Ultrasound-guided high dose rate conformal brachytherapy boost in prostate cancer: treatment description and preliminary results of a phase I/II clinical trial

Fractionation and protraction for radiotherapy of prostate carcinoma

PURPOSE

To investigate whether current fractionation and brachytherapy protraction schemes for the treatment of prostatic cancer with radiation are optimal, or could be improved.

METHODS AND MATERIALS

We analyzed two mature data sets on radiotherapeutic tumor control for prostate cancer, one using EBRT and the other permanent seed implants, to extract the sensitivity to changes in fractionation of prostatic tumors. The standard linear-quadratic model was used for the analysis.

RESULTS

Prostatic cancers appear significantly more sensitive to changes in fractionation than most other cancers. The estimated alpha/beta value is 1.5 Gy [0.8, 2.2]. This result is not too surprising as there is a documented relationship between cellular proliferative status and sensitivity to changes in fractionation, and prostatic tumors contain exceptionally low proportions of proliferating cells.

CONCLUSIONS

High dose rate (HDR) brachytherapy would be a highly appropriate modality for treating prostate cancer. Appropriately designed HDR brachytherapy regimens would be expected to be as efficacious as low dose rate, but with added advantages of logistic convenience and more reliable dose distributions. Similarly, external beam treatments for prostate cancer can be designed using larger doses per fraction; appropriately designed hypofractionation schemes would be expected to maintain current levels of tumor control and late sequelae, but with reduced acute morbidity, together with the logistic and financial advantages of fewer numbers of fractions.

Use of three-dimensional radiation therapy planning tools and intraoperative ultrasound to evaluate high dose rate prostate brachytherapy implants

PURPOSE

We performed a pilot study to evaluate the quality of high dose rate (HDR) prostate implants using a new technique combining intraoperative real-time ultrasound images with a commercially available 3-dimensional radiation therapy planning (3D RTP) system.

METHODS AND MATERIALS

Twenty HDR prostate implants performed by four different physicians on a phase I/II protocol were evaluated retrospectively. Radiation therapy (RT) consisted of pelvic external beam RT (EBRT) to a dose of 46 Gy in 2-Gy fractions over 5 weeks and 2 HDR implants (prescribed dose of 950 cGy per implant). Our in-house real-time geometric optimization technique was used in all patients. Each HDR treatment was delivered without moving the patient. Ultrasound image sets were acquired immediately after needle placement and just prior to HDR treatment. The ultrasound image sets, needle and source positions and dwell times were imported into a commercial computerized tomography (CT) based 3D RTP system. Prostate contours were outlined manually caudad to cephalad. Dose-volume histograms (DVHs) of the prostate were evaluated for each implant.

RESULTS

Four patients with stage T2a carcinoma, 4 with stage T2b, and 3 with stage T1c were studied. The median number of needles used per implant was 16 (range 14-18). The median treated volume of the implant (volume of tissue covered by the 100% isodose surface) was 82.6 cc (range 52.6-96.3 cc). The median target volume based on the contours entered in the 3D RTP system was 44.83 cc (range 28.5-67.45 cc). The calculated minimum dose to the target volume was 70% of the prescribed dose (range 45-97%). On average 92% of the target volume received the prescribed dose (range 75-99 %). The mean homogeneity index (fraction of the target volume receiving between 1.0 to 1.5 times the prescribed dose) was 80% or 0.8 (range 0.55-0.9). These results compare favorably to recent studies of permanent implants which report a minimum target volume dose of 43% (range 29-50%) and an average of 85% of the target volume (range 76-92%) receiving the prescribed dose.

CONCLUSIONS

The feasibility of evaluating HDR prostate implants using ultrasound images (acquired immediately prior to treatment) with a commercially available 3D RTP system was established. The dosimetric characteristics of these HDR implants appear to be substantially different compared to permanent implants. These developments allow quantitative evaluation of the dosimetric quality of HDR prostate treatments. Future studies will examine any correlation between the dosimetric quality of the implant and clinical/biochemical outcomes.

Pubic arch detection in transrectal ultrasound guided prostate cancer therapy

New biopsy techniques, increased life expectancy, and prostate-specific antigen (PSA) screening have contributed to an increase in the reported incidence of prostate cancer. Among several treatment options available to the patients, transperineal prostate brachytherapy has emerged as a medically successful, cost-effective outpatient procedure for treating localized prostate cancer. Transperineal prostate brachytherapy employs transrectal ultrasound (TRUS) as the primary imaging modality to accurately preplan and subsequently execute the placement of radioactive seeds into the prostate. Under TRUS guidance, a needle (preloaded with radioactive seeds) is inserted through a template guide, through the perineum and into a predetermined prostate target. The pubic arch, formed by the central union of pelvic bones, is a potential barrier to the passage of these needles in the prostate. A critical aspect, therefore, in the planning and execution of the brachytherapy procedure is the accurate assessment of pubic arch interference (PAI) in relation to the prostate. Traditionally, the evaluation of PAI has involved computed tomography correlate scanning or crude subjective evaluations. In this paper, we describe a new method of assessing PAI by detecting the pubic arch via image processing on the TRUS images. The PAI detection (PAID) algorithm first uses a technique known as sticks to selectively enhance the contrast of linear features in ultrasound images. Next, the enhanced image is thresholded via percentile thresholding. Finally, we fit a parabola (a model for the pubic arch) recursively to the thresholded image. Our evaluation result from 15 cases indicates that the algorithm can successfully detect the pubic arch with 90% accuracy. Based on this study, we believe that detecting the pubic arch and assessing PAI can be done practically and more accurately in the clinical setting using TRUS rather than the current available methods.

High-dose rate interstitial with external beam irradiation for localized prostate cancer--results of a prospective trial

PURPOSE

A prospective phase II trial was carried out to test the feasibility and effectiveness of a combined interstitial with external beam radiotherapy approach for localized prostate cancer.

MATERIALS AND METHODS

Between October 1992 and December 1994, 82 evaluable patients were treated. T2 and T3 tumours, according to the AJCC classification system of 1992, were found in 21 and 61 cases, respectively. The median follow-up was 24 months; three patients were lost during follow-up. All of the patients were pathologically proven to be node-negative by laparoscopic node dissection of the fossa obturatoria region. A dose of 9 Gy a week was prescribed during the first and second weeks of treatment (10 Gy each week from October 1992 to December 1993) interstitially with high-dose rate Iridium-192 brachytherapy to the prostate and tumour extension beyond the capsule. External beam four-field box irradiation was then given to the prostate to a dose of 45 Gy/25 fractions (40 Gy/20 fractions from October 1992 to December 1993).

RESULTS

Before starting treatment, a PSA value of > or =10 ng/ml was found in 64.6% (53/82) of patients with a median PSA of 14.0 ng/ml. The median PSA 3, 12 and 24 months after completion of therapy was 1.20, 0.78 and 0.70 ng/ml, respectively. The PSA value was < 1.0 ng/ ml in 52.9% of patients at 2 years. Negative punch biopsies 12 and 24 months after therapy were observed in 69.8% (44/63) and 73. 1% (38/ 52) of patients, respectively. A positive biopsy combined with a PSA value of > 1.0 ng/ml was considered as local failure. The local tumour control rate was 79.5% at 2 years. Acute side-effects were not increased relative to external beam irradiation alone. Severe side-effects were observed in three patients (two of the three patients had additional risk factors (colitis ulcerosa and diabetes mellitus)); they developed rectourethral fistulae requiring colostomy after biopsies from the anterior rectal wall.

CONCLUSION

The described method is feasible and well tolerable. The three complications observed were not caused by irradiation alone. Biopsies from the anterior rectal wall after definitive high-dose radiotherapy for prostate cancer have to be seen as obsolete. The rate of negative prostate biopsies of 73.1% after 24 months represents an encouraging result.

[Indications and results of exclusive radiotherapy in early prostatic adenocarcinoma]

Prostate adenocarcinoma incidence are rising rapidly, especially in early stages. Even if some of these carcinomas may be latent or slow growing either spontaneously or under hormonal therapy, most patients 75 years old or less presenting a localized tumor, T1b-c, T2, T3, N0, M0, whatever the grading, will require treatment with curative intent: radical prostatectomy, external beam radiation therapy (ERT) and/or brachytherapy. After ERT limited to the prostate or including seminal vesicles and/or pelvic lymph nodes, the overall survival and the survival without clinical evolution at 5, 10 and 15 years are good. However survival rates without biochemical evolution are about 30% lower and 70% or less at 5 years for the more favorable group (T < or = T2a and Gleason < 7 and PSA < 10 ng/mL). Brachytherapy alone yields good results for the same favorable group. In the unfavorable group (T > or = 2c and Gleason > or = 7 and PSA > or = 20 ng/mL), adjuvant hormonal therapy improves survival. Conformal radiation therapy allows an increase in dose to the tumor by about 15% without increasing complications. It can increase the biological remission rate in the intermediate group (T < or = 2a or Gleason > or = 7 or PSA > or = 20 ng/mL).

The correlation between the ASTRO Consensus Panel definition of biochemical failure and clinical outcome for patients with prostate cancer treated with external beam irradiation. American Society of Therapeutic Radiology and Oncology

PURPOSE

We reviewed our institution's experience treating patients with external beam irradiation (RT) to determine if the ASTRO Consensus Panel definition of biochemical failure (BF) following radiation therapy correlates with clinical distant metastases free survival (DMFS), disease-free survival (DFS), cause-specific survival (CSS), and local control (LC).

METHODS AND MATERIALS

Between 1/1/87 and 12/31/92, 568 patients with clinically localized prostate cancer received external beam irradiation (RT) using localized prostate fields at William Beaumont Hospital (median total dose 66.6 Gy; range: 60-70.4 Gy). Biochemical failure was defined as three consecutive increases in post-treatment prostate specific antigen (PSA) after achieving a nadir. Biochemical failure was recorded as the time midway between the nadir and the first rising PSA. Five-year actuarial rates of clinical DMFS, DFS, CSS, and LC were calculated for patients who were biochemically controlled (BC) versus those who failed biochemically. Median follow-up was 56 months (range: 24-118 months).

RESULTS

Five-year actuarial rates of DMFS, DFS, CSS, and LC were significantly greater in patients who were biochemically controlled versus those who were not (p < 0.001). In patients who were BC, the 5-year actuarial rates of DMFS, DFS, CSS, and LC were 99%, 99%, 98%, and 99% respectively. For patients who failed biochemically, the 5-year actuarial rates of DMFS, DFS, CSS, and LC were 74%, 64%, 89%, and 86% respectively. When stratifying by pretreatment PSA, Gleason score, and T stage these differences remained significant for DMFS, DFS, and CSS. The Cox proportional hazards model demonstrated that BC was the single most important predictor of clinical outcome for DMFS, DFS, CSS, and LC. Pretreatment PSA and Gleason score were also independent predictors of outcome for DMFS and DFS.

CONCLUSIONS

The ASTRO Consensus Panel definition of BF following radiation therapy correlates well with clinical DMFS, DFS, and CSS. These findings suggest that the Consensus Panel definition may be a surrogate for clinical progression and survival and should be considered a valid endpoint for separating successful versus unsuccessful treatment. Additional studies with longer follow-up will be needed to corroborate these findings.

Radiotherapy options for localized prostate cancer based upon pretreatment serum prostate-specific antigen levels and biochemical control: a comprehensive review of the literature

PURPOSE

To review all the available radiotherapy (RT) literature on localized prostate cancer treatment where serum prostate-specific antigen (PSA) levels were used to both stratify patients and evaluate outcome and determine if any conclusions can be reached regarding an optimal radiotherapeutic management for this disease.

METHODS AND MATERIALS

A MEDLINE search was conducted to obtain all articles in English on prostate cancer treatment employing RT from 1986-1997. Studies were considered eligible for review only if they met all the following criteria: 1) pretreatment PSA values were recorded and grouped for subsequent evaluation, 2) posttreatment PSA values were continuously monitored, 3) definitions of biochemical control were stated, and 4) the median follow-up was given.

RESULTS

Of the 246 articles identified, only 20 met the inclusion criteria; 4 using conformal external beam RT, 8 using conventional external beam RT, and 8 using interstitial brachytherapy (4 using a permanent implant alone, 3 combining external beam RT with a permanent implant, and 1 combining a conformal temporary interstitial implant boost with external beam RT). No studies using neutrons (with or without external beam RT) or androgen deprivation (combined with external beam RT) were identified where patients were stratified by pretreatment PSA levels. Results for all therapies were extremely variable with the 3-5-year rates of biochemical control for patients with pretreatment PSA levels < or = 4 ng/ml ranging from 48 to 100%, for PSA levels >4 and < or = 10 ng/ml ranging from 44 to 90%, for PSA levels >10 and < or = 20 ng/ml ranging from 27 to 89%, and for PSA levels >20 ranging from 14 to 89%. The median Gleason score, T-stage, definition of biochemical control, and follow-up were substantially different from series to series. No RT option consistently produced superior results.

CONCLUSIONS

When data are reviewed from studies using serum PSA levels to stratify patients and to evaluate treatment outcome, no consistently superior RT technique was identified. These data suggest that standard definitions of disease stage (combining clinical, pathologic, and biochemical criteria) and a common definition of biochemical cure (as developed by the American Society for Therapeutic Radiology and Oncology Consensus Panel) need to be adopted to evaluate treatment efficacy and advise patients on the most appropriate radiotherapeutic option for their disease.

Source localization following permanent transperineal prostate interstitial brachytherapy using magnetic resonance imaging

PURPOSE

Dosimetric evaluation of completed brachytherapy implant procedures is crucial in developing proper technique and has prognostic implications. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningful dosimetric data. Methods using radiographs and CT accurately localize sources, but poorly delineate the prostate gland. MRI has been recognized as a superior imaging modality in delineating the prostate gland, but poor in localizing sources due to lack of source visibility. The purpose of this study was to optimize the visualization of sources using MRI and compare to CT derived source localization.

METHODS AND MATERIALS

Multiple MRI scanning techniques were attempted until an acceptable sequence to visualize both the prostate gland and the implanted sources was found. The exams were performed using a pelvic coil only in approximately 15 min. The CT and MRI scans of 20 consecutive patients who had received TRUS-guided permanent transperineal interstitial prostate 125Iodine or 103Palladium brachytherapy were evaluated using an in-house dosimetry system. To eliminate anatomical dependence, the MRI-derived DVHs for the entire calculation volume were then compared to those derived from the CT scans.

RESULTS

The differences in isodose volumes, of the calculation volumes, for all implants at all dose levels were not statistically significant at the 95% confidence level. Calculation volume isodose volumes derived from MR images were statistically similar to those derived from CT images at the prescription dose for both 125Iodine (p < 0.01) and 103Palladium (p < 0.026).

CONCLUSION

This study presents the first evidence that MRI may be reliably used to identify permanently implanted 125Iodine and 103Palladium sources. Given the advantage of target definition characteristics of MRI, substantially more accurate dosimetric analysis of prostate implants is now possible. The cost of the optimized and abbreviated MR scanning sequence used in this study is comparable to a pelvic CT scan. Postimplant MRI allows more accurate volumetric and anatomically relevant evaluation of permanent prostate implants, which may provide useful clinical correlation.

Brachytherapy in cancer of the prostate: an historical perspective

Carcinoma of the prostate in the United States has increased dramatically in the last few years due to improved detection methods including prostatic specific antigen testing and transrectal ultrasound. More than half of all prostate cancers are discovered while still localized. Radical prostatectomy and definitive radiation are reserved for patients in good health, who have localized disease. Brachytherapy, with its inherent ability to deliver a high dose to an organ-confined tumor, while minimally irradiating the surrounding tissues, has successfully competed with external beam for the treatment of early prostatic tumors. Their respective role is constantly under scrutiny and re-evaluation to improve the accuracy of delivery of radiation. The present review focuses on the role of brachytherapy for treatment of early cancer of the prostate over the span of this century and its future in the next millennium.

Interstitial implantation techniques in prostate cancer

Brachytherapy is a radiotherapeutic technique that allows the physician to implant radioactive isotopes into a body cavity or directly into tissue. Different radioisotopes have unique characteristics that the brachytherapist may utilize for a particular situation. The use of brachytherapy is part of standard radiation oncology practice in gynecological and head and neck cancer management. The prostate is approachable for interstitial implantation due to its close proximity to the perineum. Over 20 years ago, primitive methods of brachytherapy were utilized in the treatment of prostate cancer. However, poor results due to inconsistency in achieving adequate coverage of the entire prostate and poor patient selection caused this treatment modality to fall out of favor. Technological advances over the last decade have restored attention to brachytherapy for prostate cancer. Particularly important has been the development of transrectal ultrasound, new radioisotopes such as palladium-103, computer tomography, computerized dosimetry systems, and earlier diagnosis. Modern interstitial implantation utilizing transperineal template and transrectal ultrasound guidance has resulted in improved consistency in radiation dose delivery to the entire prostate. Early results are encouraging in terms of the relatively low morbidity of the procedure, improved local control rates, and biochemical progression free survival. This has resulted in an outpatient treatment that has high patient acceptance.

Should brachytherapy be considered a therapeutic option in localized prostate cancer?

Contemporary prostate brachytherapy incorporates advances in computer analysis, imaging technology, and delivery apparatus, allowing exacting and reproducible results compared with historical approaches. The advances permit brachytherapy to be performed on a cost-effective, outpatient basis with low morbidity in the appropriately selected patient. Although unsettled questions remain regarding dosimetric issues, long-term outcomes, and morbidity, the weight of evidence to date appears to support the use of brachytherapy in selected patients. Brachytherapy may be considered a therapeutic option: as monotherapy for early-stage disease and also a boost following moderate doses of external beam irradiation for locally advanced disease.

Does brachytherapy have a role in the treatment of prostate cancer?

The goal of radiation therapy is to deliver a high dose to the tumor while preserving normal surrounding tissue. For early-stage prostate cancer, the ultimate conformal irradiation is to place radioactive sources directly into the gland either as permanent or temporary seeds. Permanent seed implantation is capable of delivering two times the radiobiologically equivalent dose of external beam irradiation to the prostate and tumor. In the past, the results of prostate brachytherapy were likely poor owing to the technical difficulty in accurately placing the radioactive seeds uniformly throughout the prostate. The use of low-dose-rate I-125 to treat high-grade cancers probably also contributed to the poorer results as compared with external beam irradiation. Over the last 10 years, however, technologic advances in transrectal ultrasonography, computer dosimetry, and template-based transperineal techniques have dramatically improved the accuracy and consistency of the brachytherapist to place radioactive sources directly into the prostate gland. Transperineal ultrasound or CT directed seed implantation has replaced the older retropubic method. Brachytherapists are now able to accurately map out the gland prior to the implant and carefully evaluate preoperatively seed placement. The availability of such radioactive sources as iodine-125, palladium-103, and iridium-192 has also given the brachytherapist isotopes that can be more carefully matched to the biology and stage of the tumor. More sensitive definitions of failure have prompted radiation oncologists and urologists to carefully evaluate the efficacy of external beam irradiation and surgery. Accurate comparison of the efficacy of brachytherapy to surgery and to external beam radiation requires a randomized study. Comparisons of retrospective studies are fraught with the problems of the heterogeneous nature of early-stage prostate cancer. Imbalances in stage, grade, initial PSA extraprostatic disease, and nodal status of patient groups make comparisons difficult. Most of the long-term data for permanent seed implantation are the result of work at a single institution. These results will need to be repeated at other institutions treating patients in a similar manner. Because techniques vary from institution to institution, permanent implant results will need to be carefully evaluated for technique as well as stratified for pretreatment variables. Pretreatment PSA and grade appear to be more sensitive variables than stage in predicting failure after radiation. As more patients are diagnosed with very early and nonpalpable disease, future studies will need to stratify patients based on these pretreatment factors. Patients with early-stage disease but identified as high risk for extraprostatic disease will require more intensive regimens. The treatment outcomes based on biopsy results are inconclusive. A lack of consensus on the definition of a truly positive biopsy remains forthcoming. The value of a positive prostate biopsy as an outcome predictor for clinical failure is still unclear. The use of prostate nuclear cell antigen staining may help clarify the issue. Comparison of treatment outcome based on absolute PSA is also difficult. The Seattle series suggest that brachytherapy by permanent seed implantation is as efficacious as external beam irradiation for early-stage disease in patients with a low PSA (< 10 ng/mL). As the PSA value rises above 10 ng/mL, the probability of failure after external beam rises substantially. Results from the Seattle series suggest an advantage to seed implant alone or the judicious application of seed implant boost to external beam radiation for these patients with more advanced cancer. The most sensitive measurement of therapeutic outcome is progression-free survival. Few studies to date have evaluated progression-free survival.

Conformal prostate brachytherapy: initial experience of a phase I/II dose-escalating trial

PURPOSE

To improve treatment results on prostatic adenocarcinoma, conformal radiation therapy (CRT) has been used. Two major drawbacks of external CRT are: (a) internal organ motion/daily set-up variations, and (b) exclusion of several patients for CRT based on poor geometrical relationships as identified by three dimensional (3D) treatment planning. To overcome the above problems, we began the first prospective Phase I/II dose-escalating clinical trial of conformal brachytherapy (CB) and concurrent external beam irradiation.

METHODS AND MATERIALS

Fifty-nine patients with T2b-T3c prostatic adenocarcinoma received 176 transperineal ultrasound-guided conformal high-dose rate (HDR) boost implants. All patients received concomitant external beam pelvic irradiation. Dose escalation of the three HDR-CB fractions proceeded as follows: 5.5 Gy (30 patients), 6 Gy (20 patients), and 6.5 Gy (9 patients). The CB dose was prescribed to the prostate contour as outlined using an online biplanar transrectal ultrasound probe. The urethra, anterior rectal wall, and prostate boundaries were identified individually and outlined at 5 mm intervals from the base to the apex of the gland. The CB using real-time ultrasound guidance with interactive online isodose distributions was performed on an outpatient basis. As needles were placed into the prostate, corrections for prostate displacement were recorded and the isodose distributions were recalculated to represent the new relationship between the needles, prostate, and normal structures. No computerized tomography (CT) planning or implant preplanning was required.

RESULTS

No patient was rejected based on poor geometrical relation of pelvic structures. In every implant performed, prostate displacement was noted. Craniocaudal motion of the gland ranged from 0.5-2.0 cm (mean = 1.0 cm), whereas lateral displacement was 0.1-0.4 cm. With the interactive online planning system, organ motion was immediately detected, accounted for, and corrected prior to each HDR treatment. The rectal dose has ranged from 45 to 87%, and the urethral dose from 97 to 112% of the prostate dose. It is significant to note that operator dependence has been completely removed because the interactive online planning system uniformly guides the physicians.

CONCLUSIONS

With ultrasound guidance and the interactive online dosimetry system, organ motion (as compared to external beam) is insignificant because it can be corrected during the procedure without increasing target volume margins. Common pitfalls of brachytherapy, including operator dependence and difficulty with reproducibility, have been eliminated with the intraoperative online planning system.