Magnetic resonance imaging in postprostatectomy radiotherapy planning

ESTRO ACROP guideline on prostate bed delineation for postoperative radiotherapy in prostate cancer

Purpose/Objective

Radiotherapy to the prostate bed is a potentially curative salvage option after radical prostatectomy. Although prostate bed contouring guidelines are available in the literature, important variabilities exist. The objective of this work is to provide a contemporary consensus guideline for prostate bed delineation for postoperative radiotherapy.

Methods

An ESTRO-ACROP contouring consensus panel consisting of 11 radiation oncologists and one radiologist, all with known subspecialty expertise in prostate cancer, was established. Participants were asked to delineate the prostate bed clinical target volumes (CTVs) in 3 separate clinically relevant scenarios: adjuvant radiation, salvage radiation with PSA progression, and salvage radiation with persistently elevated PSA. These cases focused on the presence of positive surgical margin, extracapsular extension, and seminal vesicles involvement. None of the cases had radiographic evidence of local recurrence on imaging. A single computed tomography (CT) dataset was shared via FALCON platform and contours were performed using EduCaseTM software. Contours were analyzed qualitatively using heatmaps which provided a visual assessment of controversial regions and quantitatively analyzed using Sorensen-Dice similarity coefficients. Participants also answered case-specific questionnaires addressing detailed recommendations on target delineation. Discussions via electronic mails and videoconferences for final editing and consensus were performed.

Results

The mean CTV for the adjuvant case was 76 cc (SD = 26.6), salvage radiation with PSA progression was 51.80 cc (SD = 22.7), and salvage radiation with persistently elevated PSA 57.63 cc (SD = 25.2). Compared to the median, the mean Sorensen-Dice similarity coefficient for the adjuvant case was 0.60 (SD 0.10), salvage radiation with PSA progression was 0.58 (SD = 0.12), and salvage radiation with persistently elevated PSA 0.60 (SD = 0.11). A heatmap for each clinical scenario was generated. The group agreed to proceed with a uniform recommendation for all cases, independent of the radiotherapy timing. Several controversial areas of the prostate bed CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences where the panel achieved consensus on the prostate bed CTV to be used as a novel guideline for postoperative prostate cancer radiotherapy.

Conclusion

Variability was observed in a group formed by experienced genitourinary radiation oncologists and a radiologist. A single contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in prostate bed delineation, independent of the indication.There is important variability in existing contouring guidelines for postoperative prostate bed (PB) radiotherapy (RT) after radical prostatectomy. This work aimed at providing a contemporary consensus guideline for PB delineation. An ESTRO ACROP consensus panel including radiation oncologists and a radiologist, all with known subspecialty expertise in prostate cancer, delineated the PB CTV in 3 scenarios: adjuvant RT, salvage RT with PSA progression, and salvage RT with persistently elevated PSA. None of the cases had evidence of local recurrence. Contours were analysed qualitatively using heatmaps for visual assessment of controversial regions and quantitatively using Sorensen-Dice coefficient. Case-specific questionnaires were also discussed via e-mails and videoconferences for consensus. Several controversial areas of the PB CTV were identified based on both heatmaps and questionnaires. This formed the basis for discussions via videoconferences. Finally, a contemporary ESTRO-ACROP consensus guideline was developed to address areas of dissonance and improve consistency in PB delineation, independent of the indication.

A Prospective Study Assessing the Post-Prostatectomy Detection Rate of a Presumed Local Failure at mpMR with Either 64CuCl2 or 64CuPSMA PET/CT

Simple Summary

The role of PET/CT with two novel tracers was investigated in prostate cancer patients with both a biochemical failure after surgery and a presumed local failure at multiparametric MR. Overall, both PET tracers detected only about 50% of local failures. Therefore, multiparametric MR remains the exam of choice to investigate the prostatic fossa in patients who fail surgery.

Abstract

Background: We aimed assess the detection rate (DR) of positron emission tomography/computed tomography with two novel tracers in patients referred for salvage radiotherapy (sRT) with a presumed local recurrence at multiparametric magnetic resonance (mpMR) after radical prostatectomy (RP). Methods: The present prospective study was conducted at a single institution between August 2017 and June 2020. Eligibility criteria were undetectable PSA after RP; subsequent biochemical recurrence (two consecutive PSA rises to 0.2 ng/mL or greater); a presumed local failure at mpMR; no distant metastases at ¹⁸F-fluorocholine PET/CT (CH/PET); no previous history of androgen deprivation therapy. Patients were offered both ⁶⁴CuCl₂ PET/CT (CU/PET) and ⁶⁴Cu-PSMA PET/CT (PSMA/PET) before sRT. After image co-registration, PET findings were compared to mpMR ones in terms of DR and independent predictors of DR investigated at logistic regression. Results: A total of 62 patients with 72 nodules at mpMR were accrued. Compared to mpMR (DR = 100%, 95%CI: 94.9–100%), DRs were 47.2% (95%CI: 36.1–58.6%) and 54.4% (95%CI: 42.7–65.7%) for CU/PET and PSMA/PET, respectively (p < 0.001 for both). Both experimental PET/CT performed particularly poorly at PSA levels consistent with early sRT. Conclusions: The two novel radiotracers are inferior to mpMR in restaging the prostatic fossa for sRT planning purposes, particularly in the context of early salvage radiotherapy.

Response on DCE-MRI predicts outcome of salvage radiotherapy for local recurrence after radical prostatectomy

OBJECTIVE

To assess the predictive role of response on dynamic contrast enhancement on magnetic resonance imaging (DCE-MRI) of visible local lesions in the setting of salvage radiotherapy (sRT) after radical prostatectomy.

METHODS

All patients referred for sRT for biochemical failure after radical prostatectomy from February 2014 to September 2016 were considered eligible if they had been restaged with DCE-MRI and had been found to have a visible lesion in the prostatic bed, but no distant/nodal disease on choline positron emission tomography (PET)-computed tomography (CT). Eligible patients were contacted during follow-up and offered reimaging with serial DCE-MRI until lesion resolution. Complete response (CR) was defined as the disappearance of the target lesion on DCE-MRI; prostate-specific antigen (PSA) recurrence was defined as a 0.2 ng/mL PSA rise above the nadir. Median follow-up after sRT was 41.5 months (range, 12.1-61.2 months).

RESULTS

Fifty-nine patients agreed to undergo repeated DCE-MRI for a total of 64 studied lesions. Overall, 57 lesions (89.1%) showed a CR after 1 (51 patients) or 2 (6 patients) scans, while 7 lesions did not show any change (no response [NR]). At 42 months, no evidence of biochemical disease (bNED) survival was 74.7±6.4% and 64.3±21.0% for patients with CR and NR lesions, respectively (hazard ratio [HR], 3.181; 95% confidence interval [CI], 0.157-64.364; p = 0.451). When only patients treated with sRT without androgen deprivation were selected (n = 41), bNED survival rates at 42 months were 72.1±8.0% and 0, respectively (HR, 52.830; 95% CI, 1.893-1474.110; p = 0.020).

CONCLUSIONS

Patients whose lesions disappear during follow-up have a better outcome than those with unchanged lesions after sRT alone.

Volumetry of the dominant intraprostatic tumour lesion: intersequence and interobserver differences on multiparametric MRI

OBJECTIVE

To establish the interobserver reproducibility of tumour volumetry on individual multiparametric (mp) prostate MRI sequences, validate measurements with histology and determine whether functional to morphological volume ratios reflect Gleason score.

METHODS

41 males with prostate cancer treated with prostatectomy (Cohort 1) or radical radiotherapy (Cohort 2), who had pre-treatment mpMRI [T2 weighted (T2W) MRI, diffusion-weighted (DW)-MRI and dynamic contrast-enhanced (DCE)-MRI], were studied retrospectively. Dominant intraprostatic lesions (DIPLs) were manually delineated on each sequence and volumes were compared between observers (n = 40 analyzable) and with radical prostatectomy (n = 20). Volume ratios of DW-MRI and DCE-MRI to T2W MRI were documented and compared between Gleason grade 3 + 3, 3 + 4 and 4 + 3 or greater categories.

RESULTS

Limits of agreement of DIPL volumes between observers were: T2W MRI 0.9, -1.1 cm3, DW-MRI 1.3, -1.7 cm3 and DCE-MRI 0.74, -0.89 cm3. In Cohort 1, T2W volumes overestimated fixed specimen histological volumes (+33% Observer 1, +16% Observer 2); DW- and DCE-MRI underestimated histological volume, the latter markedly so (-32% Observer 1, -79% Observer 2). Differences between T2W, DW- and DCE-MRI volumes were significant (p < 10-8). The ratio of DW-MRI volume (73.9 ± 18.1% Observer 1, 72.5 ± 21.9% Observer 2) and DCE-MRI volume (42.6 ± 24.6% Observer 1, 34.3 ± 24.9% Observer 2) to T2W volume was significantly different (p < 10-8), but these volume ratios did not differ between the Gleason grades.

CONCLUSION

The low variability of the DIPL volume on T2W MRI between Observers and agreement with histology indicates its suitability for delineation of gross tumour volume for radiotherapy planning. The volume of cellular tumour represented by DW-MRI is greater than the vascular (DCE) abnormality; ratios of both to T2W volume are independent of Gleason score. Advances in knowledge: (1) Manual volume measurement of tumour is reproducible within 1 cm3 between observers on all sequences, confirming suitability across observers for radiotherapy planning. (2) Volumes derived on T2W MRI most accurately represent in vivo lesion volumes. (3) The proportion of cellular (DW-MRI) or vascular (DCE-MRI) volume to morphological (T2W MRI) volume is not affected by Gleason score.

Proposal for magnetic resonance imaging-guided salvage radiotherapy for prostate cancer

BACKGROUND

A subset of patients experience a biochemical recurrence following radical prostatectomy. Radiotherapy can salvage those patients, provided that all disease is encompassed within the target volume. We hypothesized that this can be achieved more adequately with magnetic resonance imaging (MRI)-guided treatment planning.

MATERIAL AND METHODS

From January 2009 to April 2014, 183 patients were referred to our department for salvage radiotherapy (SRT). According to protocol, patients received a planning computed tomography (CT) as well as an MRI in treatment position. All MRI scans were retrospectively reviewed by an experienced uro-radiologist.

RESULTS

Median prostate-specific antigen (PSA) value at time of referral was 0.3 ng/ml (range 0.02-4.7 ng/ml). MRI did not show any suspected macroscopic disease in 137 patients (75%). In 46 (25%) patients, MRI did indicate a pelvic recurrence. The mean PSA level was significantly higher in patients with a suspected recurrence on MRI (0.4 vs. 1.4 ng/ml, p < .001) on a Student's t-test. The mean follow-up was 33 months (range 5-69 months). Biochemical disease-free survival (bDFS) was significantly worse in patients with suspected disease on MRI [hazard ratio (HR) 2.9, p < .0001]. bDFS was significantly worse in the subgroup where the macroscopic recurrences on MRI received a lower radiation dose (HR 3.4, p = .01).

CONCLUSION

MRI detects loco-regional disease in a substantial subset of patients with a biochemical recurrence after prostatectomy, especially in a PSA above 0.5 μg/l. Lack of MRI-based dose escalation on these macroscopic recurrences could explain some of the biochemical progression observed after SRT.

Volumetric image-guided highly conformal radiotherapy of the prostate bed: Toxicity analysis

AIM

To evaluate toxicity of high conformal image-guided radiotherapy of the prostate bed.

BACKGROUND

Radiotherapy of the prostate bed has a pivotal role in the post-operative and salvage settings, but few clinical data are available on the use of daily image guidance in combination with highly conformal techniques, and data on long-term results are lacking.

MATERIALS AND METHODS

We analyzed 118 patients irradiated on the prostate bed using conformal plans processed with a micro-multileaf collimator, and daily checking treatment set-up with a cone-beam CT system. Correlation between toxicity and clinical-dosimetric parameters was assessed by the Cox regression model and log-rank test. Survival analyses were performed with the Kaplan-Meier method.

RESULTS

Median follow-up was 54.08 months. Late grade ≥2 gastro-intestinal (GI) and genito-urinary (GU) toxicity were 3.4% and 4.2%, respectively. Actuarial 4-year late grade ≥2 GI and GU toxicities were 4% and 6%, respectively. Four-year relapse-free survival was 87%. At log-rank test, acute grade ≥2 GI toxicity is associated with the use of antihypertensives (p = 0.03), and there is a trend toward significance between the use of anticoagulants and late grade ≥2 GI toxicity (p = 0.07). At Cox analysis, acute grade ≥2 GU toxicity is correlated with the percentage of bladder volume receiving more than 65 Gy (p = 0.02, HR 1.87 CI 1.25-2.8), and the maximal dose to the rectum is correlated to the development of late grade ≥2 GI toxicity (p = 0.03, HR 2.75 CI 1.10-6.9).

CONCLUSIONS

Conformal volumetric image-guided radiotherapy of the prostate bed leads to low toxicity rates.

Dynamic contrast-enhanced MRI for automatic detection of foci of residual or recurrent disease after prostatectomy

PURPOSE

This study aimed to develop an automated procedure for identifying suspicious foci of residual/recurrent disease in the prostate bed using dynamic contrast-enhanced-MRI (DCE-MRI) in prostate cancer patients after prostatectomy.

MATERIALS AND METHODS

Data of 22 patients presenting for salvage radiotherapy (RT) with an identified gross tumor volume (GTV) in the prostate bed were analyzed retrospectively. An unsupervised pattern recognition method was used to analyze DCE-MRI curves from the prostate bed. Data were represented as a product of a number of signal-vs.-time patterns and their weights. The temporal pattern, characterized by fast wash-in and gradual wash-out, was considered the "tumor" pattern. The corresponding weights were thresholded based on the number (1, 1.5, 2, 2.5) of standard deviations away from the mean, denoted as DCE1.0, …, DCE2.5, and displayed on the T2-weighted MRI. The resultant four volumes were compared with the GTV and maximum pre-RT prostate-specific antigen (PSA) level. Pharmacokinetic modeling was also carried out.

RESULTS

Principal component analysis determined 2-4 significant patterns in patients' DCE-MRI. Analysis and display of the identified suspicious foci was performed in commercial software (MIM Corporation, Cleveland, OH, USA). In general, DCE1.0/DCE1.5 highlighted larger areas than GTV. DCE2.0 and GTV were significantly correlated (r = 0.60, p < 0.05). DCE2.0/DCA2.5 were also significantly correlated with PSA (r = 0.52, 0.67, p < 0.05). K^trans for DCE2.5 was statistically higher than the GTV's K^trans (p < 0.05), indicating that the automatic volume better captures areas of malignancy.

CONCLUSION

A software tool was developed for identification and visualization of the suspicious foci in DCE-MRI from post-prostatectomy patients and was integrated into the treatment planning system.

Prospective MRI-based imaging study to assess feasibility of proton therapy for post-prostatectomy radiation

PURPOSE/OBJECTIVES

To optimize delivery of post-prostatectomy radiation (PPRT) with protons by examining dosimetric effects of variations in physician contouring, organ motion, and patient alignment during a course of PPRT.

MATERIAL AND METHODS

We enrolled 10 patients receiving PPRT in a prospective imaging study. All patients underwent combined computed tomography (CT)/magnetic resonance imaging (MRI) simulation with endorectal balloon (ERB) and received intensity modulated radiation therapy (IMRT) per institutional standards. Study patients underwent weekly MRI verification scans in the treatment position. Three radiation oncologists contoured clinical target volumes (CTV) on initial and verification scans using two consensus guidelines (RTOG and EORTC). We generated IMRT, double scattering (DS), and pencil beam scanning (PBS) proton plans and examined the dosimetric impact of contour variations, inter-fraction motion, and patient alignment techniques.

RESULTS

Inter-observer variations in contouring reduced median CTV coverage (D100) by 0.9% for IMRT plans, 2.8% for DS proton plans, 3.4-4.9% for PBS Proton Plans. Inter-fraction changes in target volumes due to internal organ motion resulted in a median loss of target dose coverage (D98) of 0% with IMRT, 3.5% with DS, and 8.1-8.3% with PBS. Median bladder V65Gy increased during the treatment course with all techniques (6.0-7.5%). Changes in the median rectal V60Gy remained small regardless of the treatment technique (0.5-3.1% increase). Alignment to the ERB after cranio-caudal bony alignment reduced CTV displacement compared to bony alignment alone, and as a result CTV coverage (D98) changed <2% with IMRT, DS, and PBS.

CONCLUSION

Proton-based treatments are more sensitive to changes in inter-fraction organ motion during PPRT compared to IMRT, and therefore motion management and patient alignment methods are critical. Patient alignment using bony anatomy as well as the ERB minimizes displacement of the CTV, and reduces variation in target dose coverage particularly for PBS proton therapy.

Magnetic resonance imaging for localization of prostate cancer in the setting of biochemical recurrence

The clinical suspicion of local recurrence of prostate cancer after radical treatment is based on the onset of biochemical failure. The use of multiparametric magnetic resonance imaging (MRI) for prostate cancer has increased over recent years, mainly for detection, staging, and active surveillance. However, suspicion of recurrence in the set of biochemical failure is becoming a significant reason for clinicians to request multiparametric MRI. Radiologists should be able to recognize the normal posttreatment MRI findings. Fibrosis and atrophic remnant seminal vesicles (SV) after radical prostatectomy are often found and must be differentiated from local relapse. Moreover, brachytherapy, external beam radiotherapy, and focal therapies tend to diffusely decrease the signal intensity of the peripheral zone on T2-weighted images due to the loss of water content, consequently mimicking tumor and hemorrhage. The combination of T2-weighted images and functional studies like diffusion-weighted imaging and dynamic contrast-enhanced imaging improves the identification of local relapse. Tumor recurrence tends to restrict on diffusion images and avidly enhances after contrast administration. The authors provide a review of the normal findings and the signs of local tumor relapse after radical prostatectomy, external beam radiotherapy, brachytherapy and focal therapies.

Imaging for Prostate Cancer Recurrence

CONTEXT

Correct identification of metastatic sites in recurrent prostate cancer (PCa) is of crucial importance because it leads to further treatment decisions.

OBJECTIVE

To provide an overview on current imaging procedures and their performance in recurrent PCa.

EVIDENCE ACQUISITION

Medline search via PubMed was performed with the keywords imaging, recurrent, and prostate cancer as well as more detailed searches including the keywords bone scan, bone scintigraphy, computed tomography, magnetic resonance imaging, positron emission tomography, PET, choline, FDG, prostate-specific membrane antigen, and PSMA, with emphasis on recent literature from 2010 to the present. Non-English published literature was excluded. Abstracts and full-text articles were reviewed and assessed for relevant content.

EVIDENCE SYNTHESIS

In diagnostic imaging and particularly with newer technologies like positron emission tomography (PET), a profound lack of prospectively designed studies in recurrent PCa has to be noted. In most studies histologic validation has only been performed in a subset of patient cohorts. Heterogeneity of included patient cohorts, lack of standardized assessment, as well as diverging end points, hamper systematic comparison of different image modalities. Thus evidence for currently used imaging in recurrent PCa is only presented descriptively.

CONCLUSIONS

Computed tomography and magnetic resonance imaging (MRI) as well as bone scintigraphy still represent the standard imaging for recurrent PCa; however, particularly for detection of local recurrence, multiparametric MRI is a valuable imaging modality. PET using choline and particularly tracers against prostate-specific membrane antigen might improve visualization of metastatic lesions. These findings need to be validated in prospective trials.

PATIENT SUMMARY

Imaging of recurrent prostate cancer (PCa) is important to guide further treatment. Computed tomography, magnetic resonance imaging, and bone scintigraphy represent the current standard. Positron emission tomography, especially with cancer-specific tracers, might improve imaging of recurrent PCa in the future.

Review of potential improvements using MRI in the radiotherapy workflow

The goal of modern radiotherapy is to deliver a lethal amount of dose to tissue volumes that contain a significant amount of tumour cells while sparing surrounding unaffected or healthy tissue. Online image guided radiotherapy with stereotactic ultrasound, fiducial-based planar X-ray imaging or helical/conebeam CT has dramatically improved the precision of radiotherapy, with moving targets still posing some methodical problems regarding positioning. Therefore, requirements for precise target delineation and identification of functional body structures to be spared by high doses become more evident. The identification of areas of relatively radioresistant cells or areas of high tumor cell density is currently under development. This review outlines the state of the art of MRI integration into treatment planning and its importance in follow up and the quantification of biological effects. Finally the current state of the art of online imaging for patient positioning will be outlined and indications will be given what the potential of integrated radiotherapy/online MRI systems is.

Role of 3T multiparametric magnetic resonance imaging without endorectal coil in the detection of local recurrent prostate cancer after radical prostatectomy: the radiation oncology point of view

OBJECTIVE

The aims of this study were to evaluate the role of 3 tesla multiparametric magnetic resonance imaging (3TmMRI) without endorectal coil in the detection of radiographic local recurrences (rLRs) in a contemporary cohort of patients with prostate cancer who presented with biochemical recurrence after radical prostatectomy (RP) with low prostate-specific antigen (PSA) levels, and to identify clinical parameters associated with the 3TmMRI findings.

MATERIALS AND METHODS

Between 2009 and 2013, 57 patients with biochemical recurrence of prostate cancer after RP who were considered for salvage radiation therapy (SRT) were included. 3TmMRI with T2-weighted imaging, diffusion weighted imaging (DWI) and dynamic contrast-enhanced imaging without endorectal coil was carried out in all patients before treatment.

RESULTS

In 14 out of 57 patients (24.56%) local recurrence was detected through 3TmMRI. Median pre-SRT PSA was 0.40 ng/ml (interquartile range 0.30-2.05 ng/ml). The recurrence was perianastomotic in eight out of 14 patients (57.14%) and retrovesical in six out of 14 patients (42.86%). The median size of the local recurrence was 15.2 mm (range 8.0-46.0 mm). The probability of rLR was significantly higher in patients with PSA levels above 0.5 ng/ml [adjusted odds ratio (OR) 6.25, 95% confidence interval (CI) 1.27-30.79, p = 0.02] or PSA doubling time (PSADT) over 14 months (adjusted OR 7.12, 95% CI 1.40-36.25, p = 0.01).

CONCLUSIONS

This is the first study to find a significant relationship between the PSADT and the rLR through MRI. Patients with PSADT longer than 14 months or pre-SRT PSA above 0.5 ng/ml benefited most from 3TmMRI. Its routine use could have significant clinical implications for SRT.

Multiparametric MRI for recurrent prostate cancer post radical prostatectomy and postradiation therapy

The clinical suspicion of local recurrence of prostate cancer (PCa) after radical prostatectomy (RP) and after radiation therapy (RT) is based on the onset of biochemical failure. The aim of this paper was to review the current role of multiparametric-MRI (mp-MRI) in the detection of locoregional recurrence. A systematic literature search using the Medline and Cochrane Library databases was performed from January 1995 up to November 2013. Bibliographies of retrieved and review articles were also examined. Only those articles reporting complete data with clinical relevance for the present review were selected. This review article is divided into two major parts: the first one considers the role of mp-MRI in the detection of PCa local recurrence after RP; the second part provides an insight about the impact of mp-MRI in the depiction of locoregional recurrence after RT (interstitial or external beam). Published data indicate an emerging role for mp-MRI in the detection and localization of locally recurrent PCa both after RP and RT which represents an information of paramount importance to perform focal salvage treatments.

The influence of MRI scan position on patients with oropharyngeal cancer undergoing radical radiotherapy

Background

The purpose of this study was to demonstrate how magnetic resonance imaging (MRI) patient position protocols influence registration quality in patients with oropharyngeal cancer undergoing radical radiotherapy and the consequences for gross tumour volume (GTV) definition and radiotherapy planning.

Methods and materials

Twenty-two oropharyngeal patients underwent a computed tomography (CT), a diagnostic MRI (MRI_D) and an MRI in the radiotherapy position within an immobilization mask (MRI_RT). Clinicians delineated the GTV on the CT viewing the MRI_D separately (GTV_C); on the CT registered to MRI_D (GTV_D) and on the CT registered to MRI_RT (GTV_RT). Planning target volumes (PTVs) were denoted similarly. Registration quality was assessed by measuring disparity between structures in the three set-ups. Volumetric modulated arc therapy (VMAT) radiotherapy planning was performed for PTV_C, PTV_D and PTV_RT. To determine the dose received by the reference PTV_RT, we optimized for PTV_C and PTV_D while calculating the dose to PTV_RT. Statistical significance was determined using the two-tailed Mann–Whitney or two-tailed paired student t-tests.

Results

A significant improvement in registration accuracy was found between CT and MRI_RT versus the MRI_D measuring distances from the centre of structures (geometric mean error of 2.2 mm versus 6.6 mm). The mean GTV_C (44.1 cm³) was significantly larger than GTV_D (33.7 cm³, p value = 0.027) or GTV_RT (30.5 cm³, p value = 0.014). When optimizing the VMAT plans for PTV_C and investigating the mean dose to PTV_RT neither the dose to 99% (58.8%) nor 95% of the PTV (84.7%) were found to meet the required clinical dose constraints of 90% and 95% respectively. Similarly, when optimizing for PTV_D the mean dose to PTV_RT did not meet clinical dose constraints for 99% (14.9%) nor 95% of the PTV (66.2%). Only by optimizing for PTV_RT were all clinical dose constraints achieved.

Conclusions

When oropharyngeal patients MRI scans are performed in the radiotherapy position there are significant improvements in CT-MR image registration, target definition and PTV dose coverage.

The influence of MRI scan position on image registration accuracy, target delineation and calculated dose in prostatic radiotherapy

OBJECTIVE

To investigate the necessity of performing MRI in the radiotherapy position when using MRI for prostatic radiotherapy.

METHODS

20 prostate patients received a CT, diagnostic MRI and an MRI scan in the radiotherapy position. The quality of registration between CT and MRI was compared between the two MRI set-ups. The prostate and seminal vesicles were contoured using all scans and intensity modulated radiotherapy (IMRT) plans were generated. Changes in the target volume and IMRT plans were investigated. Two-tailed paired Student's t-tests determined the statistical significance.

RESULTS

There was a decrease in the mean distance from the centre of the bony anatomy between CT and MRI (from 3.9 to 1.9 mm, p-value<0.0001) when the MRI scan was acquired in the radiotherapy position. Assuming that registering CT with an MRI scan in the radiotherapy position is the gold standard for delineating the prostate and seminal vesicles, using a planning target volume delineated on the CT with a diagnostic MRI scan viewed separately, resulted in a mean conformation number of 0.80 instead of the expected 0.98 (p<0.0001).

CONCLUSION

By registering CT with an MRI scan in the radiotherapy position, there is a statistically significant improvement in the registration and IMRT quality.

ADVANCES IN KNOWLEDGE

To achieve an acceptable registration and IMRT quality in prostatic radiotherapy, neither CT with a separate diagnostic MRI nor CT registered to a diagnostic MRI will suffice. Instead, a CT registered with an MRI in the radiotherapy position should be used.

Evaluation of the prostate bed for local recurrence after radical prostatectomy using endorectal magnetic resonance imaging

PURPOSE

To summarize the results of a 4-year period in which endorectal magnetic resonance imaging (MRI) was considered for all men referred for salvage radiation therapy (RT) at a single academic center; to describe the incidence and location of locally recurrent disease in a contemporary cohort of men with biochemical failure after radical prostatectomy (RP), and to identify prognostic variables associated with MRI findings in order to define which patients may have the highest yield of the study.

METHODS AND MATERIALS

Between 2007 and 2011, 88 men without clinically palpable disease underwent eMRI for detectable prostate-specific antigen (PSA) after RP. The median interval between RP and eMRI was 32 months (interquartile range, 14-57 months), and the median PSA level was 0.30 ng/mL (interquartile range, 0.19-0.72 ng/mL). Magnetic resonance imaging scans consisting of T2-weighted, diffusion-weighted, and dynamic contrast-enhanced imaging were evaluated for features consistent with local recurrence. The prostate bed was scored from 0-4, whereby 0 was definitely normal, 1 probably normal, 2 indeterminate, 3 probably abnormal, and 4 definitely abnormal. Local recurrence was defined as having a score of 3-4.

RESULTS

Local recurrence was identified in 21 men (24%). Abnormalities were best appreciated on T2-weighted axial images (90%) as focal hypointense lesions. Recurrence locations were perianastomotic (67%) or retrovesical (33%). The only risk factor associated with local recurrence was PSA; recurrence was seen in 37% of men with PSA >0.3 ng/mL vs 13% if PSA ≤0.3 ng/mL (P<.01). The median volume of recurrence was 0.26 cm(3) and was directly associated with PSA (r=0.5, P=.02). The correlation between MRI-based tumor volume and PSA was even stronger in men with positive margins (r=0.8, P<.01).

CONCLUSIONS

Endorectal MRI can define areas of local recurrence after RP in a minority of men without clinical evidence of disease, with yield related to PSA. Further study is necessary to determine whether eMRI can improve patient selection and success of salvage RT.