Purpose: Brenner and Hall’s 1999 paper estimating an α/β value of 1.5 Gy for prostate tumors has stimulated much interest in the question of whether this ratio (of intrinsic radiosensitivity to repair capacity) is much lower in prostate tumors than in other types of tumors that proliferate faster. The implications for possibly treating prostatic cancer using fewer and larger fractions are important. In this paper we review updated clinical data and present somewhat different calculations to estimate α/β. Methods and Materials: Seventeen clinical papers published from 1995 to 2000 were reviewed to obtain estimates of biochemical control from radiotherapy alone using external beam, I-125 implants, or Pd-103 implants. The focus was on intermediate risk patients. Three methods of estimating α/β were employed. First, a simple two-step graphical comparison of isoeffective doses from external beam and implant modalities was made, to see which value of α/β predicted the observed identity of biologic effect. Second, the same data were subjected to Direct Analysis (maximum likelihood estimation), from which an estimate of α/β and also of the T 1 2 of repair of sublethal damage in the tumors (both with confidence intervals) were obtained. Third, preliminary clinical data comparing two different sizes of high-dose boost doses were analyzed in which significantly different bNED was observed at 2 years. Results: The second method gave the definitive result of α/β = 1.49 Gy (95% CI 1.25–1.76) and T 1 2 = 1.90 h (95% CI 1.42–2.86 h). The first method gave a range from 1.4 to 1.9 Gy and showed that if mean or median dose were used instead of prescribed dose, the estimate of α/β would be substantially below 1 Gy. The third method, although based on early follow-up, was consistent with low values of α/β in the region of 2 Gy or below. The estimate for T 1 2 is the first value reported for prostate tumors in situ. Conclusions: All the estimates point toward low values of α/β, at least as low as the estimates of Brenner and Hall, and possibly lower than the expected values of about 3 Gy for late complications. Hypofractionation trials for intermediate-risk prostatic cancer appear to be indicated.

Is α/β for prostate tumors really low?

For commissioning a linear accelerator for clinical use, medical physicists are faced with many challenges including the need for precision, a variety of testing methods, data validation, the lack of standards, and time constraints. Since commissioning beam data are treated as a reference and ultimately used by treatment planning systems, it is vitally important that the collected data are of the highest quality to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. Beam data commissioning should be performed with appropriate knowledge and proper tools and should be independent of the person collecting the data. To achieve this goal, Task Group 106 (TG-106) of the Therapy Physics Committee of the American Association of Physicists in Medicine was formed to review the practical aspects as well as the physics of linear accelerator commissioning. The report provides guidelines and recommendations on the proper selection of phantoms and detectors, setting up of a phantom for data acquisition (both scanning and no-scanning data), procedures for acquiring specific photon and electron beam parameters and methods to reduce measurement errors (<1%), beam data processing and detector size convolution for accurate profiles. The TG-106 also provides a brief.discussion on the emerging trend in Monte Carlo simulation techniques in photon and electron beam commissioning. The procedures described in this report should assist a qualified medical physicist in either measuring a complete set of beam data, or in verifying a subset of data before initial use or for periodic quality assurance measurements. By combining practical experience with theoretical discussion, this document sets a new standard for beam data commissioning.

/pdf/accelerator-beam-data-commissioning-equipment-and-procedures-1itmek5xiv.pdf

Accelerator beam data commissioning equipment and procedures: report of the TG-106 of the Therapy Physics Committee of the AAPM.

Purpose: To assess long-term prostate-specific antigen (PSA) outcome after permanent prostate brachytherapy (BT) and identify predictors of improved disease-free survival. Methods and Materials: Eleven institutions combined data on 2,693 patients treated with permanent interstitial BT monotherapy for T1–T2 prostate cancer. Of these patients, 1,831 (68%) were treated with I-125 (median dose, 144 Gy) and 862 (32%) were treated with Pd-103 (median dose, 130 Gy). Criteria for inclusion were: available pre-BT PSA, BT ≥5 years before data submission, BT between 1988–1998, and no androgen deprivation before failure. The median follow-up was 63 months. Results: Among patients where the I-125 dose to 90% of the prostate (D90) was ≥130 Gy, the 8-year PSA relapse-free survival (PRFS) was 93% compared with 76% for those with lower D90 dose levels ( p p = 0.002), Gleason score ( p p p = 0.001), and the isotope used ( p = 0.004) as pretreatment and treatment variables associated with PRFS. When restricted to patients with available postimplantation dosimetric information, D90 emerged as a significant predictor of biochemical outcome ( p = 0.01), and isotope was not significant. The 8-year PRFS was 92%, 86%, 79%, and 67%, respectively, for patients with PSA nadir values of 0–0.49, 0.5–0.99, 1.0–1.99, and >2.0 ng/mL ( p Conclusions: Outcome after permanent BT for prostatic cancer relates to tumor stage, Gleason score, pretreatment PSA, BT year, and post-BT dosimetric quality. PSA nadir ≤0.5 ng/mL was particularly associated with durable long-term PSA disease-free survival. The only controllable factor to impact on long-term outcome was the D90 which is a reflection of implant quality.

Multi-institutional analysis of long-term outcome for stages T1-T2 prostate cancer treated with permanent seed implantation.

Cancer and Sexual Problems

High Dose Rate Brachytherapy as Prostate Cancer Monotherapy Reduces Toxicity Compared to Low Dose Rate Palladium Seeds

Purpose: To report the 5-year prostate-specific antigen (PSA) relapse-free survival outcome and incidence of long-term morbidity for patients with localized prostate cancer treated with CT-planned permanent I-125 prostate implantation using a transperineal technique (TPI). Methods and Materials: Between 1989–1996, 248 patients with clinically localized prostate cancer were treated with TPI. The median age was 65 years (range: 45–80 years). The clinical stage was T1c in 143 patients (58%), Stage T2a in 102 (41%), and T2b in 3 (1%). Thirty patients (12%) had Gleason scores 10 ng/mL and Gleason score >6) were classified as having intermediate and unfavorable risk disease, respectively. PSA relapse was defined according to the American Society of Therapeutic Radiation Oncology Consensus Statement, and toxicity was scored according to the Radiation Therapy Oncology Group morbidity scoring scale. The median follow-up was 48 months (range: 12–126 months). Results: Thirty-eight patients (15%) developed a PSA relapse, and the overall 5-year PSA relapse-free survival (PRFS) rate was 71%. The 5-year PRFS rates for favorable-risk ( n = 146), intermediate-risk ( n = 85), and unfavorable-risk ( n = 17) patients were 88%, 77%, and 38%, respectively ( p p = 0.03). Multivariate analysis identified pretreatment PSA > 10 ng/mL and Gleason score >6 as independent predictors for biochemical relapse after TPI. The 5-year actuarial likelihood of late Grade 2 urinary toxicity was 41%. The 5-year likelihood of urethral stricture development was 10%, and the median time to stricture development was 18 months. One patient (0.4%) in the early phase of this clinical experience developed a Grade 4 urethral complication. The actuarial incidence of late Grade 2 rectal bleeding was 9%. One patient (0.4%) developed a Grade 4 rectal complication. Conclusions: Especially for favorable risk disease, the 5-year biochemical outcome with this approach was excellent and appears to be comparable to other therapeutic interventions. Grade 2 urinary symptoms were common in these patients but gradually resolved in most. Improved treatment planning approaches that further constrain the urethral dose without compromising the target volume dose will likely decrease the incidence of Grade 2 and 3 urinary symptoms after TPI.

Five-year biochemical outcome and toxicity with transperineal CT-planned permanent I-125 prostate implantation for patients with localized prostate cancer

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Five-year biochemical outcome and toxicity with transperineal CT-planned permanent I-125 prostate implantation for patients with localized prostate cancer