ESTRO 37 Abstract book

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ESTRO 37

consider the technical aspects that may impact on trial results and the translation of those results into wider clinical practice. In this presentation we will consider issues of plan robustness and the ability of LDR and HDR treatments to precisely deliver the planned dose distribution. Real-time, adaptive treatment approaches can account for seed or source position uncertainties as treatment progresses, in contrast to approaches which incorporate uncertainties into the planning process. With precise knowledge of the actual dose delivered (in contrast to the planned dose distribution) we can develop reliable correlations of dose-to-normal tissue and toxicity. Similarly, this knowledge can be applied to biological modelling of tumour control probability to provide more reliable estimates of response to radiation in the presence of variable dose rates. Whilst long term clinical data supports the use of LDR in low risk patients, these data are based on the traditional approach to treatment of the entire prostate gland with high doses of radiation which is known to lead to a high incidence of acute urinary toxicity. Modern approaches suggest focal therapy may have a favourable affect on the therapeutic window. When comparing LDR and HDR monotherapy, clinical trials should consider current and future trends in treatment approaches to ensure outcomes represent treatment techniques that are likely to be commonplace in the future. SP-0348 Long-term results of LDR seed monotherapy in the treatment of prostate cancer S. Machtens 1 1 Marien-Krankenhaus Bergisch Gladbach, Urology and Paediatric Urology, Bergisch Gladbach, Germany Abstract text Permanent interstitial LDR-brachytherapy with seeds is an established guideline recommended treatment of patients with localized prostate cancer in the low- and low-intermediate risk category. Long-term tumour control data demonstrate comparable non-inferior results in comparison to radical prostatectomy (RP) and percutaneous radiation therapy (EBRT). 15-years results show tumor-dependent death rates between 5-10% in the low- and 10-25% in the low-intermediate risk category. Additional hormonal deprivation or the combination with EBRT did not show significant improval of tumour dependent death rates in this risk category. The side effect profil either in early and late toxicity is mild. The preservation of erectile function is in most retrospective studies superior to patients after RP or EBRT. Gastrointestinal toxicity (GI) is described to be less often than after EBRT. Genitouronary toxicity (GU) and irritative symptoms in particular are more often described than after EBRT or RP. Urinary incontinence is significantly less often reported than after RP. As prospective randomized trials in the direct comparison of the three treatment modalities are missing retrospective data are demonstrated in the presentation. SP-0349 Long-term results of HDR monotherapy in the treatment of prostate cancer Y. Yoshioka 1 1 Cancer Institute Hospital of JFCR, Radiation Oncology, Tokyo, Japan Abstract text 9- to 7-fraction HDR monotherapy: HDR brachytherapy used as monotherapy for prostate cancer was initiated in Japan in 1995, which was reported in 2000 by Yoshioka et al. They delivered 8 or 9 fractions of 6 Gy each, in total 48 or 54 Gy over 5 days. After 10 years, they changed their dose fractionation into 45.5 Gy in 7 fractions over 4 days, with 6.5 Gy per each fraction. With a median 8- year follow-up and a total of 20 years of experience, they

reported biochemical control rates of 91% for intermediate-risk and 77% for high-risk patients at 8 years. Late Grade 3 GU and GI toxicity rates were 1% and 2% at 8 years. In 2017, collected data of Japan nationwide, multicenter, retrospective study on HDR monotherapy was published by Yoshioka et al. From 1995 through 2013, 524 patients, including 14% low-risk, 40% intermediate-risk, and 47% high-risk patients, were treated with HDR brachytherapy as monotherapy at 5 institutions in Japan. Patients >85% were treated with 7 to 9 fraction regimens. Respective 34%/58%/91% of low/intermediate/high-risk patients received ADT also. Median follow-up was 5.9 years. The 5-year biochemical control rates were 95%/94%/89% for low/intermediate/high-risk patients (Figure).

Late Grade 3 GU and GI toxicity rates were 1% and 0.2% at 5 years. Compared to American series, one distinct characteristic of Japanese series is that Japanese indication for HDR monotherapy included high-risk patients, and subsequently the use of ADT was more frequent than in the American series as will be described in the next section. 6- to 4-fraction HDR monotherapy: Demanes et al. at California Endocuriethérapy Cancer Center (CET) in the USA, started HDR monotherapy in 1996 with 42 to 43.5 Gy in 6 fractions, including 2 implants with 3 fractions each. With a median follow-up period of 6.5 years, they reported long-term results for 448 patients including 288 low-risk and 160 intermediate-risk patients. The actuarial 6- and 10-year PSA progression -free survival rate was 99% and 98%. Late Grade 3 to 4 GU toxicity rate was 5%, with GI 0%. Martinez et al. at William Beaumont Hospital (WBH) in the USA, launched HDR monotherapy with 38 Gy in 4 fractions in 1999. This 4-fraction regimen, which can be accomplished within 2 days, was introduced into Europe, at least into Germany and Switzerland. In general, American researchers seem to indicate HDR monotherapy for low- and favorable intermediate-risk patients, by contrast with Japanese or European researchers. 3- or 2-fraction HDR monotherapy: Three-fraction HDR monotherapy has been reported in early period from 3 countries including Australia, UK and Germany. Barkati et al. in Australia conducted a dose escalation study using 3 fractions of 10 Gy, 10.5 Gy, 11 Gy and 11.5 Gy. They successfully reached to the highest dose level, showing acceptable acute and late toxicities. Zamboglou et al. published the largest series of HDR monotherapy with >700 patients from a single institution in Germany. The transition of dose fractionations used by them looks interesting; first, they treated with 1 implant in 4 fractions of 9.5 Gy. Second, they used 2 implants,