Accuracy of image-guided radiotherapy of prostate cancer based on the BeamCath® urethral catheter technique

A Phase 1 Trial of Focal Salvage Stereotactic Body Radiation Therapy for Radiorecurrent Prostate Cancer

PURPOSE

NCT03253744 was a phase 1 trial to identify the maximum tolerated dose (MTD) of image-guided, focal, salvage stereotactic body radiation therapy (SBRT) for patients with locally radiorecurrent prostate cancer. Additional objectives included biochemical control and imaging response.

METHODS AND MATERIALS

The trial design included 3 dose levels (DLs): 40 Gy (DL1), 42.5 Gy (DL2), and 45 Gy (DL3) in 5 fractions delivered ≥48 hours apart. The prescription dose was delivered to the magnetic resonance- and prostate-specific membrane antigen imaging-defined tumor volume. Dose escalation followed a 3+3 design with a 3-patient expansion at the MTD. Toxicities were scored until 2 years after completion of SBRT using Common Terminology Criteria for Adverse Events, version 5.0, criteria. Escalation was halted if 2 dose-limiting toxicities occurred, defined as any persistent (>4 days) grade 3 toxicity occurring within the first 3 weeks after SBRT and any grade 3 genitourinary (GU) or grade 4 gastrointestinal (GI) toxicity thereafter.

RESULTS

Between August 2018 and May 2022, 8 patients underwent salvage focal SBRT, with a median follow-up of 35 months. No dose-limiting toxic effects were observed on DL1. Two patients were enrolled in DL2 and experienced grade 3 GU toxicities, prompting de-escalation and expansion (n = 6) at the MTD (DL1). The most common toxicities observed were grade ≥2 GU toxicities, with only a single grade 2 GI toxicity and no grade ≥3 GI toxicities. One patient experienced biochemical failure (prostate-specific antigen nadir + 2.0) at 33 months.

CONCLUSIONS

The MTD for focal salvage SBRT for isolated intraprostatic radiorecurrence was 40 Gy in 5 fractions, producing a 100% 24-month biochemical progression free survival, with 1 poststudy failure at 33 months. The most frequent clinically significant toxicity was late grade ≥2 GU toxicity.

Radiotherapy and Hormone Treatment in Prostate Cancer

BACKGROUND

Prostate cancer has the highest incidence of any type of cancer in Germany; an estimated 67 000 new diagnoses of prostate cancer will be made in 2016. In the current German S3 guideline for the treatment of prostate cancer, radiotherapy-sometimes in combination with androgen deprivation therapy (ADT)-is one of the two recommended options for treatment with curative intent (the other is radical prostatectomy). There have been many publications on this subject, yet it is still often unclear in routine practice how ADT should be administered, and for how long.

METHODS

This review is based on publications retrieved by a selective literature search, with special attention to controlled trials.

RESULTS

For low risk patients, radiotherapy without ADT is indicated (evidence level 1). Patients with localized prostate cancer and an intermediate risk benefit from radiotherapy combined with a four-to-six-month course of ADT. In this situation, a higher radiation dose might be an effective substitute for ADT (evidence level 1-2). For patients at high risk, radiotherapy combined with long-term hormonal treatment is the standard therapy, as it significantly improves all oncological end points (evidence level 1). For example, in the largest randomized and controlled trial, this form of treatment reduced cancer-specific mortality from 19% to 9% . Higher radiation doses of 66-74 Gy and longer ADT can improve local control at the cost of increased urethral toxicity.

CONCLUSION

Androgen deprivation combined with external beam radiotherapy is a curative standard option for patients with prostate cancer who are at high risk of recurrence. The modern radiotherapeutic techniques that are now available, such as intensity-modulated radiotherapy, enable a further improvement of the risk/benefit ratio.

Current standards and future directions for prostate cancer radiation therapy

Definitive radiation therapy is a well-recognized curative treatment option for localized prostate cancer. A suitable technique, dose, target volume and the option of a combination with androgen deprivation therapy need to be considered. An optimal standard external beam radiotherapy currently includes intensity-modulated and image-guided radiotherapy techniques with total doses of ≥76-78 Gy in conventional fractionation. Protons or carbon ions are alternatives available only in specific centers. Data from several randomized studies increasingly support the rationale for hypofractionated radiotherapy. A simultaneous integrated boost with dose escalation focused on a computed tomography/PET- or MRI/magnetic resonance spectroscopy-detected malignant lesion is one option to increase tumor control, with potentially no additional toxicity. The application of a spacer is a promising concept for optimal protection of the rectal wall.

[External beam radiotherapy in the treatment of prostate cancer]

Prostate cancer represents the most frequently diagnosed malignant tumor in Germany. Primary radiotherapy is one of the two recommended curative treatment options for this disease. There are two types of radiotherapy: external beam radiotherapy and interstitial brachytherapy. Technical developments during the last two decades have made it possible to achieve improved chances of being cured of tumors and improved relief from disease-related symptoms for patients at all tumor stages. Moreover, treatment can be administered with a reduced rate of side effects. Results of classical 3D conformal radiotherapy as well as modern radiation therapy techniques are comprehensively presented including the concept of hypofractionation with results from available randomized trials. After comprehensive assessment of all relevant risk factors, recommendations for the type of treatment must be based on a multidisciplinary approach.