Sparing of the penile bulb and proximal penile structures with intensity-modulated radiation therapy for prostate cancer

Sexual Structure Sparing for Prostate Cancer Radiotherapy: A Systematic Review

CONTEXT

Erectile dysfunction represents a major side effect of prostate cancer (PCa) treatment, negatively impacting men's quality of life. While radiation therapy (RT) advances have enabled the mitigation of both genitourinary and gastrointestinal toxicities, no significant improvement has been showed in sexual quality of life over time.

OBJECTIVE

The primary aim of this review was to assess sexual structures' dose-volume parameters associated with the onset of erectile dysfunction.

EVIDENCE ACQUISITION

We searched the PubMed database and ClinicalTrials.gov until January 4, 2023. Studies reporting the impact of the dose delivered to sexual structures on sexual function or the feasibility of innovative sexual structure-sparing approaches were deemed eligible.

EVIDENCE SYNTHESIS

Sexual-sparing strategies have involved four sexual organs. The mean penile bulb doses exceeding 20 Gy are predictive of erectile dysfunction in modern PCa RT trial. Maintaining a D100% of ≤36 Gy on the internal pudendal arteries showed preservation of erectile function in 88% of patients at 5 yr. Neurovascular bundle sparing appears feasible with magnetic resonance-guided radiation therapy, yet its clinical impact remains unanswered. Doses delivered to the testicles during PCa RT usually remain <2 Gy and generate a decrease in testosterone levels ranging from -4.6% to -17%, unlikely to have any clinical impact.

CONCLUSIONS

Current data highlight the technical feasibility of sexual sparing for PCa RT. The proportion of erectile dysfunction attributable to the dose delivered to sexual structures is still largely unknown. While the ability to maintain sexual function over time is impacted by factors such as age or comorbidities, only selected patients are likely to benefit from sexual-sparing RT.

PATIENT SUMMARY

Technical advances in radiation therapy (RT) made it possible to significantly lower the dose delivered to sexual structures. While sexual function is known to decline with age, the preservation of sexual structures for prostate cancer RT is likely to be beneficial only in selected patients.

Penile bulb sparing in prostate cancer radiotherapy : Dose analysis of an in-house MRI system to improve contouring

OBJECTIVE

This study aimed to assess the reduction in dose to the penile bulb (PB) achieved by MRI-based contouring following drinking and endorectal balloon (ERB) instructions.

PATIENTS AND METHODS

A total of 17 prostate cancer patients were treated with intensity-modulated radiation therapy (IMRT) and interstitial brachytherapy (IBT). CT and MRI datasets were acquired back-to-back based on a 65 cm³ air-filled ERB and drinking instructions. After rigid co-registration of the imaging data, the CT-based planning target volume (PTV) used for treatment planning was retrospectively compared to an MRI-based adaptive PTV and the dose to the PB was determined in each case. The adapted PTV encompassed a caudally cropped CT-based PTV which was defined on the basis of the MRI-based prostate contour plus an additional 5 mm safety margin.

RESULTS

In the seven-field IMRT treatment plans, the MRI-based adapted PTV achieved mean (D_mean) and maximum (D_max) doses to the PB which were significantly lower (by 7.6 Gy and 10.9 Gy, respectively; p <0.05) than those of the CT-contoured PTV. For 6 patients, the estimated PB D_max (seven-field IMRT and IBT) for the adapted PTV was <70 Gy, whereas only 1 patient fulfilled this criterium with the CT-based PTV.

CONCLUSION

MRI-based contouring and seven-field IMRT-based treatment planning achieved dose sparing to the PB. Whereas the comparison of MRI and CT contouring only relates to external beam radiotherapy (EBRT) sparing, considering EBRT and IBT shows the improvement in PB sparing for the total treatment.

Intensity-modulated radiotherapy for prostate cancer

Radiation therapy (RT) is a curative treatment modality for localized prostate cancer. Over the past two decades, advances in technology and imaging have considerably changed RT in prostate cancer treatment. Treatment has evolved from 2-dimensional (2D) planning using X-ray fields based on pelvic bony landmarks to 3-dimensional (3D) conformal RT (CRT) which uses computed tomography (CT) based planning. Despite improvements with 3D-CRT, dose distributions often remained suboptimal with portions of the rectum and bladder receiving unacceptably high doses. In more recent years, intensity-modulated radiation therapy (IMRT) has become the standard of care to deliver external beam RT. IMRT uses multiple radiation beams of different shapes and intensities delivered from a wide range of angles to ‘paint’ the radiation dose onto the tumor. IMRT allows for a higher dose of radiation to be delivered to the prostate while reducing dose to surrounding organs. Multiple clinical trials have demonstrated improved cancer outcomes with dose escalation, but toxicities using 3D-CRT and escalated doses have been problematic. IMRT is a method to deliver dose escalated RT with more conformal dose distributions than 3D-CRT and has been associated with improved toxicity profiles. IMRT also appears to be the safest method to deliver hypofractionated RT and pelvic lymph node radiation. The purpose of this review is to summarize the technical aspects of IMRT planning and delivery, and to review the literature supporting the use of IMRT for prostate cancer.

Reproducibility in contouring the neurovascular bundle for prostate cancer radiation therapy

PURPOSE

Efforts to define the neurovascular bundle (NVB) for prostate radiation have varied. In this series, we sought to determine the reproducibility and reliability of contouring the classical posterolateral NVB on dedicated pelvic magnetic resonance imaging (MRI) scans.

METHODS AND MATERIALS

A total of 120 NVB structures were defined on 10 3-Tesla pelvic MRI scans in patients with prostate cancer but without extraprostatic extension. One pelvic radiologist served as the expert in contouring the right and left NVB for each case. Five radiation oncologists, with varying levels of experience, contoured the right and left NVBs on these same cases. The intraclass correlation coefficient across each rater and the expert, Pearson correlation coefficient between each rater and the expert, and the Dice similarity coefficient (DSC) between each rater and the expert were calculated to evaluate contour agreement and overlap.

RESULTS

The overall intraclass correlation coefficient was 0.89 (95% confidence interval [CI], 0.81-0.95). The Pearson correlation coefficient was 0.95 (95% CI, 0.86-0.98) for rater 1, 0.98 (95% CI, 0.95-0.99) for rater 2, 0.94 (95% CI, 0.86-0.98) for rater 3, 0.98 (95% CI, 0.95-0.99) for rater 4, and 0.84 (95% CI, 0.63-0.93) for rater 5. The mean DSC was 0.72 (standard deviation [SD], 0.07) for rater 1, 0.72 (SD, 0.06) for rater 2, 0.73 (SD, 0.09) for rater 3, 0.74 (SD, 0.09) for rater 4, and 0.68 (SD, 0.13) for rater 5. Overall, across all raters, the average DSC was 0.72 (SD, 0.09).

CONCLUSIONS

The classic posterolateral NVB can be accurately and reliably contoured on 3-Tesla pelvic MRI scans by radiation oncologists.

Influence of vascular comorbidities and race on erectile dysfunction after prostate cancer radiotherapy

INTRODUCTION

Vascular comorbidities (VC) (hypertension, diabetes, and hyperlipidemia) are known factors related to erectile dysfunction (ED) in men. However, no data are yet available for the effects of VC on ED incidence after prostate cancer radiotherapy (XRT).

AIM

To investigate the influence of VC on post-XRT ED incidence and to further characterize ED incidence by racial groups.

MAIN OUTCOME MEASURES

ED incidence.

METHODS

We reviewed 732 charts of patients (267 Caucasian and 465 African American [AA]) who received prostate XRT (external beam radiotherapy and/or brachytherapy) with or without hormone therapy between 1999 and 2010. The number of pre-XRT VC (0, 1, 2, or 3) was determined by medical history and medication list. ED (defined by use of erectile aids or by documentation of moderate or high sexual dysfunction on patient history) was determined pre-XRT as well as 1, 2, and 4 years post-XRT.

RESULTS

ED incidence progressively increased from 22% pre-XRT to 58% 4 years post-XRT (P < 0.01). Additionally, ED incidence significantly increased with number of VC-4-year incidence between patients with 1 vs. 0 (P = 0.02), 2 vs. 0 (P < 0.01), 3 vs. 0 (P < 0.01), 3 vs. 1 (P < 0.01), and 3 vs. 2 (P = 0.04) VC (2 vs. 1 VC was nonsignificant). Compared with the Caucasian patients, ED incidences were slightly higher for the AA group with 0, 1, 2, and 3 comorbidities at 4 years follow-up (but statistically nonsignificant).

CONCLUSIONS

The number of VCs have a significant effect on development of post-XRT ED. Pre- and post-XRT ED appear to be independent of race when number of VCs are considered. Our results can be used to guide physicians in counseling patients on the incidence of ED by number of VC and as preliminary data for prospective efforts aimed at reducing post-XRT ED.

Inter-observer variability in contouring the penile bulb on CT images for prostate cancer treatment planning

Several investigations have recently suggested the existence of a correlation between the dose received by the penile bulb (PB) and the risk of erectile dysfunction (ED) after radical radiotherapy for clinically localized prostate carcinoma. A prospective multi-Institute study (DUE-01) was implemented with the aim to assess the predictive parameters of ED. Previously, an evaluation of inter-observer variations of PB contouring was mandatory in order to quantify its impact on PB dose-volume parameters by means of a dummy run exercise. Fifteen observers, from different Institutes, drew the PB on the planning CT images of ten patients; inter-observer variations were analysed in terms of PB volume variation and cranial/caudal limits. 3DCRT treatment plans were simulated to evaluate the impact of PB contouring inter-variability on dose-volume statistics parameters. For DVH analysis the values of PB mean dose and the volume of PB receiving more than 50 Gy and 70 Gy (V50 and V70, respectively) were considered. Systematic differences from the average values were assessed by the Wilcoxon test. Seven observers systematically overestimated or underestimated the PB volume with deviations from the average volumes ranging between -48% and +34% (p < 0.05). The analysis of the cranial and caudal borders showed a prevalence of random over systematic deviations. Inter-observer contouring variability strongly impacts on DVH parameters, although standard deviations of inter-patient differences were larger than inter-observer variations: 14.5 Gy versus 6.8 Gy for mean PB dose, 23.0% versus 11.0% and 16.8% versus 9.3% for V50 and V70 respectively. In conclusion, despite the large inter-observer variation in contouring PB, a large multi-centric study may have the possibility to detect a possible correlation between PB % dose-volume parameters and ED. The impact of contouring uncertainty could be reduced by "a posteriori" contouring from a single observer or by introducing Magnetic Resonance Imaging (MRI) in the planning procedures and/or in improving the skill of observers through post-dummy run tutoring of those observers showing large systematic deviations from the mean.

Statistical analysis of IMRT dosimetry quality assurance measurements for local delivery guideline

Purpose

To establish our institutional guideline for IMRT delivery, we statistically evaluated the results of dosimetry quality assurance (DQA) measurements and derived local confidence limits using the concept confidence limit of |mean|+1.96σ.

Materials and methods

From June 2006 to March 2009, 206 patients with head and neck cancer, prostate cancer, liver cancer, or brain tumor were treated using LINAC-based IMRT technique. In order to determine site specific DQA tolerances at a later stage, a hybrid plan with the same fluence maps as in the treatment plan was generated on CT images of a cylindrical phantom of acryl. Points of measurement using a 0.125 cm³ ion-chamber were typically located in the region of high and uniform doses. The planar dose distributions perpendicular to the central axis were measured by using a diode array in solid water with all fields delivered, and assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop the local confidence and tolerance limits. The dose differences and gamma pass rates for the different treatment sites were also evaluated in terms of total monitor uints (MU), MU/cGy, and the number of PTV's pieces.

Results

The mean values and standard deviations of ion-chamber dosimetry differences between calculated and measured doses were -1.6 ± 1.2% for H&N cancer, -0.4 ± 1.2% for prostate and abdominal cancer, and -0.6 ± 1.5% for brain tumor. Most of measured doses (92.2%) agreed with the calculated doses within a tolerance limit of ±3% recommended in the literature. However, we found some systematic under-dosage for all treatment sites. The percentage of points passing the gamma criteria, averaged over all treatment sites was 97.3 ± 3.7%. The gamma pass rate and the agreement of ion-chamber dosimetry generally decreased with increasing the number of PTV's pieces, the degree of modulation (MU/cGy), and the total MU beyond 700. Our local confidence limits were comparable to those of AAPM TG 119 and ESTRO guidelines that were provided as a practical baseline for center-to-center commissioning comparison. Thus, our institutional confidence and action limits for IMRT delivery were set into the same levels of those guidelines.

Discussion and Conclusions

The systematic under-dosage were corrected by tuning up the MLC-related factors (dosimetric gap and transmission) in treatment planning system (TPS) and further by incorporating the tongue-and groove effect into TPS. Institutions that have performed IMRT DQA measurements over a certain period of time need to analyze their accrued DQA data. We confirmed the overall integrity of our IMRT system and established the IMRT delivery guideline during this procedure. Dosimetric corrections for the treatment plans outside of the action level can be suggested only with such rigorous DQA and statistical analysis.

A review of the clinical evidence for intensity-modulated radiotherapy

AIMS

Intensity-modulated radiotherapy (IMRT) is a development of three-dimensional conformal radiotherapy that offers improvements in dosimetry in many clinical scenarios. Here we review the clinical evidence for IMRT and present ongoing or unpublished randomised controlled trials (RCTs).

METHODS

We identified randomised and non-randomised comparative studies of IMRT and conventional radiotherapy using MEDLINE, hand-searching Radiotherapy and Oncology and the International Journal of Radiation Oncology, Biology and Physics and the proceedings of the American Society for Therapeutic Radiology and Oncology and the European Society for Therapeutic Radiology and Oncology annual meetings. The metaRegister of Controlled Trials was searched to identify completed-unpublished, ongoing and planned RCTs.

RESULTS

Sixty-one studies comparing IMRT and conventional radiotherapy were identified. These included three RCTs in head and neck cancer (205 patients) and three in breast cancer (664 patients) that had reported clinical outcomes; these were all powered for toxicity-related end points, which were significantly better with IMRT in each trial. There were 27 additional non-randomised studies in head and neck (1119 patients), 26 in prostate cancer (>5000 patients), four in breast cancer (875 patients) and nine in other tumour sites. The results of these studies supported those of the RCTs with benefits reported in acute and late toxicity, health-related quality of life and tumour control end points. Twenty-eight completed-unpublished, ongoing or planned RCTs incorporating IMRT were identified, including at least 12,310 patients, of which 15 compared conventional radiotherapy within IMRT as a randomisation or pre-planned stratification.

DISCUSSION

Inverse-planned IMRT maintains parotid saliva production and reduces acute and late xerostomia during radiotherapy for locally advanced head and neck cancer, reduces late rectal toxicity in prostate cancer patients allowing safe dose escalation and seems to reduce toxicity in several other tumour sites. Forward-planned IMRT reduces acute toxicity and improves late clinician-assessed cosmesis compared with conventional tangential breast radiotherapy.

Erectile dysfunction after radiotherapy for prostate cancer

Erectile Dysfunction (ED) is a relatively common complication after radiotherapy for prostate cancer. The etiology of ED is unclear. It is likely related to age, pretreatment erectile function, androgen deprivation therapy, and the volume of tissue irradiated. It is unclear whether the dose to various parts of the penis, such as the penile bulb and corpora cavernosa, is related to the development of ED. Following radiotherapy, the early use of phosphodiesterase inhibitors probably reduces the risk of ED.

Sparing the penile bulb in the radical irradiation of clinically localised prostate carcinoma: A comparison between MRI and CT prostatic apex definition in 3DCRT, Linac-IMRT and Helical Tomotherapy

BACKGROUND AND PURPOSE

To assess the impact of using MRI and Helical Tomotherapy (HT) compared to 3DCRT and dynamic IMRT on the dose to the penile bulb (PB).

MATERIALS AND METHODS

Eight patients diagnosed with prostate cancer entered a treatment protocol including CT and MRI simulation. The prostate apex was defined on both MRI and CT. Treatment plans (HT, Linac-IMRT, 3DCRT and conventional technique), were elaborated on both MRI and CT images. A dose of 71.4Gy (2.55Gy/fraction) was prescribed; it was requested that PTVs be covered by 95% isodose line. The mean dose and V50 of PB were evaluated.

RESULTS

PTV-MRI plans reduced PB mean dose and V50 compared to PTV-CT plans. This improvement, deriving also from the treatment modality, was 89% for 3DCRT, 99% for Linac-IMRT and 97% for HT (p<0.01), considering V50. Conventional plans resulted in a significantly higher mean PB dose/V50 compared to 3DCRT-PTV-CT (+27%/+38%), Linac-IMRT-PTV-CT (+42%/+57%) and HT-PTV-CT (+32%/+48%) (p<0.01). The comparison between conventional and PTV-MRI techniques showed a still larger increase: +73%/+93% 3DCRT; +86%/+99% Linac-IMRT; +56%/+99% HT (p<0.01). The PB mean dose reduction with Linac-IMRT compared to 3DCRT was 24% (p=0.034) and 40% (p=0.027) for PTV-CT and PTV-MRI, respectively. This gain remained significant even when comparing Linac-IMRT to HT: 21% (p=0.07) PTV-CT and 68% (p=0.00002) PTV-MRI. HT was superior to 3DCRT with respect to PTV-CT (average gain 4%, p=0.044), whereas it resulted to be detrimental considering PTV-MRI (26Gy vs 16.5Gy), possibly due to the helical delivery of HT; however, in a patient where the distance bulb-PTV <1cm, HT provided better PB sparing than 3DCRT (29.5Gy vs 45.2Gy).

CONCLUSIONS

MRI allowed efficient sparing of PB irrespective of the treatment modality. Linac-IMRT was shown to further reduce the dose to the bulb compared to 3DCRT and HT.

Erectile dysfunction following radiotherapy and brachytherapy for prostate cancer: pathophysiology, prevention and treatment

OBJECTIVES

Although detrimental impact on sexual function following radiotherapy (RT) and brachytherapy decreases the quality of life of prostate cancer survivors, the etiology, pathophysiology, prophylaxis and treatment of this condition has not yet been fully clarified. We reviewed the published literature in terms of etiology, treatment and possible prevention of erectile dysfunction (ED) following RT and/or brachytherapy.

METHOD

We have reviewed the literature through a MEDLINE search. Prostate cancer, erectile dysfunction, radiotherapy, brachytherapy, treatment and quality of life were used as keywords.

CONCLUSION

Both RT and brachytherapy result in high rates of ED. Although arterial damage seems to be the main cause of ED after RT, exposure of neurovascular bundle to high levels of radiation dose has been also implicated in some studies with brachytherapy. The radiation dose received by the corpora cavernosa at the crurae of the penis may also be important in the etiology of ED. The most important predictive factor of ED following RT is the treatment modality. Intensity-modulated radiotherapy and vessel-sparing prostate radiotherapy are new techniques but those treatments may not guarantee complete preservation of the erectile function. Patients need to be correctly informed on the possible sequela of radiation-based treatments on their sexual well-being while planning their treatment. Patients should also be informed about the possible treatment modalities for ED, which may develop in due course.

[AMS 800 artificial urinary sphincter implantation: can the penoscrotal approach constitute an alternative to the perineal approach?]

OBJECTIVE

To compare the short-term results of penoscrotal and perineal artificial urinary sphincter implantation.

PATIENTS AND METHODS

From May 2005 to February 2007, 37 artificial urinary sphincters were implanted successively, via a penoscrotal approach in 16 cases and via a perineal approach in 21 cases. Incontinence was secondary to prostate surgery (n=36) and pelvic trauma (n=1). Seventeen patients had a history of external beam radiotherapy. The times and modalities of activation of the sphincter were identical in the two groups.

RESULTS

The mean age of the patients, the mean operating time, the mean catheterization duration, the mean hospital stay and the mean postoperative follow-up were equivalent in the two groups. Six urethral erosions (37.5%) and one scrotal erosion due to the pump (6.6%) were observed in the penoscrotal group and infection of the sphincter in two patients (9.5%) and pump migration in another two patients (9.5%), but no urethral erosions were observed in the perineal group. The success rate without revision was 56% in the penoscrotal group and 71.5% in the perineal group.

CONCLUSION

The perineal approach is the reference incision, as the penoscrotal approach is associated with a high rate of erosion. The penoscrotal urethral approach can constitute an alternative when the bulbar urethra cannot be used.

Influence of intensity-modulated radiotherapy on acute genitourinary and gastrointestinal toxicity in the treatment of localized prostate cancer

The objective of this investigation is to compare acute genitourinary (GU) and gastrointestinal (GI) toxicity results of radiotherapy to localized fields delivered using intensity-modulated radiotherapy (IMRT) versus conventional radiotherapy (ConvRT). The records of 481 consecutive prostate cancer patients receiving RT to localized fields at a single institution were reviewed; 108 received IMRT and 373 received ConvRT. Acute GU and GI toxicity, as defined by the Radiation Therapy Oncology Group (RTOG) grading system, were compared using the chi-square test. Ordered logit regression analyses were performed using all major disease and treatment factors as covariates. Acute GU grade 0, 1, 2, 3, and 4 toxicity rates were 23%, 40%, 34%, 3%, and 0%, respectively, in the IMRT cohort and 31%, 37%, 30%, 1%, and 1%, respectively, in the ConvRT cohort -- these rates were not significantly different (p=0.118). Acute GI grade 0, 1, 2, 3, and 4 toxicity rates were 42%, 37%, 22%, 0%, and 0%, respectively, in the IMRT cohort and 33%, 32%, 35%, 0%, and 0%, respectively, in the ConvRT cohort--this lower toxicity in the IMRT group was significant (p=0.013). The regression analyses showed that only IMRT use (p=0.046) predicted reduction in acute GI toxicity but no factors correlated with acute GU toxicity rate. In conclusion, in our retrospective single-institution analysis, IMRT was not associated with reduction of acute GU toxicity but was associated with a reduction of acute GI toxicity over ConvRT in the treatment of prostate cancer to localized fields.

An analysis of erectile function after intensity modulated radiation therapy for localized prostate carcinoma

Radiation therapy for prostate cancer can cause erectile dysfunction (ED). Intensity Modulated Radiation Therapy (IMRT) can reduce the amount of radiation to surrounding tissues associated with ED. We characterize the incidence of and factors associated with ED in prostate cancer patients after IMRT at the National Naval Medical Center (NNMC). Patients potent by definition of the Sexual Health Inventory for Men (SHIM) before treatment completed the specific erectile questions of the SHIM after IMRT. Statistical analyses were performed to examine the relationships between several factors and ED. Thirty-two of 45 patients with mean age of 68.2 years (50-86 years) completed the SHIM. The median follow-up was 36.8 months (16-63.6 months) as defined by the time from completion of therapy to reassessment with the SHIM. Eight of 32 patients (25%) had no post-treatment ED (SHIM score 22-25), three of 32 (9%) had mild post-treatment ED (SHIM score 17-21), five of 32 (16%) had mild to moderate ED (SHIM score 12-16), five of 32 (16%) had moderate ED (SHIM score 8-11) and 11 of 32 (34%) had severe post-treatment ED (SHIM score<8). Post-treatment potency was significantly associated with the pre-treatment SHIM score (P=0.001) and history of hypertension (P=0.03). The mean radiation dose to the penile bulb and volume of penile bulb treated were not associated with post-treatment potency (P=0.38, 0.76, respectively). IMRT maintains potency in the majority of patients. This analysis compares favorably in preserving erectile function to previously reported series using conventional external beam radiation therapy techniques. The dose of radiation received by the penile bulb and volume of penile bulb were not associated with post-treatment ED in this analysis.

Use of benchmark dose–volume histograms for selection of the optimal technique between three-dimensional conformal radiation therapy and intensity-modulated radiation therapy in prostate cancer

PURPOSE

The aim of this study was to develop and validate our own benchmark dose-volume histograms (DVHs) of bladder and rectum for both conventional three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT), and to evaluate quantitatively the benefits of using IMRT vs. 3D-CRT in treating localized prostate cancer.

METHODS AND MATERIALS

During the implementation of IMRT for prostate cancer, our policy was to plan each patient with both 3D-CRT and IMRT. This study included 31 patients with T1b to T2c localized prostate cancer, for whom we completed double-planning using both 3D-CRT and IMRT techniques. The target volumes included prostate, either with or without proximal seminal vesicles. Bladder and rectum DVH data were summarized to obtain an average DVH for each technique and then compared using two-tailed paired t test analysis.

RESULTS

For 3D-CRT our bladder doses were as follows: mean 28.8 Gy, v60 16.4%, v70 10.9%; rectal doses were: mean 39.3 Gy, v60 21.8%, v70 13.6%. IMRT plans resulted in similar mean dose values: bladder 26.4 Gy, rectum 34.9 Gy, but lower values of v70 for the bladder (7.8%) and rectum (9.3%). These benchmark DVHs have resulted in a critical evaluation of our 3D-CRT techniques over time.

CONCLUSION

Our institution has developed benchmark DVHs for bladder and rectum based on our clinical experience with 3D-CRT and IMRT. We use these standards as well as differences in individual cases to make decisions on whether patients may benefit from IMRT treatment rather than 3D-CRT.

Radiation therapy for prostate cancer and erectile (dys)function: the role of imaging

Incidence of erectile dysfunction (ED) after radiotherapy reported in the literature varies from 7 to 72% after external-beam radiotherapy to 5-51% after brachytherapy. Most of these studies are retrospective, the definition of ED is variable and sexual functioning is frequently assessed by asking only one question. Already in the 1980's it was suggested that post-radiation ED was attributable to vascular damage. The most reliable method to assess vasculogenic ED is the use of the Doppler ultrasound. More recently, many studies have assessed the relationship between radiation dose and volume of the penile bulb and post-radiation ED, though the outcome is controversial. The penile structures and the neurovascular bundles are best seen on magnetic resonance imaging (MRI). Therefore the use of a computer tomography scan/MRI image fusion can result in reducing the planning target volume and consequently the radiation dose to the penile bulb and bodies. If radiation induces vascular damage that causes ED, any means of reducing the dose to the pelvic vascular structures would likely decrease ED, therefore new radiation techniques such as the intensity modulated radiation therapy or the implant of fiducial markers can help decrease the margins and therefore ED.

Intensity-modulated radiation therapy (IMRT) in the treatment of anal cancer: toxicity and clinical outcome

PURPOSE

To assess survival, local control, and toxicity of intensity modulated radiation therapy (IMRT) in squamous cell carcinoma of the anal canal.

METHODS AND MATERIALS

Seventeen patients were treated with nine-field IMRT plans. Thirteen received concurrent 5-fluorouracil and mitomycin C, whereas 1 patient received 5-fluorouracil alone. Seven patients were planned with three-dimensional anteroposterior/posterior-anterior (AP/PA) fields for dosimetric comparison to IMRT.

RESULTS

Compared with AP/PA, IMRT reduced the mean and threshold doses to small bowel, bladder, and genitalia. Treatment was well tolerated, with no Grade > or =3 acute nonhematologic toxicity. There were no treatment breaks attributable to gastrointestinal or skin toxicity. Of patients who received mitomycin C, 38% experienced Grade 4 hematologic toxicity. IMRT did not afford bone marrow sparing, possibly resulting from the clinical decision to prescribe 45 Gy to the whole pelvis in most patients, vs. the Radiation Therapy Oncology Group-recommended 30.6 Gy whole pelvic dose. Three of 17 patients, who did not achieve a complete response, proceeded to an abdominoperineal resection and colostomy. At a median follow-up of 20.3 months, there were no other local failures. Two-year overall survival, disease-free survival, and colostomy-free survival are: 91%, 65%, and 82% respectively.

CONCLUSIONS

In this hypothesis-generating analysis, the acute toxicity and clinical outcome with IMRT in the treatment of anal cancer is encouraging. Compared with historical controls, local control is not compromised despite efforts to increase conformality and reduce normal structure dose.