A variable speed translating couch technique for total body irradiation

We have developed a variable speed translating patient couch system for the delivery of total body irradiation (TBI). For a whole body Rando-type phantom, dose variation at mid-plane relative to the prescription point (navel) can be as high as 15% (neck or legs) with a constant velocity. By taking into account variations in body thickness, the intensity modulation radiation therapy, resulting from variable velocities, effectively delivers a uniform dose distribution at mid plane. The couch control user interface, technical aspects and dose planning optimization procedure for determining velocity distribution are described.

Seed misplacement and stabilizing needles in transperineal permanent prostate implants

BACKGROUND AND PURPOSE

Seed misplacement occurring in transperineal permanent implants contributes to the degradation in dose coverage. It has been suggested that needles could be used to immobilize the prostate and help reduce misplacement. This study investigates the effects of parallel stabilizing needles on seed misplacement.

MATERIALS AND METHODS

A group of ten patients implanted with stabilizing needles was compared with a group of 20 patients implanted without stabilization. Measurements were performed on the displacement of individual seeds and needles. The needle measurements are: insertion angle, the ratio of post-implant over pre-implant lengths and the clustering tendency, a measure of relative misplacement among the seeds of the same needle.

RESULTS

No difference was observed in seed misplacement. No difference was observed in needle insertion angle, a measure which was expected to improve with the use of stabilizing needles.

CONCLUSION

None of the expected effects from the use of parallel stabilizing needles have been observed. This method of prostate contention appears to be without benefits. Seed misplacement is most pronounced along the insertion axis and is caused by friction between prostatic tissues and implantation needles. Reducing friction could be a promising alternative to prostate contention in trying to reduce misplacement.

Observation study of electronic portal images for off-line verification

PURPOSE

The goals of this study were to evaluate the use of electronic portal imaging device (EPID) paper images as off-line verification tools and to assess the feasibility of replacing portal films by EPID printed images.

MATERIALS AND METHODS

Electronic portal images were acquired using a video-based imaging system. After contrast enhancement, these images were printed and compared to portal films when prescribed, and judged about their usefulness for off-line verification. A total of 2025 images were acquired from 322 fields on 137 patients. The images were shown to eight radiation oncologists and two senior residents in radiation oncology, each one of them judging fields relevant to his (her) daily practice. The questions asked were related to the choice of important anatomical structures and the visibility of such structures, the usefulness of the printed images, the comparison with portal films and the possible replacement of such films by paper images.

RESULTS

Answers to the different questions were treated as quantitative scores. For the visibility question, means and standard deviations were calculated for each individual structure, then a global score was obtained for a given treatment site. Means and standard deviations were also computed for the comparison question. Proportions and confidence intervals were used for the other questions. The results show that EPID paper images are useful for some treatment sites such as breast, thorax, prostate, abdomen, pelvis (other than rectum) and axilla. The image quality remains insufficient for some other sites such as head and neck and spine.

CONCLUSION

Although global anatomical landmarks scores are good, the usefulness score is not always as high because some essential anatomical structures scores must be taken into account. There is also a strong habit factor related to acceptance of EPID printed images as verification tools. As long as they see more and more images, radiation oncologists can more easily visualize anatomical structures and are less stringent when evaluating the efficiency of EPID paper images as off-line verification tools.

Miniature scintillating detector for small field radiation therapy

In planning stereotactic radiosurgery treatments, depth dose curves, profiles, and dose rate of treatment beams are difficult to obtain with conventional detectors because of loss of lateral electronic equilibrium and volume averaging. A scintillating detector with high spatial resolution and good reliability has been developed to overcome this problem. The miniature dosimeter consists of two identical radiation-resistant 10 m long silica optical fibers, each connected to an independent silicon photodiode. A small cylindrical polystyrene scintillator (3.9 mm3) is optically glued to the detection fiber. The light seen by the photodiode connected to this fiber arises from fluorescence of the scintillator and from the Cerenkov effect produced in silica. The reference signal produced by the fiber without scintillator is used to subtract the Cerenkov light contribution from the raw detector response. The sensitive volume of the scintillating detector is nearly water-equivalent and thus minimizes dose distribution perturbation in water. The miniature dosimeter has a spatial resolution comparable to the film-densitometer system. Profiles of 1 cm diam, 6 MV photon beam measured with both systems show very similar shapes. Furthermore, the use of photodiodes instead of photomultiplier tubes gives a better stability response and offers the possibility to perform absolute dosimetry.

Monte Carlo simulations of prostate implants to improve dosimetry and compare planning methods

The objective of this study is to use Monte Carlo simulations to assess the sensitivity of implant planning methods to seed misplacement. A model of seed misplacement is first developed. It is based upon data gathered after a study on source migration performed on 30 patients treated with I-125 transperineal implants. It consists of applying elementary transformations to every needle in a loading plan to produce a distorted implant mimicking the effect of migration. After being validated, the model has been used to tune the inverse planning system in use at our institution. The new planning system is now used clinically and actual results are compared with those predicted by simulations. Simulations were also used to compare our planning method with others. The new planning system increased the average postimplant dose-volume histogram DVH(160) from 82% to 93%, which is the value predicted by the simulations. This improvement is due to an increased dose margin providing coverage even in the presence of migration. At the same time, the dose to the urethra remained at 267 Gy because of a special protection feature included in the planning system. Some other implant planning methods are not as robust [average DVH(160) ranging from 76% to 85%] and deliver a higher dose to the urethra (close to 400 Gy). To conclude, a simple model of source migration can provide realistic feedback about sensitivity to migration of planning methods. It allowed a significant clinical improvement at our institution. The improved inverse planning system provided better coverage with fewer seeds (but equal total activity) than a manual method. Hence, a properly tuned inverse planning system has the potential to deliver the less sensitive plans. The model also helped demonstrate that planning methods are not equally robust to migration and that they should not be evaluated solely by the plans they produce, but also by their clinical (or simulated) results.

Automatic setup deviation measurements with electronic portal images for pelvic fields

The purpose of this work was to develop a fully automatic tool for the detection of setup deviation for small pelvic field using, in external beam radiotherapy, an electronic portal imaging device (EPID). The algorithm processes electronic portal images of prostate cancer patients. No fiducial points or user interventions are needed. Deviation measurements are based on bone edge detection performed with Laplacian of a Gaussian (LoG) operator. Two bone edge images are then correlated, one of which is a reference image taken as the first fraction image for the purpose of this study. The electronic portal images (EPI) also show band artefacts which are removed using the morphological top-hat transform. The algorithm was first validated with 59 phantom images acquired in clinical treatment conditions with known displacements. The algorithm was then validated with 79 clinical images where bone contours were delineated manually. For the phantom images, the setup deviations were measured with a absolute mean error of 0.59 mm and 0.47 mm with a standard deviation of 0.64 mm and 0.42 mm, horizontally and vertically, respectively. A second validation was performed using clinical prostate cancer images. The measured patient displacements have an absolute mean error of 0.48 mm and 1.41 mm with a standard deviation of 0.58 mm and 1.30 mm in the X and Y directions, respectively. The algorithm execution time on a SUN workstation is 5 s. This algorithm shows good potential as a setup deviation measurement tool in clinical practice. The possibility of using this algorithm combined with decision rules based on statistical observations is very promising.

A new penumbra generator for electron fields matching

Abutment of two or more electron fields to irradiate extended areas may lead to significant dose inhomogeneities in the junction region. This paper describes the geometric and dosimetric characteristics of a device developed to modify the penumbra of an electron beam and thereby improve the dose uniformity in the overlap region when fields are abutted. The device is a Lipowitz metal block placed on top of the electron applicator's insertion plate and positioned to stop part of the electron beam on the side of field abutment. The air-scattered electrons beyond the block increase the penumbra width from about 1.4 to 2.7-3.4 cm with an SSD of 100 cm. The modified penumbra is broad and almost linear at all depths for the 9 and 12 MeV electron beams used in this study. Film dosimetry was used to obtain beam profiles and isodose distributions of single modified beams and matched fields of 9 and 12 MeV as well as matched fields of both energies. Computer simulation was used to optimize the skin gap to be used and to quantify the dose uniformity as a function of the field separation for both modified and nonmodified beams. Results are presented for various field configurations. Without the penumbra generator, lateral setup errors of 2-3 mm may introduce dose variations of 20% or more in the junction region. Similar setup errors cause less than 5% dose variations when the penumbra generator is used to match the fields. The potential of the technique for the irradiation of curved surfaces is presented. A possible method for implementing the modified penumbra into a conventional treatment planning system is evaluated.

Electronic portal imaging device detection of radioopaque markers for the evaluation of prostate position during megavoltage irradiation: a clinical study

PURPOSE

This study was designed to assess daily prostatic apex motion relative to pelvic bone structures during megavoltage irradiation.

METHODS AND MATERIALS

Radioopaque markers were implanted under ultrasound guidance near the prostatic apex of 11 patients with localized prostatic carcinoma. Patients were subsequently treated with a four field-box technique at a beam energy of 23 MV. During treatment, on-line images were obtained with an electronic portal imaging device (EPID). The marker was easily identified, even on unprocessed images, and the distance between the marker and a bony landmark was measured. Timelapse movies were also reviewed. After the completion of treatment, a transrectal ultrasound examination was performed in 8 of 11 patients, to verify the position of the marker.

RESULTS

We acquired over 900 digital portal images and analyzed posterioanterior and right lateral views. The quality of portal images obtained with megavoltage irradiation was good. It was possible to evaluate pelvic bone structures even without image histogram equalization. Moreover, the radioopaque marker was easily visible on every online portal image. The review of timelapse movies showed important interfraction motion of the marker while bone structures remained stable. We measured the position of the marker for each fraction. Marker displacements up to 1.6 cm were measured between 2 consecutive days of treatment. Important marker motions were predominantly in the posteroanterior and cephalocaudal directions. In eight patients, we verified the position of the marker relative to the prostatic apex with ultrasound at the end of the treatments. The marker remained in the trapezoid zone. Intratreatment images reviewed in two cases showed no-change in marker position. Our results, obtained during the treatment courses, indicate similar or larger prostate motions than previously observed in studies that used intertreatment x-ray films and CT images. Marker implantation under transrectal ultrasound was well tolerated.

CONCLUSIONS

Radioopaque marker and the use of electronic portal imaging give a direct evaluation of prostatic motion during radiation treatment. As suggested in previous studies the motions observed are predominantly in the posteroanterior and cephalocaudal directions. Therefore, prostate motion during treatment is important and must be considered especially when using conformal therapy.

Optimization of permanent 125I prostate implants using fast simulated annealing

PURPOSE

Treatment planning of ultrasound-guided transperineal 125I permanent prostatic implants is a time-consuming task, due to the large number of seeds used and the very large number of possible source arrangements within the target volume. The goal of this work is to develop an algorithm based on fast simulated annealing allowing consistent and automatic dose distribution optimization in permanent 125I prostatic implants.

METHODS AND MATERIALS

Fast simulated annealing is used to optimize the dose distribution by finding the best seed distribution through the minimization of a cost function. The cost function includes constraints on the dose at the periphery of the planned target volume and on the dose uniformity within this volume. Adjustment between peripheral dose and the dose uniformity can be achieved by varying the weight factor in the cost function.

RESULTS

Fast simulated annealing algorithm finds very good seed distributions within 20,000 iterations. The computer time needed for the optimization of a typical permanent implant involving 60 seeds and 14 needles is approximately 15 min. An additional 5 min are necessary for isodose distribution computations and miscellaneous outputs.

CONCLUSION

The use of fast simulated annealing allows for an efficient and rapid optimization of dose distribution. This algorithm is now routinely used at our institution in the clinical planning of 125I permanent transperineal prostate implants for early stage prostatic carcinoma.

Verification and correction of setup deviations in tangential breast irradiation using EPID: gain versus workload

PURPOSE

When a deviation in the treatment setup is identified, when or how should it be corrected? With the aim of improving the precision and reducing the systematic errors while maintaining the workload to a minimum, a study was performed to define the proper set of actions for the correction of tangential breast setup deviations during the course of the treatment.

PATIENTS AND METHODS

Clinical data were taken from a prospective study of more than 2200 on-line Electronic Portal Images (EPI) from 20 patients treated with tangential irradiation following a partial mastectomy for an early stage (I and II) breast cancer. The values of the central lung distance were then entered in the verification/correction procedure and modified to correct only the portion of the deviation most likely attributed to systematic errors according to the maximum likelihood. The verification/ correction procedure uses an action level equal to FML x alpha/square root of N, where alpha is proportional to the standard deviation (alpha = n sigma) and N is the number of consecutive fractions delivered after the start of the treatment. FML is the fraction of the deviation due to the systematic errors estimated from the maximum likelihood of the two distributions. In addition to n, one needs to specify Nmax, the maximum number of consecutive measurements without correction, to apply the procedure. The combination of these two parameters C(n,Nmax) will determine the reduction of systematic errors (gain) and the number of measurements and corrections (workload) associated to the procedure.

RESULTS

The effects of three combinations, C(1,1), C(2,2), and C(3,4) were studied. Also, the analysis of the results after application of the procedure with and without the factor of maximum likelihood made individually for each patient demonstrates the importance of the FML.

CONCLUSIONS

The verification/correction procedure with the inclusion of the FML can effectively improve the accuracy when applied to clinical data. With the specific workload related to measurements and corrections performed at our institution, we have found that in the case of the tangential breast treatment, the optimum combination uses an action level equal to 2 sigma and a maximum of two consecutive measurements without correction.

The role of electronic portal imaging in tangential breast irradiation: a prospective study

Side effects due to irradiation of normal tissues and local failure can be associated with deviations in the patient positioning in radiation therapy. In particular, tangential breast irradiation may include normal lung tissue or even a small portion of the heart in the field. A prospective study was performed to assess the precision and the reproducibility of the tangential breast irradiation technique with the help of on-line electronic portal imaging devices (EPID). The influence of respiration on the treatment set-up was evaluated. Also, a comparison was made with simulation films to study the degree of concordance with the intended treatment. Twenty patients with early breast cancer receiving post-operative radiotherapy were entered in the study. Geometrical parameters were measured from daily on-line portal images taken for approximately 17 fractions of each tangential fields. Multiple images were also acquired (six per field) for six fractions for all patients, yielding a total of 2120 images including the simulator films. Random and systematic errors were obtained. Variations of the parameters between various fractions and within the same fraction were about 3 mm (1 SD) or less. Variation between simulation and treatment set-up was 4.3 mm or less. Large maximum deviations, reaching 22.9 mm, were observed in rare cases. This confirms the need to implement daily verification procedures and to correct deviations in the treatment set-up. The study has shown that EPID can help reaching a high accuracy in patient treatment.

Standardized pain flowsheet: impact on patient-reported pain experiences after cardiovascular surgery

BACKGROUND

Administration of analgesics per patient request or random pain assessments may provide inadequate pain management.

OBJECTIVE

To examine the impact of nurses' use of a standardized pain flowsheet to document pain assessment and pharmacologic management on patient-reported pain intensity.

METHODS

A pre-post intervention design was used to compare 61 patients. In the preimplementation group, traditional charting of pain presence or absence was documented in the narrative notes and pharmacologic management was recorded on the medication profile. In the postimplementation group, the intensity of pain and pharmacologic management were documented on a pain flowsheet. Within 24 hours after transfer to the step-down unit, patients were interviewed regarding pain intensity experienced in the surgical heart unit and at the time of questioning. The distribution of these pain intensity scores was compared.

RESULTS

The postimplementation group reported significantly lower pain intensity ratings for the average amount of pain experienced while in the surgical heart unit, the least amount of pain experienced while in the surgical heart unit, and the pain experienced at the moment of questioning.

CONCLUSIONS

Use of a standardized pain flowsheet to assess pain intensity and document pharmacologic intervention may improve pain management in postsurgical cardiovascular patients.

Standardized pain flowsheet: impact on patient-reported pain experiences after cardiovascular surgery

BACKGROUND: Administration of analgesics per patient request or random pain assessments may provide inadequate pain management. OBJECTIVE: To examine the impact of nurses' use of a standardized pain flowsheet to document pain assessment and pharmacologic management on patient-reported pain intensity. METHODS: A pre-post intervention design was used to compare 61 patients. In the preimplementation group, traditional charting of pain presence or absence was documented in the narrative notes and pharmacologic management was recorded on the medication profile. In the postimplementation group, the intensity of pain and pharmacologic management were documented on a pain flowsheet. Within 24 hours after transfer to the step-down unit, patients were interviewed regarding pain intensity experienced in the surgical heart unit and at the time of questioning. The distribution of these pain intensity scores was compared. RESULTS: The postimplementation group reported significantly lower pain intensity ratings for the average amount of pain experienced while in the surgical heart unit, the least amount of pain experienced while in the surgical heart unit, and the pain experienced at the moment of questioning. CONCLUSIONS: Use of a standardized pain flowsheet to assess pain intensity and document pharmacologic intervention may improve pain management in postsurgical cardiovascular patients.

Higher pentamidine levels in AIDS patients with hypoglycemia and azotemia during treatment of Pneumocystis carinii pneumonia

Trimethoprim-sulfamethoxazole (TMP-SMZ) and pentamidine are both licensed for the treatment of Pneumocystis carinii pneumonia (PCP). However, their use is associated with various adverse side effects. In this prospective study, 26 AIDS patients with 32 episodes of PCP were treated with pentamidine (4 mg/kg/d). Each patient was treated for 12 to 21 days, depending on the rapidity of onset of the clinical response. During the 32 PCP episodes, hypoglycemia occurred in 16 instances, azotemia in 12, liver toxicity in 10, and leukopenia in 8. The occurrence of thrombopenia, leukopenia, and liver toxicity was not related to age, pentamidine levels, or other complications. However, patients who had hypoglycemia during pentamidine treatment had higher serum pentamidine levels than patients who did not have hypoglycemia (107 +/- 40 versus 70 +/- 26 ng/ml, p less than 0.004). In addition, we observed that patients with azotemia showed higher pentamidine levels during treatment (120 +/- 35 versus 64 +/- 22 ng/ml, p less than 0.001). In fact, 100% (11/11) of patients with serum pentamidine concentration greater than 100 ng/ml had fasting hypoglycemia and/or azotemia, while 33% (7/21) of those with pentamidine levels less than 100 ng/ml had these side effects (p less than 0.001). The relative risk of these complications with pentamidine levels greater than 100 ng/ml was 3 (95% confidence interval, 1.6 to 5.5). Fine-tuning the dose of pentamidine may eventually prove useful to avoid toxicity and optimize therapy.

High pentamidine levels associated with hypoglycemia and azotemia in a patient with Pneumocystis carinii pneumonia

We report on a patient who presented with a Pneumocystis carinii pneumonia. Intravenous pentamidine (4 mg/kg/day) was given for 14 days without the occurrence of adverse effects. During this treatment, the mean (+/- SD) serum pentamidine trough concentration was 94 +/- 16 ng/ml. Three days later, the patient was admitted because of fever, and pentamidine (4 mg/kg/day) was again started. Fasting hypoglycemia and azotemia then occurred; the mean serum trough pentamidine level was 190 +/- 10 ng/ml during this week of treatment. We conclude that the occurrence of hypoglycemia and azotemia during pentamidine therapy may not be idiosyncrasic, but seemed associated in our patient with high levels of serum pentamidine.