An open-source and easily replicable hardware for Electrical Impedance Tomography

Electrical Impedance Tomography (EIT) is a powerful imaging tool for investigating electrical properties of tissues such as that of human bodies. The cheap, harmless and portable nature of this tool has made EIT a popular choice in many biomedical applications. However, performing EIT requires strong development at both hardware and software levels. In particular, performing in-lab experiences remains a challenge due to the cost of commercially available devices or the complexity of systems proposed in scientific literature. In this paper, an efficient and easily replicable EIT hardware is presented. This hardware was developed with the objective of making EIT accessible to as many people as possible. It has been designed for operating frequencies between 1 kHz and 50 kHz, and can be used for in-lab validation of proof of concept. Special care has been paid to the choice of components in order to optimize the performance versus cost ratio. Also, the overall footprint has been reduced by using recent and up-to-date integrated circuits. In particular, the use of a lock-in amplifier is a compact solution that allows both narrow-band filtering of the signal and provides an easily quantifiable DC signal at the output. Circuit schematics as well as manufacturing files are shared so that understanding, replication and improvement of circuits are facilitated. Fabrication and usage procedures are given as well. At last, the proposed hardware is experimentally tested and validated first by comparing experimental data to simulations, then by reconstructing an inclusion in biological tissues.

Open low-field magnetic resonance imaging for target definition, dose calculations and set-up verification during three-dimensional CRT for glioblastoma multiforme

AIMS

To assess the effect on target delineation of using magnetic resonance simulation for planning of glioblastoma multiforme (GBM). Dose calculations derived from computed tomography- and magnetic resonance-derived plans were computed. The accuracy of set-up verification using magnetic resonance imaging (MRI)-based digital reconstructed radiographs (DRRs) was assessed.

MATERIALS AND METHODS

Ten patients with GBM were simulated using computed tomography and MRI. MRI was acquired with a low-field (0.23 T) MRI unit (SimMRI). Gross tumour volumes (GTVs) were delineated by two radiation oncologists on computed tomography and MRI. In total, 30 plans were generated using both the computed tomography, with (planbathoCT) and without (planCT) heterogeneity correction, and MRI data sets (planSimMRI). The minimum dose delivered (Dmin) to the GTV between computed tomography- and MRI-based plans was compared. The accuracy of set-up positioning using MRI DRRs was assessed by four radiation oncologists.

RESULTS

The mean GTVs delineated on computed tomography were significantly (P<0.001) larger than those contoured on MRI. The mean (+/-standard deviation) Dmin difference percentage was 0.3+/-0.8, 0.1+/-0.6 and -0.2+/-1.0% for the planCT/planbathoCT-, planCT/planSimMRI- and planbathoCT/planSimMRI-derived plans, respectively. The set-up differences observed with the computed tomography and MRI DRRs ranged from 1.0 to 4.0 mm (mean 1.5 mm; standard deviation+/-1.4).

CONCLUSIONS

GTVs defined on computed tomography were significantly larger than those delineated on MRI. Compared with computed tomography-derived plans, MRI-based dose calculations were accurate. The precision of set-up verifications based on computed tomography- and MRI-derived DRRs seemed similar. The use of MRI only for the planning of GBM should be further assessed.

Assessment of target dose delivery in anal cancer using in vivo thermoluminescent dosimetry

PURPOSE

To measure anal dose during external beam radiotherapy (EBRT) using in vivo dosimetry, to study the difference of measured from prescribed dose values, and to evaluate possible associations of such differences with acute and late skin/mucosal toxicity and anorectal function.

MATERIALS

Thirty-one patients with localized anal carcinoma underwent in vivo measurements during the first EBRT session. Themoluminescent dosimeters (TLD) were placed at the center of the anal verge according to a localization protocol. No bolus was used. Patients received a median dose of 39.6 Gy (range: 36-45 Gy) by anteroposterior opposed AP/PA pelvic fields with 6 or 18 MV photons, followed by a median boost dose of 20 Gy (range: 13-24 Gy). Concomitant chemotherapy (CCT), consisting of 1-2 cycles of continuous infusion 5-fluorouracil (5-FU) and bolus mitomycin-C (MMC), was usually administered during the first weeks of the pelvic and boost EBRT courses. Acute and late skin/mucosal reactions were recorded according to the Radiation Therapy Oncology Group (RTOG) toxicity scale. Anal sphincter function was assessed using the Memorial Sloan Kettering Cancer Center (MSKCC) scale.

RESULTS

TLD anal doses differed by a mean of 5.8% (SD: 5.8) in comparison to the central axis prescribed dose. Differences of at least 10% and at least 15% were observed in eight (26%) and three (9.7%) patients, respectively. TLD doses did not significantly correlate with acute or late grade 2-3 skin or mucosal toxicity. However, patients having good-fair MSKCC anal function had a significantly greater mean difference in anal TLD dose (10.5%, SD: 5.9) than patients having excellent function (3.8%, SD: 4.6) (P = 0.004). Prescribed dose values, length of follow-up, and age at diagnosis did not correlate with late sphincter function.

CONCLUSIONS

These data show that AP/PA fields using megavoltage photons deliver adequate dose to the anal verge. However, in about one quarter of patients treated with this technique the anal dose varied from the prescribed dose by at least 10%. The observed correlation of TLD values and late sphincter function suggests that direct measurement of the dose delivered to the anal verge might be clinically relevant.

X-ray dose to the skin in patients undergoing percutaneous transluminal coronary angioplasty

Dose measurements were performed with an ionization chamber placed on the surface of a polystyrene phantom to estimate the radiation dose to the skin from fluoroscopy in patients undergoing PTCA and to define parameters predicting for high-risk irradiation conditions. Dose rate changes were analyzed as a function of phantom thickness, X-ray source-to-phantom distance, image intensifier-to-phantom distance, and field size. Skin dose calculations were made in 38 PTCA patients to validate the model. Thickness was the most important factor determining dose rate changes in the phantom's surface. Dose rate increased by a factor of almost 4 with each 10-cm increment in thickness, doubled upon decreasing the field diameter from 17 cm to 14 cm, and increased by a factor of 1.2 to 1.8 upon decreasing the source-to-phantom distance or by increasing the image intensifier-to-patient distance. All these parameters may significantly increase the dose to the skin and augment the risk for skin injuries post-PTCA.

Patient positioning in prostate radiotherapy: is prone better than supine?

PURPOSE

To assess potential dose reductions to the rectum and to the bladder with three-dimensional conformal radiotherapy (3D-CRT) to the prostate in the prone as compared with the supine position; and to retrospectively evaluate treatment position reproducibility without immobilization devices.

METHODS AND MATERIALS

Eighteen patients with localized prostate cancer underwent pelvic CT scans and 3D treatment planning in prone and supine positions. Dose-volume histograms (DVHs) were constructed for the clinical target volume, the rectum and the bladder for every patient in both treatment positions. "Comparative DVHs" (cDVHs) were defined for the rectum and for the bladder: cDVH was obtained by subtracting the organ volume receiving a given dose increment in the prone position from the corresponding value in the supine position. These values were then integrated over the entire dose range. The prescribed dose to the planning target volume (PTV) was 74 Gy using a 6-field technique. To evaluate reproducibility, portal films were subsequently reviewed in 12 patients treated prone and 10 contemporary patients treated supine (controls). No immobilization devices were used. Deviations in the anterio-posterior (X) and cranio-caudal (Y) axes were measured. Mean treatment position variation, total setup variation, systematic setup variation, and random setup variation were obtained.

RESULTS

Prone position was associated with a higher dose to the rectum or to the bladder in 6 (33%) and 7 (39%) patients, respectively. A simultaneously higher dose to rectum and bladder was noted in 2 (11%) patients in prone and in 7 (39%) patients in supine. Rectal and bladder volumes were frequently larger in prone than in supine: mean prone/supine volume ratios were 1.21 (SD, 0.68) and 1.03 (SD, 1.32), respectively. In these cases cDVH analysis more often favored the prone position. Mean treatment position variation and total setup variation were similar for both prone and supine plans. A higher systematic setup variation was observed in prone positioning: 2.7 mm vs. 1.9 mm (X axis) and 4.1 mm vs. 2.2 mm (Y axis). The random variation was similar for both prone and supine: 4. 0 mm vs. 3.6 mm (X axis) and 3.7 mm vs. 3.6 mm (Y axis).

CONCLUSIONS

Prone position 3D-CRT is frequently, but not always, associated with an apparent dose reduction to the rectum and/or to the bladder for prostate cancer patients. As suggested by the increased mean prone/supine rectal volume ratio, the advantage of prone positioning for the rectum may be artifactual, at least partly reflecting a position-dependent rectal air volume, which may significantly vary from treatment to treatment. In the absence of immobilization devices, daily setup reproducibility appears less accurate for the prone position, primarily due to systematic setup variations.

Feasibility and tolerance of pulsed dose rate interstitial brachytherapy

PURPOSE

Pulsed dose rate (PDR) treatment is a new approach that associates the physical advantages of high-dose-rate (HDR) technology with the potential radiobiological advantages of low-dose-rate (LDR) brachytherapy. This retrospective study analyzes the feasibility, toxicity, and preliminary oncologic results in a series of 43 patients treated with PDR interstitial brachytherapy.

METHODS AND MATERIALS

Twenty-four patients with pelvic, 17 patients with head and neck, and 2 patients with breast cancers were treated. Twenty-eight patients had primary and 15 recurrent tumors; 14 had received prior external irradiation to the same site. The doses per pulse at the prescription isodose were 0.4-1 Gy (median 0.5 Gy), delivered using a single cable-driven 0.3-1.0 Ci 192-iridium source (PDR Nucletron Micro-Selectron).

RESULTS

The median treated volumes (at the prescribed isodose) were 28 cc for pelvic, 8.33 cc for head and neck, and 40 cc for breast malignancies. Of 14,499 source and 14,499 dummy source transfer procedures, 3 technical machine failure events were observed (0.02%). Grade 3 acute toxicities were seen in 5/43 patients (4 oral stomatitis, 1 vaginal mucositis) and grade 4 acute toxicity in one patient (rectovaginal fistula). Grade 3-4 late complications were observed in 4/41 (9.8%) patients: 1 pubic fracture, 1 rectovaginal fistula, 1 vesicovaginal fistula and 1 local necrosis. With a median follow-up of 18 months, 10/41 patients progressed locoregionally (6 pelvic, 4 head and neck), 3 developed local recurrence and distant metastasis (3 pelvic), 3 only distant metastasis (2 pelvic, 1 head and neck). Two patients are lost to follow-up.

CONCLUSION

PDR interstitial brachytherapy for pelvic, head and neck, and breast malignancies is feasible and the acute and late toxicities seem acceptable. Although the physical advantages of PDR are clear, further follow-up is required to determine how results compare with those obtained with standard LDR brachytherapy.

Radiotherapy of bladder cancer: relevance of bladder volume changes in planning boost treatment

PURPOSE

This study aims to evaluate tumor motion with controlled changes of the bladder volume, and to assess the reproducibility of bladder (and tumor) position using a urinary catheter balloon as an immobilization device.

METHODS AND MATERIALS

First, three patients with tumor growths in three different bladder regions (trigone, left lateral wall, anterior wall) were evaluated. Three-dimensional CT-based reconstructed images were used to measure the displacement of the tumors when 100 cc were removed from a bladder originally filled with 170 cc of contrast. The 3D calculated boost beam arrangements and field sizes for the three tumors in the partially emptied bladders were used to simulate treatment of the same tumors in the maximally filled bladders. Dose-volume histograms were obtained. Second, verification of an ellipsoid model for bladder volume changes was undertaken in 41 patients. Third, in eight additional patients a urinary catheter balloon filled with 80-cc sterile saline solution was used in an attempt to reproduce the shape and spatial coordinates of the bladder during the boost treatment. A pair of orthogonal films with the 80-cc balloon filled with contrast material were taken at simulation and repeated twice at weekly intervals during radiotherapy. The reproducibility was quantified by sequentially calculating the common surface of the bladder images in each orthogonal view.

RESULTS

Target motion, especially in the craniocaudal axis, appeared to be more relevant for tumors arising in the bladder walls (15 mm) than in the trigone (5 mm). Underdosage (<95% of the prescribed dose to the target volume) was observed in 20, 20, and 50% (with 1 cm margins around the tumor) and in 10, 10, and 15% (with 1.5 cm margins around the tumor) of the tumors arising in the trigone, left lateral wall, and anterior wall, respectively. The ellipsoidal model was validated with a strong correlation coefficient allowing to establish a predictive model for bladder wall displacements as a function of bladder volume. In the balloon reproducibility study, mean reproducibility factors of 0.84 (+/-0.06) and 0.82 (+/-0.07) were obtained for both anteroposterior and lateral views, respectively.

CONCLUSIONS

Changes in bladder volume and shape related to bladder filling can result in clinically significant displacements of the target volume. A minimum of 2-cm margins around the target may compensate for extreme bladder volume changes during boost treatment. An ellipsoidal model for the bladder is consistent with these observations. Although an 80-cc urinary catheter balloon helped to immobilize the bladder, reproducibility was less than perfect.

Feasibility of intracoronary beta-irradiation to reduce restenosis after balloon angioplasty. A clinical pilot study

BACKGROUND

With the aim of decreasing the incidence of restenosis after coronary balloon angioplasty, we developed a technique of intracoronary beta-irradiation using an endoluminally centered pure metallic 90Y source. The purpose of the present study was to evaluate the clinical feasibility and safety profile of this approach with a dose of 18 Gy delivered to the inner arterial surface.

METHODS AND RESULTS

Between June 21 and November 15, 1995, fifteen patients (6 women and 9 men; mean age, 71 +/- 5 years) underwent intracoronary beta-irradiation immediately after a conventional percutaneous transluminal coronary angioplasty (PTCA) procedure. The PTCA/irradiation procedure was technically feasible in all attempted cases, and the delivery of the 18 Gy dose was accomplished without complications. In 4 patients, the intervention was completed through intra-arterial stent implantation because of dissection induced by the initial PTCA. During the follow-up period of 178 +/- 17 days (range, 150 to 225 days), no complication occurred that could be attributed to radiation therapy. No aneurysm or angiographically detectable thrombus was observed in any of the irradiated arterial segments. The clinical event rate (4 of 15 patients underwent further target lesion revascularization) and the angiographic follow-up (6 of 15 patients had a > 50%-diameter stenosis at the previously treated site) did not suggest a marked impact on the expected restenosis rate.

CONCLUSIONS

This early experience demonstrates that our approach is feasible, and no side effects attributable to radiation were noted during a 6-month period of follow-up. Whether higher doses of beta-irradiation will favorably affect post-PTCA restenosis in patients must await further evaluation.

Pediatric medulloblastoma: radiation treatment technique and patterns of failure

PURPOSE

In this study factors are analyzed that may potentially influence the site of failure in pediatric medulloblastoma. Patient-related, disease-related, and treatment-related variables are analyzed with a special focus on radiotherapy time-dose and technical factors.

METHODS AND MATERIALS

Eighty-six children and adolescents with a diagnosis of medulloblastoma were treated in Switzerland during the period 1972-1991. Postoperative megavoltage radiotherapy was delivered to all patients. Simulation and portal films of the whole-brain irradiation (WBI) fields were retrospectively reviewed in 77 patients. The distance from the field margin to the cribiform plate and to the floor of the temporal fossa was carefully assessed and correlated with supratentorial failure-free survival. In 19 children the spine was treated with high-energy electron beams, the remainder with megavoltage photons. Simulation and port films of the posterior fossa fields were also reviewed in 72 patients. The field size and the field limits were evaluated and correlated with posterior fossa failure-free survival.

RESULTS

In 36 patients (47%) the WBI margins were judged to miss the inferior portion of the frontal and temporal lobes. Twelve patients failed in the supratentorial region and 9 of these patients belonged to the group of 36 children in whom the inferior portion of the brain had been underdosed. On multivariate analysis only field correctness was retained as being significantly correlated with supratentorial failure-free survival (p = 0.049). Neither the total dose to the spinal theca nor the treatment technique (electron vs. photon beams) were significantly correlated with outcome. Posterior fossa failure-free survival was not influenced by total dose, overall treatment time, field size, or field margin correctness. Overall survival was not influenced by any of the radiotherapy-related technical factors.

CONCLUSION

A correlation between WBI field correctness and supratentorial failure-free survival was observed. Treatment protocols should be considered that limit supratentorial irradiation mainly to subsites at highest risk of relapse. Optimized conformal therapy or proton beam therapy may help to reach this goal. Treating the spine with electron beams was not deletereous. A significant correlation between local control and other technical factors was not observed, including those relating to posterior fossa treatment. The use of small conformal tumor bed boost fields may be prefered to the larger posterior fossa fields usually considered as the standard treatment approach.

A novel system for intracoronary beta-irradiation: description and dosimetric results

PURPOSE

A dosimetric evaluation of a new device dedicated to intravascular irradiation, associating a beta source and a centering device, was carried out before initiation of a clinical pilot study.

METHODS AND MATERIALS

A 29-mm-long 90Y coil, coated with titanium and fixed to the end of a thrust wire, was introduced into the inner lumen of purpose-built centering balloons of different diameters (2.5, 3, 3.5, and 4 mm). Dose homogeneity was evaluated by studying both axial and circumferential dose variations, based on readings from thermoluminescent dosimeters (TLDs) placed on the balloon surface. Axial homogeneity was determined by comparing the readout values of dosimeters located on peripheral balloon segments with those located on segments adjacent to the midpoint of the source. The centering ability of the device was studied by comparing measurements on opposing surfaces of the balloon. The dose attenuation by water and contrast medium was evaluated and compared with that in air. The balloon contamination was studied using a contamination counter. The total 90Y coil activity was measured by liquid scintillation to relate activity to surface dose.

RESULTS

Activity-surface dose correlation showed that for a linear coil activity of 1 mCi/mm, the mean dose rate at the surface of a 2.5-mm balloon filled with contrast medium was 8.29 Gy/min. The doses at the surface of larger balloons (3, 3.5, and 4 mm) filled with contrast were 78%, 59%, and 47%, respectively, of the dose measured at the surface of the 2.5-mm balloon. The coefficient of variation (CV) in surface dose for 2.5-, 3-, 3.5-, and 4-mm centering devices filled with contrast medium were 9%, 8%, 9%, and 12%, respectively. There was no statistically significant difference between readouts from central and peripheral balloon segments or among rows of dosimeters facing each other. For a 2.5-mm balloon, compared with air the dose attenuation by water and contrast medium was similar (0.70 and 0.69, respectively), but a significant difference was seen between the readouts of water- and contrast-filled balloons when the diameter was larger than 3 mm (p < 0.001). No contamination was found in the balloon shaft after source retrieval.

CONCLUSION

The dosimetric tests showed very good surface dose homogeneity, demonstrating satisfactory centering of the source within the centering balloons. The achievable dose rates will permit intravascular irradiation within a short time interval. The absence of residual balloon contamination after source retrieval meets the requirements for a sealed source used in a clinical setting.

Reproducibility of conformal radiation therapy in localized carcinoma of the prostate without rigid immobilization

The reproducibility of 3-dimensional (3D) conformal therapy in localized prostate cancer was studied in 14 patients, based on retrospective analysis of 196 anteroposterior-posteroanterior (AP/PA) and lateral portal images. The patients were treated supine without rigid immobilization using six isocentric coplanar conformal fields. Three different observers independently compared the portal and simulation images, determining the deviation of each portal film from the corresponding simulation film. No significant deviations were observed in the cephalo-caudal or lateral axes (0 mm median values). However, a systematic median shift of 5 mm (0 to + 10, range) was observed in the anteroposterior direction, presumably as a consequence of a sagging in the treatment couch under the patient's weight. After modification of the treatment couch, no further systematic anteroposterior shifts have been observed. These results demonstrate that the daily setup of conformal prostate irradiation fields can be performed with acceptable reproducibility without the use of special immobilization devices.

Intra-arterial beta irradiation prevents neointimal hyperplasia in a hypercholesterolemic rabbit restenosis model

BACKGROUND

Intra-arterial gamma irradiation has been shown to reduce restenosis after balloon angioplasty. The use of beta emitters should allow similar effects while inducing less undue tissue irradiation radioprotection problems.

METHODS AND RESULTS

Flexible 90-yttrium (90Y) coils inside a centering balloon were used to allow homogeneous intraarterial dose delivery. One carotid and one iliac artery of 21 hypercholesterolemic rabbits were deendothelialized and then irradiated. Four dose schedules were studied: (1) control (dilated, nonirradiated); (2) 6 Gy; (3) 12 Gy; and (4) 18 Gy. Arterial specimens were histologically evaluated at 8 days and at 6 weeks. For all radiation doses at 8 days compared with controls, there was a significant decrease in bromodeoxyuridine-labeled cells (245 +/- 93 cells/cm in control, 42 +/- 27 in 6 Gy, 72 +/- 107 in 12 Gy, and 2 +/- 2 in 18 Gy groups; P < .001) and in total neointimal cells (891 +/- 415 cells/cm in control, 79 +/- 43 in 6 Gy, 192 +/- 264 in 12 Gy and 22 +/- 13 in 18 Gy groups; P < .0002). At 6 weeks, computer-derived histological percent area stenosis was reduced from 26 +/- 10% in the control group to 1 +/- 1.3% in the 18 Gy group (P < .0001), but lower doses had no significant effect.

CONCLUSIONS

Administration of intra-arterial beta irradiation with a 90Y source is technically feasible and compatible with an ordinary catheterization laboratory environment. A dose of 18 Gy effectively induces long-term inhibition of neointimal hyperplasia.

Intra-arterial 90Y brachytherapy: preliminary dosimetric study using a specially modified angioplasty balloon

PURPOSE

Irradiation has been shown to be effective in preventing restenosis after dilatation in human peripheral arteries. We have developed a dedicated system for coronary intraarterial irradiation using a 90Y pure beta-emitting source inside a specially modified angioplasty balloon. This paper presents a preliminary dosimetric evaluation of this system.

METHODS AND MATERIALS

Specially fabricated titanium-covered and activated yttrium wires (outer diameter 0.32 mm) were used for these studies. Dosimetry was performed using small thermoluminescent dosimeters (TLDs) placed on the surface of the 2-cm long angioplasty balloons, inflated with contrast medium to a diameter of 2.5, 3, 3.5, and 4 mm. Radioactive 90Y wires were left in the inner balloon catheter and the surface dose rate was measured and extrapolated to 72 h after activation to allow a comparison between the values obtained. After observing the poor centering of the source within the standard angioplasty balloon, a new centering balloon was developed. A conventional balloon was subdivided into four evenly spaced interconnecting chambers, thus assuring adequate centering of the inner catheter. Thermoluminescent dosimetric measurements were performed with a 3.5 mm centering balloon to evaluate the homogeneity of the surface doses compared to those measured with the conventional balloon.

RESULTS

Thermoluminescent dosimetric measurements using the standard balloons filled with contrast medium were plotted semilogarithmically as a function of distance from the balloon surface. The logarithms of the measured doses fit a straight line as a function of depth. The doses at 1 mm and 3 mm are approximately 50 and 10% of the surface dose, respectively. Due to the poor centering of the source in the conventional balloons, the dispersion and standard deviations (SDs) of the measured surface doses increased proportionally to the balloon diameter (SDs are 1.89, 5.52, 5.79, and 6.46 Gy for 2.5, 3, 3.5, and 4 mm balloon diameters, respectively). For the 3.5 mm centering and conventional balloons the respective mean, minimum, and maximum surface doses were 8.41 Gy (min. 7.26; max. 9.46) and 7.89 Gy (min. 2.18; max. 16.06) and their standard deviations were 0.66 and 5.79 Gy, respectively.

CONCLUSIONS

Conventional angioplasty balloons cannot ensure a homogeneous dose delivery to an arterial wall with an intralumenal 90Y beta source. Preliminary dosimetric results using a modified centering balloon show that it permits improved surface dose distribution (axial and circumferential homogeneity), making it suitable for clinical applications.

High dose rate brachytherapy for prevention of restenosis after percutaneous transluminal coronary angioplasty: preliminary dosimetric tests of a new source presentation

PURPOSE

Balloon dilatation of coronary artery stenosis has become a standard treatment of atherosclerotic heart disease. Restenosis due to excessive intimal cell proliferation, which subsequently occurs in 20-50% of patients, represents one of the major clinical problems in contemporary cardiology, and no satisfactory method for its prevention has thus far been found. Because modest doses of radiation have proved effective in preventing certain types of abnormal cellular proliferation resulting from surgical trauma, and brachytherapy has already been used successfully after dilation of peripheral arteries, development of a radioactive source suitable for coronary artery applications would be of great interest.

METHODS AND MATERIALS

Nonradioactive flexible yttrium-89 wires (diameter of 0.15 and 0.26 mm) were activated within the thermal neutron flux of an experimental reactor. Standard angioplasty balloons (2 cm long, 2.5 mm in diameter when inflated) were inserted for dosimetry into a specially manufactured tissue equivalent phantom. Four wells, drilled perpendicular to the axis of the balloon, allowed for the insertion of thermal luminescent dosimeters (TLDs; 2 mm of diameter) and spacers. The angioplasty balloon was inflated with air or with contrast media. Radioactive yttrium-90 wires were left in the central lumen of the balloon for 2 min. Doses at the surface of the balloon, and at 1, 2, and 3 mm were determined from TLD readings.

RESULTS

Doses obtained at the surface of the balloon, for a 2-min exposure for the 0.26 mm wire (balloon inflated with air) and the 0.15 mm wire (air or contrast), were 56.5 Gy, 17.8 Gy, 5.4 Gy, respectively. As expected for a beta emitter, the fall-off in dose as a function of depth was rapid. External irradiation from the beta source was negligible.

CONCLUSIONS

Our experiments indicate that the dose rates attainable at the surface of the angioplasty balloon using this technique allow the doses necessary for the inhibition of intimal cell proliferation to be reached within a relatively short period of time. The thin yttrium-90 wires are very easy to handle, and their mechanical and radioactive properties are well suited to the requirements of the catheterization procedure.

Can a total body irradiation technique be fast and reproducible?

PURPOSE

Total body irradiation (TBI) is frequently a complex and time-consuming technique that significantly overloads Radiation Oncology departments. In an attempt to shorten TBI setup and treatment time we aimed to develop a system where the lung blocks are fixed with optimal precision to the build-up booster lucite screen while the patient is immobilized in a reproducible upright position.

METHODS AND MATERIALS

Fifteen patients diagnosed with leukemia were conditioned before bone marrow transplant since March 1992. Patients were immobilized in a semistanding position in a special stand with arm bars and hand grips. Treatment was delivered with a 6 MV x-ray horizontal beam. Six fractions of 2.25 Gy (mean instantaneous dose rate of 13.8 +/- 3.8 cGy/min) were delivered twice a day over 3 days (total dose: 13.5 Gy). Each fraction was given in alternating AP (facing the beam) and PA (turning the back) projections. Customized lung blocks (35% transmission) were used to assure a maximum lung dose of 10 +/- 0.5 Gy. The blocks were taped to a 1 cm thick lucite screen interposed between the source and the patient. Lung shields were checked by port films before each fraction. The reproducibility of the patient's positioning (and lung shielding) was evaluated by measuring the horizontal and vertical deviations of the infero-external corners of the lung blocks in the port films in relation to the same point in the simulation films. In vivo dosimetry (thermoluminescence and diodes) was performed by placing dosimeters and probes in the central axis and in several off-axis sites.

RESULTS

The mean horizontal and vertical deviations were 3.5 +/- 4.1 mm and 7.5 +/- 5.9 mm for the anterior fields, and 4.1 +/- 4.1 mm and 6.9 +/- 6.4 mm for the posterior fields. An acceptable position of the blocks was considered when deviations were < 5 mm horizontally and/or < 10 mm vertically. The mean time per fraction (i.e., interval between the patient's entering and leaving the treatment room) was 35 +/- 5 min.

CONCLUSIONS

A satisfactory level of reproducibility can be reached with this technique. The reasonably short treatment time contributes to reproducibility and patient comfort.

Conditioning the leukemic patient before allogeneic BMT: value of intensifying immunosuppression in the context of different levels of T lymphocyte depletion of the graft

We have studied the value of additional immune suppression in BMT conditioning regimens in 45 patients with leukemia and 4 with myelodysplastic syndrome allografted between 1984 and 1991. A dose of 6 Gy total lymphoid irradiation (TLI) was delivered to 12 of 24 and 15 of 25 patients conditioned with 10 Gy and 12 Gy total body irradiation (TBI), respectively. Thirteen patients also received methylprednisolone (MP) before BMT to enhance immunosuppression. Differences in immunosuppression between the TBI with or without TLI or MP regimens and the influence of different levels of graft T cell depletion were measured in terms of transplant rejection, and complete versus mixed chimerism. The treatment-related complications were evaluated in terms of GVHD and incidence of pneumonitis. The overall transplant rejection rate was 6% (3 of 49). Complete chimerism was not significantly modified by increasing the TBI dose or by additional TLI (p > 0.10) but was more often seen in patients receiving MP given as pre-transplant immunosuppressor booster (p = 0.01). The incidence of GVHD was only influenced by the level of T cell depletion (p = 0.003). All 49 patients received a TBI lung dose in the range 9.5-10 Gy. A crude pneumonitis range of 19% (9 of 47 evaluable patients) was found. Neither the addition of TLI, MP nor the T cell depletion influenced the lung toxicity rate (p > 0.10) but pneumonitis was more frequent in patients with GVHD (p = 0.005).