ESTRO 2024 was, as always, an excellent opportunity to exchange scientific insights and to establish clinical contacts for the development of radiation oncology. It gathered more than 7000 participants and a record number of submitted abstracts.

Prostate cancer is the most frequent cancer in men, one in eight of whom will develop it. Brachytherapy, also known as interventional radiotherapy (I-RT), is a well-established method for the treatment of prostate cancer as a single modality or as a “boost” after external beam radiotherapy (EBRT) for more advanced disease.

On the subject of prostate brachytherapy, 20 abstracts were selected for presentation at ESTRO 2024. These comprised three proffered papers, two mini-oral presentations, three poster discussions and 12 digital poster presentations.

In the proffered papers session, which was moderated by Vratislav Strnad and Mateusz Bilski, Jörg Zimmermann presented early results of low-dose-rate (LDR) brachytherapy with 108Gy and ultra-hypofractionated 5x5Gy stereotactic body radiotherapy (SBRT) for 174 prostate cancer patients. Biochemical control rates (BCR) of 100% for low- and intermediate-risk disease, and 98% for high-risk disease, were presented. Local control (LC) was 100% in the total cohort. Only grades 1/2 urinary or rectal toxicities were observed and it was stated that this combination might be not only an effective, yet cost-effective, treatment.

Visus Ignacio investigateds the impact of comorbidity in the association between biochemical failure (BCF) and overall survival (OS) rates in a high-risk and very-high-risk prostate cancer series of patients who had been treated with high-dose-rate (HDR) boost (HDR-BT) or exclusively with external beam radiation therapy (EBRT). A total of 801 patients were included. Seven groups of drugs were identified to define comorbidities. Patients were divided between low comorbidity (up to three drugs from these groups) and high comorbidity (more than three drugs). The results showed that patients with low comorbidity and in high- and very high-risk groups, benefited from treatment with brachytherapy boost.

Ioannis Androulakis’s study affirmed the stability of electromagnetic tracking (EMT) measurements in intraoperative prostate transrectal-ultrasound-based HDR-BT. The introduction of EMT measurements in this setting revealed minor to severe needle reconstruction errors that remained undetected in clinical practice.

In the mini oral session, Laura Zaragoza showed results of a prospective comparative analysis of toxicity, quality of life and disease control in 239 patients who were treated with SBRT vs. SBRT + HDR-BT.

Either a combination of HDR-BT of 15Gy followed by 5x5Gy SBRT or SBRT with 36.25Gy or 40Gy were used. The cumulative incidence of acute Grade 2 genitourinary (GU) toxicity was lower in the HDR-BT+SBRT vs. SBRT arm: 13.7% vs. 35.5% (p=0.00). Similar rates of late Grade 2 GU toxicity were observed. Acute Grade 2 gastrointestinal (GI) toxicity was significantly lower in the HDR-BT+SBRT group:s 30% vs. 70% (p=0.02). It was stated that both treatment modalities demonstrated positive outcomes but that exclusive SBRT seemed to be associated with higher rates of acute Grade 2 GU and GI toxicity.

 In the poster discussion session, Ivone Ribeiro presented the results of 720 unfavourable and high-risk prostate cancer patients who had been treated with HDR-BT + EBRT. Thirteen fractions of 2.8Gy in the intermediate-risk and 23 fractions of 2Gy in the high-risk patients were used. The four-year actuarial biochemical progression-free survival (PFS) rate was 95.2%; for distant PFS, 96.0%; for cancer-specific survival, 99.7%; and for OS, 93.7%. Early GU and GI Grade 2 toxicities were observed in 20.14% and 4.17% of patients, respectively. No Grade ≥3 early toxicity was observed. Late Grade 3 GU and GI toxicity was 1.81%. No Grade ≥3 GI toxicity was reported. It was concluded that HDR-BT + EBRT was a safe and effective approach for intermediate- and high-risk prostate cancer, with an excellent tolerance in terms of early and late toxicities.

In the digital poster session, Alai Goñi presented long-term biochemical, survival, and toxicity outcomes for 1302 patients who had been treated with LDR brachytherapy. Doses of 144Gy were used for low- and intermediate-risk prostate cancer. Rates of freedom from BCF were 87%, 78% and 69% at 10, 15 and 20 years, respectively. OS rates were 55% and 36% at 15 and 20 years, respectively. Late Grade 3 GU toxicity rates were 9%, 14% and 18% at 10, 15 and 20 years, respectively. Grade 3 GI late toxicity rates were 2% at both 15 and 20 years.

Magdalena Stankiewicz showed results of two HDR brachytherapy fractionation schedules that were used as monotherapy for prostate cancer. Three fractions of 11Gy and 2x13Gy were selected to treat 270 patients. There were no significant differences in biochemical control (BC) (p=0.2), LC (p=0.6), distant metastasis-free survival rates (p=0.4) or disease-free survival rates (p=0.5) between groups. It was stated that both schedules showed similar efficacy.

Ingrid Sidibé demonstrated results for the treatment of 201 patients with intermediate-risk prostate cancer with 5x5Gy plus a 15Gy HDR-BT. They were compared with control groups that were treated with either 36Gy in 12 fractions or 37.5Gy in 15 fractions with an identical HDR-BT. There was no statistical difference in OS among the three groups at 60 months. Acute Grade 2 GU toxicities were significantly lower in the SBRT+HDR boost group (77.35%) compared with the other groups (85.5% and 82.5%) (p<0.001). There was no Grade 3 toxicity in the 25Gy/five fraction. group compared with 0.7% in 36Gy/12 fractions and 5.1% in 37.5Gy/15 fractions. It was shown that 25Gy/five fractions. resulted in  better early GU and GI toxicity profiles. Late GU and GI toxicities, BCR, biochemical relapse-free survival rates and OS rates appeared to be similar among the selected modalities.

It seems that more trials are now focused on combining brachytherapy/ I-RT with SBRT for prostate cancer patients and that this shows very promising results. Will they be confirmed with longer follow-up at ESTRO 2025? I hope you are as eager as  me to find out in Vienna!

Mateusz Bilski, MD PhD

Deputy head of brachytherapy department, Saint John’s Cancer Center, Lublin, Poland

Radiotherapy Department, Medical University of Lublin, Poland

Radiotherapy Department, Saint John’s Cancer Center, Lublin, Poland