SBRT and extreme hypofractionation: A new era in prostate cancer treatments?

Comparison of MRI, PET, and 18F-choline PET/MRI in patients with oligometastatic recurrent prostate cancer

Objectives

The aims of the study were (i) to examine the PCa detection rate of 18F-choline (FCH) PET/MRI and (ii) to assess the impact of PET/MRI findings in patients with PCa who develop OMD using PSA response as a biomarker.

Methods

We retrospectively analyzed a cohort of 103 patients undergoing FCH PET/MRI for biochemical recurrence of PCa. The inclusion criteria were (1) previous radical prostatectomy (RP) with or without adjuvant radiotherapy (RT); (2) PSA levels available at the time of PET; (3) OMD, defined as a maximum of 5 lesions on PET/MRI; and (4) follow-up data available for at least 6 months after PET. All images were reviewed by two nuclear medicine physicians and interpreted with the support of two radiologists.

Results

Seventy patients were eligible for the study: 52 patients had a positive FCH PET/MRI and 18 had a negative scan. The overall PCa detection rates for MRI, PET, and PET/MRI were 65.7%, 37.1%, and 74.3%, respectively. Thirty-five patients were treated with radiotherapy (RT), 16 received hormonal therapy (HT), 3 had a combined therapy (RT + HT), and 16 (23%) underwent PSA surveillance. At follow-up, PSA levels decreased in 51 patients (73%), most of whom had been treated with RT or RT + HT. Therapeutic management was guided by PET/MRI in 74% of patients, which performed better than MRI alone (68% of patients).

Conclusion

FCH PET/MRI has a higher detection rate than MRI or PET alone for PCa patients with OMD and PSA levels > 0.5 ng/mL, prompting a better choice of treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00261-021-03131-7.

Epigenetic mechanisms underlying prostate cancer radioresistance

Radiotherapy (RT) is one of the mainstay treatments for prostate cancer (PCa), a highly prevalent neoplasm among males worldwide. About 30% of newly diagnosed PCa patients receive RT with a curative intent. However, biochemical relapse occurs in 20–40% of advanced PCa treated with RT either alone or in combination with adjuvant-hormonal therapy. Epigenetic alterations, frequently associated with molecular variations in PCa, contribute to the acquisition of a radioresistant phenotype. Increased DNA damage repair and cell cycle deregulation decreases radio-response in PCa patients. Moreover, the interplay between epigenome and cell growth pathways is extensively described in published literature. Importantly, as the clinical pattern of PCa ranges from an indolent tumor to an aggressive disease, discovering specific targetable epigenetic molecules able to overcome and predict PCa radioresistance is urgently needed. Currently, histone-deacetylase and DNA-methyltransferase inhibitors are the most studied classes of chromatin-modifying drugs (so-called ‘epidrugs’) within cancer radiosensitization context. Nonetheless, the lack of reliable validation trials is a foremost drawback. This review summarizes the major epigenetically induced changes in radioresistant-like PCa cells and describes recently reported targeted epigenetic therapies in pre-clinical and clinical settings.

MR-Guided Hypofractionated Radiotherapy: Current Emerging Data and Promising Perspectives for Localized Prostate Cancer

In this review we summarize the currently available evidence about the role of hybrid machines for MR-guided radiotherapy for prostate stereotactic body radiotherapy. Given the novelty of this technology, to date few data are accessible, but they all report very promising results in terms of tolerability and preliminary clinical outcomes. Most of the studies highlight the favorable impact of on-board magnetic resonance imaging as a means to improve target and organs at risk identification with a consequent advantage in terms of dosimetric results, which is expected to relate to a more favorable toxicity pattern. Still, the longer treatment time per session may potentially affect the patient's compliance to the treatment, although first quality of life assessment studies have reported substantial tolerability and no major impact on quality of life. Finally, in this review we hypothesize some future scenarios of further investigation, based on the possibility to explore the superior anatomy visualization and the role of daily adapted treatments provided by hybrid MR-Linacs.

Practical considerations for prostate hypofractionation in the developing world

External beam radiotherapy is an effective curative treatment option for localized prostate cancer, the most common cancer in men worldwide. However, conventionally fractionated courses of curative external beam radiotherapy are usually 8-9 weeks long, resulting in a substantial burden to patients and the health-care system. This problem is exacerbated in low-income and middle-income countries where health-care resources might be scarce and patient funds limited. Trials have shown a clinical equipoise between hypofractionated schedules of radiotherapy and conventionally fractionated treatments, with the advantage of drastically shortening treatment durations with the use of hypofractionation. The hypofractionated schedules are supported by modern consensus guidelines for implementation in clinical practice. Furthermore, several economic evaluations have shown improved cost effectiveness of hypofractionated therapy compared with conventional schedules. However, these techniques demand complex infrastructure and advanced personnel training. Thus, a number of practical considerations must be borne in mind when implementing hypofractionation in low-income and middle-income countries, but the potential gain in the treatment of this patient population is substantial.

Preliminary result of carbon-ion radiotherapy using the spot scanning method for prostate cancer

BACKGROUND

Carbon-ion radiotherapy (CIRT) for prostate cancer was initiated at Kanagawa Cancer Center in 2015. The present study analyzed the preliminary clinical outcomes of CIRT for prostate cancer.

METHODS

The clinical outcomes of 253 patients with prostate cancer who were treated with CIRT delivered using the spot scanning method between December 2015 and December 2017 were retrospectively analyzed. The irradiation dose was set at 51.6 Gy (relative biological effectiveness) delivered in 12 fractions over 3 weeks. Biochemical relapse was defined using the Phoenix definition. Toxicities were assessed according to CTCAE version 4.0.

RESULTS

The median patient age was 70 (47-86) years. The median follow-up duration was 35.3 (4.1-52.9) months. According to the D'Amico classification system, 8, 88, and 157 patients were classified as having low, intermediate, and high risks, respectively. Androgen deprivation therapy was administered in 244 patients. The biochemical relapse-free rate in the low-, intermediate-, and high-risk groups at 3 years was 87.5, 88.0, and 97.5%, respectively (P = 0.036). Grade 2 acute urinary toxicity was observed in 12 (4.7%) patients. Grade 2 acute rectal toxicity was not observed. Grade 2 late urinary toxicity and grade 2 late rectal toxicity were observed in 17 (6.7%) and 3 patients (1.2%), respectively. Previous transurethral resection of the prostate was significantly associated with late grade 2 toxicity in univariate analysis. The predictive factor for late rectal toxicity was not detected.

CONCLUSION

The present study demonstrated that CIRT using the spot scanning method for prostate cancer produces favorable outcomes.

Post-HIFU locally relapsed prostate cancer: high-dose salvage radiotherapy guided by molecular imaging

PURPOSE

To evaluate tolerance and biochemical control rates of salvage external beam radiotherapy (EBRT) in patients with local relapse from prostate cancer (PC) after high-intensity focused ultrasound (HIFU) as primary treatment.

METHODS

Twenty-four patients presented biochemical failure of PC. Salvage EBRT to the residual prostate was performed with moderate hypofractionation schedule (MHRT) in 28 fractions (n = 16) or with extreme hypofractionation schedule (SBRT) in 5 fractions (n = 8) by means of image-guided volumetric modulation arc therapy. In case of MHRT, the median dose was 71.4 Gy, whereas in case of SBRT it was 32.5 Gy.

RESULTS

The median follow-up was 28 months. The median PSA nadir was 0.26 ng/mL. In case of MHRT, the median PSA nadir was 0.15 ng/mL and occurred within a median time of 19 months. In case of SBRT, the median PSA nadir was 0.64 ng/mL and occurred within a median time of 8 months. No G3 higher acute or late toxicity after EBRT was observed. Only three patients presented with G2 acute GI toxicity (actinic proctitis). Twelve patients experienced acute G1 GU toxicity: 8/16 of men treated with MHRT and 4/8 of men treated with SBRT. Complete local control of disease was achieved in 23/24 patients (96%).

CONCLUSIONS

Our data confirm the feasibility and the low toxicity of salvage EBRT with both schedules of treatment after HIFU failure. The findings of low acute toxicity and good biochemical control rates are encouraging, but a larger number of patients and a longer follow-up are needed to confirm these results.

The Utility of Penile Bulb Contouring to Localise the Prostate Apex as Compared to Urethrography

PURPOSE

High-precision radiotherapy relies on accurate anatomic localisation. Urethrography is often used to localise the prostatic apex. However, urethrography is an invasive localisation procedure and may introduce a systemic error. The penile bulb (PB) is contoured to minimise the risk of erectile dysfunction. The purpose of this study is to assess the value of using the PB, as an alternative to urethrography, to localise the prostate.

METHODS AND MATERIALS

The PB was localised on 10 patients treated with simplified intensity-modulated arc radiotherapy at computed tomography simulation during treatment weeks 1 and 7. All patients underwent placement of fiducial markers. Urethrography was used only at simulation. Distances from the superior PB contour to the inferior prostate contour, the apex fiducial marker, and to the inferior prostate contour were obtained as well. The PB was contoured by two observers independently. Agreement coefficients and analysis of variance were used to assess reliability between rates and consistency of measurements over time.

RESULTS

The PB-apex distance was greater than or equal to the urethrogram-apex distance in 24/30 (80%) measurements, and the median difference was 3 mm and was consistent between raters. The greatest variation in PB-IM distance between weeks was 6 mm, the median was 3 mm, and the agreements of measurements between weeks for raters 1 and 2 were 0.79 and 0.69, respectively. These differences were not statistically different and were consistent with the computed tomography slice thickness.

CONCLUSIONS

The PB can be used to identify the prostate apex and can be reliably contoured between observers. Measurements are consistent between patients and through the duration of treatment. The PB distance measurements support studies indicating that urethrography causes a shift of the prostate superiorly. The distance from the PB to prostate apex remains stable during treatment for individual patients but varies between patients.

Changes in prostate orientation due to removal of a Foley catheter

PURPOSE

Investigate the impact on prostate orientation caused by use and removal of a Foley catheter, and the dosimetric impact on men prospectively treated with prostate stereotactic body radiotherapy (SBRT).

METHODS

Twenty-two men underwent a CT simulation with a Foley in place (FCT), followed immediately by a second treatment planning simulation without the Foley (TPCT). The change in prostate orientation was determined by rigid registration of three implanted transponders between FCT and TPCT and compared to measured orientation changes during treatment. The impact on treatment planning and delivery was investigated by analyzing the measured rotations during treatment relative to both CT scans, and introducing rotations of ±15° in the treatment plan to determine the maximum impact of allowed rotations.

RESULTS

Removing the Foley caused a statistically significant prostate rotation (P < 0.0028) compared to normal biological motion in 60% of patients. The largest change in rotation due to removing a Foley occurs about the left-right axis (tilt) which has a standard deviation two to five times larger than changes in rotation about the Sup-Inf (roll) and Ant-Post (yaw) axes. The change in tilt due to removing a Foley for prone and supine patients was -1.1° ± 6.0° and 0.3° ± 7.4°, showing no strong directional bias. The average tilt during treatment was -1.6° ± 7.1° compared to the TPCT and would have been -2.0° ± 7.1° had the FCT been used as the reference. The TPCT was a better or equivalent representation of prostate tilt in 82% of patients, vs 50% had the FCT been used for treatment planning. However, 92.7% of fractions would still have been within the ±15° rotation limit if only the FCT were used for treatment planning. When rotated ±15°, urethra V_{105% = 38.85Gy}  < 20% was exceeded in 27% of the instances, and prostate (CTV) coverage was maintained above D_95%  > 37 Gy in all but one instance.

CONCLUSIONS

Removing a Foley catheter can cause large prostate rotations. There does not appear to be a clear dosimetric benefit to obtaining the CT scan with a Foley catheter to define the urethra given the changes in urethral position from removing the Foley catheter. If urethral sparing is desired without the use of a Foley, utilization of an MRI to define the urethra may be necessary, or a pseudo-urethral planning organ at risk volume (PRV) may be used to limit dosimetric hot spots.

Proceedings of the National Cancer Institute Workshop on Charged Particle Radiobiology

In April 2016, the National Cancer Institute hosted a multidisciplinary workshop to discuss the current knowledge of the radiobiological aspects of charged particles used in cancer therapy to identify gaps in that knowledge that might hinder the effective clinical use of charged particles and to propose research that could help fill those gaps. The workshop was organized into 10 topics ranging from biophysical models to clinical trials and included treatment optimization, relative biological effectiveness of tumors and normal tissues, hypofractionation with particles, combination with immunotherapy, "omics," hypoxia, and particle-induced second malignancies. Given that the most commonly used charged particle in the clinic currently is protons, much of the discussion revolved around evaluating the state of knowledge and current practice of using a relative biological effectiveness of 1.1 for protons. Discussion also included the potential advantages of heavier ions, notably carbon ions, because of their increased biological effectiveness, especially for tumors frequently considered to be radiation resistant, increased effectiveness in hypoxic cells, and potential for differentially altering immune responses. The participants identified a large number of research areas in which information is needed to inform the most effective use of charged particles in the future in clinical radiation therapy. This unique form of radiation therapy holds great promise for improving cancer treatment.