Dosimetric considerations to determine the optimal technique for localized prostate cancer among external photon, proton, or carbon-ion therapy and high-dose-rate or low-dose-rate brachytherapy

Deep learning-based ultrasound auto-segmentation of the prostate with brachytherapy implanted needles

BACKGROUND

Accurate segmentation of the clinical target volume (CTV) corresponding to the prostate with or without proximal seminal vesicles is required on transrectal ultrasound (TRUS) images during prostate brachytherapy procedures. Implanted needles cause artifacts that may make this task difficult and time-consuming. Thus, previous studies have focused on the simpler problem of segmentation in the absence of needles at the cost of reduced clinical utility.

PURPOSE

To use a convolutional neural network (CNN) algorithm for segmentation of the prostatic CTV in TRUS images post-needle insertion obtained from prostate brachytherapy procedures to better meet the demands of the clinical procedure.

METHODS

A dataset consisting of 144 3-dimensional (3D) TRUS images with implanted metal brachytherapy needles and associated manual CTV segmentations was used for training a 2-dimensional (2D) U-Net CNN using a Dice Similarity Coefficient (DSC) loss function. These were split by patient, with 119 used for training and 25 reserved for testing. The 3D TRUS training images were resliced at radial (around the axis normal to the coronal plane) and oblique angles through the center of the 3D image, as well as axial, coronal, and sagittal planes to obtain 3689 2D TRUS images and masks for training. The network generated boundary predictions on 300 2D TRUS images obtained from reslicing each of the 25 3D TRUS images used for testing into 12 radial slices (15° apart), which were then reconstructed into 3D surfaces. Performance metrics included DSC, recall, precision, unsigned and signed volume percentage differences (VPD/sVPD), mean surface distance (MSD), and Hausdorff distance (HD). In addition, we studied whether providing algorithm-predicted boundaries to the physicians and allowing modifications increased the agreement between physicians. This was performed by providing a subset of 3D TRUS images of five patients to five physicians who segmented the CTV using clinical software and repeated this at least 1 week apart. The five physicians were given the algorithm boundary predictions and allowed to modify them, and the resulting inter- and intra-physician variability was evaluated.

RESULTS

Median DSC, recall, precision, VPD, sVPD, MSD, and HD of the 3D-reconstructed algorithm segmentations were 87.2 [84.1, 88.8]%, 89.0 [86.3, 92.4]%, 86.6 [78.5, 90.8]%, 10.3 [4.5, 18.4]%, 2.0 [-4.5, 18.4]%, 1.6 [1.2, 2.0] mm, and 6.0 [5.3, 8.0] mm, respectively. Segmentation time for a set of 12 2D radial images was 2.46 [2.44, 2.48] s. With and without U-Net starting points, the intra-physician median DSCs were 97.0 [96.3, 97.8]%, and 94.4 [92.5, 95.4]% (p < 0.0001), respectively, while the inter-physician median DSCs were 94.8 [93.3, 96.8]% and 90.2 [88.7, 92.1]%, respectively (p < 0.0001). The median segmentation time for physicians, with and without U-Net-generated CTV boundaries, were 257.5 [211.8, 300.0] s and 288.0 [232.0, 333.5] s, respectively (p = 0.1034).

CONCLUSIONS

Our algorithm performed at a level similar to physicians in a fraction of the time. The use of algorithm-generated boundaries as a starting point and allowing modifications reduced physician variability, although it did not significantly reduce the time compared to manual segmentations.

A Randomized Trial Comparing Quality of Life After Low-Dose Rate or High-Dose Rate Prostate Brachytherapy Boost With Pelvic External Beam Radiation Therapy

PURPOSE

To compare health-related quality of life (QoL) in urinary, bowel, and sexual domains after combined external beam radiation therapy (EBRT) and either low-dose rate (LDR) or high-dose rate (HDR) prostate brachytherapy (BT).

METHODS AND MATERIALS

Eligible men with intermediate or high-risk prostate cancer treated with combined pelvic EBRT and BT were randomly assigned to either HDR (15 Gy) or LDR (110 Gy) boost. International Prostate Symptom Score, Index of Erectile Function, and Expanded Prostate Cancer Composite were collected at baseline, 1, 3, 6, and 12 months, every 6 months to 3 years and then annually along with prostate-specific antigen/testosterone. Fisher's exact test compared categorical variables and the Mann-Whitney U test Expanded Prostate Cancer Index Composite (EPIC) domain scores.

RESULTS

From January 2014 to December 2019, a random number generator assigned 195 men: 108 to HDR and 87 to LDR. Median age was 71 years. Risk group was high in 57% and unfavorable intermediate in 43%. Androgen deprivation (used in 74%) began with 3 months neoadjuvant and continued for median 12 months. Baseline EPIC scores were similar for the LDR/HDR cohorts: 89 and 88 respectively for Genito-urinary; 92 and 93 for Gastro-intestinal. EPIC urinary scores decreased at 1 month for HDR but recovered promptly to a steady state by 6 months. LDR scores reached a nadir at 3 months with slow recovery to 18 months, after which urinary QoL was similar for HDR and LDR. Bowel QOL scores fell in both cohorts reaching respective nadirs at 12 months. HDR patients recovered close to baseline and maintained higher scores than LDR patients to 5 years. The decline for LDR patients remained more than the minimum clinically important difference out to 5 years.

CONCLUSIONS

The patient experience for combined EBRT and prostate BT is improved with HDR BT. Urinary QoL improves over time to be equivalent between the 2 modalities after 18 months, but LDR patients report lasting bowel symptoms.

Comparison of sexual function after robot-assisted radical prostatectomy and carbon-ion radiotherapy for Japanese prostate cancer patients using propensity score matching

BACKGROUND

The quality of life of patients is an important consideration when selecting treatments for localized prostate cancer (PCa). We retrospectively compared sexual function after robot-assisted radical prostatectomy (RARP) and carbon-ion radiotherapy (CIRT) using propensity score matching.

METHODS

In total, 127 Japanese PCa patients treated with RARP and 190 treated with CIRT monotherapy were evaluated. We evaluated the Expanded Prostate Cancer Index Composite (EPIC) score before treatment and 12 and 24 months after treatment. After propensity score matching, data from 101 patients from each group were analyzed. The study protocol was approved by the Institutional Review Board of Gunma University Hospital (no. IRB2020-050, 1839).

RESULTS

After propensity score matching, the mean EPIC sexual function summary scores in the RARP and CIRT groups were 46.4 and 48.2, respectively. At 12 and 24 months after treatment, these scores were 27.9 (39.9% decrease) and 28.2 (39.2% decrease) in the RARP group and 41.4 (14.1% decrease) and 41.6 (13.7% decrease) in the CIRT group, respectively. Both groups demonstrated significantly decreased scores after 12 and 24 months of treatment compared to before treatment (all p < 0.05). At 12 and 24 months, the sexual function summary score was significantly higher in the CIRT group than in the RARP group (p < 0.001).

CONCLUSIONS

There was a smaller decrease in the EPIC sexual function score in the CIRT group than in the RARP group. These results provide useful information for treatment decision-making of Japanese PCa patients.

Circular RNA circEYA3 promotes the radiation resistance of hepatocellular carcinoma via the IGF2BP2/DTX3L axis

BACKGROUND

Hepatocellular carcinoma (HCC) has a high incidence and mortality rate despite various treatment options, including 125I seed implantation. However, recurrence and radiation resistance remain challenging issues. Hsa_circ_0007895 (circEYA3)-derived from exons 2-6 of EYA3-facilitates the proliferation and progression of pancreatic ductal adenocarcinoma. However, the role of circEYA3 in HCC 125I radiation resistance remains unclear. Thus, we aimed to investigate the functions and underlying molecular mechanisms of circEYA3 in HCC under 125I and X-ray irradiation conditions.

METHODS

CircEYA3 was identified by RNA-seq in patients with HCC before and after 125I seed implantation treatment, followed by fluorescence in situ hybridization and RNase R assays. The radiosensitivity of HCC cell lines irradiated with 125I seeds or external irradiation were evaluated using the Cell Counting Kit 8, flow cytometry, γH2A.X immunofluorescence and comet assays. RNA pull-down and RNA immunoprecipitation assays were performed to explore the interactions between circEYA3 and IGF2BP2. DTX3L mRNA was identified by RNA-seq in PLC/PRF/5 cells with overexpressed circEYA3. The corresponding in vitro results were verified using a mouse xenograft model.

RESULTS

CircEYA3 decreased the radiosensitivity of HCC cells both in vitro and in vivo. Notably, using a circRNA pulldown assay and RNA-binding protein immunoprecipitation, we identified IGF2BP2 as a novel and robust interacting protein of circEYA3. Mechanistically, circEYA3 binds to IGF2BP2 and enhances its ability to stabilize DTX3L mRNA, thereby specifically alleviating radiation-induced DNA damage in HCC cells.

CONCLUSIONS

Our findings demonstrate that circEYA3 increases the radioresistance of HCC to 125I seeds and external irradiation via the IGF2BP2/DTX3L axis. Thus, circEYA3 might be a predictive indicator and intervention option for 125I brachytherapy or external radiotherapy in HCC.

Normal Tissue Integral Dose as a Result of Prostate Radiation Therapy: A Quantitative Comparison Between High-Dose-Rate Brachytherapy and Modern External Beam Radiation Therapy Techniques

Purpose

Quantification of integral radiation dose delivered during treatment for prostate cancer is lacking. We performed a comparative quantification of dose to nontarget body tissues delivered via 4 common radiation techniques: conventional volumetric modulated arc therapy, stereotactic body radiation therapy, pencil-beam scanning proton therapy, and high-dose-rate brachytherapy.

Methods and Materials

Plans for each radiation technique were generated for 10 patients with typical anatomy. For brachytherapy plans, virtual needles were placed to achieve standard dosimetry. Standard planning target volume margins or robustness margins were applied as appropriate. A "normal tissue" structure (entire computed tomography simulation volume minus planning target volume) was generated for integral dose computation. Dose-volume histogram parameters for targets and normal structures were tabulated. Normal tissue integral dose was calculated by multiplying normal tissue volume by mean dose.

Results

Normal tissue integral dose was lowest for brachytherapy. Pencil-beam scanning protons, stereotactic body radiation therapy, and brachytherapy resulted in 17%, 57%, and 91% absolute reductions compared with standard volumetric modulated arc therapy, respectively. Mean nontarget tissues receiving 25%, 50%, and 75% of the prescription dose were reduced by 85%, 76%, and 83% for brachytherapy relative to volumetric modulated arc therapy, by 79%, 64%, and 74% relative to stereotactic body radiation therapy, and 73%, 60%, and 81% relative to proton therapy. All reductions observed using brachytherapy were statistically significant.

Conclusions

High-dose-rate brachytherapy is an effective technique for reducing dose to nontarget body tissues relative to volumetric modulated arc therapy, stereotactic body radiation therapy, and pencil-beam scanning proton therapy.

Salvage Prostate Brachytherapy in Radiorecurrent Prostate Cancer: An International Delphi Consensus Study

BACKGROUND AND PURPOSE

Local recurrences after previous radiotherapy (RT) are increasingly being identified in biochemically recurrent prostate cancer. Salvage prostate brachytherapy (BT) is an effective and well tolerated treatment option. We sought to generate international consensus statements on the use and preferred technical considerations for salvage prostate BT.

MATERIALS AND METHODS

International experts in salvage prostate BT were invited (n=34) to participate. A three-round modified Delphi technique was utilized, with questions focused on patient- and cancer-specific criteria, type and technique of BT, and follow-up. An a priori threshold for consensus of ≥ 75% was set, with a majority opinion being ≥ 50%.

RESULTS

Thirty international experts agreed to participate. Consensus was achieved for 56% (18/32) of statements. Consensus was achieved in several areas of patient selection: 1) A minimum of 2-3 years from initial RT to salvage BT; 2) MRI and PSMA PET should be obtained; and 3) Both targeted and systematic biopsies should be performed. Several areas did not reach consensus: 1) Maximum T stage/PSA at time of salvage; 2) Utilization/duration of ADT; 3) Appropriateness of combining local salvage with SABR for oligometastatic disease and 4) Repeating a second course of salvage BT. A majority opinion preferred High Dose-Rate salvage BT, and indicated that both focal and whole gland techniques could be appropriate. There was no single preferred dose/fractionation.

CONCLUSION

Areas of consensus within our Delphi study may serve as practical advice for salvage prostate BT. Future research in salvage BT should address areas of controversy identified in our study.

Rotating Gantries Provide Individualized Beam Arrangements for Charged Particle Therapy

PURPOSE

This study evaluates beam angles used to generate highly individualized proton therapy treatment plans for patients eligible for carbon ion radiotherapy (CIRT).

METHODS AND MATERIALS

We retrospectively evaluated patients treated with pencil beam scanning intensity modulated proton therapy from 2015 to 2020 who had indications for CIRT. Patients were treated with a 190° rotating gantry with a robotic patient positioning system. Treatment plans were individualized to provide maximal prescription dose delivery to the tumor target volume while sparing organs at risk. The utilized beam angles were grouped, and anatomic sites with at least 10 different beam angles were sorted into histograms.

RESULTS

A total of 467 patients with 484 plans and 1196 unique beam angles were evaluated and characterized by anatomic treatment site and the number of beam angles utilized. The most common beam angles used were 0° and 180°. A wide range of beam angles were used in treating almost all anatomic sites. Only esophageal cancers had a predominantly unimodal grouping of beam angles. Pancreas cancers showed a modest grouping of beam angles.

CONCLUSIONS

The wide distribution of beam angles used to treat CIRT-eligible patients suggests that a rotating gantry is optimal to provide highly individualized beam arrangements.

Multimodal locoregional procedures for cancer pain management: a literature review

Pain is the most common and fearsome symptom in cancer patients, particularly in the advanced stage of disease. In cancer pain management, the first option is represented by analgesic drugs, whereas surgery is rarely used. Prior to considering surgical intervention, less invasive locoregional procedures are available from the wide pain management arsenal. In this review article, comprehensive information about the most commonly used locoregional options available for treating cancer pain focusing on interventional radiology (neurolysis, augmentation techniques, and embolization) and interventional radiotherapy were provided, also highlighting the potential ways to increase the effectiveness of treatments.

Comparison of dosimetries of carbon-ion pencil beam scanning, proton pencil beam scanning and volumetric modulated arc therapy for locally recurrent rectal cancer

We compared the dose distributions of carbon-ion pencil beam scanning (C-PBS), proton pencil beam scanning (P-PBS) and Volumetric Modulated Arc Therapy (VMAT) for locally recurrent rectal cancer. The C-PBS treatment planning computed tomography (CT) data sets of 10 locally recurrent rectal cancer cases were randomly selected. Three treatment plans were created using identical prescribed doses. The beam angles for C-PBS and P-PBS were identical. Dosimetry, including the dose received by 95% of the planning target volume (PTV) (D95%), dose to the 2 cc receiving the maximum dose (D2cc), organ at risk (OAR) volume receiving > 15Gy (V15) and > 30Gy (V30), was evaluated. Statistical significance was assessed using the Wilcoxon signed-rank test. Mean PTV-D95% values were > 95% of the volume for P-PBS and C-PBS, whereas that for VMAT was 94.3%. However, PTV-D95% values in P-PBS and VMAT were < 95% in five and two cases, respectively, due to the OAR dose reduction. V30 and V15 to the rectum/intestine for C-PBS (V30 = 4.2 ± 3.2 cc, V15 = 13.8 ± 10.6 cc) and P-PBS (V30 = 7.3 ± 5.6 cc, V15 = 21.3 ± 13.5 cc) were significantly lower than those for VMAT (V30 = 17.1 ± 10.6 cc, V15 = 55.2 ± 28.6 cc). Bladder-V30 values with P-PBS/C-PBS (3.9 ± 4.8 Gy(RBE)/3.0 ± 4.0 Gy(RBE)) were significantly lower than those with VMAT (7.9 ± 8.1 Gy). C-PBS provided superior dose conformation and lower OAR doses compared with P-PBS and VMAT. C-PBS may be the best choice for cases in which VMAT and P-PBS cannot satisfy dose constraints. C-PBS could be another choice for cases in which VMAT and P-PBS cannot satisfy dose constraints, thereby avoiding surgical resection.

Proton therapy for prostate cancer: current state and future perspectives

OBJECTIVE

Localized prostate cancer can be treated with several radiotherapeutic approaches. Proton therapy (PT) can precisely target tumors, thus sparing normal tissues and reducing side-effects without sacrificing cancer control. However, PT is a costly treatment compared with conventional photon radiotherapy, which may undermine its overall efficacy. In this review, we summarize current data on the dosimetric rationale, clinical benefits, and cost of PT for prostate cancer.

METHODS

An extensive literature review of PT for prostate cancer was performed with emphasis on studies investigating dosimetric advantage, clinical outcomes, cost-effective strategies, and novel technology trends.

RESULTS

PT is safe, and its efficacy is comparable to that of standard photon-based therapy or brachytherapy. Data on gastrointestinal, genitourinary, and sexual function toxicity profiles are conflicting; however, PT is associated with a low risk of second cancer and has no effects on testosterone levels. Regarding cost-effectiveness, PT is suboptimal, although evolving trends in radiation delivery and construction of PT centers may help reduce the cost.

CONCLUSION

PT has several advantages over conventional photon radiotherapy, and novel approaches may increase its efficacy and safety. Large prospective randomized trials comparing photon therapy with proton-based treatments are ongoing and may provide data on the differences in efficacy, toxicity profile, and quality of life between proton- and photon-based treatments for prostate cancer in the modern era.

ADVANCES IN KNOWLEDGE

PT provides excellent physical advantages and has a superior dose profile compared with X-ray radiotherapy. Further evidence from clinical trials and research studies will clarify the role of PT in the treatment of prostate cancer, and facilitate the implementation of PT in a more accessible, affordable, efficient, and safe way.

CT-guided palladium-103 seed brachytherapy for metastatic adenoid cystic carcinoma: a retrospective study to assess initial safety and effectiveness of percutaneous CT fluoroscopy-guided permanent seed brachytherapy

Purpose

Multiple pulmonary metastases present treatment difficulties in available treatment techniques, which are inconvenient or may damage sufficient pulmonary tissue to cause pulmonary crippling. This retrospective study of a single-community practice evaluated responses to computed tomography (CT)-guided ¹⁰³Pd permanent seed brachytherapy (CTGPSB) in adenoid cystic carcinoma (ACC) synchronous pulmonary metastases. The purpose of the current study was to document that metastatic pulmonary ACC lesions can be controlled with CTGPSB.

Material and methods

Twenty-nine discrete lesions in 14 patients were evaluated with serial CT scans. All were treated with CTGPSB. Lesions were tracked over serial CT scans and volumes measured. Primary endpoint was a reduction in tumor volume on subsequent CT scan. Secondary endpoint was occurrence of CTCAE grades 2-5.

Results

There was a 100% measured reduction in tumor volume (n = 29) at follow-up. Follow-up was a mean of 3.13 years. Baseline tumor volume was a mean of 1.85 ml (range, 0.69-9.15 ml). There were two grade 1 and one grade 2 adverse events, which did not require hospitalization.

Conclusions

CTGPSB for the treatment of multiple ACC pulmonary metastases is effective, with minimal acute complications, as shown in small cohort of subjects of the present study. Further studies evaluating specific dosimetry parameters in this free-hand technique are needed to specify minimal and maximal dose constraints.

The value of brachytherapy in the age of advanced external beam radiotherapy: a review of the literature in terms of dosimetry

Brachytherapy (BT) has long been used for successful treatment of various tumour entities, including prostate, breast and gynaecological cancer. However, particularly due to advances in modern external beam techniques such as intensity-modulated radiotherapy (IMRT), volume modulated arc therapy (VMAT) and stereotactic body radiotherapy (SBRT), there are concerns about its future. Based on a comprehensive literature review, this article aims to summarize the role of BT in cancer treatment and highlight its particular dosimetric advantages. The authors conclude that image-guided BT supported by inverse dose planning will successfully compete with high-tech EBRT in the future and continue to serve as a valuable modality for cancer treatment.

Retrospective comparison of rectal toxicity between carbon-ion radiotherapy and intensity-modulated radiation therapy based on treatment plan, normal tissue complication probability model, and clinical outcomes in prostate cancer

This retrospective study assessed the treatment planning data and clinical outcomes for 152 prostate cancer patients: 76 consecutive patients treated by carbon-ion radiation therapy and 76 consequtive patients treated by moderate hypo-fractionated intensity-modulated photon radiation therapy. These two modalities were compared using linear quadratic model equivalent doses in 2 Gy per fraction for rectal or rectal wall dose-volume histogram, 3.6 Gy per fraction-converted rectal dose-volume histogram, normal tissue complication probability model, and actual clinical outcomes. Carbon-ion radiation therapy was predicted to have a lower probability of rectal adverse events than intensity-modulated photon radiation therapy based on dose-volume histograms and normal tissue complication probability model. There was no difference in the clinical outcome of rectal adverse events between the two modalities compared in this study.

Therapeutic Sequences in the Treatment of High-Risk Prostate Cancer: Paving the Way Towards Multimodal Tailored Approaches

Various definitions are currently in use to describe high-risk prostate cancer. This variety in definitions is important for patient counseling, since predicted outcomes depend on which classification is applied to identify patient’s prostate cancer risk category. Historically, strategies for the treatment of localized high-risk prostate cancer comprise local approaches such as surgery and radiotherapy, as well as systemic approaches such as hormonal therapy. Nevertheless, since high-risk prostate cancer patients remain the group with higher-risk of treatment failure and mortality rates, nowadays, novel treatment strategies, comprising hypofractionated-radiotherapy, second-generation antiandrogens, and hadrontherapy, are being explored in order to improve their long-term oncological outcomes. This narrative review aims to report the current management of high-risk prostate cancer and to explore the future perspectives in this clinical setting.

Ultrahypofractionated radiotherapy for localized prostate cancer with simultaneous boost to the dominant intraprostatic lesion: a plan comparison

OBJECTIVE

To compare different stereotactic body techniques-intensity-modulated radiotherapy with photons and protons, applied to radiotherapy of prostatic cancer-with simultaneous integrated boost (SIB) on the dominant intraprostatic lesion (DIL).

METHODS

Ten patients were selected for this planning study. Dosimetric results were compared between volumetric modulated arc therapy, intensity-modulated radiation therapy (IMRT), and intensity-modulated proton therapy both with two (IMPT 2F) and five fields (IMPT 5F) planning while applying the prescription schemes of 7.25 Gy/fraction to the prostate gland and 7.5 Gy/fraction to the DIL in 5 fractions.

RESULTS

Comparison of the coverages of the planning target volumes showed that small differences exist. The IMPT-2F-5F techniques allowed higher doses in the targets; conformal indexes resulted similar; homogeneity was better in the photon techniques (2%-5%). Regarding the organs at risk, all the techniques were able to maintain the dose well below the prescribed constraints: in the rectum, the IMPT-2F-5F and IMRT were more efficient in lowering the intermediate doses; in the bladder, the median dose was significantly better in the case of IMPT (2F-5F). In the urethra, the best sparing was achieved only by IMPT-5F.

CONCLUSIONS

Stereotactic radiotherapy with SIB for localized prostate cancer is feasible with all the investigated techniques. Concerning IMPT, the two-beam technique does not seem to have a greater advantage compared to the standard techniques; the 5-beam technique seems more promising also accounting for the range uncertainty.

Visualizing the urethra by magnetic resonance imaging without usage of a catheter for radiotherapy of prostate cancer

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Post urination MRI is useful for urethra-sparing radiotherapy treatment planning.

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This prospective clinical trial included 11 prostate cancer patients.

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Post urination MRI is the identification method of prostatic urinary tract in non-invasive manner.

The urethra position may shift due to the presence/absence of the catheter. Our proposed post-urination-magnetic resonance imaging (PU-MRI) technique is possible to identify the urethra without catheter. We aimed to verify the inter-operator difference in contouring the urethra by PU-MRI. The mean values of the evaluation indices of dice similarity coefficient, mean slice-wise Hausdorff distance, and center coordinates were 0.93, 0.17 mm, and 0.36 mm for computed tomography, and 0.75, 0.44 mm, and 1.00 mm for PU-MRI. Therefore, PU-MRI might be useful for identifying the prostatic urinary tract without using a urethral catheter.

Clinical trial registration: Hokkaido University Hospital for Clinical Research (018-0221).

X-change symposium: status and future of modern radiation oncology-from technology to biology

Future radiation oncology encompasses a broad spectrum of topics ranging from modern clinical trial design to treatment and imaging technology and biology. In more detail, the application of hybrid MRI devices in modern image-guided radiotherapy; the emerging field of radiomics; the role of molecular imaging using positron emission tomography and its integration into clinical routine; radiation biology with its future perspectives, the role of molecular signatures in prognostic modelling; as well as special treatment modalities such as brachytherapy or proton beam therapy are areas of rapid development. More clinically, radiation oncology will certainly find an important role in the management of oligometastasis. The treatment spectrum will also be widened by the rational integration of modern systemic targeted or immune therapies into multimodal treatment strategies. All these developments will require a concise rethinking of clinical trial design. This article reviews the current status and the potential developments in the field of radiation oncology as discussed by a panel of European and international experts sharing their vision during the "X-Change" symposium, held in July 2019 in Munich (Germany).

Analysis of Radiation Dose/Volume Effect Relationship for Anorectal Morbidity in Children Treated for Pelvic Malignancies

PURPOSE

To examine dose-volume effect relationships for anorectal morbidity in children treated with image-guided brachytherapy for pelvic tumors.

METHODS AND MATERIALS

Medical records of all consecutive children with pelvic tumors treated in our center and receiving image-guided pulsed-dose-rate brachytherapy with or without external beam radiation therapy (EBRT) between 2005 and 2019 were reviewed. The effect of the minimal doses to the most exposed 0.5 cm³, 1 cm³, and 2 cm³ of the anorectum (respectively: D_0.5cm³, D_1cm³, and D_2cm³), total reference air kerma (TRAK), and volume of 100% isodose was examined for anorectal toxicities.

RESULTS

Seventy-eight consecutive children were included. Median age was 2.9 years (range, 0.8-14.9 years). Most of the tumors were bladder or prostate (67%) or vaginal (22%) rhabdomyosarcoma. Six patients received EBRT in addition to brachytherapy. Median follow-up was 21.3 months. At last follow-up, 30 children (38%) had experienced Common Terminology Criteria for Adverse Events version 5 grade ≥1 acute or late anorectal events: 24% had grade 1 events, 7.7% had grade 2 events, and 6.4% had grade 3 events. No toxicity greater than grade 3 was observed (eg, fistula or stricture). In univariate analysis, the D_0.5cm³ and D_1cm³ were significant for probability of grade 1 to 3 (P = .009 and P = .017, respectively) and grade 2 to 3 anorectal morbidity (P = .007 and P = .049, respectively). There was no significant correlation for D_2cm³ (P = .057 for grade 1-3; P = .407 for grade 2-3). A 10% probability (95% confidence interval, 4%-20%) for anorectal toxicity of grade 2 or greater was reached for a D_0.5cm³ = 52 Gy. The age, EBRT use, TRAK, and treated volume values were not significant.

CONCLUSIONS

To our knowledge, this study is the first to show a significant dose-volume effect relationships for anorectal morbidity in children undergoing treatment with brachytherapy. Integrating these data into brachytherapy treatment planning could help to optimize the therapeutic index in these young patients.

Biological dose summation of intensity-modulated arc therapy and image-guided high-dose-rate interstitial brachytherapy in intermediate- and high-risk prostate cancer

Purpose

To present an alternative method for summing biologically effective doses of intensity-modulated arc therapy (IMAT) as teletherapy (TT), with interstitial high-dose-rate (HDR) brachytherapy (BT) boost in prostate cancer. Total doses using IMAT boost was compared with BT boost using our method.

Material and methods

Initially, 25 IMAT TT plus interstitial HDR-BT plans were included, and additional plans using IMAT TT boost were created. The prescribed dose was 2/44 Gy to the whole pelvis, 2/60 Gy to the prostate and seminal vesicles, and 1 × 10 Gy BT or 2/18 Gy IMAT TT to the prostate. Teletherapy computed tomography (CT) was registered with ultrasound (US) of BT, and the most exposed volume of critical organs in BT were identified on these CT images. The minimal dose of these from IMAT TT was summed with their BT dose, and these EQD₂ doses were compared using BT vs. IMAT TT boost. This method was compared with uniform dose conception (UDC).

Results

D₉₀ of the prostate was significantly higher with BT than with IMAT TT boost: 99.3 Gy vs. 77.9 Gy, p = 0.0034. The D₂ to rectum, bladder, and hips were 50.3 Gy vs. 76.8 Gy (p = 0.0117), 64.7 Gy vs. 78.3 Gy (p = 0.0117), and 41.9 Gy vs. 50.6 Gy (p = 0.0044), while D_0.1 to urethra was 96.1 Gy vs. 79.3 Gy (p = 0.0180), respectively. UDC overestimated D₂ (rectum) by 37% (p = 0.0117), D₂ (bladder) by 5% (p = 0.0214), and underestimated D_0.1 (urethra) by 1% (p = 0.0277).

Conclusions

Based on our biological dose summation method, the total dose of prostate is higher using BT boost than the IMAT. BT boost yields lower rectum, bladder, and hips doses, but higher dose to urethra. UDC overestimates rectum and bladder dose and underestimates the dose to urethra.

Modern development of high-dose-rate brachytherapy

Brachytherapy is an invasive therapy with placement of radiation source into or near the tumor. The difference between planning target volume and clinical target volume is minimal, and the dose out of the tumor reduces rapidly due to the inverse-square law. High-dose-rate brachytherapy enables three-dimensional image guidance, and currently, tumor dose as well as doses of the surrounding normal structures can be evaluated accurately. High-dose-rate brachytherapy is the utmost precision radiation therapy even surpassing carbon ion therapy. Biological disadvantages of high-dose rate have been overcome by the fractional irradiation. High-dose-rate brachytherapy is indispensable in the definitive radiation therapy of cervical cancer. Also in prostate cancer and breast cancer, high-dose-rate brachytherapy plays a significant role. Brachytherapy requires techniques and skills of radiation oncologists at the time of invasive placement of the radiation source into the tumor area. Education of young radiation oncologists is most urgent and important.

Interstitial high-dose-rate brachytherapy as a boost in synchronous prostate and rectal cancer treatment: case report and literature review

PURPOSE

Prostate and colorectal cancers are the first and the third most popular malignancies in male population, in which some patients may develop these tumors metachronously or synchronously. At present, there are no standard recommendations, and oncologists need to provide an optimal management for two different cancers with an acceptable risk of possible treatment of adverse effects.

MATERIAL AND METHODS

This case report presents the treatment of a 61-year-old patient suffering from synchronous prostate and rectal cancer. Both malignancies were locally advanced, histologically proven, and defined as cT2cN0M0 stage prostate and cT3N2M0 stage rectal adenocarcinoma.

RESULTS

Multidisciplinary treatment team decided on synchronous radical treatment of both malignancies. The patient was qualified to long-term androgen deprivation therapy (ADT) and preoperative chemoradiation, with a total dose of 50.4 Gy in 28 fractions delivered with intensity modulated radiation therapy/image-guided radiation therapy (IMRT/IGRT) to a proper prostatic and rectal gross and nodal clinical target volume (CTV) with concurrent 5-fluorouracil. Additional dose of 15 Gy in a single fraction was delivered to prostate with interstitial HDR brachytherapy within a week after external beam radiotherapy (EBRT). After 8 weeks, the patient underwent sphincter-sparing surgery, with total mesorectal excision. Treatment tolerance was good, and genitourinary toxicity was not observed until now. At present, the patient is 45 months after completion of chemoradiation and surgery. Current prostate specific antigen (PSA) level is < 0.003 ng/ml, with no evidence of locoregional recurrence or distant metastases. Patient completed long-term ADT.

CONCLUSIONS

High-dose-rate (HDR) brachytherapy as a boost seems to be well-tolerated and effective option for delivering proper treatment dose to prostate in case of simultaneous treatment of rectal and prostate cancer.

Needle-free cervical cancer treatment using helical multishield intracavitary rotating shield brachytherapy with the 169 Yb Isotope

PURPOSE

To assess the capability of an intracavitary ¹⁶⁹ Yb-based helical multishield rotating shield brachytherapy (RSBT) delivery system to treat cervical cancer. The proposed RSBT delivery system contains a pair of 1.25 mm thick platinum partial shields with 45° and 180° emission angles, which travel in a helical pattern within the applicator.

METHODS

A helically threaded tandem applicator with a 45° tandem curvature containing a helically threaded catheter was designed. A 0.6 mm diameter ¹⁶⁹ Yb source with a length of 10.5 mm was simulated. A 37-patient treatment planning study, based on Monte Carlo dose calculations using MCNP5, was conducted with high-risk clinical target volumes (HR-CTVs) of 41.2-192.8 cm³ (average ± standard deviation of 79.9 ± 35.8 cm³ ). All patients were assumed to receive 25 fractions of 1.8 Gy of external beam radiation therapy (EBRT) before receiving 5 fractions of high-dose-rate brachytherapy (HDR-BT). For each patient, ¹⁹² Ir-based intracavitary (IC) HDR-BT, ¹⁹² Ir-based intracavitary/interstitial (IC/IS) HDR-BT using a hybrid applicator with eight IS needles, and ¹⁶⁹ Yb-based RSBT plans were generated.

RESULTS

For the IC, IC/IS, and RSBT treatment plans, 38%, 84%, and 86% of the plans, respectively, met the planning goal of an HR-CTV D₉₀ (minimum dose to hottest 90%) of 85 Gy_EQD2 (α/β = 10 Gy). Median (25th percentile, 75th percentile) treatment times for IC, IC/IS, and RSBT were 11.71 (6.62, 15.40) min, 68.00 (45.02, 80.02) min, and 25.30 (13.87, 35.39) min, respectively. ¹⁹² Ir activities ranging from 159.1-370 GBq (4.3-10 Ci) and ¹⁶⁹ Yb activities ranging from 429.2-999 GBq (11.6-27 Ci) were used, which correspond to the same clinical ranges of dose rates at 1 cm off-source-axis in water. Extra needle insertion and planning time beyond that needed for intracavitary-only approaches was accounted for in the IC/IS treatment time calculations.

CONCLUSION

¹⁶⁹ Yb-based RSBT for cervical cancer met the HR-CTV D₉₀ goal of 85 Gy in a greater percentage of the patients considered than IC/IS (86% vs 84%, respectively) and can reduce overall treatment time relative to IC/IS. ¹⁶⁹ Yb-based RSBT could be used to replace IC/IS in instances where IC/IS treatment is not available, especially in instances when HR-CTV volumes are ≥30 cm³ .

A planning study of focal dose escalations to multiparametric MRI-defined dominant intraprostatic lesions in prostate proton radiation therapy

OBJECTIVES

The purpose of this study is to investigate the dosimetric effect and clinical impact of delivering a focal radiotherapy boost dose to multiparametric MRI (mp-MRI)-defined dominant intraprostatic lesions (DILs) in prostate cancer using proton therapy.

METHODS

We retrospectively investigated 36 patients with pre-treatment mp-MRI and CT images who were treated using pencil beam scanning (PBS) proton radiation therapy to the whole prostate. DILs were contoured on co-registered mp-MRIs. Simultaneous integrated boost (SIB) plans using intensity-modulated proton therapy (IMPT) were created based on conventional whole-prostate-irradiation for each patient and optimized with additional DIL coverage goals and urethral constraints. DIL dose coverage and organ-at-risk (OAR) sparing were compared between conventional and SIB plans. Tumor control probability (TCP) and normal tissue complication probability (NTCP) were estimated to evaluate the clinical impact of the SIB plans.

RESULTS

Optimized SIB plans significantly escalated the dose to DILs while meeting OAR constraints. SIB plans were able to achieve 125, 150 and 175% of prescription dose coverage in 74, 54 and 17% of 36 patients, respectively. This was modeled to result in an increase in DIL TCP by 7.3-13.3% depending on α / β and DIL risk level.

CONCLUSION

The proposed mp-MRI-guided DIL boost using proton radiation therapy is feasible without violating OAR constraints and demonstrates a potential clinical benefit by improving DIL TCP. This retrospective study suggested the use of IMPT-based DIL SIB may represent a strategy to improve tumor control.

ADVANCES IN KNOWLEDGE

This study investigated the planning of mp-MRI-guided DIL boost in prostate proton radiation therapy and estimated its clinical impact with respect to TCP and NTCP.

Moderately hypofractionated carbon ion radiotherapy for prostate cancer; a prospective observational study "GUNMA0702"

BACKGROUND

Carbon ion Radiotherapy for prostate cancer is widely used, however reports are limited from single institute or short follow up. We performed a prospective observational study (GUNMA0702) to evaluate the feasibility and efficacy of carbon ion radiotherapy for localized and locally advanced prostate cancer.

METHODS

Between June 2010 and August 2013, 304 patients with localized prostate cancer were treated, with a median follow-up duration of 60 months. All patients received carbon ion radiotherapy with 57.6 Gy (RBE) in 16 fractions over 4 weeks. Hormonal therapy was given according to the risk group. Toxicity was reported according to the Common Toxicity Criteria for Adverse Event, Version 4.0 by the National Cancer Institute.

RESULTS

The overall 5-year biochemical relapse-free rate was 92.7%, with rates of 91.7, 93.4, and 92.0% in low-risk, intermediate-risk, and high-risk patients, respectively. The 5-year local control and overall survival rates were 98.4 and 96.6%, respectively. Acute grade 3 or greater toxicity was not observed. Late grade 2 and grade 3 genitourinary and gastrointestinal toxicity rates were 9 and 0.3%, and 0.3, and 0%, respectively.

CONCLUSIONS

The present protocol of carbon ion radiotherapy for prostate cancer provided low genitourinary and gastrointestinal toxicity with good biochemical control within 5 years.

TRIAL REGISTRATION

University Medical Information Network Clinical Trial Registry number: UMIN000003827.

Maximum RBE change in 192Ir, 125I, and 169Yb brachytherapy and the corresponding effect on treatment planning

PURPOSE

The purpose of this study was to examine RBE variation as a function of distance from the radioactive source, and the potential impact of this variation on a realistic prostate brachytherapy treatment plan.

METHODS

Three brachytherapy sources (¹²⁵I, ¹⁹²Ir, and ¹⁶⁹Yb) were modelled in Geant4 Monte Carlo code, and the resulting electron energy spectrum in water in 3D space around these sources was scored (voxel size of 2 mm³). With this energy spectrum, microdosimetric techniques were used to calculate the maximum RBE, RBE_M, as a function of distance from the source. RBE_M of ¹²⁵I relative to ¹⁹²Ir was calculated in order to validate simulations against literature; all other RBE_M calculations were done by normalizing electron fluence at various distances to the source position. In order to examine the impact of RBE_M variation in treatment planning, a realistic ¹⁹²Ir prostate plan was re-evaluated in terms of RBE instead of absorbed dose.

RESULTS

The RBE_M of ¹²⁵I, ¹⁹²Ir, and ¹⁶⁹Yb at 8 cm away from the source was 0.994 (+/-0.002), 1.030 (+/-0.003), and 1.066 (+/-0.008), respectively. RBE_M in the HDR prostate treatment plan exhibited several hot (+3.6% in RBE_M) spots.

CONCLUSIONS

The large increase RBE_M observed in ¹⁶⁹Yb has not yet been described in the literature. Despite the presence of radiobiological hotspots in the HDR treatment, these variations are likely nominal and clinically insignificant.

Safety and efficacy of CT-guided radioactive iodine-125 seed implantation assisted by a 3D printing template for the treatment of thoracic malignancies

OBJECTIVE

To ascertain the safety and efficacy of radioactive iodine-125 seed implantation (RISI) for the treatment of thoracic tumors.

METHODS

Clinical patients with primary or metastatic tumors in the chest treated with RISI were analyzed. The RISI process included the following stages: preoperative planning, template design and 3D printing, CT-guided RISI assisted by a template, and postoperative dosimetric verification. The prescribed dose was ≥ 80 Gy. The main analytic measures were the local control (LC) rate and toxicity.

RESULTS

From April 2015 to July 2018, a total of 92 patients, including 41 with lung cancer and 51 with lung metastases, were analyzed. The median lesion diameter was 5 cm. The median postoperative D90 was 142.6 Gy. The median follow-up was 10.7 months. The overall survival rates at 1 year and 3 years were 59.7% and 22.2%, respectively. The LC rates at 1 year and 3 years were 64.9% and 32.8%, respectively. The LC rates at 3 years for patients with D90 < 140 Gy and D90 > 140 Gy were 23.1% and 54.3%, respectively (P = 0.014). The LC rate of metastatic lung cancer was more favorable than that of primary lung cancer. The multivariate analyses showed that the dose and lesion type were independent factors for LC (P < 0.05). No factors were related to OS. The incidence of pneumothorax and hemoptysis was 35.8% and 3.2%, respectively. Few cases of radiotherapy-related toxicity effects were observed.

CONCLUSIONS

RISI may be safe and efficacious and is associated with few complications during the treatment of thoracic tumors. If patients need local treatment and surgery or radiotherapy is not available, RISI could be considered.

Radiation-related Adverse Effects of CT-guided Implantation of 125I Seeds for Thoracic Recurrent and/or Metastatic Malignancy

During radioactive Iodine-125 seed implantation (RISI), Iodine-125 radionuclide is implanted directly into a lesion and kills tumor cells by steadily emitting radiation. In our study, we analyzed the adverse effects of RISI for thoracic malignancy, and investigated the safety, dosage, and adverse effects of RISI for these cases. Between June 2007 and January 2018, 77 patients with thoracic recurrent and/or metastatic tumors who underwent CT-guided RISI were enrolled. Radiation-related adverse effects were analyzed, including pneumonia, esophagitis, hemorrhage, fistula, skin injury, heart injury, and spinal cord injury. We used the Common Terminology Criteria for Adverse Events (CTCAE) v4.03 to evaluate adverse effects and analyzed the relationship between adverse effects and dosimetric parameters of organs at risk (OAR), including D0.1cc, D2cc, Dmean, and V20. The results of the study were as follows: The median follow-up period was 11 months. The median postoperative dose (D90) was 122 Gy (45.7–241.8 Gy). Three patients (3.9%) showed radiation pneumonitis of grade ≥2. Two patients (2.6%) showed radiation-induced esophagitis of grade ≥2. One patient (1.3%) showed an esophageal fistula. Two patients (2.6%) had a tracheal fistula. Five patients (6.5%) had radiation-related skin reactions. One patient (1.3%) reported chest wall pain, while three (3.9%) showed hemoptysis. No patients showed radiation myelitis or cardiotoxicity. The mean D2cc of organs at risk were 165.7 Gy (lung), 10.61 Gy (esophagus), 10.25 Gy (trachea), 18.07 Gy (blood vessel), 12.64 Gy (heart), 14.77 Gy (spinal cord), 17.47 Gy (skin). Dosimetric parameters, such as D0.1cc, D2cc and Dmean, were higher in patients with toxic reactions (above the upper limit of 95% confidence interval among the overall data). Chi-square test showed that skin D0.1cc > 600 Gy, D2cc > 500 Gy, and Dmean >90 Gy were associated with grade ≥2 radiation dermatitis (p < 0.05), but no clear dose-toxicity correlation was found in other OARs. So, we concluded that the overall incidence of toxicity and adverse effects from RISI for the treatment of thoracic tumors is low. The dose-toxicity characteristics have not been fully defined. Doses within the upper limit of the 95% confidence interval may be considered safe. This was a retrospective analysis, and follow-up period was minimal, indicating possible limitations of this study.

Quality of life in prostate cancer patients receiving particle radiotherapy: A review of the literature

Proton and carbon ion radiotherapy for the treatment of prostate cancer is associated with a lower incidence of adverse events than conventional radiotherapy. There are few reports on the quality of life of patients treated with particle therapy, and limited patient-reported outcomes. Analysis of quality of life is important for patients treated with radiotherapy alone or in combination with hormonal therapy, and long-term results, dose fractionation and costs need to be included in the analysis. This information might help both clinical decision-making and selection of appropriate treatments according to the individual needs of patients. This study reviews the literature on the quality of life and outcomes of patients treated with particle therapy, and discusses future directions.

[Brachytherapy: When needs overtake care offer]

Brachytherapy has the unique characteristic of being able to deliver high doses to a very localized volume, and remains one of the radiotherapy techniques that has an unparalleled therapeutic index. However, its use has been declining in the past years. Globally, only 55 to 88 % of patients with locally advanced cervical cancer benefit from utero-vaginal brachytherapy, despite the fact that it is proven to enhance both progression-free and overall survival. A decline in the use of low dose rate brachytherapy has likewise been described in the treatment of low-risk and favorable intermediate-risk prostate cancers. Several factors could explain this. First, the radiation oncologists who have the proficiency to perform brachytherapy seems to be inadequate, as it is a technique that requires training and expertise for optimal applications. In many cancer care centers, the caseload is insufficient to provide this experience. Second, the increasing use of technically advanced external beam radiation therapy, such as intensity modulated radiation therapy, offers an easier substitute with more lucrative benefits, resulting in decreased utilization of brachytherapy. However, when brachytherapy is not delivered, a poorer survival rate is reported in locally advanced cervical cancer, and is suggested in intermediate and high-risk prostate cancer. The increasing level of evidence of treatment with brachytherapy necessitates an improvement in its accessibility by having more radiation oncologists as well as cancer centers equipped to perform the procedure.

Template-assisted 192Ir-based stereotactic ablative brachytherapy as a neoadjuvant treatment for operable peripheral non-small cell lung cancer: a phase I clinical trial

Purpose

To evaluate safety, feasibility, and efficacy of template-assisted ¹⁹²Ir-based stereotactic ablative brachytherapy (SABT), combined with surgery for peripheral non-small cell lung cancer (NSCLC).

Material and methods

Patients with pathologically confirmed operable peripheral NSCLC, who underwent template-assisted SABT (30 Gy delivered in one fraction) and were scheduled for tumor resection 4-6 weeks after SABT were included in this study. The perioperative adverse reactions of SABT were recorded to evaluate safety and feasibility of SABT for neoadjuvant therapy. Dosimetric data from both simulated and actual plans were collected and compared. Imaging with ¹⁸F-fluorodeoxyglucose-positron emission tomography/computed tomography (¹⁸F-FDG-PET/CT) and dynamic contrast-enhanced computed tomography were scheduled before SABT and surgery to evaluate the efficacy of the neoadjuvant therapy with SABT.

Results

Patients did not experience any serious adverse events. None of the patients had a delay in receiving surgery. After 4-6 weeks, the indicators for the efficacy of neoadjuvant therapy significantly decreased in all patients: gross tumor volume (p < 0.001), maximum standardized uptake value (p < 0.001), tumor blood volume (p < 0.001), and tumor blood flow (p = 0.008). Dosimetric parameters in the delivered SABT plan slightly changed from the preoperative simulation, but the difference was not statistically significant (p > 0.05).

Conclusions

The efficacy of template-assisted SABT for neoadjuvant therapy was significant in operable peripheral NSCLC. Moreover, no serious adverse reactions were observed; when the coplanar template guidance technique was applied, dosimetric parameters were in good agreement between the actual SABT plan and the preoperative simulated plan.

SpaceOAR to improve dosimetric outcomes for monotherapy high-dose-rate prostate implantation in a patient with ulcerative colitis

High-dose-rate (HDR) brachytherapy is an attractive option for patients receiving definitive radiation therapy for prostate cancer with decreased overall dose to the pelvis. However, ulcerative colitis increases rectal toxicity risk and may be a contraindication. A synthetic hydrogel, SpaceOAR (Augmentix Inc., Waltham, MA, USA), can facilitate the use of HDR brachytherapy for patients where rectal toxicity is a limiting factor. SpaceOAR gel (13.19 cc) was utilized in a monotherapy HDR prostate treatment with Ir-192 under transrectal ultrasound guidance, with the intention of decreasing rectal dose. SpaceOAR gel was inserted transperineally into the patient 18 days prior to the procedure. The HDR brachytherapy procedure was tolerated without incident. All planning constraints were met, and the following dosimetry was achieved: Prostate - V_100% = 97.3%, V_150% = 35%, V_200% = 14.5%; Urethra - V_118% = 0%; Rectum - D_{2 cc} = 51.6%, V_75% = 0 cc. The rectum-catheter spacing was on average between 6-8 mm. Average spacing for our 10 most recent patients without SpaceOAR was 3 mm. SpaceOAR did not hinder or distort ultrasound imaging or increase treatment time. SpaceOAR successfully increases catheter-rectal wall spacing and decreases rectal dose due to improved planning capabilities, while decreasing the likelihood of rectal perforation. One application of this tool is presented to mitigate potential toxicities associated with ulcerative colitis. At five months, one week, and one day follow-up, the patient reported no bowel issues following HDR brachytherapy.

Proton therapy for prostate cancer: A review of the rationale, evidence, and current state

Men diagnosed with localized prostate cancer have many curative treatment options including several different radiotherapeutic approaches. Proton radiation is one such radiation treatment modality and, due to its unique physical properties, offers the appealing potential of reduced side effects without sacrificing cancer control. In this review, we examine the intriguing dosimetric rationale and theoretical benefit of proton radiation for prostate cancer and highlight the results of preclinical modeling studies. We then discuss the current state of the clinical evidence for proton efficacy and toxicity, derived from both large claim-based datasets and prospective patient-reported data. The result is that the data are mixed, and clinical equipoise persists in this area. We place these studies into context by summarizing the economics of proton therapy and the changing practice patterns of prostate proton irradiation. Finally, we await the results of a large prospective randomized clinical trial currently accruing and also a large prospective pragmatic comparative study which will provide more rigorous evidence regarding the clinical and comparative effectiveness of proton therapy for prostate cancer.

Phase I study of dose escalation to dominant intraprostatic lesions using high-dose-rate brachytherapy

Purpose

Radiation dose escalation for prostate cancer improves biochemical control but is limited by toxicity. Magnetic resonance spectroscopic imaging (MRSI) can define dominant intraprostatic lesions (DIL). This phase I study evaluated dose escalation to MRSI-defined DIL using high-dose-rate (HDR) brachytherapy.

Material and methods

Enrollment was closed early due to low accrual. Ten patients with prostate cancer (T2a-3b, Gleason 6-9, PSA < 20) underwent pre-treatment MRSI, and eight patients had one to three DIL identified. The eight enrolled patients received external beam radiation therapy to 45 Gy and HDR brachytherapy boost to the prostate of 19 Gy in 2 fractions. MRSI images were registered to planning CT images and DIL dose-escalated up to 150% of prescription dose while maintaining normal tissue constraints. The primary endpoint was genitourinary (GU) toxicity.

Results

The median total DIL volume was 1.31 ml (range, 0.67-6.33 ml). Median DIL boost was 130% of prescription dose (range, 110-150%). Median urethra V₁₂₀ was 0.15 ml (range, 0-0.4 ml) and median rectum V₇₅ was 0.74 ml (range, 0.1-1.0 ml). Three patients had acute grade 2 GU toxicity, and two patients had late grade 2 GU toxicity. No patients had grade 2 or higher gastrointestinal toxicity, and no grade 3 or higher toxicities were noted. There were no biochemical failures with median follow-up of 4.9 years (range, 2-8.5 years).

Conclusions

Dose escalation to MRSI-defined DIL is feasible. Toxicity was low but incompletely assessed due to limited patients’ enrollment.

High dose-rate brachytherapy in the treatment of prostate cancer

High dose-rate (HDR) brachytherapy involves delivery of a high dose of radiation to the cancer with great sparing of surrounding organs at risk. Prostate cancer is thought to be particularly sensitive to radiation delivered at high dose-rate or at high dose per fraction. The rapid delivery and high conformality of dose results in lower toxicity than that seen with low dose-rate (LDR) implants. HDR combined with external beam radiotherapy results in higher cancer control rate than external beam only, and should be offered to eligible high and intermediate risk patients. While a variety of dose and fractionations have been used, a single 15 Gy HDR combined with 40-50 Gy external beam radiotherapy results in a disease-free survival of over 90% for intermediate risk and 80% for high risk. HDR monotherapy in two or more fractions (e.g., 27 Gy in 2 fractions or 34.5 Gy in 3) is emerging as a viable alternative to LDR brachytherapy for low and low-intermediate risk patients, and has less toxicity. The role of single fraction monotherapy to a dose of 19-20 Gy is evolving, with some conflicting data to date. HDR should also be considered as a salvage approach for recurrent disease following previous external beam radiotherapy. A particular advantage of HDR in this setting is the ease of delivering focal treatments, which combined with modern imaging allows focal dose escalation with minimal toxicity. Trans-rectal ultrasound (TRUS) based planning is replacing CT-based planning as the technique of choice as it minimizes or eliminates the need to move the patient between insertion, planning and treatment delivery, thus ensuring high accuracy and reproducibility of treatment.

Dosimetric comparison of CT-guided iodine-125 seed stereotactic brachytherapy and stereotactic body radiation therapy in the treatment of NSCLC

This study aimed to assess the dosimetric differences between iodine-125 seed stereotactic brachytherapy (SBT) and stereotactic body radiation therapy (SBRT) in the treatment of non-small cell lung cancer (NSCLC). An SBT plan and an SBRT plan were generated for eleven patients with T1-2 NSCLC. Prescription of the dose and fractionation (fr) for SBRT was 48Gy/4fr. The planning aim for SBT was D90 (dose delivered to 90% of the target volume)≥120Gy. Student’s paired t test was used to compare the dosimetric parameters. The SBT and SBRT plans had comparable PTV D90 (104.73±2.10Gyvs.107.64±2.29Gy), and similar mean volume receiving 100% of the prescription dose (V100%) (91.65% vs.92.44%, p = 0.410). The mean volume receiving 150% of the prescribed dose (V150%) for SBT was 64.71%, whereas it was 0% for SBRT. Mean heterogeneity index (HI) deviation for SBT vs. SBRT was 0.73 vs. 0.19 (p<0.0001), and the mean conformity index (CI) for SBT vs. SBRT was 0.77 vs. 0.81 (p = 0.031). The mean lung doses (MLD) in SBT were significantly lower than those in SBRT (1.952±0.713 vs. 5.618±2.009, p<0.0001). In conclusion, compared with SBRT, SBT can generate a comparable dose within PTV, while the organs at risk (OARs) only receive a very low dose. But the HI and CI in SBT were lower than in SBRT.

The influence of inter-fractional anatomy variation on secondary cancer risk estimates following radiotherapy

PURPOSE

In silico studies comparing estimated risks of radiation-induced secondary cancer (SC) are frequently performed in assessment of radiotherapy techniques. Since inter-patient anatomy variations can result in considerable differences in estimated risk we aimed to explore the influence of inter-fractional organ motion patterns on SC risk.

METHODS

Volumetric modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT) plans were generated on the planning CT (pCT) scans of eight prostate cancer patients. In addition, the treatment plans were re-calculated on 8-9 repeat CTs (rCTs) of each patient acquired throughout the treatment course. Relative risk (RR) of SC (VMAT/IMPT) was calculated for the planned and the re-calculated dose distributions using the organ equivalent dose concept adapted to a linear and a bell-shaped competition dose-response model.

RESULTS

Day-to-day variations in anatomy lead to fluctuations in SC risk estimates of the same order of magnitude as those caused by inter-patient variations. Using the competition model, the RR range for bladder cancer based on the pCTs was 0.4-3.4, while a considerably wider range was found when including all rCTs (0.2-6.7). There was nevertheless a correlation in RR based on repeat CTs for individual patients, indicating that patient-specific SC risks could be estimated.

CONCLUSIONS

The estimated relative risks varied considerably across rCTs and could change the risk in favour of VMAT/IMPT depending on the anatomy of the day. The results demonstrate the importance of performing in silico studies of SC risk on a cohort of patients or multiple CTs when structures subject to organ motion are involved.

Accuracy and variability of high-dose-rate prostate brachytherapy needle tip localization using live two-dimensional and sagittally reconstructed three-dimensional ultrasound

PURPOSE

To measure the accuracy and variability of manual high-dose-rate (HDR) prostate brachytherapy (BT) needle tip localization using sagittally reconstructed three-dimensional (3D) transrectal ultrasound (TRUS) augmented with live two-dimensional (2D) sagittal TRUS.

METHODS AND MATERIALS

Ten prostate cancer patients underwent HDR-BT during which the sagittally assisted sagittally reconstructed (SASR) segmentation technique was completed in parallel with commercially available sagittally assisted axially reconstructed (SAAR) TRUS for comparison. The SASR technique makes use of live 2D ultrasound intraoperatively and allows needle tip updates using the final 3D image in the absence of image artifacts. These updates were repeated offline twice by two separate users. Needle end-length measurements were used to calculate insertion depth errors (IDEs) for each technique.

RESULTS

Images of 147 needles were analyzed. For the SASR technique, both users were confident in tip positions on the final 3D image within 3 mm for 52% of needles, so these tip positions were updated. For the remaining 48% of needles, the tip positions from the live 2D images were used. This SASR technique enabled the localization of all needles with IDEs within ±3 mm for 84% of needles and IDE range of [-6.2 mm, 5.9 mm], compared with 57% and [-8.1 mm, 7.7 mm] when using the commercially available SAAR technique.

CONCLUSIONS

The SASR technique mitigates the impact of 3D TRUS image artifacts on HDR-BT needle tip localization by incorporating live 2D sagittal TRUS intraoperatively and provides a statistically significant reduction in IDE variance compared with the routine SAAR technique.

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.

Prostate Cancer Radiation Therapy: What Do Clinicians Have to Know?

Radiotherapy (RT) for prostate cancer (PC) has steadily evolved over the last decades, with improving biochemical disease-free survival. Recently population based research also revealed an association between overall survival and doses ≥ 75.6 Gray (Gy) in men with intermediate- and high-risk PC. Examples of improved RT techniques are image-guided RT, intensity-modulated RT, volumetric modulated arc therapy, and stereotactic ablative body RT, which could facilitate further dose escalation. Brachytherapy is an internal form of RT that also developed substantially. New devices such as rectum spacers and balloons have been developed to spare rectal structures. Newer techniques like protons and carbon ions have the intrinsic characteristics maximising the dose on the tumour while minimising the effect on the surrounding healthy tissue, but clinical data are needed for confirmation in randomised phase III trials. Furthermore, it provides an overview of an important discussion issue in PC treatment between urologists and radiation oncologists: the comparison between radical prostatectomy and RT. Current literature reveals that all possible treatment modalities have the same cure rate, but a different toxicity pattern. We recommend proposing the possible different treatment modalities with their own advantages and side-effects to the individual patient. Clinicians and patients should make treatment decisions together (shared decision-making) while using patient decision aids.

A treatment planning study comparing tomotherapy, volumetric modulated arc therapy, Sliding Window and proton therapy for low-risk prostate carcinoma

BACKGROUND

Comparing radiation treatment plans to ascertain the optimal intensity-modulated radiation technique for low-risk prostate cancer.

METHODS

Treatment plans for 20 randomly selected patients were generated using the same dose objectives. A dosimetric comparison was performed between various intensity-modulated techniques, including protons. All treatment plans provided conventional treatment with 79.2Gy. Dosimetric indices for the target volume and organs at risk (OAR), including homogeneity index and four conformity indices were analyzed.

RESULTS

No statistically significant differences between techniques were observed for homogeneity values. Dose distributions showed significant differences at low-to-medium doses. At doses above 50Gy all techniques revealed a steep dose gradient outside the planning target volume (PTV). Protons demonstrated superior rectum sparing at low-to-higher doses (V10-V70, P < .05) and bladder sparing at low-to-medium doses (V10-V30, P < .05). Helical tomotherapy (HT) provided superior rectum sparing compared to Sliding Window (SW) and Rapid Arc (RA) (V10-V70, P < .05). SW displayed superior bladder sparing compared to HT and RA (V10-V50, P < .05). Protons generated significantly higher femoral heads exposure and HT had superior sparing of those.

CONCLUSION

All techniques are able to provide a homogeneous and highly conformal dose distribution. Protons demonstrated superior sparing of the rectum and bladder at a wide dose spectrum. The radiation technique itself as well as treatment planning algorithms result in different OAR sparing between HT, SW and RA, with superior rectum sparing by HT and superior bladder sparing by SW. Radiation plans can be further optimized by individual modification of dose objectives dependent on treatment plan strategy.

Learning curve of MRI-based planning for high-dose-rate brachytherapy for prostate cancer

PURPOSE

To evaluate introduction of MRI-based high-dose-rate brachytherapy (HDRBT), including procedure times, dose-volume parameters, and perioperative morbidity.

METHODS AND MATERIALS

Study included 42 high-risk prostate cancer patients enrolled in a clinical protocol, offering external beam radiotherapy + two HDRBT 8.5 Gy boosts. Time was recorded for initiation of anesthesia (A), fixation of needle implant (B), end of MR imaging (C), plan approval (D), and end of HDRBT delivery (E). We defined time A-E as total procedure time, A-B as operating room time, B-C as MRI procedure time, C-D as treatment planning time, and D to E as treatment delivery time. Dose-volume parameters were retrieved from the dose planning system. Results from the first 21 patients were compared with the last 21 patients.

RESULTS

Total procedure time, operating room time, MRI procedure time, and treatment planning time decreased significantly from average 7.6 to 5.3 hours (p < 0.01), 3.6 to 2.4 hours (p < 0.01), 1.6 to 0.8 hours (p < 0.01), and 2.0 to 1.3 hours (p < 0.01), respectively. HDRBT delivery time remained unchanged at 0.5 hours. Clinical target volume prostate+3mmD90 fulfilled planning aim in 92% of procedures and increased significantly from average 8.3 to 9.0 Gy (p < 0.01). Urethral D0.1 cm(3) and rectal D2 cm(3) fulfilled planning aim in 78% and 95% of procedures, respectively, and did not change significantly. Hematuria occurred in (95%), hematoma (80%), moderate to strong pain (35%), and urinary retention (5%) of procedures.

CONCLUSIONS

After introduction of MRI-based HDRBT, procedure times were significantly reduced. D90 Clinical target volumeprostate+3mm fulfilled constraints in most patients and improved over time, but not at expense of an increased urethral or rectal dose.

Dosimetric and radiobiological impact of intensity modulated proton therapy and RapidArc planning for high-risk prostate cancer with seminal vesicles

INTRODUCTION

The purpose of this study was to evaluate the dosimetric and radiobiological impact of intensity modulated proton therapy (IMPT) and RapidArc planning for high-risk prostate cancer with seminal vesicles.

METHODS

Ten high-risk prostate cancer cases were included in this retrospective study. For each case, IMPT plans were generated using multiple field optimisation (MFO) technique (two fields) with XiO treatment planning system (TPS), whereas RapidArc plans were generated using double-arc technique (two full arcs) with Eclipse TPS. IMPT and RapidArc plans were optimised for a total prescription dose of 79.2 Gy (relative biological effectiveness (RBE)) and 79.2 Gy, respectively, using identical dose-volume constraints. IMPT and RapidArc plans were then normalised such that at least 95% of the planning target volume (PTV) received the prescription dose.

RESULTS

The mean and maximum PTV doses were comparable in IMPT plans (80.1 ± 0.3 Gy (RBE) and 82.6 ± 1.0 Gy (RBE) respectively) and RapidArc plans (80.3 ± 0.3 Gy and 82.8 ± 0.6 Gy respectively) with P = 0.088 and P = 0.499 respectively. The mean doses of the rectum and bladder were found to be significantly lower in IMPT plans (16.9 ± 5.8 Gy (RBE) and 17.5 ± 5.4 Gy (RBE) respectively) when compared to RapidArc plans (41.9 ± 5.7 Gy and 32.5 ± 7.8 Gy respectively) with P < 0.000 and P < 0.000 respectively. For the rectum, IMPT produced lower V₃₀ (21.0 ± 9.6% vs. 68.5 ± 10.0%; P < 0.000), V₅₀ (14.3 ± 5.8% vs. 45.0 ± 10.0%; P < 0.000) and V₇₀ (6.9 ± 3.4% vs. 12.8 ± 3.6%; P < 0.000) compared to RapidArc. For the bladder, IMPT produced lower V₃₀ (23.2 ± 7.0% vs. 50.9 ± 15.6%; P < 0.000) and V₅₀ (16.6 ± 5.4% vs. 25.1 ± 9.6%; P = 0.001), but similar V₇₀ (9.7 ± 3.5% vs. 10.5 ± 4.2%; P = 0.111) compared to RapidArc. RapidArc produced lower mean dose for both the right femoral head (19.5 ± 4.2 Gy vs. 27.4 ± 4.5 Gy (RBE); P < 0.000) and left femoral head (18.0 ± 4.3 Gy vs. 28.0 ± 5.6 Gy (RBE); P < 0.000). Both IMPT and RapidArc produced comparable bladder normal tissue complication probability (NTCP) (0.6 ± 0.2% vs. 0.5 ± 0.2%; P = 0.152). The rectal NTCP was found to be lower using IMPT (0.8 ± 0.7%) than using RapidArc (1.7 ± 0.7%) with P < 0.000.

CONCLUSION

Both IMPT and RapidArc techniques provided comparable mean and maximum PTV doses. For the rectum, IMPT produced better dosimetric results in the low-, medium- and high-dose regions and lower NTCP compared to RapidArc. For the bladder, the NTCP and dosimetric results in the high-dose region were comparable in both sets of plans, whereas IMPT produced better dosimetric results in the low- and medium-dose regions.

Identification of a rectal subregion highly predictive of rectal bleeding in prostate cancer IMRT

BACKGROUND AND PURPOSE

To identify rectal subregions at risks (SRR) highly predictive of 3-year rectal bleeding (RB) in prostate cancer IMRT.

MATERIALS AND METHODS

Overall, 173 prostate cancer patients treated with IMRT/IGRT were prospectively analyzed, divided into "training" (n=118) and "validation" cohorts (n=53). Dose-volume histograms (DVHs) were calculated in three types of rectal subregions: "geometric", intuitively defined (hemi-rectum,…); "personalized", obtained by non-rigid registration followed by voxel-wise statistical analysis (SRRp); "generic", mapped from SRRps, located within 8×8 rectal subsections (SRRg). DVHs from patients with and without RB were compared and used for toxicity prediction.

RESULTS

Training cohort SRRps were primarily within the inferior anterior hemi-rectum and upper anal canal, with 3.8Gy mean dose increase for Grade⩾1 RB patients. The SRRg, representing 15% of the absolute rectal volume, was located in 10 inferior-anterior rectal subsections. V18-V70 for SRRps and V58-V65 for SRRg were significantly higher for RB patients than non-RB. Maximum areas under the curve (AUCs) for SRRp and SRRg RB prediction were 71% and 64%, respectively. The validation cohort confirmed the predictive value of SRRg for Grade⩾1 RB. The total cohort confirmed the predictive value of SRRg for Grade⩾2 RB. Geometrical subregions were not RB predictors.

CONCLUSION

The inferior-anterior hemi anorectum was highly predictive of RB.