Needle imaging during ultrasound-guided permanent prostate implants.

As demonstrated by water phantom experiments and clinical observations, the reverberation artifact associated with the ultrasound needle image during permanent prostate implants is extremely useful in determining precise radioactive seed positioning. It also serves as an independent quality assurance check of the number of seeds in the strand.

Centralized multiinstitutional postimplant analysis for interstitial prostate brachytherapy.

PURPOSE: To investigate the feasibility and utility of performing centralized postimplant analysis for transperineal interstitial permanent prostate brachytherapy (TIPPB) by conducting a pilot study that compares the results obtained from 125I implants conducted at five different institutions. METHODS AND MATERIALS: Dose-volume histogram (DVH) analysis was performed on 10 postimplant CT scans from each of five institutions. This analysis included the total implanted activity of 125I, ultrasound, and CT volumes of the prostate, target-volume ratios, dose homogeneity quantifiers, prostate dose coverage indices, and rectal doses. As a result of the uncertainty associated with the delineation of the prostatic boundaries on a CT scan, the contours were redrawn by a single, study center physician, and a repeat DVH analysis was performed. This provided the basis for comparison between institutions in terms of implant technique and quality. RESULTS: By comparing total activity to preimplant ultrasound volume we clearly demonstrated that differences exist in implant technique among these five institutions. The difficulty associated with determining glandular boundaries on CT scans was apparent, based upon the variability in prostate volumes drawn by the various investigators compared to those drawn by the study center physician. This made no difference, of course, in the TVR or homogeneity quantifiers that are independent of target location. Furthermore, this variability made surprisingly little difference in terms of dose coverage of the prostate gland. Rectal doses varied between institutions according to the various implant techniques. CONCLUSIONS: Centralized, outcome-based evaluation of transperineal interstitial permanent prostate brachytherapy is viable and appropriate. Such an approach could be reasonably used in the conduct of multiinstitutional trials used to study the efficacy of the procedure.

A survey of physics and dosimetry practice of permanent prostate brachytherapy in the United States.

PURPOSE: To obtain data with regard to current physics and dosimetry practice in transperineal interstitial permanent prostate brachytherapy (TIPPB) in the U.S. by conducting a survey of institutions performing this procedure with the greatest frequency. METHODS AND MATERIALS: Seventy brachytherapists with the greatest volume of TIPPB cases in 1995 in the U.S. were surveyed. The four-page comprehensive questionnaire included questions on both clinical and physics and dosimetry practice. Individuals not responding initially were sent additional mailings and telephoned. Physics and dosimetry practice summary statistics are reported. Clinical practice data is reported separately. RESULTS: Thirty-five (50%) surveys were returned. Participants included 29 (83%) from the private sector and 6 (17%) from academic programs. Among responding clinicians, 125I (89%) is used with greater frequency than 103Pd (83%). Many use both (71%). Most brachytherapists perform preplans (86%), predominately employing ultrasound imaging (85%). Commercial treatment planning systems are used more frequently (75%) than in-house systems (25%). Preplans take 2.5 h (avg.) to perform and are most commonly performed by a physicist (69%). A wide range of apparent activities (mCi) is used for both 125I (0.16-1.00, avg. 0.41) and 103Pd (0.50-1.90, avg. 1.32). Of those assaying sources (71%), the range in number assayed (1 to all) and maximum accepted difference from vendor stated activity (2-20%) varies greatly. Most respondents feel that the manufacturers criteria for source activity are sufficiently stringent (88%); however, some report that vendors do not always meet their criteria (44%). Most postimplant dosimetry imaging occurs on day 1 (41%) and consists of conventional x-rays (83%), CT (63%), or both (46%). Postimplant dosimetry is usually performed by a physicist (72%), taking 2 h (avg.) to complete. Calculational formalisms and parameters vary substantially. At the time of the survey, few institutions have adopted AAPM TG-43 recommendations (21%). Only half (50%) of those not using TG-43 indicated an intent to do so in the future. Calculated doses at 1 cm from a single 1 mCi apparent activity source permanently implanted varied significantly. For 125I, doses calculated ranged from 13.08-40.00 Gy and for 103Pd, from 3.10 to 8.70 Gy. CONCLUSION: While several areas of current physics and dosimetry practice are consistent among institutions, treatment planning and dose calculation techniques vary considerably. These data demonstrate a relative lack of consensus with regard to these practices. Furthermore, the wide variety of calculational techniques and benchmark data lead to calculated doses which vary by clinically significant amounts. It is apparent that the lack of standardization with regard to treatment planning and dose calculation practice in TIPPB must be addressed prior to performing any meaningful comparison of clinical results between institutions.

A survey of current clinical practice of permanent prostate brachytherapy in the United States.

PURPOSE: To help establish standards of care for transperineal interstitial permanent prostate brachytherapy (TIPPB) by obtaining data regarding current clinical practice among the most experienced TIPPB brachytherapists in the United States. METHODS AND MATERIALS: The 70 brachytherapists who performed the greatest number of TIPPB cases in 1995 in the U.S. were surveyed. Each received a comprehensive four page questionnaire that included sections on training and experience, patient and isotope selection criteria, manpower, technique, and follow-up. Thirty-five (50%) surveys were ultimately returned after three mailings and follow-up phone calls. The cumulative experience of the 35 respondents represented approximately 45% of the total TIPPB volume in the U.S. for 1995. Respondents included 29 from the private sector and six from academic programs. RESULTS: The median physician experience with TIPPB was reported as 4.9 years. Each performed an average of 73 TIPPB procedures in 1995 (range 40-300). This represented an increase in volume for most (74%) of the respondents. Sixty-three percent of the respondents attended a formal training course, 54% had TIPPB-specific residency training, and 31% had been proctored (16 had received two or more types of training experience). The most commonly reported selection criteria for implant alone was on Gleason score < or = 7, PSA < 15, < or = Stage T2a, and gland size < or = 60 cc, although no clear consensus was found. Fifty-four percent considered a history of TURP to be a relative contraindication, while 34% considered TURP to have no impact on patient selection. Eighty-six percent of respondents combine brachytherapy with external beam radiation in an average of 32% of their patients. Boosts were given with both 125I prescribed to 120 Gy (75%) or 103Pd to 90 Gy (50%). Sixty percent reported using a Mick applicator, 46% prefer using preloaded needles, and (11%) use both techniques. Real-time imaging was usually performed with ultrasound (94%); most included fluoroscopy (60%). Definitions of PSA control varied widely. CONCLUSIONS: TIPPB clinical practice in the U.S. demonstrates similarities in technique, but differences in patient selection and definitions of biochemical control. It is, therefore, incumbent on those beginning TIPPB programs to carefully review the specific practice details of those institutions with a broad experience.

Problems with rigid seed strand lodging during prostate implantation: a proposed mechanism and solution.

Since the introduction of rigid strands of radioactive seeds embedded in absorbable suture material, many brachytherapists have experienced problems with the strands lodging inside the implant needle during the deposition process. By using a scanning electron microscope, we examined some potential factors which could lead to this problem. It seems plausible that the lodging is due to two factors: prostate tissue hindering the motion of the strand initially, and friction between the strand braids and the inner surface of the needle. Both result in an "accordion effect" as the stylet applies pressure on the strand. Based on this assumption, a solution was found. A combination of using needles with a polished inner surface, and repeated clockwise and counterclockwise 360 degrees twisting of the needle about the stylet during the deposition process allows for smooth deposition of the strand at the intended location. By using this technique, one is able to exploit the potential dosimetric advantages of rigid seed strand implants without additional problems.

Improvement in dosimetry of ultrasound-guided prostate implants with the use of multiple stabilization needles.

The use of three stabilization needles for ultrasound-guided permanent prostate implants results in better dosimetric coverage of the prostate, all other variables being equal. This technique prevents rocking motion of the prostate when anterior needles are inserted and thus improves accuracy of seed placement and shortens the length of the procedure. On post-implant CT-based dosimetric evaluation, the three stabilization needles technique provides better coverage, with the prescription isodose line encompassing 95% of the target volume compared to 90% for the implant utilizing two stabilization needles. Further improvements in the technique are currently under investigation, with the goal of consistently achieving truly "conformal anatomical prostate brachyradiotherapy."

A simple method for verifying activity of iodine-125 seeds in rigid absorbable suture.

A simple system which facilitates the verification of the calibration of iodine-125 sources in rigid absorbable suture, on the remote traceability basis, was developed. It consists of a plastic jig accommodating a sterile closed-end 16 gauge plastic catheter. The iodine-125 source in rigid absorbable suture is placed into the sterile closed-end 16 gauge plastic catheter. The jig fits in a standard dose calibrator. The sterility of the strand is maintained while a reasonable number of seeds used for an actual implant can be easily measured. This is an improvement over the current recommended practice of assaying just one separate seed of the same strength designation. This system brings the calibration procedure for the rigid sterile seed strands in line with the AAPM TG-40 recommendation for the rest of radioactive seed products.

A spreadsheet technique for dosimetry of transperineal prostate implants.

Although conceptually straightforward, dosimetry of permanent 125I seed prostate implants is not necessarily easy to implement in clinical practice, especially for institutions that are unwilling or unable to modify their commercial RTP systems. Spreadsheet techniques that aid in both preimplant treatment planning and post-implant dosimetric evaluation have been developed. The first spreadsheet converts the seed distribution expressed in terms of template grid coordinates to the format suitable for input into the RTP system, and determines the positions and loading patterns of individual needles. The second spreadsheet macroprogram is designed, as a modification of the Roy et al. [Int. J. Radiat. Oncol. Biol. Phys. 26, 163-169 (1993)] technique, to interactively determine physical seed locations from the post-implant CT images. Although less automated than described elsewhere, this approach was found acceptable for clinical practice at our institution.

Radiosensitizing and cytocidal effects of misonidazole: evidence for separate modes of action.

Hypoxic BP-8 murine sarcoma cells were exposed to misonidazole and/or radiation and the kinetics and extent of cell death were evaluated with the [125I]iododeoxyuridine-prelabeling assay. Cell death after treatment with lethal doses of misonidazole was rapid and essentially complete within 2 or 3 days after drug exposure. In contrast, radiation death became apparent only after a delay period of 4 days and was complete by Day 10 after irradiation. Radiosensitization by short exposures to sublethal doses of misonidazole affected only the delayed component of cell death, that is, the radiation component of death. In experiments involving sequential radiation and drug treatment, prior irradiation of cells did not enhance the direct cytocidal effects of misonidazole, as evidenced by the fact that the early component of cell death was equal in control and preirradiated cells. However, postirradiation treatment with misonidazole did enhance the delayed radiation component of cell death. These results suggest that radiosensitization and direct killing by misonidazole are two distinct phenomena mediated by different cellular mechanisms, and radiosensitization by misonidazole represents a two-component effect composed of true dose modification and dose additive damage interactions, but these additive effects must occur at a site different from the cellular structure responsible for direct drug-induced cell death.