Net survival of men with localized prostate cancer after LDR brachytherapy

OBJECTIVES

To compare survival of patients who received LDR prostate brachytherapy relative to that of peers in the general population of England, UK.

PATIENTS AND METHODS

Net survival was estimated for 2472 cases treated between 2002 and 2016 using population-based analysis guidelines. Life tables adjusted for social deprivation in England from the Office for National Statistics were used to match patients by affluence based on their postcode.

RESULTS

The median (range) age at time of brachytherapy was 66 (55-84) years, 84% resided in Southeast England, 51% under an index of deprivation quintile 5 (most affluent), 55% were clinical stage T1 and the remainder T2. Death from any cause occurred in 270 patients at a median (range) of 7 (1-17) years postimplant. Five and 10-year estimates (95% CI) of overall survival were 96% (95-97) and 90% (89-92), and net survival 103% (102-104) and 109% (107-110) respectively. The net survival remained above 100% in all age-at-treatment and clinical stage groups.

CONCLUSION

Net survival above 100% indicates patients survive longer than the matched general population. The study shows for the first time the net survival of patients treated with a radical therapy for localized prostate cancer in England. The impact of treatment choice on the long-term net survival advantage requires further investigation.

Low dose rate radiation impairs early follicles in young mice

Low-dose radiation is generally considered less harmful than high-dose radiation. However, its impact on ovaries remains debated. Since previous reports predominantly employed low-dose radiation delivered at a high dose rate on the ovary, the effect of low-dose radiation at a low dose rate on the ovary remains unknown. We investigated the effect of low-dose ionizing radiation delivered at a low dose rate on murine ovaries. Three- and ten-week-old mice were exposed to 0.1 and 0.5 Gy of radiation at a rate of 6 mGy/h and monitored after 3 and 30 days. While neither body weight nor ovarian area showed significant changes, ovarian cells were damaged, showing apoptosis and a decrease in cell proliferation after exposure to 0.1 and 0.5 Gy radiation. Follicle numbers decreased over time in both age groups proportionally to the radiation dose. Younger mice were more susceptible to radiation damage, as evidenced by decreased follicles in 3-week-old mice after 30 days of 0.1 Gy exposure, while 10-week-old mice showed reduced follicles only following 0.5 Gy exposure. Primordial or primary follicles were the most vulnerable to radiation. These findings suggest that even low-dose radiation, delivered at a low dose rate, can adversely affect ovarian function, particularly in the early follicles of younger mice.

Insights into radiation carcinogenesis based on dose-rate effects in tissue stem cells

PURPOSE

Increasing epidemiological and biological evidence suggests that radiation exposure enhances cancer risk in a dose-dependent manner. This can be attributed to the 'dose-rate effect,' where the biological effect of low dose-rate radiation is lower than that of the same dose at a high dose-rate. This effect has been reported in epidemiological studies and experimental biology, although the underlying biological mechanisms are not completely understood. In this review, we aim to propose a suitable model for radiation carcinogenesis based on the dose-rate effect in tissue stem cells.

METHODS

We surveyed and summarized the latest studies on the mechanisms of carcinogenesis. Next, we summarized the radiosensitivity of intestinal stem cells and the role of dose-rate in the modulation of stem-cell dynamics after irradiation.

RESULTS

Consistently, driver mutations can be detected in most cancers from past to present, supporting the hypothesis that cancer progression is initiated by the accumulation of driver mutations. Recent reports demonstrated that driver mutations can be observed even in normal tissues, which suggests that the accumulation of mutations is a necessary condition for cancer progression. In addition, driver mutations in tissue stem cells can cause tumors, whereas they are not sufficient when they occur in non-stem cells. For non-stem cells, tissue remodeling induced by marked inflammation after the loss of tissue cells is important in addition to the accumulation of mutations. Therefore, the mechanism of carcinogenesis differs according to the cell type and magnitude of stress. In addition, our results indicated that non-irradiated stem cells tend to be eliminated from three-dimensional cultures of intestinal stem cells (organoids) composed of irradiated and non-irradiated stem cells, supporting the stem-cell competition.

CONCLUSIONS

We propose a unique scheme in which the dose-rate dependent response of intestinal stem cells incorporates the concept of the threshold of stem-cell competition and context-dependent target shift from stem cells to whole tissue. The concept highlights four key issues that should be considered in radiation carcinogenesis: i.e. accumulation of mutations; tissue reconstitution; stem-cell competition; and environmental factors like epigenetic modifications.

Outcomes after PD-103 versus I-125 for low dose rate prostate brachytherapy monotherapy: An international, multi-institutional study

BACKGROUND AND PURPOSE

Pd-103 and I-125 are commonly used in low dose rate (LDR) brachytherapy for prostate cancer. Comparisons of outcomes by isotope type are limited, but Pd-103 has distinct radiobiologic advantages over I-125 despite its lesser availability outside the United States. We evaluated oncologic outcomes after Pd-103 vs I-125 LDR monotherapy for prostate cancer.

MATERIALS AND METHODS

We retrospectively analyzed databases at 8 institutions for men who received definitive LDR monotherapy with Pd-103 (n = 1,597) or I-125 (n = 7,504) for prostate cancer. Freedom from clinical failure (FFCF) and freedom from biochemical failure (FFBF) stratified by isotope were analyzed by Kaplan-Meier univariate and Cox multivariate analyses. Biochemical cure rates (prostate-specific antigen level ≤ 0.2 ng/mL between 3.5 and 4.5 years of follow-up) by isotype were calculated for men with at least 3.5 years of follow-up and compared by univariate and multivariate logistic regression.

RESULTS

Compared with I-125, Pd-103 led to higher 7-year rates of FFBF (96.2% vs 87.6%, P < 0.001) and FFCF (96.5% vs 94.3%, P < 0.001). This difference held after multivariate adjustment for baseline factors (FFBF hazard ratio [HR] = 0.31, FFCF HR = 0.49, both P < 0.001). Pd-103 was also associated with higher cure rates on univariate (odds ratio [OR] = 5.9, P < 0.001) and multivariate (OR = 6.0, P < 0.001) analyses. Results retained significance in sensitivity analyses of data from the 4 institutions that used both isotopes (n = 2,971).

CONCLUSIONS

Pd-103 monotherapy was associated with higher FFBF, FFCF, and biochemical cure rates, and suggests that Pd-103 LDR may lead to improved oncologic outcomes compared with I-125.

Transgenerational effects of gamma radiation dose and dose rate on Drosophila flies irradiated at an early embryonal stage

Ionizing radiation (IR) kills cells mainly through induction of DNA damages and the surviving cells may suffer from mutations. Transgenerational effects of IR are well documented, but the exact mechanisms underlying them are less well understood; they include induction of mutations in germ cells and epigenetic inheritance. Previously, effects in the offspring of mice and zebrafish exposed to IR have been reported. A few studies also showed indications of transgenerational effects of radiation in humans, particularly in nuclear power workers. In the present project, short- and long-term effects of low-dose-rate (LDR; 50 and 97 mGy/h) and high-dose-rate (HDR; 23.4, 47.1 and 495 Gy/h) IR in Drosophila embryos were investigated. The embryos were irradiated at different doses and dose rates and radiosensitivity at different developmental stages was investigated. Also, the survival of larvae, pupae and adults developed from embryos irradiated at an early stage (30 min after egg laying) were studied. The larval crawling and pupation height assays were applied to investigate radiation effects on larval locomotion and pupation behavior, respectively. In parallel, the offspring from 3 Gy irradiated early-stage embryos were followed up to 12 generations and abnormal phenotypes were studied. Acute exposure of embryos at different stages of development showed that the early stage embryo is the most sensitive. The effects on larval locomotion showed no significant differences between the dose rates but a significant decrease of locomotion activity above 7 Gy was observed. The results indicate that embryos exposed to the low dose rates have shorter eclosion times. At the same cumulative dose (1 up to 7 Gy), HDR is more embryotoxic than LDR. We also found a radiation-induced depigmentation on males (A5 segment of the dorsal abdomen, A5pig^-) that can be transmitted up to 12 generations. The phenomenon does not follow the classical Mendelian laws of segregation.

Low dose rate brachytherapy for primary treatment of localized prostate cancer: A systemic review and executive summary of an evidence-based consensus statement

PURPOSE

The purpose of this guideline is to present evidence-based consensus recommendations for low dose rate (LDR) permanent seed brachytherapy for the primary treatment of prostate cancer.

METHODS AND MATERIALS

The American Brachytherapy Society convened a task force for addressing key questions concerning ultrasound-based LDR prostate brachytherapy for the primary treatment of prostate cancer. A comprehensive literature search was conducted to identify prospective and multi-institutional retrospective studies involving LDR brachytherapy as monotherapy or boost in combination with external beam radiation therapy with or without adjuvant androgen deprivation therapy. Outcomes included disease control, toxicity, and quality of life.

RESULTS

LDR prostate brachytherapy monotherapy is an appropriate treatment option for low risk and favorable intermediate risk disease. LDR brachytherapy boost in combination with external beam radiation therapy is appropriate for unfavorable intermediate risk and high-risk disease. Androgen deprivation therapy is recommended in unfavorable intermediate risk and high-risk disease. Acceptable radionuclides for LDR brachytherapy include iodine-125, palladium-103, and cesium-131. Although brachytherapy monotherapy is associated with increased urinary obstructive and irritative symptoms that peak within the first 3 months after treatment, the median time toward symptom resolution is approximately 1 year for iodine-125 and 6 months for palladium-103. Such symptoms can be mitigated with short-term use of alpha blockers. Combination therapy is associated with worse urinary, bowel, and sexual symptoms than monotherapy. A prostate specific antigen <= 0.2 ng/mL at 4 years after LDR brachytherapy may be considered a biochemical definition of cure.

CONCLUSIONS

LDR brachytherapy is a convenient, effective, and well-tolerated treatment for prostate cancer.

Methodological improvements to meta-analysis of low dose rate studies and derivation of dose and dose-rate effectiveness factors

Epidemiological studies of cancer rates associated with external and internal exposure to ionizing radiation have been subject to extensive reviews by various scientific bodies. It has long been assumed that radiation-induced cancer risks at low doses or low-dose rates are lower (per unit dose) than those at higher doses and dose rates. Based on a mixture of experimental and epidemiologic evidence the International Commission on Radiological Protection recommended the use of a dose and dose-rate effectiveness factor for purposes of radiological protection to reduce solid cancer risks obtained from moderate-to-high acute dose studies (e.g. those derived from the Japanese atomic bomb survivors) when applied to low dose or low-dose rate exposures. In the last few years there have been a number of attempts at assessing the effect of extrapolation of dose rate via direct comparison of observed risks in low-dose rate occupational studies and appropriately age/sex-adjusted analyses of the Japanese atomic bomb survivors. The usual approach is to consider the ratio of the excess relative risks in the two studies, a measure of the inverse of the dose rate effectiveness factor. This can be estimated using standard meta-analysis with inverse weighting of ratios of relative risks using variances derived via the delta method. In this paper certain potential statistical problems in the ratio of estimated excess relative risks for low-dose rate studies to the excess relative risk in the Japanese atomic bomb survivors are discussed, specifically the absence of a well-defined mean and the theoretically unbounded variance of this ratio. A slightly different method of meta-analysis for estimating uncertainties of these ratios is proposed, motivated by Fieller's theorem, which leads to slightly different central estimates and confidence intervals for the dose rate effectiveness factor. However, given the uncertainties in the data, the differences in mean values and uncertainties from the dose rate effectiveness factor estimated using delta-method-based meta-analysis are not substantial, generally less than 70%.

Establishing a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy: Building validation evidence

PURPOSE

The purpose of this study was to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy. The first step in formalizing any education program is a validation process that builds evidence-based verification that the learning environment is appropriate.

METHODS AND MATERIALS

The primary education task allowed practitioners to use an anthropomorphic breast phantom to simulate a permanent seed implant brachytherapy delivery. Validation evidence is built by generating data to assess learner and expert cohorts according to their proficiency. Each practitioner's performance during the simulation was evaluated by seed placement accuracy, procedural time-to-complete, and two qualitative evaluation tools-a global rating scale and procedural checklist.

RESULTS

The average seed placement accuracy (±SD) was 8.1 ± 3.5 mm compared to 6.1 ± 2.6 mm for the learner and expert cohort, respectively. The median (range) procedural time-to-complete was 64 (60-77) minutes and 43 (41-50) minutes for the learner and expert cohort, respectively. Seed placement accuracy (student t-test, p < 0.05) and procedural time-to-complete (Mann-Whitney U-test, p < 0.05) were statistically different between the cohorts. In both the global rating scale and procedural checklist, the expert cohort demonstrated improved proficiency compared to the learner cohort.

CONCLUSIONS

This validation evidence supports the utilization of this simulation environment toward appropriately capturing the delivery experience of practitioners. The results demonstrate that, in all areas of evaluation, expert cohort proficiency was superior to learner cohort proficiency. This methodology will be used to establish a simulation-based education program for radiation oncology learners in permanent seed implant brachytherapy.

Long-term biochemical outcomes using cesium-131 in prostate brachytherapy

PURPOSE

Long-term outcomes reveal equivalent biochemical outcomes with low-dose-rate (LDR) brachytherapy (BT) compared with radical prostatectomy and external-beam radiotherapy for the management of prostate cancer. Iodine-125, the most commonly used isotope, may be associated with long-term urinary consequences. Cesium-131 (¹³¹Cs) has a higher dose rate and shorter dose delivery time, predicting a shorter duration of urinary morbidity. We report our institution's high-volume experience and the most mature data to date on outcomes with ¹³¹Cs prostate BT.

METHODS AND MATERIALS

571 men (median age: 65.38 years) with low (55%)-, intermediate (36%)-, and high-risk disease (9%) received monobrachytherapy, dual-modality, or trimodality using ¹³¹Cs at a single institution. Risk groups were defined according to the National Comprehensive Cancer Network definition. Median prescription dose for definitive LDR-BT and LDR-BT boost was 115 Gy and 70 Gy, respectively. Median initial PSA was 6.1 ng/mL (IQR: 4.6-8.7).

RESULTS

Median followup time was 5 years. 5/7-year overall survival for low-, intermediate-, and high-risk patients was 96.9%/96/9%, 92.8%/89.7%, and 95.8%/87.1%, respectively (p = 0.02). 5/7-year freedom from biochemical failure for low-, intermediate-, and high-risk patients was 98.5%/96.3%, 94.1%/86.4%, and 93.2%/74.5%, respectively (p < 0.01). 5/7-year prostate cancer -specific survival was 100%/100%, 99.3%/99.3%, and 98.0%/98.0% for low-, intermediate-, and high-risk patients, respectively (p < 0.01).

CONCLUSIONS

¹³¹Cs is a viable alternative isotope for prostate brachytherapy for organ-confined disease. Long-term biochemical control and survival outcomes are excellent and on par with those attained with the use of ¹²⁵I or ¹⁰³Pd. This report therefore supports the continued use of ¹³¹Cs as an effective and comparable alternative isotope.

Dose to the dominant intraprostatic lesion using HDR vs. LDR monotherapy: A Phase II randomized trial

PURPOSE

To present the dosimetric results of a Phase II randomized trial comparing dose escalation to the MRI-defined dominant intraprostatic lesion (DIL) using either low-dose-rate (LDR) or high-dose-rate (HDR) prostate brachytherapy.

MATERIAL AND METHODS

Patients receiving prostate brachytherapy as monotherapy were randomized to LDR or HDR brachytherapy. Prostate and DILs were contoured on preoperative multiparametric MRI. These images were registered with transrectal ultrasound for treatment planning. LDR brachytherapy was preplanned using I-125 seeds. HDR brachytherapy used intraoperative transrectal ultrasound-based planning to deliver 27 Gy/2 fractions in separate implants. DIL location was classified as peripheral, central, or anterior. A student t-test compared DIL D₉₀ between modalities and DIL locations.

RESULTS

Of 60 patients, 31 underwent LDR and 29 HDR brachytherapy. Up to three DILs were identified per patient (100 total) with 74 peripheral, six central, and 20 anterior DILs. Mean DIL volume was 1.9 cc (SD: 1.7 cc) for LDR and 1.6 cc (SD 1.3 cc) for HDR (p = 0.279). Mean DIL D₉₀ was 151% (SD 30%) for LDR and 132% (SD 13%) for HDR. For LDR, mean peripheral DIL D₉₀ was 159% (SD 27%) and central or anterior 127% (SD 13%). HDR peripheral DILs received 137% (SD 12%) and central or anterior 119% (SD 7%). DIL D₉₀ for peripheral lesions was higher than anterior and central (p < 0.001).

CONCLUSIONS

DIL location affects dose escalation, particularly because of urethral proximity, such as for anterior and central DILs. HDR brachytherapy may dose escalate better when target DIL is close to critical organs.

Occupational radiation exposure and risk of cataract incidence in a cohort of US radiologic technologists

It has long been known that relatively high-dose ionising radiation exposure (> 1 Gy) can induce cataract, but there has been no evidence that this occurs at low doses (< 100 mGy). To assess low-dose risk, participants from the US Radiologic Technologists Study, a large, prospective cohort, were followed from date of mailed questionnaire survey completed during 1994-1998 to the earliest of self-reported diagnosis of cataract/cataract surgery, cancer other than non-melanoma skin, or date of last survey (up to end 2014). Cox proportional hazards models with age as timescale were used, adjusted for a priori selected cataract risk factors (diabetes, body mass index, smoking history, race, sex, birth year, cumulative UVB radiant exposure). 12,336 out of 67,246 eligible technologists reported a history of diagnosis of cataract during 832,479 person years of follow-up, and 5509 from 67,709 eligible technologists reported undergoing cataract surgery with 888,420 person years of follow-up. The mean cumulative estimated 5-year lagged eye-lens absorbed dose from occupational radiation exposures was 55.7 mGy (interquartile range 23.6-69.0 mGy). Five-year lagged occupational radiation exposure was strongly associated with self-reported cataract, with an excess hazard ratio/mGy of 0.69 × 10-3 (95% CI 0.27 × 10-3 to 1.16 × 10-3, p < 0.001). Cataract risk remained statistically significant (p = 0.030) when analysis was restricted to < 100 mGy cumulative occupational radiation exposure to the eye lens. A non-significantly increased excess hazard ratio/mGy of 0.34 × 10-3 (95% CI - 0.19 × 10-3 to 0.97 × 10-3, p = 0.221) was observed for cataract surgery. Our results suggest that there is excess risk for cataract associated with radiation exposure from low-dose and low dose-rate occupational exposures.

High-dose-rate brachytherapy monotherapy versus low-dose-rate brachytherapy with or without external beam radiotherapy for clinically localized prostate cancer

BACKGROUND

To compare the outcome of high-dose-rate interstitial brachytherapy (HDR-BT) monotherapy and low-dose-rate brachytherapy (LDR-BT) with or without external beam radiotherapy (EBRT) for localized prostate cancer.

METHODS AND MATERIALS

We compared 352 patients treated with HDR-BT as monotherapy (median follow-up time 84 months, NCCN risk classification; low: intermediate: high = 28:145:179) and 486 patients with LDR-BT with or without EBRT (90 months, 194:254:38). HDR-BT treated advanced disease with more hormonal therapy than LDR-BT. LDR-BT excluded patients with T3b-T4 tumor and initial PSA >50 ng/ml. Inverse probability of treatment weighting (IPTW) involving propensity scores was used to reduce background selection bias.

RESULTS

The actuarial 5-year biochemical failure-free survival rates (bNED) were 92.9% and 95.6% (p = 0.25) in the HDR-BT and LDR-BT groups, respectively, and it was 100% and 97.3% (p = 0.99) in the low-risk, 95.6% and 94.3% (p = 0.19) in the intermediate, 89.6% and 94.9% (p = 0.26) in the high-risk groups, and 93.1% and 94.9% (p = 0.98) in selected high-risk group excluding T3b-4 and initial PSA ≥50. IPTW correction also indicated no difference in bNED between LDR-BT and HDR-BT groups. LDR-BT showed a higher incidence of genitourinary (GU) toxicity grade ≥2 than that of HDR-BT in the acute phase and grade 1 toxicity in late phase. Acute GU toxicity grade ≥1 predicted late GU toxicity grade ≥2. External beam radiotherapy plus LDR-BT elevated GI toxicity than LDR-BT only group. Accumulated incidence of late grade ≥2 GU and GU toxicity was equivalent between HDR-BT and LDR-BT. No grade 4 or 5 toxicities were detected in either modality.

CONCLUSION

HDR-BT monotherapy showed an equivalent outcome to that of LDR-BT with or without EBRT for low-, intermediate- and selected high-risk patients. LDR-BT showed equivalent incidence of grade ≥2 late GI and GU toxicities and higher grade ≥2 acute GU toxicity as that of HDR-BT as a monotherapy.

[Brachytherapy for head and neck cancers]

The main indications of the brachytherapy of head and neck cancers are the limited tumours of the lip, the nose, the oral cavity and the oropharynx. Nasopharynx tumours are nowadays treated by intensity-modulated radiotherapy. This technique can be exclusive, associated with external radiotherapy or postoperative. It can also be a salvage treatment for the second primaries in previously irradiated areas. If the low dose rate brachytherapy rules remain the reference, the pulse dose rate technique allows the prescription of the dose rate and the optimisation of the dose distribution. Results of high dose rate brachytherapy are now published. This paper reports the recommendations of the Gec-ESTRO, published in 2017, and takes into account the data of the historical low dose rate series, and is upgraded with the pulsed-dose rate and high dose rate series.

Outcome of the European initiative for radiation protection research and future perspectives

In 2009, the European Commission published the report of the high-level expert group that had been mandated to consider the scientific challenges posed by the issues of low dose effects of ionising radiation, and to formulate proposals for research policy evolution in this field at European level. This report formulated a first draft of a strategic research agenda. International scientific cooperation and an integrated approach are essential for the further development and enhancement of the international framework of radiation protection. This paper reflects on the results which have been gained through this integration approach: strategic research agendas have been established, policies and action plans have been developed for infrastructures and training education, several ambitious research projects have been launched, and a first draft of a European 'joint road map' for radiation protection research will be published. Reflecting on the challenges that lie ahead, this paper also presents the initiatives that the five European research platforms (MELODI: low dose research; ALLIANCE: radioecology; EURADOS: dosimetry; NERIS: emergency preparedness; EURAMED: radiation protection in medical applications) have jointly presented to the European Commission and Euratom member states to further enhance radiation protection research.

Dose and dose rate extrapolation factors for malignant and non-malignant health endpoints after exposure to gamma and neutron radiation

Murine experiments were conducted at the JANUS reactor in Argonne National Laboratory from 1970 to 1992 to study the effect of acute and protracted radiation dose from gamma rays and fission neutron whole body exposure. The present study reports the reanalysis of the JANUS data on 36,718 mice, of which 16,973 mice were irradiated with neutrons, 13,638 were irradiated with gamma rays, and 6107 were controls. Mice were mostly Mus musculus, but one experiment used Peromyscus leucopus. For both types of radiation exposure, a Cox proportional hazards model was used, using age as timescale, and stratifying on sex and experiment. The optimal model was one with linear and quadratic terms in cumulative lagged dose, with adjustments to both linear and quadratic dose terms for low-dose rate irradiation (<5 mGy/h) and with adjustments to the dose for age at exposure and sex. After gamma ray exposure there is significant non-linearity (generally with upward curvature) for all tumours, lymphoreticular, respiratory, connective tissue and gastrointestinal tumours, also for all non-tumour, other non-tumour, non-malignant pulmonary and non-malignant renal diseases (p < 0.001). Associated with this the low-dose extrapolation factor, measuring the overestimation in low-dose risk resulting from linear extrapolation is significantly elevated for lymphoreticular tumours 1.16 (95% CI 1.06, 1.31), elevated also for a number of non-malignant endpoints, specifically all non-tumour diseases, 1.63 (95% CI 1.43, 2.00), non-malignant pulmonary disease, 1.70 (95% CI 1.17, 2.76) and other non-tumour diseases, 1.47 (95% CI 1.29, 1.82). However, for a rather larger group of malignant endpoints the low-dose extrapolation factor is significantly less than 1 (implying downward curvature), with central estimates generally ranging from 0.2 to 0.8, in particular for tumours of the respiratory system, vasculature, ovary, kidney/urinary bladder and testis. For neutron exposure most endpoints, malignant and non-malignant, show downward curvature in the dose response, and for most endpoints this is statistically significant (p < 0.05). Associated with this, the low-dose extrapolation factor associated with neutron exposure is generally statistically significantly less than 1 for most malignant and non-malignant endpoints, with central estimates mostly in the range 0.1-0.9. In contrast to the situation at higher dose rates, there are statistically non-significant decreases of risk per unit dose at gamma dose rates of less than or equal to 5 mGy/h for most malignant endpoints, and generally non-significant increases in risk per unit dose at gamma dose rates ≤5 mGy/h for most non-malignant endpoints. Associated with this, the dose-rate extrapolation factor, the ratio of high dose-rate to low dose-rate (≤5 mGy/h) gamma dose response slopes, for many tumour sites is in the range 1.2-2.3, albeit not statistically significantly elevated from 1, while for most non-malignant endpoints the gamma dose-rate extrapolation factor is less than 1, with most estimates in the range 0.2-0.8. After neutron exposure there are non-significant indications of lower risk per unit dose at dose rates ≤5 mGy/h compared to higher dose rates for most malignant endpoints, and for all tumours (p = 0.001), and respiratory tumours (p = 0.007) this reduction is conventionally statistically significant; for most non-malignant outcomes risks per unit dose non-significantly increase at lower dose rates. Associated with this, the neutron dose-rate extrapolation factor is less than 1 for most malignant and non-malignant endpoints, in many cases statistically significantly so, with central estimates mostly in the range 0.0-0.2.

Focal or whole-gland salvage prostate brachytherapy with iodine seeds with or without a rectal spacer for postradiotherapy local failure: How best to spare the rectum?

PURPOSE

Salvage prostate permanent implant (sPPI) for postradiation local failure provides high rates of biochemical control. The cumulative dose delivered to the prostate and the rectum is still unknown.

METHODS AND MATERIALS

We reviewed the postimplant CT-based dosimetry of 18 selected patients who underwent sPPI with (125)I seeds for isolated biopsy-proven local failure several years after external beam radiation therapy. Ten patients had whole-prostate sPPI, and 8 patients had multiparametric MRI-based focal sPPI. In 8 patients, hyaluronic acid (HA) gel was injected into the prostate-rectum space.

RESULTS

The median cumulative biological effective dose after EBRT + sPPI for the prostate and the rectum was higher in patients treated with whole-gland sPPI than in patients treated with focal sPPI (313.5 Gy2 vs. 174.4 Gy2; p = 0.06 and 258.1 Gy3 vs. 172.6 Gy3; p < 0.01, respectively). The median D0.1cc for the rectum was significantly lower in patients who had HA gel: 63.3 Gy (29.0-78.3) vs. 83.9 Gy (34.9-180.0) (p = 0.04).

CONCLUSIONS

Cumulative prostate and rectum biological effective doses were lower with focal sPPI. D0.1cc delivered to the rectum was significantly lower with HA gel, while there was no difference between focal or whole-gland plans.

Brachytherapy as part of the conservative treatment for primary and recurrent vulvar carcinoma

PURPOSE

There are only scarce data on the place of brachytherapy (BT) for treatment of vulvar carcinoma. Our institutional experience of interstitial BT for vulvar carcinoma patients is reported.

METHODS AND MATERIALS

Clinical records of patients receiving low-dose-rate or pulsed-dose-rate BT as part of the primary treatment for primary/recurrent vulvar squamous cell carcinoma or as part of postoperative treatment between 2000 and 2015 were included. Patients, tumors, and treatment characteristics as well as clinical outcome were examined.

RESULTS

A total of 26 patients treated with BT were identified. BT was delivered as part of primary intent treatment for locally advanced/recurrent cancer in 11 patients and as part of postoperative treatment in 15 patients. Median age at time of BT was 63 years (range, 41-88 years). Pulsed-dose-rate and low-dose-rate were used in 15 patients and 11 patients, respectively. BT was performed as a boost to the tumor bed following external beam radiotherapy (n = 13) or as the sole irradiation modality (n = 13). Total median dose at the level of primary tumor was 60 GyEQD2 (range, 55-60 GyEQD2). With mean followup of 41 months (range, 5 months-11.3 years), 11 patients experienced tumor relapse, and in two of them, site of relapse was only local. Three-year estimated disease-free survival and overall survival rates were 57% (95% confidence interval: 45-69%) and 81% (95% confidence interval: 72-90%), respectively. All toxicities were Grade 2 or less.

CONCLUSIONS

Interstitial BT used as part of the primary or postoperative treatment of vulvar carcinoma is feasible with a satisfactory toxicity profile. Prognosis remains, however, dismal, with a high frequency of failures in patients with locally advanced tumors.

Intraoperative factors associated with stranded source placement accuracy in low-dose-rate prostate brachytherapy

PURPOSE

The quality of a low-dose rate prostate brachytherapy implant depends on the accurate placement of sources in their planned locations. This study investigates intraoperative factors that potentially contribute to stranded source placement inaccuracy in prostate brachytherapy.

METHODS AND MATERIALS

Intraoperative video images of the brachytherapist's hand motions and needle insertions during the implant procedure were acquired for analysis. Using video analysis software, maximum and average needle insertion velocities were determined. The number of needle insertion attempts and the use of the brachytherapist's other hand to manipulate the needle direction were also recorded. Sources misplacements were analyzed using an ultrasound-based method described elsewhere.

RESULTS

Fifteen patients agreed to undergo this study; 1619 ¹²⁵I seeds were inserted using 357 needles; 1197 seeds were confidently identified using ultrasound images and included in the analysis. The mean overall misplacement was 0.49 cm (0-2 cm, 95% CI = 0.47-0.51); 614 seeds were delivered with a single pass and 583 seeds with >1 passes (range 2-6). The mean maximum needle velocity was 12.34 cm s^-1 (range 4-28 cm s^-1) and mean average velocity was 4.76 cm s^-1 (range 0.4-17.4 cm s^-1); 747 seeds were delivered with manipulation of the needle. The generalized linear model test was used to analyze factors contributing to seed misplacement, and it was found that a maximum speed <12 cm s^-1 was associated with a decrease in seed misplacement by 0.049 cm vs. a maximum speed >12 cm s^-1, p = 0.0121). Other evaluated factors were found to have no statistically significant correlation with seed misplacement: average speed (p = 0.4947), manual manipulation of needle (p = 0.9264), and number of needle passes (p = 0.8907).

CONCLUSIONS

This study identified that needles inserted with lower maximum velocity were associated with less seed misplacement. Manual manipulation of the needle, number of passes, and average speed did not show statistically significant correlation with seed misplacement.

An open-source genetic algorithm for determining optimal seed distributions for low-dose-rate prostate brachytherapy

PURPOSE

An open source optimizer that generates seed distributions for low-dose-rate prostate brachytherapy was designed, tested, and validated.

METHODS

The optimizer was a simple genetic algorithm (SGA) that, given a set of prostate and urethra contours, determines the optimal seed distribution in terms of coverage of the prostate with the prescribed dose while avoiding hotspots within the urethra. The algorithm was validated in a retrospective study on 45 previously contoured low-dose-rate prostate brachytherapy patients. Dosimetric indices were evaluated to ensure solutions adhered to clinical standards. The SGA performance was further benchmarked by comparing solutions obtained from a commercial optimizer (inverse planning simulated annealing [IPSA]) with the same cohort of 45 patients.

RESULTS

Clinically acceptable target coverage by the prescribed dose (V100) was obtained for both SGA and IPSA, with a mean ± standard deviation of 98 ± 2% and 99.5 ± 0.5%, respectively. For the prostate D90, SGA and IPSA yielded 177 ± 8 Gy and 186 ± 7 Gy, respectively, which were both clinically acceptable. Both algorithms yielded reasonable dose to the rectum, with V100 < 0.3 cc. A reduction in dose to the urethra was seen using SGA. SGA solutions showed a slight prostate volume dependence, with smaller prostates (<25 cc) yielding less desirable, although still clinically viable, dosimetric outcomes. SGA plans used, on average, fewer needles than IPSA (21 vs. 24, respectively), which may lead to a reduction in urinary toxicity and edema that alters post-implant dosimetry.

CONCLUSIONS

An open source SGA was validated that provides a research tool for the brachytherapy community.

Dosimetric quality and evolution of edema after low-dose-rate brachytherapy for small prostates: implications for the use of newer isotopes

PURPOSE

To characterize prostate swelling and dosimetry in patients with small prostate volumes (PVs) undergoing brachytherapy.

METHODS AND MATERIALS

We studied 25 patients with PV <25 cc (range, 15.1-24.8) and 65 patients with PV ≥25 cc (range, 25.0-66.2) based on three-dimensional ultrasound contours who underwent brachytherapy monotherapy with intraoperative planning. Postoperative Days 1 and 30 dosimetry was done by CT-MRI fusion.

RESULTS

Small PVs had greater Day 1 swelling than large PVs (32.5% increase in volume vs. 23.7%, p = 0.04), but by Day 30, swelling was minimal and not significantly different (p = 0.44). Small PVs had greater seed and needle densities at implant (p < 0.001). Rectal and urethral doses were nearly identical by Day 30 (small PV rectum receiving 100% of the prescription dose [145 Gy] [V100] = 0.32 cc; large PV rectum V100 = 0.33 cc, p = 0.99; small PV urethra receiving 150% of the prescription dose [145 Gy] [V150] = 0.20, large PV urethra V150 = 0.20, p = 0.91). Swelling at Day 1 created some cool implants (rate dose that covers 90% of the prostate volume [D90 <140 Gy = 12.0% and 9.4% for the small and large PV groups, respectively, p = 0.71), but Day 30 planning target volume coverage was excellent (rate D90 <140 Gy = 0% for both groups).

CONCLUSIONS

Although smaller prostates have greater Day 1 swelling, good Day 30 dosimetry can be achieved, making them excellent candidates for (125)I seeds (half-life [t½] = 60 days). Smaller prostates may be suboptimal for shorter t½ sources such as (131)Cs (t½ = 9.7 days), in which the majority of the dose may be delivered to an edematous gland, unless the planning is adjusted to anticipate the edema.