall survival rates were 98%/98%/94%, the 5-year cause-specific survival rates were 98%/100%/98%, and the 5-year metastasis-free survival rates were 98%/95%/90%, respectively. The cumulative incidence of late grade 2 to 3 genitourinary toxicity at 5 years was 19%, and that of late grade 3 was 1%. The corresponding incidences of gastrointestinal toxicity were 3% and 0% (0.2%). No grade 4 or 5 of either type of toxicity was detected.

CONCLUSIONS

The findings of this nationwide, multicenter, retrospective study demonstrate that HDR-BT as monotherapy was safe and effective for all patients with low-, intermediate-, and high-risk prostate cancer.

Two-fraction high-dose-rate brachytherapy within a single day combined with external beam radiotherapy for prostate cancer: single institution experience and outcomes

We investigated the outcomes of treatment for patients with localized prostate cancer (PCa) treated with 3D conformal radiation therapy (3D-CRT) followed by two-fraction high-dose-rate brachytherapy within a single day (2-fr.-HDR-BT/day) at a single institution. A total of 156 consecutive Asian males (median age, 67 years) were enrolled. To compare our findings with those of other studies, we analyzed our results using the D'Amico classification, assigning the patients to low- ( N =: 5; 3.2%), intermediate- ( N =: 36; 23.1%) and high-risk ( N =: 115; 73.7%) groups (Stage T3 PCa patients were classified as high-risk). One patient in the D'Amico low-risk group (20%), 13 intermediate-risk patients (36.1%) and 99 high-risk patients (86.1%) underwent androgen deprivation therapy. We administered a prescription dose of 39 Gy in 13 fractions of 3D-CRT combined with 18 Gy of HDR-BT in two 9-Gy fractions delivered within a single day. We did not distinguish between risk groups in determining the prescription dose. The median follow-up period was 38 months. Of the 156 patients, one died from primary disease and five died from other diseases. The 3-year overall survival (OS) rates were 100%, 100% and 93.7%, and the 3-year 'biochemical no evidence of disease (bNED)' rates were 100%, 100% and 96.9% for the D'Amico low-, intermediate- and high-risk groups, respectively. No patient developed ≥ Grade 3 early toxicity. The Grade 3 late genitourinary toxicity rate was 2.6%, and no ≥ Grade 3 late gastrointestinal toxicity occurred. The efficacy and safety of this study were satisfactory, and longer-term follow-up is necessary.

Assessing patient characteristics and radiation-induced non-targeted effects in vivo for high dose-rate (HDR) brachytherapy

PURPOSE

To test whether blood, urine, and tissue based colony-forming assays are a useful clinical detection tool for assessing fractionated treatment responses and non-targeted radiation effects in bystander cells.

MATERIALS AND METHODS

To assess patients' responses to radiation treatments, blood serum, urine, and an esophagus explant-based in vivo colony-forming assay were used from oesophageal carcinoma patients. These patients underwent three fractions of high dose rate (HDR) intraluminal brachytherapy (ILBT).

RESULTS

Human keratinocyte reporters exposed to blood sera taken after the third fraction of brachytherapy had a significant increase in cloning efficiency compared to baseline samples (p < 0.001). Such results may suggest an induced radioresistance response in bystander cells. The data also revealed a clear inverse dose-rate effect during late treatment fractions for the blood sera data only. Patient characteristics such as gender had no statistically significant effect (p > 0.05). Large variability was observed among the patients' tissue samples, these colony-forming assays showed no significant changes throughout fractionated brachytherapy (p > 0.05).

CONCLUSION

Large inter-patient variability was found in the urine and tissue based assays, so these techniques were discontinued. However, the simple blood-based assay had much less variability. This technique may have future applications as a biological dosimeter to predict treatment outcome and assess non-targeted radiation effects.

Quality of life after high-dose-rate brachytherapy monotherapy for prostate cancer

Purpose

There is little information in the literature on health-related quality of life (HRQOL) changes due to high-dose-rate (HDR) brachytherapy monotherapy for prostate cancer.

Materials and Methods

We conducted a prospective study of HRQOL changes due to HDR brachytherapy monotherapy for low risk or favorable intermediate risk prostate cancer. Sixty-four of 84 (76%) patients who were treated between February 2011 and April 2013 completed 50 questions comprising the Expanded Prostate Cancer Index Composite (EPIC) before treatment and 6 and/or 12 months after treatment.

Results

Six months after treatment, there was a significant decrease (p<0.05) in EPIC urinary, bowel, and sexual scores, including urinary overall, urinary function, urinary bother, urinary irritative, bowel overall, bowel bother, sexual overall, and sexual bother scores. By one year after treatment, EPIC urinary, bowel, and sexual scores had increased and only the bowel overall and bowel bother scores remained significantly below baseline values.

Conclusions

HDR brachytherapy monotherapy is well-tolerated in patients with low and favorable intermediate risk prostate cancer. EPIC urinary and sexual domain scores returned to close to baseline 12 months after HDR brachytherapy.

High-dose-rate brachytherapy delivered in two fractions as monotherapy for low-risk prostate cancer

PURPOSE

High-dose-rate (HDR) brachytherapy has been accepted as an effective and safe method to treat prostate cancer. The aim of this study was to describe acute toxicity following HDR brachytherapy to the prostate, and to examine the association between dosimetric parameters and urinary toxicity in low-risk prostate cancer patients.

MATERIAL AND METHODS

Patients with low-risk prostate cancer were given HDR brachytherapy as monotherapy in two 12.5 Gy fractions. Planning objectives for the planning target volume (PTV) were V100% ≥ 90% and V150% ≤ 35%. Planning objectives for organs at risk were V75% ≤ 1 cc for the bladder, rectum and perineum, and V125% ≤ 1 cc for the urethra. Toxicity was assessed three months after treatment using the Common Terminology Criteria for Adverse Events.

RESULTS

Seventy-three patients were included in the analysis. Thirty-three patients (45%) reported having any type of toxicity in the three months following HDR brachytherapy. Most toxicity cases (26%) were grade 1 urinary toxicity. Mean coverage index was 0.89 and mean V100 was 88.85. Doses administered to the urethra were associated with urinary toxicity. Patients who received more than 111.3% of the prescribed dose in 1 cc of the urethra were four times more likely to have urinary toxicity compared to patients receiving less than 111.3% (OR = 4.71, 95% CI: 1.43-15.6; p = 0.011).

CONCLUSIONS

High-dose-rate brachytherapy administered as monotherapy for prostate cancer proved to be a safe alternative treatment for patients with low-risk prostate cancer. Urinary toxicity was associated with the dose administered to 1 cc and 0.1 cc of the urethra and was remarkably inferior to the reported toxicity in similar studies.

Recent developments and best practice in brachytherapy treatment planning

Brachytherapy has evolved over many decades, but more recently, there have been significant changes in the way that brachytherapy is used for different treatment sites. This has been due to the development of new, technologically advanced computer planning systems and treatment delivery techniques. Modern, three-dimensional (3D) imaging modalities have been incorporated into treatment planning methods, allowing full 3D dose distributions to be computed. Treatment techniques involving online planning have emerged, allowing dose distributions to be calculated and updated in real time based on the actual clinical situation. In the case of early stage breast cancer treatment, for example, electronic brachytherapy treatment techniques are being used in which the radiation dose is delivered during the same procedure as the surgery. There have also been significant advances in treatment applicator design, which allow the use of modern 3D imaging techniques for planning, and manufacturers have begun to implement new dose calculation algorithms that will correct for applicator shielding and tissue inhomogeneities. This article aims to review the recent developments and best practice in brachytherapy techniques and treatments. It will look at how imaging developments have been incorporated into current brachytherapy treatment and how these developments have played an integral role in the modern brachytherapy era. The planning requirements for different treatments sites are reviewed as well as the future developments of brachytherapy in radiobiology and treatment planning dose calculation.

Toxicity and efficacy of three dose-fractionation regimens of intensity-modulated radiation therapy for localized prostate cancer

Outcomes of three protocols of intensity-modulated radiation therapy (IMRT) for localized prostate cancer were evaluated. A total of 259 patients treated with 5-field IMRT between 2005 and 2011 were analyzed. First, 74 patients were treated with a daily fraction of 2.0 Gy to a total of 74 Gy (low risk) or 78 Gy (intermediate or high risk). Then, 101 patients were treated with a 2.1-Gy daily fraction to 73.5 or 77.7 Gy. More recently, 84 patients were treated with a 2.2-Gy fraction to 72.6 or 74.8 Gy. The median patient age was 70 years (range, 54-82) and the follow-up period for living patients was 47 months (range, 18-97). Androgen deprivation therapy was given according to patient risk. The overall and biochemical failure-free survival rates were, respectively, 96 and 82% at 6 years in the 2.0-Gy group, 99 and 96% at 4 years in the 2.1-Gy group, and 99 and 96% at 2 years in the 2.2-Gy group. The biochemical failure-free rate for high-risk patients in all groups was 89% at 4 years. Incidences of Grade ≥ 2 acute genitourinary toxicities were 9.5% in the 2.0-Gy group, 18% in the 2.1-Gy group, and 15% in the 2.2-Gy group (P = 0.29). Cumulative incidences of Grade ≥ 2 late gastrointestinal toxicity were 13% in the 2.0-Gy group at 6 years, 12% in the 2.1-Gy group at 4 years, and 3.7% in the 2.2-Gy group at 2 years (P = 0.23). So far, this stepwise shortening of treatment periods seems to be successful.

High-dose-rate brachytherapy as monotherapy for prostate cancer: technique, rationale and perspective

High-dose-rate (HDR) brachytherapy as monotherapy is a comparatively new brachytherapy procedure for prostate cancer. Although clinical results are not yet mature enough, it is a highly promising approach in terms of potential benefits for both radiation physics and radiobiology. In this article, we describe our technique for monotherapeutic HDR prostate brachytherapy, as well as the rationale and theoretical background, with educational intent.