A practical method to achieve prostate gland immobilization and target verification for daily treatment

Dataset for predicting single-spot proton ranges in proton therapy of prostate cancer

The number of radiotherapy patients treated with protons has increased from less than 60,000 in 2007 to more than 220,000 in 2019. However, the considerable uncertainty in the positioning of the Bragg peak deeper in the patient raised new challenges in the proton therapy of prostate cancer (PCPT). Here, we describe and share a dataset where 43 single-spot anterior beams with defined proton energies were delivered to a prostate phantom with an inserted endorectal balloon (ERB) filled either with water only or with a silicon-water mixture. The nuclear reactions between the protons and the silicon yield a distinct prompt gamma energy line of 1.78 MeV. Such energy peak could be identified by means of prompt gamma spectroscopy (PGS) for the protons hitting the ERB with a three-sigma threshold. The application of a background-suppression technique showed an increased rejection capability for protons hitting the prostate and the ERB with water only. We describe each dataset, document the full processing chain, and provide the scripts for the statistical analysis.

Towards real-time PGS range monitoring in proton therapy of prostate cancer

Proton therapy of prostate cancer (PCPT) was linked with increased levels of gastrointestinal toxicity in its early use compared to intensity-modulated radiation therapy (IMRT). The higher radiation dose to the rectum by proton beams is mainly due to anatomical variations. Here, we demonstrate an approach to monitor rectal radiation exposure in PCPT based on prompt gamma spectroscopy (PGS). Endorectal balloons (ERBs) are used to stabilize prostate movement during radiotherapy. These ERBs are usually filled with water. However, other water solutions containing elements with higher atomic numbers, such as silicon, may enable the use of PGS to monitor the radiation exposure of the rectum. Protons hitting silicon atoms emit prompt gamma rays with a specific energy of 1.78 MeV, which can be used to monitor whether the ERB is being hit. In a binary approach, we search the silicon energy peaks for every irradiated prostate region. We demonstrate this technique for both single-spot irradiation and real treatment plans. Real-time feedback based on the ERB being hit column-wise is feasible and would allow clinicians to decide whether to adapt or continue treatment. This technique may be extended to other cancer types and organs at risk, such as the oesophagus.

Rectum Protection by Rectal Gel Injection in Cervical Cancer Brachytherapy: A Dosimetric Study via Deformable Surface Dose Accumulation and Machine-Learning-Based Discriminative Modeling

PURPOSE

This retrospective study aimed to evaluate the dosimetric effects of a rectal insertion of Kushen Ningjiao on rectal protection using deformable dose accumulation and machine learning-based discriminative modelling.

MATERIALS AND METHODS

Sixty-two patients with cervical cancer enrolled in a clinical trial, who received a Kushen Ningjiao injection of 20 g into their rectum for rectal protection via high-dose rate brachytherapy (HDR-BT, 6 Gy/f), were studied. The cumulative equivalent 2-Gy fractional rectal surface dose was deformably summed using an in-house-developed topography-preserved point-matching deformable image registration method. The cumulative three-dimensional (3D) dose was flattened and mapped to a two-dimensional (2D) plane to obtain the rectal surface dose map (RSDM). For analysis, the rectal dose (RD) was further subdivided as follows: whole, anterior, and posterior 3D-RD and 2D-RSDM. The dose-volume parameters (DVPs) were extracted from the 3D-RD, while the dose geometric parameters (DGPs) and textures were extracted from the 2D-RSDM. These features were fed into 192 classification models (built with 8 classifiers and 24 feature selection methods) for discriminating the dose distributions between pre-Kushen Ningjiao and pro-Kushen Ningjiao.

RESULTS

The rectal insertion of Kushen Ningjiao dialated the rectum in the ambilateral direction, with the rectal column increased from pre-KN 15 cm3 to post-KN 18 cm3 (P < 0.001). The characteristics of DGPs accounted for the largest portions of the top-ranked features. The top-ranked dosimetric features extracted from the posterior rectum were more reliable indicators of the dosimetric effects/changes introduced by the rectal insertion of Kushen Ningjiao. A significant dosimetric impact was found on the dose-volume parameters D1.0cc-D2.5cc extracted on the posterior rectal wall.

CONCLUSIONS

The rectal insertion of Kushen Ningjiao incurs significant dosimetric changes on the posterior rectal wall. Whether this effect is eventually translated into clinical gains requires further long-term follow-up and more clinical data for confirmation.

A comparison of bladder volumes based on treatment planning CT and BladderScan® BVI 6100 ultrasound device in a prostate radiation therapy population

OBJECTIVE:

The aim of this study is to investigate if a handheld ultrasound device (BladderScan® BVI 6100) can accurately measure bladder volumes in prostate radiotherapy (RT) patients.

METHODS:

A comparison was made of contoured bladder volumes based on treatment planning CT (TPCT) and BladderScan® BVI 6100 ultrasound device in a large prostate RT population. Three bladder volume (BV) measurements were taken using the bladder volume instrument (BVI) device on prostate RT patients immediately prior to TPCT (n = 190). The CT delineation bladder volumes were also recorded. The mean of the three BVI readings (BVImean) and the maximum (BVImax) of the readings were considered for a comparative analysis.

RESULTS:

There was a strong positive correlation between the BVI and CT delineated bladder volumes (BVImean r = 0.825; BVImax r = 0.830). The mean difference [± standard deviation (SD)] was an underestimation of BV for both BVImean and BVImax (44.8 ± 88.2 ml and 32.9 ± 87.5 ml, respectively).

CONCLUSION:

This is the largest study to date (n = 190), assessing the accuracy of the BladderScan® BVI 6100 in the prostate RT population. The BVI 6100 provides an acceptable indication of BV for use in prostate RT patients for the purposes of monitoring BV.

ADVANCES IN KNOWLEDGE:

The BladderScan® BVI 6100 provides a convenient and non-irradiating method of indicating BV for use in prostate RT 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.

Reducing rectal injury in men receiving prostate cancer radiation therapy: current perspectives

Dose escalation is now the standard of care for the treatment of prostate cancer with radiation therapy. However, the rectum tends to be the dose-limiting structure when treating prostate cancer, given its close proximity. Early and late toxicities can occur when the rectum receives large doses of radiation therapy. New technologies allow for prevention of these toxicities. In this review, we examine the evidence that supports various dose constraints employed to prevent these rectal injuries from occurring. We also examine the use of intensity-modulated radiation therapy and how this compares to older radiation therapy techniques that allow for further sparing of the rectum during a radiation therapy course. We then review the literature on endorectal balloons and the effects of their daily use throughout a radiation therapy course. Tissue spacers are now being investigated in greater detail; these devices are injected into the rectoprostatic fascia to physically increase the distance between the prostate and the anterior rectal wall. Last, we review the use of systemic drugs, specifically statin medications and antihypertensives, as well as their impact on rectal toxicity.

Extreme hypofractionation for early prostate cancer: Biology meets technology

The aim of this review is to present the available radiobiological, technical and clinical data about extreme hypofractionation in primary prostate cancer radiotherapy. The interest in this technique is based on the favourable radiobiological characteristics of prostate cancer and supported by advantageous logistic aspects deriving from short overall treatment time. The clinical validity of short-term treatment schedule is proven by a body of non-randomised studies, using both isocentric (LINAC-based) or non-isocentric (CyberKnife^®-based) stereotactic body irradiation techniques. Twenty clinical studies, each enrolling more than 40 patients for a total of 1874 treated patients, were revised in terms of technological setting, toxicity, outcome and quality of life assessment. The implemented strategies for the tracking of the prostate and the sparing of the rectal wall have been investigated with particular attention. The urinary toxicity after prostate stereotactic body irradiation seems slightly more pronounced as compared to rectal adverse events, and this is more evident for late occurring events, but no worse as respect to conventional fractionation schemes. As far as the rate of severe acute toxicity is concerned, in all the available studies the treatment was globally well tolerated. While awaiting long-term data on efficacy and toxicity, the analysed studies suggest that the outcome profile of this approach, alongside the patient convenience and reduced costs, is promising. Forty-eight ongoing clinical trials are also presented as a preview of the expectation from the near future.

Fiducial Markers Implanted during Prostate Brachytherapy for Guiding Conformal External Beam Radiation Therapy

Prostate movement imposes limits on safe dose-escalation with external beam radiation therapy. If the precise daily location of the prostate is known, dose escalation becomes more feasible. We have developed an approach to dose escalation using a combination of prostate brachytherapy followed by external beam radiation therapy in which fiducial markers are placed along with125 I seeds during transperineal interstitial permanent prostate brachytherapy. These markers serve to verify daily prostate location during the subsequent external beam radiotherapy. Prior to implementing this approach, preliminary studies were performed to test visibility of the markers. Three different125 I seed models, as well as gold and silver marker seeds were placed within tissue-equivalent phantoms. Images were obtained with conventional x-rays (75–85 kV) and 6 MV photons from a linear accelerator. All125 I seed models were clearly visible on conventional x-rays but none were seen with 6 MV photons. The gold markers were visible with both energies. The silver markers were visible with conventional x-rays and 6 MV x-rays, but not as clearly as the gold seeds at 6 MV. Subsequently, conventional x-rays, CT scans, and 6 MV port films were obtained in 29 patients in whom fiducial gold marker seeds were implanted into the prostate during125 I prostate brachytherapy. To address the possibility of “seed migration” within the prostate, CT scans were repeated 5 weeks apart in 14 patients and relative positions of the gold seeds were evaluated. The repeated CT scans showed no change in intraprostatic gold marker location, suggesting minimal migration. The gold seeds were visible with conventional x-rays, CT, and 6 MV port films in all patients. During the course of external beam radiation therapy, the gold markers were visible on routine 6 MV port films and were seen in different locations from film to film suggesting prostate motion. Mean daily displacement was 4–5 mm in the anterior-posterior, and 4–5 mm in superior-inferior dimensions. Left-right displacement appeared less, averaging 2–3 mm. We conclude that implantation of gold marker seeds during prostate brachytherapy represents an easily implemented and practical means of prostate localization during subsequent image-guided external beam radiotherapy. With such markers, conformality of the external beam component can be confidently improved without expensive new equipment.

Analysis of prostate bed motion using an endorectal balloon and cone beam computed tomography during postprostatectomy radiotherapy

Background

The authors conducted this prospective study to analyze the amount of interfractional prostate bed motion (PBM) and quantify its components with the use of an endorectal balloon (ERB).

Methods

A total of 1,348 cone beam computed tomography images from 46 patients who underwent postprostatectomy radiotherapy were analyzed. For the pilot image, electronic portal imaging, guided by skin marks was performed to ensure proper positioning and inflation of the ERB. Then, for bone matching, manual or automatic registration of the planning and each cone beam computed tomography was performed, based on the bony anatomy of the pelvis. Shifts (bony misalignment [BM]) in three directions were recorded at each treatment session. For prostate bed matching, manual matching was conducted based on the anterior rectal wall and the shift (PBM) was recorded. Total setup error was defined as the shift from the skin mark to the prostate bed matching, based on anterior rectal wall stretched by the ERB. PBM was defined as the difference between the total setup error and BM.

Results

Systematic errors for the total setup error were 1.0, 1.3, and 1.0 mm in the right–left, anterior–posterior, and superior–inferior directions, with random errors of 1.9, 2.4, and 1.9 mm, respectively. Systematic errors were 1.6, 1.6, and 0.3 mm for BM and 0.8, 1.1, and 0.9 mm for PBM, with random errors of 2.4, 2.5, and 1.1 mm for BM and 1.8, 2.2, and 1.9 mm for PBM.

Conclusion

The BM was the main component of the total setup error, suggesting that interfractional PBM was well controlled by the ERB device. Planning target volume margins of <5 mm were needed to include 95% of the interfractional variations when using an ERB.

A dosimetric comparison of ultra-hypofractionated passively scattered proton radiotherapy and stereotactic body radiotherapy (SBRT) in the definitive treatment of localized prostate cancer

BACKGROUND

We compared target and normal tissue dosimetric indices between ultra-hypofractionated passively scattered proton radiotherapy and stereotactic body radiotherapy (SBRT) in the definitive treatment of localized prostate cancer.

MATERIAL AND METHODS

Ten patients were treated definitively for localized prostate cancer with SBRT to a dose of 36.25 Gy in 5 fractions prescribed to a volume encompassing the prostate only. Dose-volume constraints were applied to the rectum, bladder, penile bulb, femoral heads, and prostatic and membranous urethra. Three-field passively scattered proton plans were retrospectively generated using target volumes from the same patients. Dosimetric indices were compared between the SBRT and proton plans using the Wilcoxon signed rank test.

RESULTS

All dose constraints were achieved using both ultra-hypofractionated passively scattered proton and SBRT planning. Proton plans demonstrated significant improvement over SBRT in mean dose delivered to the penile bulb (5.2 CGE vs. 11.4 Gy; p=0.002), rectum (6.7 CGE vs. 10.6 Gy; p=0.002), and membranous urethra (32.2 CGE vs. 34.4 Gy; p=0.006) with improved target homogeneity resulting in a significant reduction in hot spots and volumes of tissue exposed to low doses of radiation. Compared to proton planning, SBRT planning resulted in significant improvement in target conformality with a mean index of 1.17 versus 1.72 (p=0.002), resulting in a dose reduction to the volume of bladder receiving more than 90% of the PD (V32.6, 7.5% vs. 15.9%; p=0.01) and mean dose to the left (7.1 Gy vs. 10.4 CGE; p=0.004) and right (4.0 Gy vs. 10.9 CGE; p=0.01) femoral heads.

CONCLUSION

Target and normal tissue dose constraints for ultra-hypofractionated definitive radiotherapy of localized prostate cancer are readily achieved using both CK SBRT and passively scattered proton-based therapy suggesting feasibility of either modality.

The impact of stool and gas volume on intrafraction prostate motion in patients undergoing radiotherapy with daily endorectal balloon

PURPOSE

The aim of this study was to quantify the impact of rectal stool/gas volumes on intrafraction prostate motion for patients undergoing prostate radiotherapy with daily endorectal balloon (ERB).

METHODS

Total and anterior stool/gas rectal volumes were quantified in 30 patients treated with daily ERB. Real-time intrafraction prostate motion from 494 treatment sessions, at most 6 min in length, was evaluated using Calypso(®) tracking system.

RESULTS

The deviation of prostate intrafraction motion distribution was a function of stool/gas volume, especially when stool/gas is located in the anterior part of the rectum. Compared to patients with small anterior stool/gas volumes (<10 cm(3)), those with large volume (10-60 cm(3)) had a twofold increase in 3D prostate motion and interquartile data range within the 6th minute of treatment time. The 10% of the overall CBCT session where large anterior rectal volumes were observed demonstrated larger percentage of time at displacement greater than our proposed internal margin 3 mm.

CONCLUSION

Volume and location of stool/gas can directly impact the ERB's intrafraction immobilization ability. Although our patient preparation protocol and the 100 cm(3) daily ERB effectively stabilized prostate motion for 90% of the fractions, a larger-sized ERB may improve prostate fixation for patients with greater and/or variable daily rectal volume.

Whole pelvic intensity-modulated radiotherapy for high-risk prostate cancer: a preliminary report

Purpose

To assess the clinical efficacy and toxicity of whole pelvic intensity-modulated radiotherapy (WP-IMRT) for high-risk prostate cancer.

Materials and Methods

Patients with high-risk prostate cancer treated between 2008 and 2013 were reviewed. The study included patients who had undergone WP-IMRT with image guidance using electronic portal imaging devices and/or cone-beam computed tomography. The endorectal balloon was used in 93% of patients. Patients received either 46 Gy to the whole pelvis plus a boost of up to 76 Gy to the prostate in 2 Gy daily fractions, or 44 Gy to the whole pelvis plus a boost of up to 72.6 Gy to the prostate in 2.2 Gy fractions.

Results

The study cohort included 70 patients, of whom 55 (78%) had a Gleason score of 8 to 10 and 50 (71%) had a prostate-specific antigen level > 20 ng/mL. The androgen deprivation therapy was combined in 62 patients. The biochemical failure-free survival rate was 86.7% at 2 years. Acute any grade gastrointestinal (GI) and genitourinary (GU) toxicity rates were 47% and 73%, respectively. The actuarial rate of late grade 2 or worse toxicity at 2 years was 12.9% for GI, and 5.7% for GU with no late grade 4 toxicity.

Conclusion

WP-IMRT was well tolerated with no severe acute or late toxicities, resulting in at least similar biochemical control to that of the historic control group with a small field. The long-term efficacy and toxicity will be assessed in the future, and a prospective randomized trial is needed to verify these findings.

An overlap-volume-histogram based method for rectal dose prediction and automated treatment planning in the external beam prostate radiotherapy following hydrogel injection

PURPOSE

Hydrogel injected between the rectum and prostate prior to radiotherapy provides a possible means of increased dose sparing to the rectum. Here the authors evaluate the overlap volume histogram (OVH) metric as a means to predict the rectal dose following hydrogel injection. Whether OVH predicted dose can serve as the dose objective or constraint for automated treatment planning was also investigated.

METHODS

Treatment planning was performed on 21 prostate cancer patients both pre- and posthydrogel injection, with five-field IMRT delivering 78 Gy to the planning target volume (PTV). The authors quantify the geometrical relationship between the rectum and the prostate PTV using an OVH metric which determines the fractional volume of the rectum that is within a specified distance of the PTV. For an OVH distance the authors selected, L(20), the PTV expansion distance at which 20% of the rectum overlaps. The authors calculated the rectal dose, D(20), received by 20% of the rectum volume on the dose volume histogram. Linear regression was used to examine the correlation between the L(20) and D(20), and between ΔL(20) and ΔD(20) (i.e., the change of L(20) and D(20) posthydrogel injection). Additionally, rectal dose D(15), D(25), D(35), D(50), and bladder dose D(15) were predicted from the OVH (L(15), L(25), L(35), L(50), for rectum and L(15) for bladder) by the L(x)-D(x) linear regression. The predicted doses were applied to the objectives for automated treatment planning of ten plans from five patients. Automatically generated plans were compared with plans manually generated on trial-and-error basis.

RESULTS

The rectal L(20) was increased and dose D(20) decreased due to the enlarged separation of rectum caused by the hydrogel injection. Linear regression showed an inverse linear correlation between L(20) and D(20), and between ΔL(20) and ΔD(20) (r(2) = 0.77, 0.60, respectively; p < 0.0001). The increase in rectal sparing (ΔD(20)) is only weakly correlated with the volume of injected hydrogel (r(2) = 0.17; p = 0.07), indicating OVH is a more predictive indicator of rectal sparing than the volume of hydrogel itself. Application of the predicted rectum and bladder doses to automated planning produced acceptable treatment plans, with rectal dose reduced for eight of ten plans.

CONCLUSIONS

The OVH metric can predict the rectal dose in the external beam prostate radiotherapy for patients with hydrogel injection. The predicted doses can be applied to the objectives of optimization in automated treatment planning to produce acceptable treatment plans.

Temporary organ displacement coupled with image-guided, intensity-modulated radiotherapy for paraspinal tumors

Background

To investigate the feasibility and dosimetric improvements of a novel technique to temporarily displace critical structures in the pelvis and abdomen from tumor during high-dose radiotherapy.

Methods

Between 2010 and 2012, 11 patients received high-dose image-guided intensity-modulated radiotherapy with temporary organ displacement (TOD) at our institution. In all cases, imaging revealed tumor abutting critical structures. An all-purpose drainage catheter was introduced between the gross tumor volume (GTV) and critical organs at risk (OAR) and infused with normal saline (NS) containing 5-10% iohexol. Radiation planning was performed with the displaced OARs and positional reproducibility was confirmed with cone-beam CT (CBCT). Patients were treated within 36 hours of catheter placement. Radiation plans were re-optimized using pre-TOD OARs to the same prescription and dosimetrically compared with post-TOD plans. A two-tailed permutation test was performed on each dosimetric measure.

Results

The bowel/rectum was displaced in six patients and kidney in four patients. One patient was excluded due to poor visualization of the OAR; thus 10 patients were analyzed. A mean of 229 ml (range, 80–1000) of NS 5-10% iohexol infusion resulted in OAR mean displacement of 17.5 mm (range, 7–32). The median dose prescribed was 2400 cGy in one fraction (range, 2100–3000 in 3 fractions). The mean GTV D_min and PTV D_min pre- and post-bowel TOD IG-IMRT dosimetry significantly increased from 1473 cGy to 2086 cGy (p=0.015) and 714 cGy to 1214 cGy (p=0.021), respectively. TOD increased mean PTV D95 by 27.14% of prescription (p=0.014) while the PTV D05 decreased by 9.2% (p=0.011). TOD of the bowel resulted in a 39% decrease in mean bowel D_max (p=0.008) confirmed by CBCT. TOD of the kidney significantly decreased mean kidney dose and D_max by 25% (0.022).

Conclusions

TOD was well tolerated, reproducible, and facilitated dose escalation to previously radioresistant tumors abutting critical structures while minimizing dose to OARs.

Reducing rectal injury during external beam radiotherapy for prostate cancer

Rectal bleeding and faecal incontinence are serious injuries that men with prostate cancer who receive radiotherapy can experience. Although technical advances--including the use of intensity-modulated radiotherapy coupled with image-guided radiotherapy--have enabled the delivery of dose distributions that conform to the shape of the tumour target with steep dose gradients that reduce the dose given to surrounding tissues, radiotherapy-associated toxicity can not be avoided completely. Many large-scale prospective studies have analysed the correlations of patient-related and treatment-related parameters with acute and late toxicity to optimize patient selection and treatment planning. The careful application of dose-volume constraints and the tuning of these constraints to the individual patient's characteristics are now considered the most effective ways of reducing rectal morbidity. Additionally, the use of endorectal balloons (to reduce the margins between the clinical target volume and planning target volume) and the insertion of tissue spacers into the region between the prostate and anterior rectal wall have been investigated as means to further reduce late rectal injury. Finally, some drugs and other compounds are also being considered to help protect healthy tissue. Overall, a number of approaches exist that must be fully explored in large prospective trials to address the important issue of rectal toxicity in prostate cancer radiotherapy.

Effectiveness of a novel gas-release endorectal balloon in the removal of rectal gas for prostate proton radiation therapy

Endorectal balloons (ERBs) are routinely used in prostate proton radiation therapy to immobilize the prostate and spare the rectal wall. Rectal gas can distend the rectum and displace the prostate even in the presence of ERBs. The purpose of this work was to quantify the effects an ERB with a passive gas release conduit had on the incidence of rectal gas. Fifteen patients who were treated with a standard ERB and 15 with a gas-release ERB were selected for this retrospective study. Location and cross-sectional area of gas pockets and the fraction of time they occurred on 1133 lateral kilovoltage (kV) images were analyzed. Gas locations were classified as trapped between the ERB and anterior rectal wall, between the ERB and posterior rectal wall, or superior to the ERB. For patients using the standard ERB, gas was found in at least one region in 45.8% of fractions. Gas was trapped in the anterior region in 37.1% of fractions, in the posterior region in 5.0% of fractions, and in the sigmoid region in 9.6% of fractions. For patients using the ERB with the gas-release conduit, gas was found in at least one region in 19.7% of fractions. Gas was trapped in the anterior region in 5.6% of fractions, in the posterior region in 8.3% of fractions, and in the sigmoid region in 7.4% of fractions. Both the number of fractions with gas in the anterior region and the number of fractions with gas in at least one region were significantly higher in the former group than in the latter. The cross-sectional area of trapped gas did not differ between the two groups. Thus gas-release balloon can effectively release gas, and may be able to improve clinical workflow by reducing the need for catheterization.

In-phantom dose verification of prostate IMRT and VMAT deliveries using plastic scintillation detectors

The goal of this work was to demonstrate the feasibility of using a plastic scintillation detector (PSD) incorporated into a prostate immobilization device to verify doses in vivo delivered during intensity-modulated radiation therapy (IMRT) and volumetric modulated-arc therapy (VMAT) for prostate cancer. The treatment plans for both modalities had been developed for a patient undergoing prostate radiation therapy. First, a study was performed to test the dependence, if any, of PSD accuracy on the number and type of calibration conditions. This study included PSD measurements of each treatment plan being delivered under quality assurance (QA) conditions using a rigid QA phantom. PSD results obtained under these conditions were compared to ionization chamber measurements. After an optimal set of calibration factors had been found, the PSD was combined with a commercial endorectal balloon used for rectal distension and prostate immobilization during external beam radiotherapy. This PSD-enhanced endorectal balloon was placed inside of a deformable anthropomorphic phantom designed to simulate male pelvic anatomy. PSD results obtained under these so-called "simulated treatment conditions" were compared to doses calculated by the treatment planning system (TPS). With the PSD still inserted in the pelvic phantom, each plan was delivered once again after applying a shift of 1 cm anterior to the original isocenter to simulate a treatment setup error.The mean total accumulated dose measured using the PSD differed the TPS-calculated doses by less than 1% for both treatment modalities simulated treatment conditions using the pelvic phantom. When the isocenter was shifted, the PSD results differed from the TPS calculations of mean dose by 1.2% (for IMRT) and 10.1% (for VMAT); in both cases, the doses were within the dose range calculated over the detector volume for these regions of steep dose gradient. Our results suggest that the system could benefit prostate cancer patient treatment by providing accurate in vivo dose reports during treatment and verify in real-time whether treatments are being delivered according to the prescribed plan.

Acute gastrointestinal and genitourinary toxicity of image-guided intensity modulated radiation therapy for prostate cancer using a daily water-filled endorectal balloon

Background

Our purpose was to report acute gastrointestinal (GI) and genitourinary (GU) toxicity rates for prostate cancer patients undergoing image-guided intensity modulated radiation therapy (IG-IMRT) with a daily endorectal water-filled balloon (ERB_H2O), and assess associations with planning parameters and pretreatment clinical characteristics.

Methods

The first 100 patients undergoing prostate and proximal seminal vesicle IG-IMRT with indexed-lumen 100 cc ERB_H2O to 79.2 Gy in 1.8 Gy fractions at our institution from 12/2008- 12/2010 were assessed. Pretreatment characteristics, organ-at-risk dose volume histograms, and maximum GU and GI toxicities (CTCAE 3.0) were evaluated. Logistic regression models evaluated univariate association between toxicities and dosimetric parameters, and uni- and multivariate association between toxicities and pretreatment characteristics.

Results

Mean age was 68 (range 51–88). Thirty-two, 49, and 19 patients were low, intermediate, and high-risk, respectively; 40 received concurrent androgen deprivation. No grade 3 or greater toxicities were recorded. Maximum GI toxicity was grade 0, 1, and 2 in 69%, 23%, and 8%, respectively. Infield (defined as 1 cm above/below the CTV) rectal mean/median doses, D75, V30, and V40 and hemorrhoid history were associated with grade 2 GI toxicity (Ps < 0.05). Maximum acute GU toxicity was grade 0, 1, and 2 for 17%, 41%, and 42% of patients, respectively. Infield bladder V20 (P = 0.03) and pretreatment International Prostate Symptom Scale (IPSS) (P = 0.003) were associated with grade 2 GU toxicity.

Conclusion

Prostate IG-IMRT using a daily ERB_H2O shows low rates of acute GI toxicity compared to previous reports of air-filled ERB IMRT when using stringent infield rectum constraints and comparable GU toxicities.

The effects of motion on the dose distribution of proton radiotherapy for prostate cancer

Proton radiotherapy of the prostate basal or whole seminal vesicles using scattering delivery systems is an effective treatment of prostate cancer that has been evaluated in prospective trials. Meanwhile, the use of pencil beam scanning (PBS) can further reduce the dose in the beam entrance channels and reduce the dose to the normal tissues. However, PBS dose distributions can be affected by intra‐ and interfractional motion. In this treatment planning study, the effects of intra‐ and interfractional organ motion on PBS dose distributions are investigated using repeated CT scans at close and distant time intervals. The minimum dose (Dmin) and the dose to 2% and 98% of the volumes (D2% and D98%), as well as EUD in the clinical target volumes (CTV), is used as measure of robustness. In all patients, D98% was larger than 96% and D2% was less than 106% of the prescribed dose. The combined information from Dmin, D98% and EUD led to the conclusion that there are no relevant cold spots observed in any of the verification plans. Moreover, it was found that results of single field optimization are more robust than results from multiple field optimizations.

PACS numbers: 87.55.D‐, 87.55.de, 87.53.Bn, 87.55.dk, 87.55.ne

Increased rectal wall stiffness after prostate radiotherapy: relation with fecal urgency

BACKGROUND

  Late anorectal toxicity is a frequent adverse event of external beam radiotherapy (EBRT) for prostate cancer. The pathophysiology of anorectal toxicity remains unknown, but we speculate that rectal distensibility is impaired due to fibrosis. Our goal was to determine whether EBRT induces changes of rectal distensibility as measured by an electronic barostat and to explore whether anorectal complaints are related to specific changes of anorectal function.

METHODS

  Thirty-two men, irradiated for localized prostate carcinoma, underwent barostat measurements, anorectal manometry, and completed a questionnaire prior to and 1 year after radiotherapy. The primary outcome measure was rectal distensibility in response to stepwise isobaric distensions. In addition, we assessed sensory thresholds, anal pressures, and anorectal complaints.

KEY RESULTS

  External beam radiotherapy reduced maximal rectal capacity (227 ± 14 mL vs 277 ± 15 mL; P < 0.001), area under the pressure-volume curve (3212 ± 352 mL mmHg vs 3969 ± 413 mL mmHg; P < 0.005), and rectal compliance (15.7 ± 1.2 mL mmHg(-1) vs 17.6 ± 0.9 mL mmHg(-1) ; P = 0.12). Sensory pressure thresholds did not significantly change. Sixteen of the 32 patients (50%) had one or more anorectal complaints. Patients with urgency (n = 10) had a more reduced anal squeeze and maximum pressure (decrease 29 ± 11 mmHg vs 1 ± 7 mmHg; P < 0.05 and 31 ± 12 mmHg vs 2 ± 8 mmHg; P < 0.05 respectively) compared with patients without complaints, indicating a deteriorated external anal sphincter function.

CONCLUSIONS & INFERENCES

  Irradiation for prostate cancer leads to reduced rectal distensibility. In patients with urgency symptoms, anal sphincter function was also impaired.

Localization of a portion of an endorectal balloon for prostate image-guided radiation therapy using cone-beam tomosynthesis: a feasibility study

PURPOSE

To assess the feasibility of using cone-beam tomosynthesis (CBTS) to localize the air-tissue interface for the application of prostate image-guided radiation therapy using an endorectal balloon for immobilization and localization.

METHODS AND MATERIALS

A Feldkamp-David-Kress-based CBTS reconstruction was applied to selected sets of cone-beam computed tomography (CBCT) projection data to simulate volumetric imaging achievable from tomosynthesis for a limited range of scan angles. Projection data were calculated from planning CT images of 10 prostate cancer patients treated with an endorectal balloon, as were experimental CBCT projections for a pelvic phantom in two patients. More than 50 points at the air-tissue interface were objectively identified by an intensity-based interface-finding algorithm. Using three-dimensional point sets extracted from CBTS images compared with points extracted from corresponding CBCT images, the relative shift resulting from a reduced scan angle was determined. Because the CBCT and CBTS images were generated from the same projection data set, shift identified was presumed to be due to distortions introduced by the tomosynthesis technique.

RESULTS

Scans of ≥60° were shown to be able to localize an air-tissue interface near the isocenter with accuracy on the order of a millimeter. The accuracy was quantified in terms of the mean discrepancy as a function of reconstruction angle.

CONCLUSION

This work provides an understanding of the effect of scan angle used in localization of a portion of an endorectal balloon by means of CBTS. CBTS with relatively small scan angles is capable of accurately localizing an extended interface near the isocenter and may provide clinically relevant measurements to guide IGRT treatments while reducing imaging radiation to the patient.

A study to quantify the effectiveness of daily endorectal balloon for prostate intrafraction motion management

PURPOSE

To quantify intrafraction prostate motion between patient groups treated with and without daily endorectal balloon (ERB) employed during prostate radiotherapy and establish the effectiveness of the ERB.

METHODS

Real-time intrafraction prostate motion from 29 non-ERB (1,061 sessions) and 30 ERB (1,008 sessions) patients was evaluated based on three-dimensional (3D), left, right, cranial, caudal, anterior, and posterior displacements. The average percentage of time with 3D and unidirectional prostate displacements >2, 3, 4, 5, 6, 7, 8, 9, and 10 mm in 1-min intervals was calculated for up to 6 min of treatment time. The Kolmogorov-Smirnov method was used to evaluate the intrafraction prostate motion pattern between both groups.

RESULTS

Large 3D motion (up to 1 cm or more) was only observed in the non-ERB group. The motion increased as a function of elapsed time for displacements >2-8 mm for the non-ERB group and >2-4 mm for the ERB group (p < 0.05). The percentage time distributions between the two groups were significantly different for motion >5 mm (p < 0.05). The 3D symmetrical internal margin (IM) can be reduced from 5 to 3 mm (40% reduction), whereas the asymmetrical IM can be reduced from 3 to 2 mm (33% reduction) in cranial, caudal, anterior, and posterior for 6 min of treatment, when ERB is used. Beyond 6 min, the symmetrical 3D and asymmetrical cranial, caudal, anterior, and posterior IMs can be reduced from 9, 4, 7, 7, and 8 to 5, 2, 5, 3, and 4 mm, respectively (up to 57% reduction).

CONCLUSION

The percentage of time that the prostate was displaced in any direction was less in the ERB group for almost all magnitudes of motion considered. The directional analysis shows that the ERB reduced IMs in almost all directions, especially the anterior-posterior direction.

An endorectal balloon reduces intrafraction prostate motion during radiotherapy

PURPOSE

To investigate the effect of endorectal balloons (ERBs) on intrafraction and interfraction prostate motion during radiotherapy.

METHODS AND MATERIALS

Thirty patients were treated with intensity-modulated radiotherapy, to a total dose of 80 Gy in 40 fractions. In 15 patients, a daily-inserted air-filled ERB was applied. Prostate motion was tracked, in real-time, using an electromagnetic tracking system. Interfraction displacements, measured before each treatment, were quantified by calculating the systematic and random deviations of the center of mass of the implanted transponders. Intrafraction motion was analyzed in timeframes of 150 s, and displacements >1 mm, >3 mm, >5 mm, and >7 mm were determined in the anteroposterior, left-right, and superoinferior direction, and for the three-dimensional (3D) vector. Manual table corrections, made during treatment sessions, were retrospectively undone.

RESULTS

A total of 576 and 567 tracks have been analyzed in the no-ERB group and ERB group, respectively. Interfraction variation was not significantly different between both groups. After 600 s, 95% and 98% of the treatments were completed in the respective groups. Significantly fewer table corrections were performed during treatment fractions with ERB: 88 vs. 207 (p = 0.02). Intrafraction motion was significantly reduced with ERB. During the first 150 s, only negligible deviations were observed, but after 150 s, intrafraction deviations increased with time. This resulted in cumulative percentages of 3D-vector deviations >1 mm, >3 mm, >5 mm, and >7 mm that were 57.7%, 7.0%, 0.7%, and 0.3% in the ERB-group vs. 70.2%, 18.1%, 4.6%, and 1.4% in the no-ERB group after 600 s. The largest reductions in the ERB group were observed in the AP direction. These data suggest that a 5 mm CTV-to-PTV margin is sufficient to correct for intrafraction prostate movements when using an ERB.

CONCLUSIONS

ERB significantly reduces intrafraction prostate motion, but not interfraction variation, and may in particular be beneficial for treatment sessions longer than 150 s.

Using cone-beam computed tomography to evaluate the impact of bladder filling status on target position in prostate radiotherapy

PURPOSE

To assess bladder filling status and its impact on target position during daily intensity-modulated radiation therapy (IMRT) using cone-beam computed tomography (CBCT) in prostate cancer patients.

PATIENTS AND METHODS

23 patients with prostate cancer undergoing image-guided IMRT (78 Gy in 39 fractions) were included. On-board CBCT images were acquired daily and an endorectal balloon was placed daily. All patients were instructed to have a full bladder. The interfraction changes in bladder dimensions in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions were measured from CBCT images. Distances from the uppermost part of prostate to pubic bone (PP) and from the uppermost part of prostate to treatment isocenter (PI) were measured to determine changes in target position. Standard deviation (SD) in all fractions of each patient was used to compare the variations between patients. Bladder dimension change ratio and Z-score were used to normalize data between patients.

RESULTS

A total of 867 CBCT images were evaluated. The average LR, AP, and SI bladder dimensions were 7.8 +/- 1.5 cm, 6.7 +/- 1.4 cm, and 5.6 +/- 1.7 cm, respectively. The average LR, AP, and SI bladder dimension change ratios were 0.88 +/- 0.17, 0.90 +/- 0.15, and 0.86 +/- 0.32, respectively. The SD was significantly greater in SI dimension than in LR (p < 0.001) and AP (p < 0.001) dimensions. The interfraction changes in the three bladder dimensions were significantly larger than those of target position, and did not correlate with target position changes.

CONCLUSION

Though they were not negligible, changes in bladder filling status did not have a significant impact on target position.

Evaluation of Inter-fractional Setup Shifts for Site-specific Helical Tomotherapy Treatments

This paper proposes to summarize and analyze the daily patient setup shifts based on megavoltage computed tomography (MVCT) image registration results for Helical TomoTherapy® (HT) treatment. One hundred and fifty-five consecutive treatment plans for a total of 137 patients delivered by the HT unit through one year were collected in this study. The patient data included pelvis (26%), abdomen (23%), lung (21%), head and neck (10%), prostate (8%), and others (12%). All the translational and roll rotational shifts made via auto MVCT and kilovoltage computed tomography (kVCT) image registration were recorded at each fraction. Manual fine-tuning was followed if automatic registration result was not satisfactory. The mean shift ± one standard deviation (1 SD) was calculated for each patient based on the entire treatment course. For each treatment site, the average shift was analyzed as well as displacement in 3D vector. Statistical tests were performed to analyze the relationship of patient-specific, tumor site-specific, and fraction number association with the patient setup shifts. For all the treatment sites, the largest average shift was found in the anterior-posterior direction. The population standard deviations were between 1.2 and 5.6 mm for the X, Y, and Z directions and ranged from 0.2 to 0.6 degrees for the roll rotational correction. The largest standard deviations of the setup reproducibility in X, Y, and Z directions were found in lung patients (4.2 mm), abdomen, lung and spine patients (4.4 mm), and prostate patients (5.6 mm), respectively. The maximum 3D displacement was 10.9 mm for prostate patients' setup. ANOVA tests demonstrated the setup shifts were statistically different between patients even for those that were treated at the same tumor site in the translational directions. No strong correlation between the setup and the fraction number was found. In conclusion, the MVCT guided function in the HT treatment enables us to generate relatively accurate daily setup through registration with KVCT data sets. Our results indicate that lung, prostate, and abdominal patients are more prone to setup uncertainty and should be carefully evaluated.

PET and Radiation Therapy Planning and Delivery for Prostate Cancer

PET imaging has become an integral component of the diagnosis and management of a substantial number of lymphatic and solid malignancies. One of the greatest dilemmas in prostate cancer remains the need for greater personalization of treatment recommendations based on the true extent of disease, so that patients with extraprostatic, micrometastatic disease can be identified early and managed accordingly. These sites currently remain under the level of detection with standard imaging and continue to confound clinicians. Novel PET tracers to complement anatomic data from CT and MR imaging can truly make a difference, and ongoing research holds the greatest promise.

Sodium butyrate enemas in the treatment of acute radiation-induced proctitis in patients with prostate cancer and the impact on late proctitis. A prospective evaluation

PURPOSE

To evaluate prospectively the effect of sodium butyrate enemas on the treatment of acute and the potential influence on late radiation-induced proctitis.

PATIENTS AND METHODS

31 patients had been treated with sodium butyrate enemas for radiation-induced acute grade II proctitis which had developed after 40 Gy in median. During irradiation the toxicity was evaluated weekly by the Common Toxicity Criteria (CTC) and subsequently yearly by the RTOG (Radiation Therapy Oncology Group) and LENT-SOMA scale.

RESULTS

23 of 31 patients (74%) experienced a decrease of CTC grade within 8 days on median. A statistical significant difference between the incidence and the severity of proctitis before start of treatment with sodium butyrate enemas compared to 14 days later and compared to the end of irradiation treatment course, respectively, was found. The median follow-up was 50 months. Twenty patients were recorded as suffering from no late proctitis symptom. Eleven patients suffered from grade I and 2 of these patients from grade II toxicity, too. No correlation was seen between the efficacy of butyrate enemas on acute proctitis and prevention or development of late toxicity, respectively.

CONCLUSION

Sodium butyrate enemas are effective in the treatment of acute radiation-induced proctitis in patients with prostate cancer but have no impact on the incidence and severity of late proctitis.

Changes in prostate shape and volume and their implications for radiotherapy after introduction of endorectal balloon as determined by MRI at 3T

PURPOSE

To determine the changes in prostate shape and volume after the introduction of an endorectal coil (ERC) by means of magnetic resonance imaging (MRI) at 3T.

METHODS AND MATERIALS

A total of 44 consecutive patients with biopsy-proven prostate cancer underwent separate MRI examinations at 3T with a body array coil and subsequently with an ERC inflated with 50 mL of fluid. Prospectively, two experienced readers independently evaluated all data sets in random order. The maximal anteroposterior, right-to-left, and craniocaudal prostate diameters, as well as the total prostate and peripheral zone and central gland volumes were measured before and after ERC introduction. The changes in prostate shape and volume were analyzed using Wilcoxon's test for paired samples.

RESULTS

The introduction of the ERC significantly changed the prostate shape in all three directions, with mean changes in the anteroposterior, right-to-left, and craniocaudal diameters of 15.7% (5.5 mm), 7.7% (3.5 mm), and 6.3% (2.2 mm), respectively. The mean total prostate, peripheral zone, and central gland volume decreased significantly after ERC introduction by 17.9% (8.3 cm(3)), 21.6% (4.8 cm(3)), and 14.2% (3.4 cm(3)), respectively.

CONCLUSION

ERC introduction as observed by 3T MRI changed the prostate shape and volume significantly. The mean anteroposterior diameter was reduced by nearly one-sixth of its original diameter, and the mean total prostate volume was decreased by approximately 18%. This could cause difficulties and should be considered when using ERC-based MRI for MRI-computed tomography fusion and radiotherapy planning.

Advanced image-guided external beam radiotherapy

The goal of radiation therapy is to eradicate tumor stem cells while sparing healthy tissue. Therefore, the first aim must be to delineate tumor from healthy tissue. Advanced imaging techniques will enable one to reduce the uncertainty of microscopic extension of disease. Ultimately, advanced functional imaging systems correlated with image-registered pathological specimens will allow one to delineate disease extent from normal tissue at the tumor periphery. When it is not possible to determine the CTV margin with reasonable certainty, the margins must remain generous and conformal avoidance methodology could and should be deployed to spare critical normal structures. Of equal importance to defining the CTV is the need to guarantee that this target is indeed treated. For this purpose, image guidance using a variety of systems including portal images, ultrasound devices, and CT scanners at the time of treatment has been implemented. Some image-guided methods, portal images for instance, are more amenable for use with rigid structures such as encountered in the sinus whereas others like ultrasound or CT scanners are able to account for nonrigid setup variations. Several strategies for preventing organ motion from degrading the precision that radiotherapy offers have been described. In particular, a CT scan at the time of treatment delivery can also be used as the basis to reconstruct the dose received by the patient. Dose reconstruction will allow the dose just delivered to be superimposed on the pretreatment CT scan and will allow one to compare the reconstructed delivered dose distribution with the planned dose distribution to assess discrepancies between these. Furthermore, reconstruction of the delivered dose distributions holds the promise of allowing one to accumulate dose delivered to the tumor and normal structures on a fraction per fraction basis. This will ultimately allow for the determination of treatment-specific tumor control probabilities and normal tissue complication probabilities.

A prospective study of faecal calprotectin and lactoferrin in the monitoring of acute radiation proctitis in prostate cancer treatment

OBJECTIVE

Acute radiation proctitis is a relevant complication of pelvic radiation. The purpose of this study was to investigate two markers of gut inflammation as non-invasive diagnostic tools to evaluate acute radiation proctitis.

MATERIAL AND METHODS

Twenty patients who underwent radiotherapy for prostate cancer took part in this prospective study. Radiation-induced toxicity was evaluated weekly during radiotherapy in compliance with the CTC toxicity criteria. Stool samples from patients were examined before treatment, weekly during radiotherapy and 2 weeks after the end of radiotherapy using enzyme-linked immunosorbent assay for calprotectin and lactoferrin and correlated with the CTC toxicity.

RESULTS

Calprotectin and lactoferrin faecal values increased significantly during radiation treatment and decreased about 2 weeks after cessation of radiation. Faecal concentrations of calprotectin and lactoferrin correlated with the documented radiation proctitis symptoms (all grades together) in 15/20 patients (75%). With respect to changes in faecal concentrations and correspondence to proctitis symptoms, both markers showed parallel results in 90% of the patients. On comparing calprotectin and lactoferrin concentrations between the 4th week of radiation and the 1st week, it was found that patients with any grade of toxicity exhibited a significantly higher increase in calprotectin (p = 0.044) and lactoferrin (p = 0.05), respectively, compared with those without toxicity.

CONCLUSIONS

Calprotectin and lactoferrin faecal values changed during radiation treatment and after cessation of radiation, with correlation to acute proctitis symptoms in most of the patients. Before markers are used to monitor acute radiation proctitis, further experience should be acquired. Patients will be followed to determine the predictive value of the two tested markers for chronic radiation proctitis.

Distortion-correctedT2weighted MRI: a novel approach to prostate radiotherapy planning

The purpose of this study was to evaluate distortion-corrected MRI as a radiotherapy planning tool for prostate cancer and the resultant implications for dose sparing of organs at risk. 11 men who were to be treated with radical conformal radiotherapy for localized prostate cancer had an MRI scan under radiotherapy planning conditions, which was corrected for geometric distortion. Radiotherapy plans were created for planning target volumes derived from the MRI- and CT-defined prostate. Dose volume histograms were produced for the rectum, bladder and penile bulb. The mean volume of the prostate as defined on CT and MRI was 41 cm3 and 36 cm3, respectively (p = 0.009). The predicted percentage of the rectum treated to dose levels of 45-65 Gy was significantly lower for plans delineating the prostate with MRI than for those with CT. The rectal-sparing effect was confined to the lowermost 4 cm of the rectum (anal canal). There were no differences between the predicted doses to bladder or penile bulb (as defined using MRI) between plans. In conclusion, prostate radiotherapy planning based on distortion-corrected MRI is feasible and results in a smaller target volume than does CT. This leads to a lower predicted proportion of the rectum, in particular the lower rectum (anal canal), treated to a given dose than with CT.

Magnetic resonance imaging (MRI) anatomy of the prostate and application of MRI in radiotherapy planning

Radiotherapy planning for prostate carcinoma has traditionally been performed on computed tomography (CT)-images, on which both the high dose areas (prostate with or without seminal vesicles) as well as the low dose areas (surrounding structures, such as the rectum and bladder) are anatomically delineated. However, magnetic resonance imaging (MRI) provides much more information than CT; it can superbly demonstrate the internal prostatic anatomy, prostatic margins and the extent of prostatic tumours. Hence, MRI becomes a powerful tool to improve the accuracy of planning delineations in radiotherapy for prostate carcinoma and is rapidly gaining popularity in the radiotherapy community. The present paper reviews some important anatomical landmarks and acquisition protocols relevant to radiotherapy planning and explains the rationale and importance of close collaboration between radiotherapists and radiologists in optimizing radiotherapy for patients with prostate carcinoma.

Monte Carlo Calculation of Rectal Dose When Using an Intrarectal Balloon During Prostate Radiation Therapy

Air-filled intrarectal balloons can be used to localize and immobilize the prostate for radiation therapy, allowing dose escalation to the prostate and reducing the probability of radiation proctitis, but also introducing potentially significant heterogeneity. We compare the Eclipse treatment planning system (TPS) with Monte Carlo (MC) simulations for 5 patients to assess how well a conventional TPS includes the effect of the balloon on doses near the rectum. The MC results show that, for a 27-Gy prescription to the 95% isodose line, Eclipse overestimates the volume of the rectum receiving more than 26 Gy (96%) by 2 approximately 10 cc and the volume of the rectum receiving between 12 approximately 15 Gy by 10 approximately 20 cc. Differential dose volume histograms are also computed and compared for individual fields in the anterior expansion of the rectum, and the TPS is again shown to predict higher mean dose in the region by 0.3 approximately 1.0 Gy.

Hypofractionated Intensity-Modulated Radiotherapy (70 Gy at 2.5 Gy Per Fraction) for Localized Prostate Cancer: Cleveland Clinic Experience

PURPOSE

To study the outcomes in patients treated for localized prostate cancer with 70 Gy delivered at 2.5-Gy/fraction within 5 weeks.

METHODS AND MATERIALS

The study sample included all 770 consecutive patients with localized prostate cancer treated with hypofractionated intensity-modulated radiotherapy at the Cleveland Clinic between 1998 and 2005. The median follow-up was 45 months (maximum, 86). Both the American Society for Therapeutic Radiology and Oncology (ASTRO) biochemical failure definition and the alternate nadir + 2 ng/mL definition were used.

RESULTS

The overall 5-year ASTRO biochemical relapse-free survival rate was 82% (95% confidence interval, 79-85%), and the 5-year nadir + 2 ng/mL rate was 83% (95% confidence interval, 79-86%). For patients with low-risk, intermediate-risk, and high-risk disease, the 5-year ASTRO rate was 95%, 85%, and 68%, respectively. The 5-year nadir + 2 ng/mL rate for patients with low-, intermediate-, and high-risk disease was 94%, 83%, and 72%, respectively. The Radiation Therapy Oncology Group acute rectal toxicity scores were 0 in 51%, 1 in 40%, and 2 in 9% of patients. The acute urinary toxicity scores were 0 in 33%, 1 in 48%, 2 in 18%, and 3 in 1% of patients. The late rectal toxicity scores were 0 in 89.6%, 1 in 5.9%, 2 in 3.1%, 3 in 1.3%, and 4 in 0.1% (1 patient). The late urinary toxicity scores were 0 in 90.5%, 1 in 4.3%, 2 in 5.1%, and 3 in 0.1% (1 patient).

CONCLUSION

The outcomes after high-dose hypofractionation were acceptable in the entire cohort of patients treated with the schedule of 70 at 2.5 Gy/fraction.

Set-up errors due to endorectal balloon positioning in intensity modulated radiation therapy for prostate cancer

PURPOSE

To investigate the set-up errors and deformation associated with daily placement of endorectal balloons in prostate radiotherapy.

MATERIALS AND METHODS

Endorectal balloons were placed daily in 20 prostate cancer patients undergoing radiotherapy. Electronic portal images (EPIs) were collected weekly from anterior-posterior (AP) and lateral views. The EPIs were compared with digitally reconstructed radiographs from computed tomography scans obtained during pretreatment period to estimate displacements. The interfraction deformation of balloon was estimated with variations in diameter in three orthogonal directions throughout the treatment course.

RESULTS

A total of 154 EPIs were evaluated. The mean displacements of balloon relative to bony landmark were 1.8mm in superior-inferior (SI), 1.3mm in AP, and 0.1mm in left-right (LR) directions. The systematic errors in SI, AP, and LR directions were 3.3mm, 4.9 mm, and 4.0mm, respectively. The random (interfraction) displacements, relative to either bony landmarks or treatment isocenter, were larger in SI direction (4.5mm and 4.5mm), than in AP (3.9 mm and 4.4mm) and LR directions (3.0mm and 3.0mm). The random errors of treatment isocenter to bony landmark were 2.3mm, 3.2mm, and 2.6mm in SI, AP, and LR directions, respectively. Over the treatment course, balloon deformations of 2.8mm, 2.5mm, and 2.6mm occurred in SI, AP, and LR directions, respectively. The coefficient of variance of deformation was 7.9%, 4.9%, and 4.9% in these directions.

CONCLUSIONS

Larger interfractional displacement and the most prominent interfractional deformation of endorectal balloon were both in SI direction.

Multi-institutional clinical experience with the Calypso System in localization and continuous, real-time monitoring of the prostate gland during external radiotherapy

PURPOSE

To report the clinical experience with an electromagnetic treatment target positioning and continuous monitoring system in patients with localized prostate cancer receiving external beam radiotherapy.

METHODS AND MATERIALS

The Calypso System is a target positioning device that continuously monitors the location of three implanted electromagnetic transponders at a rate of 10 Hz. The system was used at five centers to position 41 patients over a full course of therapy. Electromagnetic positioning was compared to setup using skin marks and to stereoscopic X-ray localization of the transponders. Continuous monitoring was performed in 35 patients.

RESULTS

The difference between skin mark vs. the Calypso System alignment was found to be >5 mm in vector length in more than 75% of fractions. Comparisons between the Calypso System and X-ray localization showed good agreement. Qualitatively, the continuous motion was unpredictable and varied from persistent drift to transient rapid movements. Displacements > or =3 and > or =5 mm for cumulative durations of at least 30 s were observed during 41% and 15% of sessions. In individual patients, the number of fractions with displacements > or =3 mm ranged from 3% to 87%; whereas the number of fractions with displacements > or =5 mm ranged from 0% to 56%.

CONCLUSION

The Calypso System is a clinically efficient and objective localization method for positioning prostate patients undergoing radiotherapy. Initial treatment setup can be performed rapidly, accurately, and objectively before radiation delivery. The extent and frequency of prostate motion during radiotherapy delivery can be easily monitored and used for motion management.

X-ray–assisted positioning of patients treated by conformal arc radiotherapy for prostate cancer: Comparison of setup accuracy using implanted markers versus bony structures

PURPOSE

The aim of this study was to compare setup accuracy of NovalisBody stereoscopic X-ray positioning using implanted markers in the prostate vs. bony structures in patients treated with dynamic conformal arc radiotherapy for prostate cancer.

METHODS AND MATERIALS

Random and systematic setup errors (RE and SE) of the isocenter with regard to the center of gravity of three fiducial markers were measured by means of orthogonal verification films in 120 treatment sessions in 12 patients. Positioning was performed using NovalisBody semiautomated marker fusion. The results were compared with a control group of 261 measurements in 15 patients who were positioned with NovalisBody automated bone fusion. In addition, interfraction and intrafraction prostate motion was registered in the patients with implanted markers.

RESULTS

Marker-based X-ray positioning resulted in a reduction of RE as well as SE in the anteroposterior, craniocaudal, and left-right directions compared with those in the control group. The interfraction prostate displacements with regard to the bony pelvis that could be avoided by marker positioning ranged between 1.6 and 2.8 mm for RE and between 1.3 and 4.3 mm for SE. Intrafraction random and systematic prostate movements ranged between 1.4 and 2.4 mm and between 0.8 and 1.3 mm, respectively.

CONCLUSION

The problem of interfraction prostate motion can be solved by using implanted markers. In addition, the NovalisBody X-ray system performs more accurately with markers compared with bone fusion. Intrafraction organ motion has become the limiting factor for margin reduction around the clinical target volume.

Radiation proctopathy in the treatment of prostate cancer

PURPOSE

To compile and review data on radiation proctopathy in the treatment of prostate cancer with respect to epidemiology, clinical manifestations, pathogenesis, risk factors, and treatment.

METHODS

Medical literature databases including PubMed and Medline were screened for pertinent reports, and critically analyzed for relevance in the scope of our purpose.

RESULTS

Rectal toxicity as a complication of radiotherapy has received attention over the past decade, especially with the advent of dose-escalation in prostate cancer treatment. A number of clinical criteria help to define acute and chronic radiation proctopathy, but lack of a unified grading scale makes comparing studies difficult. A variety of risk factors, related to either radiation delivery or patient, are the subject of intense study. Also, a variety of treatment options, including medical therapy, endoscopic treatments, and surgery have shown varied results, but a lack of large randomized trials evaluating their efficacy prevents forming concrete recommendations.

CONCLUSION

Radiation proctopathy should be an important consideration for the clinician in the treatment of prostate cancer especially with dose escalation. With further study of possible risk factors, the advent of a standardized grading scale, and more randomized trials to evaluate treatments, patients and physicians will be better armed to make appropriate management decisions.