Re-distribution of brachytherapy dose using a differential dose prescription adapted to risk of local failure in low-risk prostate cancer patients

Integration of functional imaging in brachytherapy

Functional imaging allows the evaluation of numerous biological properties that could be considered at all steps of the therapeutic management of patients treated with brachytherapy. Indeed, it enables better initial staging of the disease, and some parameters may also be used as predictive biomarkers for treatment response, allowing better selection of patients eligible for brachytherapy. It may also improve the definition of target volumes with the aim of dose escalations by dose-painting. Finally, it could be useful during the follow-up to assess response to treatment. In this review, we report how functional imaging is integrated at the present time during the brachytherapy procedure, and what are its potential future contributions in the main tumour locations where brachytherapy is recommended. Functional imaging has great potential in the contact of brachytherapy, but still, several issues remain to be resolved before integrating it into clinical practice, especially as a biomarker or in dose painting strategies.

Automatic intraprostatic lesion segmentation in multiparametric magnetic resonance images with proposed multiple branch UNet

PURPOSE

Contouring intraprostatic lesions is a prerequisite for dose-escalating these lesions in radiotherapy to improve the local cancer control. In this study, a deep learning-based approach was developed for automatic intraprostatic lesion segmentation in multiparametric magnetic resonance imaging (mpMRI) images contributing to clinical practice.

METHODS

Multiparametric magnetic resonance imaging images from 136 patient cases were collected from our institution, and all these cases contained suspicious lesions with Prostate Imaging Reporting and Data System (PI-RADS) score ≥ 4. The contours of the lesion and prostate were manually created on axial T2-weighted (T2W), apparent diffusion coefficient (ADC) and high b-value diffusion-weighted imaging (DWI) images to provide the ground truth data. Then a multiple branch UNet (MB-UNet) was proposed for the segmentation of an indistinct target in multi-modality MRI images. An encoder module was designed with three branches for the three MRI modalities separately, to fully extract the high-level features provided by different MRI modalities; an input module was added by using three sub-branches for three consecutive image slices, to consider the contour consistency among different image slices; deep supervision strategy was also integrated into the network to speed up the convergency of the network and improve the performance. The probability maps of the background, normal prostate and lesion were output by the network to generate the segmentation of the lesion, and the performance was evaluated using the dice similarity coefficient (DSC) as the main metric.

RESULTS

A total of 162 lesions were contoured on 652 image slices, with 119 lesions in the peripheral zone, 38 in the transition zone, four in the central zone and one in the anterior fibromuscular stroma. All prostates were also contoured on 1,264 image slices. As for the segmentation of lesions in the testing set, MB-UNet achieved a per case DSC of 0.6333, specificity of 0.9993, sensitivity of 0.7056; and global DSC of 0.7205, specificity of 0.9993, sensitivity of 0.7409. All the three deep learning strategies adopted in this study contributed to the performance promotion of the MB-UNet. Missing the DWI modality would degrade the segmentation performance more markedly compared with the other two modalities.

CONCLUSIONS

A deep learning-based approach with proposed MB-UNet was developed to automatically segment suspicious lesions in mpMRI images. This study makes it feasible to adopt boosting intraprostatic lesions in clinical practice to achieve better outcomes.

[Therapeutic innovations in radiation oncology for localized prostate cancer]

Intensity-modulated radiation therapy, image-guided radiation therapy with fiducial markers and prostate brachytherapy allow the delivery of dose escalation for localized prostate cancer with very low rates of long-term toxicity and sequelae. Nowadays, modern radiotherapy techniques make it possible to shorten treatment time with hypofractionation, to better protect surrounding healthy tissues and to escalate the dose even further. Advances in radiotherapy are closely linked to advances in magnetic resonance imaging (MRI) and/or PET imaging. Functional imaging makes it possible to deliver personalised pelvic nodal radiotherapy, targeting the nodal areas at higher risk of microscopic involvement. In patients with an index lesion at baseline or at failure, MR-based focal therapy or focal dose escalation with brachytherapy or stereotactic body radiation therapy is also currently investigated. MR-based adaptive radiotherapy, which makes it possible to track prostate shifts during radiation delivery, is another step forward in the integration of MR imaging in radiation delivery.

Cone-beam CT-based adaptive planning improves permanent prostate brachytherapy dosimetry: An analysis of 1266 patients

PURPOSE

To evaluate adaptive planning for permanent prostate brachytherapy and to identify the prostate regions that needed adaptation.

METHODS AND MATERIALS

After the implantation of stranded seeds, using real-time intraoperative planning, a transrectal ultrasound (TRUS)-scan was obtained and contoured. The positions of seeds were determined on a C-arm cone-beam computed tomography (CBCT)-scan. The CBCT-scan was registered to the TRUS-scan using fiducial gold markers. If dose coverage on the combined image-dataset was inadequate, an intraoperative adaptation was performed by placing remedial seeds. CBCT-based intraoperative dosimetry was analyzed for the prostate (D90, V100, and V150) and the urethra (D30). The effects of the adaptive dosimetry procedure for Day 30 were separately assessed.

RESULTS

We analyzed 1266 patients. In 17.4% of the procedures, an adaptation was performed. Without the dose contribution of the adaptation Day 30 V100 would be < 95% for half of this group. On Day 0, the increase due to the adaptation was 11.8 ± 7.2% (1SD) for D90 and 9.0 ± 6.4% for V100. On Day 30, we observed an increase in D90 of 12.3 ± 6.0% and in V100 of 4.2 ± 4.3%. For the total group, a D90 of 119.6 ± 9.1% and V100 of 97.7 ± 2.5% was achieved. Most remedial seeds were placed anteriorly near the base of the prostate.

CONCLUSION

CBCT-based adaptive planning enables identification of implants needing adaptation and improves prostate dose coverage. Adaptations were predominantly performed near the anterior base of the prostate.

Advancements in brachytherapy

Brachytherapy is a radiotherapy modality associated with a highly focal dose distribution. Brachytherapy treats the cancer tissue from the inside, and the radiation does not travel through healthy tissue to reach the target as with external beam radiotherapy techniques. The nature of brachytherapy makes it attractive for boosting limited size target volumes to very high doses while sparing normal tissues. Significant developments over the last decades have increased the use of 3D image guided procedures with the utilization of CT, MRI, US and PET. This has taken brachytherapy to a new level in terms of controlling dose and demonstrating excellent clinical outcome. Interests in focal, hypofractionated and adaptive treatments are increasing, and brachytherapy has significant potential to develop further in these directions with current and new treatment indications.