Biological effective dose for comparison and combination of external beam and low-dose rate interstitial brachytherapy prostate cancer treatment plans

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.

Determining Combined Modality Dosimetric Constraints by Integration of IMRT and LDR Prostate Brachytherapy Dosimetry and Correlation with Toxicity

Purpose

Intermediate- and high-risk prostate cancer patients undergoing combination external beam radiation therapy (EBRT) and low dose rate (LDR) brachytherapy have demonstrated increased genitourinary (GU) toxicity. We have previously demonstrated a method to combine EBRT and LDR dosimetry. In this work, we use this technique for a sample of patients with intermediate- and high-risk prostate cancer, correlate with clinical toxicity, and suggest preliminary summed organ-at-risk constraints for future investigation.

Methods and Materials

Intensity modulated EBRT and ¹⁰³Pd-based LDR treatment plans were combined for 138 patients using biological effective dose (BED) and deformable image registration. GU and gastrointestinal (GI) toxicity were compared with combined dosimetry for the urethra, bladder, and rectum. Differences between doses in each toxicity grade were assessed by analysis of variance (α = 0.05). Combined dosimetric constraints are proposed using the mean organ-at-risk dose, subtracting 1 standard deviation for a conservative recommendation.

Results

The majority of our 138-patient cohort experienced grade 0 to 2 GU or GI toxicity. Six grade 3 toxicities were noted. Mean prostate BED D90 (± 1 standard deviation) was 165.5±11.1 Gy. Mean urethra BED D10 was 230.3±33.9 Gy. Mean bladder BED was 35.2±11.0 Gy. Mean rectum BED D2cc was 85.6±24.3 Gy. Significant dosimetric differences between toxicity grades were found for mean bladder BED, bladder D15, and rectum D50, but differences between individual means were not statistically significant. Given the low incidence of grade 3 GU and GI toxicity, we propose urethra D10 <200 Gy, rectum D2cc <60 Gy, and bladder D15 <45 Gy as preliminary dose constraints for combined modality therapy.

Conclusions

We successfully applied our dose integration technique to a sample of patients with intermediate- and high-risk prostate cancer. Incidence of grade 3 toxicity was low, suggesting that combined doses observed in this study were safe. We suggest preliminary dose constraints as a conservative starting point to investigate and escalate prospectively in a future study.

Integrating external beam and prostate seed implant dosimetry for intermediate and high-risk prostate cancer using biologically effective dose: Impact of image registration technique

PURPOSE

Combining external beam radiation therapy (EBRT) and prostate seed implant (PSI) is efficacious in treating intermediate- and high-risk prostate cancer at the cost of increased genitourinary toxicity. Accurate combined dosimetry remains elusive due to lack of registration between treatment plans and different biological effect. The current work proposes a method to convert physical dose to biological effective dose (BED) and spatially register the dose distributions for more accurate combined dosimetry.

METHODS AND MATERIALS

A PSI phantom was CT scanned with and without seeds under rigid and deformed transformations. The resulting CTs were registered using image-based rigid registration (RI), fiducial-based rigid registration (RF), or b-spline deformable image registration (DIR) to determine which was most accurate. Physical EBRT and PSI dose distributions from a sample of 91 previously-treated combined-modality prostate cancer patients were converted to BED and registered using RI, RF, and DIR. Forty-eight (48) previously-treated patients whose PSI occurred before EBRT were included as a "control" group due to inherent registration. Dose-volume histogram (DVH) parameters were compared for RI, RF, DIR, DICOM, and scalar addition of DVH parameters using ANOVA or independent Student's t tests (α = 0.05).

RESULTS

In the phantom study, DIR was the most accurate registration algorithm, especially in the case of deformation. In the patient study, dosimetry from RI was significantly different than the other registration algorithms, including the control group. Dosimetry from RF and DIR were not significantly different from the control group or each other.

CONCLUSIONS

Combined dosimetry with BED and image registration is feasible. Future work will utilize this method to correlate dosimetry with clinical outcomes.

Dosimetric outcomes of preoperative treatment planning with intraoperative optimization using stranded seeds in prostate brachytherapy

This study aimed to evaluate the quality of low-dose-rate (LDR) prostate brachytherapy (BT) based on treatment-related dosimetric outcomes. Data of 100 patients treated using LDR BT with stranded seeds from November 2012 to November 2017 were collected. The prescription dose for the prostate was 145 Gy. The dose constraints for the preoperative plan were: V100% ≥ 95%, V150% ≤ 60%, V200% ≤ 20% for the prostate; V100% for rectum, ≤ 1 cc; and V200 Gy for urethra, 0.0 cc. Intraoperative real-time dose calculation and postoperative dose distribution analysis on days 0 and 30 were performed. Median dosimetric outcomes on days 0 and 30 respective were: V100% 92.28% and 92.23%, V200% 18.63% and 25.02%, and D90% 150.88 Gy and 151.46 Gy for the prostate; V100% for the rectum, 0.11 cc and 0.22 cc; and V200 Gy for the urethra, 0.00 cc and 0.00 cc, respectively. Twenty patients underwent additional seed implantation to compensate for insufficient dose coverage of the prostate. No loss or substantial migration of seeds or severe toxicity was reported. With stranded seed implantation and intraoperative optimization, appropriate dose delivery to the prostate without excessive dose to the organs at risk could be achieved.

Initial Clinical Experience With Novel Directional Low-dose Rate Brachytherapy for Retroperitoneal Sarcoma

BACKGROUND

A novel Palladium-103 low-dose rate (LDR) brachytherapy device was developed to provide dose-escalation to the tumor bed after resection while shielding adjacent tissues. This multicenter report describes the initial experience with this device in patients with retroperitoneal sarcoma (RPS).

MATERIALS AND METHODS

Patients with recurrent RPS, prior radiotherapy, and/or concern for positive margins were considered. An LDR brachytherapy dose of 20-60 Gy was administered, corresponding to biologically effective dose values of 15-53 Gy and equivalent dose values of 12-43 Gy.

RESULTS

Six patients underwent implantation at four institutions. Of these, five had recurrent disease in the retroperitoneum or pelvic sidewall, one had untreated locally advanced leiomyosarcoma, two had prior external beam radiation therapy at the time of initial diagnosis, and four received neoadjuvant external beam radiation therapy plus brachytherapy. The device was easily implanted and conformed to the treatment area. Median follow-up was 16 mo; radiation was delivered to the at-risk margin with minimal irradiation of adjacent structures. No local recurrences at the site of implantation, device migration, or radiation-related toxicities were observed.

CONCLUSIONS

The novel LDR directional brachytherapy device successfully delivered a targeted dose escalation to treat RPS high-risk margins. Lack of radiation-related toxicity demonstrates its safety.

Ten-step method of high-dose LDR 125 I brachytherapy for intermediate-risk prostate cancer

Dose escalation is key for improved outcomes in intermediate‐risk prostate cancer, including unfavorable intermediate‐risk (UIR) cases. This educational report is designed to provide information about our quality high‐dose ¹²⁵I seed implantation monotherapy technique in which a biologically effective dose (BED) ≧ 200 Gy is applied for treatment of intermediate‐risk prostate cancer. This protocol is named the “Ten‐step Method,” where the rationale and principle of the method are based on the following four goals: (1) The entire prostate should be covered by the prescription isodose distribution with a sufficient margin from the prostatic capsule, achieving high D90 and V100 values by ¹²⁵I seed implantation. (2) The high‐dose cloud (240 Gy) should not invade the urethra or rectum. (3) In order to achieve goals (1) and (2), make the high‐dose cloud intentionally along the periphery (bilateral wall to anterior wall) away from the urethra and rectum. (4) In order to achieve goal (3), seeds at the periphery, except those anterior to the rectal wall, should be placed just 1mm inside the capsule. The data obtained from a total of 137 patients with intermediate‐risk prostate cancer treated with low‐dose‐rate (LDR) monotherapy are shown. The dosimetry parameters were monitored at 1 month after seed implantation by using CT and MRI fusion guidance. The data at 1 month after LDR were: Average D90, BED, and V100 of ¹²⁵I LDR monotherapy were 194.1 Gy, 207.3 Gy, and 99%, respectively. This ten‐step method was reproducible in 137 patients with intermediate‐risk prostate cancer, allowing administration of high‐dose monotherapy with excellent clinical outcomes.

2D exfoliated black phosphorus influences healthy and cancer prostate cell behaviors

Nowadays, prostate cancer is the most widespread tumour in worldwide male population. Actually, brachytherapy is the most advanced radiotherapy strategy for the local treatment of prostate cancer. It consists in the placing of radioactive sources closed to the tumour side thus killing cancer cells. However, brachytherapy causes the same adverse effects of external-beam radiotherapy. Therefore, alternative treatment approaches are required for enhancing radiotherapy effectiveness and reducing toxic symptoms. Nanostructured exfoliated black phosphorus (2D BP) may represent a strategic tool for local cancer therapy because of its capability to induce singlet oxygen production and act as photosensitizer. Hence, we investigated 2D BP in vitro effect on healthy and cancer prostate cell behavior. 2D BP was obtained through liquid exfoliation. 2D BP effect on healthy and cancer prostate cell behaviors was analyzed by investigating cell viability, oxidative stress and inflammatory marker expression. 2D BP inhibited prostate cancer cell survival, meanwhile promoted healthy prostate cell survival in vitro by modulating oxidative stress and immune response with and without near-infrared light (NIR)-irradiation. Nanostructured 2D BP is able to inhibit in vitro prostate cancer cells survival and preserve healthy prostate cell vitality through the control of oxidative stress and immune response, respectively.

Prostate cancer with nodular bladder invasion (stage T4N1) cured by low-dose-rate brachytherapy with seminal vesicle implantation in combination with external beam radiotherapy of biologically effective dose ≥ 220 Gy: a case report

Purpose

Prostate cancer with nodular bladder invasion (stage T4 prostate cancer) is an extremely difficult clinical entity to achieve complete cure. So far, there has been no clear report demonstrating complete cure of prostate cancer with nodular bladder invasion, stage T4 prostate cancer.

Case presentation

In this case report, the author presents a 55-year-old man with a diagnosis of advanced prostate cancer invading into the bladder wall with pelvic lymph node metastasis (T4N1M0 disease). The patient was treated with biologically effective dose (BED) ≥ 220 Gy of high-dose radiotherapy, using low-dose-rate (LDR) brachytherapy in combination with whole pelvis (WP) external beam radiotherapy (EBRT) and short-term androgen deprivation therapy (ADT): neo-adjuvant six months plus adjuvant six months ADT. There was no grade 2 genitourinary (GU) and gastrointestinal (GI) toxicity during follow-up. There was no evidence of hematuria, nor rectal bleeding in the follow-up. The patient stays healthy without biochemical failure and without bowel and urinary troubles at six years.

Conclusions

Along with previous outstanding data of BED ≥ 220 Gy LDR-based radiotherapy for high-risk and very high-risk prostate cancer patents, including pelvic lymph node metastasis, the present report, in which the patient was treated with BED ≥ 220 Gy of high-dose radiotherapy, LDR brachytherapy in combination with WP EBRT may be an optimal treatment for prostate cancer with nodular bladder invasion with lymph node metastasis (T4N1disease).

Low dose rate prostate brachytherapy

Low dose rate (LDR) prostate brachytherapy is an evidence based radiation technique with excellent oncologic outcomes. By utilizing direct image guidance for radioactive source placement, LDR brachytherapy provides superior radiation dose escalation and conformality compared to external beam radiation therapy (EBRT). With this level of precision, late grade 3 or 4 genitourinary or gastrointestinal toxicity rates are typically between 1% and 4%. Furthermore, when performed as a same day surgical procedure, this technique provides a cost effective and convenient strategy. A large body of literature with robust follow-up has led multiple expert consensus groups to endorse the use of LDR brachytherapy as an appropriate management option for all risk groups of non-metastatic prostate cancer. LDR brachytherapy is often effective when delivered as a monotherapy, although for some patients with intermediate or high-risk disease, optimal outcome are achieved in combination with supplemental EBRT and/or androgen deprivation therapy (ADT). In addition to reviewing technical aspects and reported clinical outcomes of LDR prostate brachytherapy, this article will focus on the considerations related to appropriate patient selection and other aspects of its use in the treatment of prostate cancer.

Quality of care indicators and their related outcomes: a population-based study in prostate cancer patients treated with radiotherapy

BACKGROUND AND PURPOSE

We describe variations across the regional cancer centres in Ontario, Canada for five prostate cancer radiotherapy (RT) quality indicators: incomplete pre-treatment assessment, follow-up care, leg immobilization, bladder filling, and portal film target localization. Along with cancer centre volume, we examined each indicator's association with relevant outcomes: long-term cause-specific survival, urinary incontinence, and gastrointestinal and genitourinary late morbidities.

MATERIALS AND METHODS

We conducted a population-based retrospective cohort study of 924 prostate cancer patients diagnosed between 1990 and 1998 who received RT within 9 months of diagnosis. Data sources included treating charts and registry and administrative data. The associations between indicators and outcomes were analysed using regression techniques to control for potential confounders.

RESULTS

Practice patterns varied across the regional cancer centres for all indicators (p<0.0001). Incomplete pre-treatment assessment was associated with worse cause-specific survival although this result was not significant when adjusted for confounding (adjusted RR=1.78, 95% CI=0.79-3.98). Treatment without leg immobilization (adjusted RR=1.72, 95% CI=1.16-2.56) and with an empty bladder (adjusted RR=1.98, 95% CI=1.08-3.63) was associated with genitourinary late morbidities. Treatment without leg immobilization was also associated with urinary incontinence (adjusted RR=2.18, 95% CI=1.23-3.87).

CONCLUSIONS

We documented wide variations in practice patterns. We demonstrated that measures of quality of care can be shown to be associated with clinically relevant outcomes in a population-based sample of prostate cancer patients.

Radiation dose escalation for localized prostate cancer: intensity-modulated radiotherapy versus permanent transperineal brachytherapy

BACKGROUND

In the current study, the effects of dose escalation for localized prostate cancer treatment with intensity-modulated radiotherapy (IMRT) or permanent transperineal brachytherapy (BRT) in comparison with conventional dose 3-dimensional conformal radiotherapy (3D-CRT) were evaluated.

METHODS

This study included 853 patients; 270 received conventional dose 3D-CRT, 314 received high-dose IMRT, 225 received BRT, and 44 received external beam radiotherapy (EBRT) + BRT boost. The median radiation doses were 68.4 grays (Gy) for 3D-CRT and 75.6 Gy for IMRT. BRT patients received a prescribed dose of 144 Gy with iodine-125 (I-125) or 120 Gy with palladium-103 (Pd-103), respectively. Patients treated with EBRT + BRT received 45 Gy of EBRT plus a boost of 110 Gy with I-125 or 90 Gy with Pd-103. Risk group categories were low risk (T1-T2 disease, prostate-specific antigen level <or=10 ng/mL, and a Gleason score <or=6), intermediate risk (increase in value of 1 of the factors), and high risk (increase in value of >or=2 factors).

RESULTS

With a median follow-up of 58 months, the 5-year biochemical control (bNED) rates were 74% for 3D-CRT, 87% for IMRT, 94% for BRT, and 94% for EBRT + BRT (P <.0001). For the intermediate-risk group, high-dose IMRT, BRT, or EBRT + BRT achieved significantly better bNED rates than 3D-CRT (P <.0001), whereas no improvement was noted for the low-risk group (P = .22). There was no increase in gastrointestinal (GI) toxicity from high-dose IMRT compared with conventional dose 3D-CRT, although there was more grade 2 genitourinary (GU) toxicity (toxicities were graded at the time of each follow-up visit using a modified Radiation Therapy Oncology Group [RTOG] scale). BRT caused more GU but less GI toxicity, whereas EBRT + BRT caused more late GU and GI toxicity than IMRT or 3D-CRT.

CONCLUSIONS

The data from the current study indicate that radiation dose escalation improved the bNED rate for the intermediate-risk group. IMRT caused less acute and late GU toxicity than BRT or EBRT + BRT.

AAPM recommendations on dose prescription and reporting methods for permanent interstitial brachytherapy for prostate cancer: report of Task Group 137

During the past decade, permanent radioactive source implantation of the prostate has become the standard of care for selected prostate cancer patients, and the techniques for implantation have evolved in many different forms. Although most implants use 125I or 103Pd sources, clinical use of 131Cs sources has also recently been introduced. These sources produce different dose distributions and irradiate the tumors at different dose rates. Ultrasound was used originally to guide the planning and implantation of sources in the tumor. More recently, CT and/or MR are used routinely in many clinics for dose evaluation and planning. Several investigators reported that the tumor volumes and target volumes delineated from ultrasound, CT, and MR can vary substantially because of the inherent differences in these imaging modalities. It has also been reported that these volumes depend critically on the time of imaging after the implant. Many clinics, in particular those using intraoperative implantation, perform imaging only on the day of the implant. Because the effects of edema caused by surgical trauma can vary from one patient to another and resolve at different rates, the timing of imaging for dosimetry evaluation can have a profound effect on the dose reported (to have been delivered), i.e., for the same implant (same dose delivered), CT at different timing can yield different doses reported. Also, many different loading patterns and margins around the tumor volumes have been used, and these may lead to variations in the dose delivered. In this report, the current literature on these issues is reviewed, and the impact of these issues on the radiobiological response is estimated. The radiobiological models for the biological equivalent dose (BED) are reviewed. Starting with the BED model for acute single doses, the models for fractionated doses, continuous low-dose-rate irradiation, and both homogeneous and inhomogeneous dose distributions, as well as tumor cure probability models, are reviewed. Based on these developments in literature, the AAPM recommends guidelines for dose prescription from a physics perspective for routine patient treatment, clinical trials, and for treatment planning software developers. The authors continue to follow the current recommendations on using D90 and V100 as the primary quantitles, with more specific guidelines on the use of the imaging modalities and the timing of the imaging. The AAPM recommends that the postimplant evaluation should be performed at the optimum time for specific radionuclides. In addition, they encourage the use of a radiobiological model with a specific set of parameters to facilitate relative comparisons of treatment plans reported by different institutions using different loading patterns or radionuclides.

Generation of composite dose and biological effective dose (BED) over multiple treatment modalities and multistage planning using deformable image registration

Currently there are no commercially available tools to generate composite plans across different treatment modalities and/or different planning image sets. Without a composite plan, it may be difficult to perform a meaningful dosimetric evaluation of the overall treatment course. In this paper, we introduce a method to generate composite biological effective dose (BED) plans over multiple radiotherapy treatment modalities and/or multistage plans, using deformable image registration. Two cases were used to demonstrate the method. Case I was prostate cancer treated with intensity-modulated radiation therapy (IMRT) and a permanent seed implant. Case II involved lung cancer treated with two treatment plans generated on two separate computed tomography image sets. Thin-plate spline or optical flow methods were used as appropriate to generate deformation matrices. The deformation matrices were then applied to the dose matrices and the resulting physical doses were converted to BED and added to yield the composite plan. Cell proliferation and sublethal repair were considered in the BED calculations. The difference in BED between normal tissues and tumor volumes was accounted for by using different BED models, alpha/beta values, and cell potential doubling times. The method to generate composite BED plans presented in this paper provides information not available with the traditional simple dose summation or physical dose summation. With the understanding of limitations and uncertainties of the algorithms involved, it may be valuable for the overall treatment plan evaluation.

A detailed radiobiological and dosimetric analysis of biochemical outcomes in a case-control study of permanent prostate brachytherapy patients

The purpose of this study is to determine dosimetric and radiobiological predictors of biochemical control after recalculation of prostate implant dosimetry using updated AAPM Task Group 43 (TG-43) parameters and the radiobiological parameters recommended by TG-137. All biochemical failures among patients implanted with 125I Or 103Pd sources between 1994 and March 2006 were matched 2:1 with nonfailure controls. The individual matching was by risk group, radionuclide, prescribed dose, and time of implant (one match before and one after the failed patient) resulting in a median follow-up of 10.9 years. Complete dose volume histogram (DVH) data were recalculated for all 55 cases and 110 controls after updating the original source strength by the retrospectively determined ratios of TG-43. Differential DVH data were acquired in 179 increments of prostate volume versus percentage prescribed dose. At each incremental dose level i, the biologically equivalent dose BEDi, equivalent uniform dose EUDi, and tumor control probability TCPi were calculated from the implant dose plus any external beam delivered to the patient. Total BED, EUD, and TCP were then derived from the incremental values for comparison with single point dosimetric quality parameters and DVH-based averages. There was no significant difference between failures and controls in terms of total BED (143 vs 142 Gy), EUD (95 vs 94 Gy), or TCP (0.87 vs 0.89). Conditional logistic regression analysis factored out the matching variables and stratified the cohort into each case and its controls, but no radiobiological parameter was predictive of biochemical failure. However, there was a significant difference between radiobiological parameters of 125I and 103Pd due to less complete coverage of the target volume by the former isotope. The implant BED and TCP were highly correlated with the D90 and natural prescription doses and a series of mean DVH-based doses such as the harmonic mean and expressions of the generalized EUD. In this case-control study of prostate brachytherapy biochemical failures and nonfailures, there were no radiobiological parameters derived from detailed DVH-based analysis that predicted for biochemical control. This may indicate that in our approach, implant dosimetry is at or near the limits of clinically effective dose escalation.

Combined brachytherapy with external beam radiotherapy for localized prostate cancer: reduced morbidity with an intraoperative brachytherapy planning technique and supplemental intensity-modulated radiation therapy

PURPOSE

To report the acute and late treatment-related toxicities of combined permanent interstitial (125)I implantation delivered via real-time intraoperative planning and supplemental intensity-modulated radiotherapy (IMRT) for patients with clinically localized prostate cancer.

METHODS AND MATERIALS

One hundred twenty-seven patients were treated with a combined modality (CM) regimen consisting of (125)I implantation (110Gy) using a transrectal ultrasound-guided approach followed 2 months later by 50.4Gy of IMRT directed to the prostate and seminal vesicles. Late toxicity was scored according to the NCI Common Terminology Criteria for Adverse Events toxicity scale. The acute and late toxicities were compared to a contemporaneously treated cohort of 216 patients treated with (125)I alone to a prescribed dose of 144Gy.

RESULTS

The incidence of Grade 2 acute rectal and urinary side effects was 1% and 10%, respectively, and 2 patients developed Grade 3 acute urinary toxicities. The 4-year incidence of late Grade 2 gastrointestinal toxicity was 9%, and no Grade 3 or 4 complications have been observed. The 4-year incidence of late Grade 2 gastrourinary toxicities was 15% and 1 patient developed a Grade 3 urethral stricture, which was corrected with urethral dilatation. The percentage of patients who experienced resolution of late rectal and urinary symptoms was 92% and 65%, respectively. Multivariate analysis revealed that in addition to higher baseline International Prostate Symptom Score, those patients treated with implant alone compared to CM were more likely to experience Grade 2 acute urinary symptoms. Increased Grade 2 late rectal toxicities were noted for CM patients (9% vs. 1%; p=0.001) as well as a significant increase for late Grade 2 urinary toxicities (15% vs. 9%; p=0.004).

CONCLUSIONS

Adherence to dose constraints with combination real-time brachytherapy using real-time intraoperative planning and IMRT is associated with a low incidence of acute and late toxicities. Acute urinary side effects were significantly less common for CM patients compared to those treated with implantation alone. Late Grade 2 rectal and urinary toxicities were more common for patients treated with CM compared to implant alone.

Long-Term Rectal Function After Permanent Prostate Brachytherapy

PURPOSE

To evaluate the effect of prostate brachytherapy with or without supplemental therapies on long-term rectal function by means of a patient-administered quality-of-life instrument.

MATERIALS AND METHODS

As part of an ongoing prospective evaluation, 164 of an initial 209 patients who remain alive were mailed the Rectal Function Assessment Score (R-FAS) with a prestamped return envelope. R-FAS range from 0 to 27 with lower scores being indicative of better bowel function. Of the 162 eligible patients, 161 (99.4%) returned the survey. Median follow-up was 9.0 years (range 8.2-11.2 years). Clinical, treatment, and dosimetric parameters evaluated for bowel function included patient age, diabetes, hypertension, tobacco consumption, clinical T stage, elapsed time since brachytherapy, ultrasound volume, planning target volume, androgen deprivation therapy, supplemental external beam radiation, isotope, rectal dose, prostate D100/D150/D200, and prostate D90.

RESULTS

For the entire cohort, the current R-FAS was 3.59, which represented a nonstatistical improvement from prior surveys in 1999 (4.29) and 2002 (3.92) (P=0.134). Only 16 patients (9.9%) reported bowel function to be worse after brachytherapy. Of the clinical, treatment, and dosimetric parameters evaluated, only the number of preimplant bowel movements, tobacco use, and diabetes correlated with R-FAS. Despite lower rectal doses with Pd, isotope did not predict for bowel function. Consistent with prior surveys, patient perception of overall rectal quality of life was inversely related to supplemental external beam radiation (P=0.027).

CONCLUSION

Prostate brachytherapy adversely affects bowel function. However, in most patients the changes are minimal and slowly resolve with time. Overall rectal quality of life is inversely related to supplemental external beam radiation.

Role of external beam radiotherapy with low-dose-rate brachytherapy in treatment of prostate cancer

OBJECTIVES

To report a single-institution experience and analysis of the role of supplemental external beam radiotherapy (EBRT) with brachytherapy. EBRT is often used in addition to low-dose-rate brachytherapy in the treatment of prostate cancer, particularly for disease with adverse features.

METHODS

A cohort of 189 consecutive patients, who had undergone low-dose-rate brachytherapy at our institution and who had demographic, disease, and treatment information and a minimum of 2 years of follow-up available, constituted the study group. This cohort was divided into two major groups according to the use of supplemental EBRT. Using two successive prostate-specific antigen rises greater than 1 ng/mL as the definition of failure, biochemical failure-free survival curves were constructed for the EBRT and no-EBRT groups and compared using the log-rank test. Additionally, a multivariate analysis of all major disease and treatment factors was performed using the Cox proportional hazards model.

RESULTS

Despite the greater proportion of adverse disease factors in the EBRT group, the 5-year biochemical failure-free survival rate in the EBRT versus no-EBRT groups was 80% versus 59%, respectively (P < 0.01). On multivariate analysis, the only factor reaching significance in predicting biochemical control was the use of EBRT (P = 0.043).

CONCLUSIONS

In our study, the addition of EBRT conferred a significant biochemical control advantage when added to low-dose-rate brachytherapy. Because our study was not designed to permit detailed subset analyses, more work is needed to determine the precise brachytherapy population that will benefit from this use of supplemental EBRT.

Biologically effective dose values for prostate brachytherapy: Effects on PSA failure and posttreatment biopsy results

PURPOSE

To analyze the effect of biologically effective dose (BED) values on prostate-specific antigen (PSA) failure and posttreatment biopsy.

METHODS AND MATERIALS

From 1990 to 2003, 1,377 patients had prostate brachytherapy alone (I-125 or Pd-103) (571), hormonal and brachytherapy (371), and trimodality therapy (hormonal, implant, and external beam) (435). Dose was defined as the D90 (dose delivered to 90% of the gland from the dose-volume histogram).

RESULTS

Freedom from PSA failure (FFPF) at 10 years was 87%. The 10-year FFPF for BED<100, >100-120, >120-140, >140-160, <160-180, >180-200, and >200 were 46%, 68%, 81%, 85.5%, 90%, 90%, and 92%, respectively (p<0.0001). BED and Gleason score had the greatest effect, with p values of p<0.0001 in multivariate analysis. Posttreatment positive biopsy rate was 7% (31/446). The positive biopsy rates for BED<or=100, >100-120, >120-140, >140-160, >160-180, >180-200, and >200 were 24% (8/33), 15% (3/20), 6% (2/33), 6% (3/52), 7% (6/82), 1% (1/72), and 3% (4/131), respectively (p<0.0001). BED was the most significant predictor of biopsy outcome in multivariate analysis (p=0.006).

CONCLUSIONS

Biologically effective dose equations provide a method of comparing different isotopes and combined therapies in the brachytherapy management of prostate cancer. The effects of BED on FFPF and posttreatment biopsy demonstrate a strong dose-response relationship.

Analysis of influence of age on acute and chronic radiotherapy toxicity in treatment of prostate cancer

OBJECTIVES

To provide a single-institution analysis of the influence of age on acute and late genitourinary (GU) and gastrointestinal (GI) toxicity after radiotherapy (RT) administered in different prostate cancer scenarios. Improved understanding of the influence of age on toxicity outcome after RT for prostate cancer can assist in treatment decision-making.

METHODS

The records of 527 consecutive nonmetastatic patients receiving RT at a single institution and for whom demographic, disease, treatment, and follow-up information were available were reviewed. The cohort was divided into four major categories as a function of age: younger than 60 years, 60 to 69 years, 70 to 74 years, and 75 years and older. The toxicity rates in each of these categories were tabulated according to the Radiation Therapy Oncology Group toxicity scales and compared using the chi-square test. Additionally, an ordered logit regression analysis was performed for each of these categories using all major patient, disease, and treatment factors.

RESULTS

The toxicity rates were not significantly different as a function of age for either acute GU (P = 0.10) or acute GI (P = 0.19) toxicity or for either late GU (P = 0.22) or late GI (P = 0.09) toxicity. The ordered logit regression analysis showed that age was not a factor that correlated with toxicity in any setting (acute GU, P = 0.44; acute GI, P = 0.55; late GU, P = 0.65; late GI, P = 0.14).

CONCLUSIONS

Patient age did not independently influence GI or GU toxicity after RT for nonmetastatic prostate cancer and should not be used as an independent factor in treatment decision-making or in patient counseling with regard to GI and GU toxicity outcomes after RT.

Methodology for biologically-based treatment planning for combined low-dose-rate (permanent implant) and high-dose-rate (fractionated) treatment of prostate cancer

PURPOSE

The combination of permanent low-dose-rate interstitial implantation (LDR-BRT) and external beam radiotherapy (EBRT) has been used in the treatment of clinically localized prostate cancer. While a high radiation dose is delivered to the prostate in this setting, the actual biologic dose equivalence compared to monotherapy is not commonly invoked. We describe methodology for obtaining the fused dosimetry of this combined treatment and assigning a dose equivalence which in turn can be used to develop desired normal tissue and target constraints for biologic-based treatment planning.

METHODS AND MATERIALS

Patients treated with this regimen initially receive an I-125 implant prescribed to 110 Gy followed, 2 months later, by 50.4 Gy in 28 fractions using intensity-modulated external beam radiotherapy. Ab initio methodology is described, using clinically derived biologic parameters (alpha, beta, potential doubling time for prostate cancer cells [T(pot)], cell loss factor), for calculating tumor control probability isoeffective doses for the combined LDR and conventional fraction EBRT treatment regimen. As no such formalism exists for assessing rectal or urethral toxicity, we make use of semi-empirical expressions proposed for describing urethral and rectal complication probabilities for specific treatment situations (LDR and fractionation, respectively) and utilize the notion of isoeffective dose to extend these results to combined LDR-EBRT regimens.

RESULTS

The application to treatment planning of the methodology described in this study is illustrated with real-patient data. We evaluate the effect of changing LDR and EBRT prescription doses (in a manner that remains isoeffective with 81 Gy EBRT alone or with 144 Gy LDR monotherapy) on rectal and urethral complication probabilities, and suggest that it should be possible to improve the therapeutic ratio by exploiting joint LDR-EBRT planning.

CONCLUSIONS

We describe new methodology for biologically based treatment planning for patients who receive combined low-dose-rate brachytherapy and external beam radiotherapy for prostate cancer. Using relevant mathematical tools, we demonstrate the feasibility of fusing dose distributions from each treatment for this combined regimen, which can then be expressed as isoeffective dose distributions. Based on this information, dose constraints for the rectum and urethra are described which could be used for planning such combination regimens.