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PubMed2000

Effect of TiO2-Ag2O additives on the formation of calcium phosphate based functionally graded bioceramics.

The combined effect of titanium dioxide and silver oxide on the in situ formation of biphasic calcium phosphate ceramics was investigated. Titania (5-20 mol%) was mixed with pure hydroxyapatite (HA) or HA containing Ag2O (10-20 mol%) and was heated to 900 degrees C for 12 h. The sintered samples were found to contain tricalcium phosphate (beta-TCP) and other phases along with HA depending upon the amount as well as the type of the additives used as evidenced by X-ray powder diffraction (XRD) and fourier transform infrared (FT-IR) spectroscopic studies. Enhanced TCP formation with reduced impurity phases was observed with TiO2-Ag2O addition. In vitro solubility study in phosphate buffer at physiological conditions shows the resorbable nature of these materials. A functionally graded material (FGM) structure was formed by spreading TiO2-Ag2O mixture on the surface of the HA green compact and heating at 900 degrees C. The FGM shows gradient structure of TCP and HA from the surface to the interior of the pellet in addition to titania and silver phases.

Biocompatible Materials↗
PubMed2001

Evaluation of ceramics composed of different hydroxyapatite to tricalcium phosphate ratios as carriers for rhBMP-2.

We have investigated pellet-shaped implants prepared from biphasic calcium phosphate (BCP) ceramics with five different ratios of hydroxyapatite (HAP) to beta tricalcium phosphate (beta-TCP). The purpose of this study was to evaluate these BCP ceramics as carriers for rhBMP-2. BCP ceramics impregnated with the different doses of recombinant human bone morphogenetic protein 2 (rhBMP-2) (1, 5 and 10g) were used for the experimental purpose and the ceramics without rhBMP-2 were used as control. The pellets were placed into subcutaneous pockets on the dorsum of 4-week-old male Wistar rats. The animals were sacrificed 2 and 4 weeks after implantation. Bone induction was estimated by alkaline phosphatase (ALP) activity measured at 2 weeks after implantation. Pellets were also examined radiologically, histologically and histomorphometrically. The results showed that all experimental pellets exhibited new bone formation whereas the control pellets produced only fibrous connective tissue. Here, 100% HAP ceramic showed most amount of bone formation, whereas 25% HAP to 75% TCP ceramic produced the bone least in amount among different BCP ceramics at the end of 4 weeks. This study indicates that formation of new bone depends on the ceramic content with high HAP-TCP ratio and high dose of rhBMP-2.

Alkaline Phosphatase↗
PubMed2001

Degradation of poly(D,L)lactide implants with or without addition of calciumphosphates in vivo.

The study was aimed at examining the in vivo degradation of pure poly(D,L)lactide (PDLLA) or PDLLA with an admixture of calciumphosphates. One rod (20 x 3 x 2 mm) and one cube (3 x 2 x 2 mm) of pure PDLLA, PDLLA with tricalciumphosphate (PDLLA + TCP) or PDLLA with calciumhydrogenphosphate (PDLLA + CHP), respectively, were implanted into the dorsal muscles of 50 male Wistar Albino rats. After definite intervals (from 2nd to 72nd week), pH measurements were performed in the environment of the implants. Afterwards, the cubes with their surrounding tissues were excised for histological examinations, measurements of the outer dimensions and mechanical analyses of the explanted rods were performed. No drop of more than 0.1 pH units was detectable in the tissue surrounding any type of implants. No advantageous effect of the calciumphosphates could be proved. A mild foreign body reaction could be observed around PDLLA implants. After 72 weeks, pure PDLLA had been totally resorbed from the extracellular space, the degradation of calciumphosphate-enriched PDLLA was still in progress. A large amount of inflammations occurred in the tissues surrounding PDLLA with an admixture of slowly degrading TCP or CHP, leading to two abscesses and four fistulas at PDLLA + TCP, and two abscesses and three fistulas at PDLLA + CHP implantation site. Bending strength of pure PDLLA was constant up to the 4th week post-implantation and reduced to 60% of the initial value up to the 12th week. No traces of crystallinity could be observed during the degradation of PDLLA. As a conclusion of the study, complete resorption from the extracellular space and tissue tolerance of pure PDLLA is proved. An admixture of small calciumphosphate particles is not suitable to improve the biocompatibility of PDLLA but leads to a decrease in the mechanical characteristics.

Animals↗
PubMed2001

Release profile of antimicrobial agents from alpha-tricalcium phosphate cement.

A new method for treating carious dentine with alpha-tricalcium phosphate (alpha-TCP) dental cement containing antimicrobial agents has been recently introduced. However, the release behavior of antimicrobial agents from this cement has not yet been clarified. The aim of this study is therefore to examine the release profile of the antimicrobial agents from the alpha-TCP cement. Three kinds of antimicrobial agents (metronidazole, cefaclor and ciprofloxacin) were added to two commercially available alpha-TCP cements (new apatite liner type I and type II). The set cements were then immersed in water at 37 degrees C and the released antimicrobial agents and Ca ion were determined at regular intervals for three months. In addition, scanning electron microscopic observations were conducted before and after immersion for three months. The release profile of the cements containing antimicrobial agents varied depending on the types of antimicrobial agents. The incorporation of antimicrobial agents affected the setting reaction of the cements. The release behavior of the drugs also varied depending on the types of the cements. The differences in the release profile between type I and type II cements reflected the structures and compositions of their matrices.

Anti-Infective Agents↗
PubMed2002

Ectopic osteogenesis with biphasic ceramics of hydroxyapatite and tricalcium phosphate in rabbits.

Porous calcium phosphate ceramics consisting of hydroxyapatite (HA) and tricalcium phosphate (TCP) with different HA to TCP ratio were implanted intramuscularly in rabbits for six months in order to carry out a comparative study on osteogenic activity of the ceramics. Bone formation was detected only in HT73 (HA to TCP ratio, 7-3) specimens. Other implants, HT28 (2-8) and HT010 (0-10), could not induce bone. After a six-month period of implantation, HT28 and HT010 implants showed obvious degradation of the implants changing their shape and size macro and microscopically. Microscopically, they showed aggregates of fine particles and appearance of multinucleated cells. However, HT73 implants was less degraded and could maintain their original structure macro and microscopically. This study showed that HT73 ceramics can induce bone in rabbit muscle tissue and it is considered that maintenance of porous structure, that is, degradation rate of the materials may be one of the affecting factors in ceramic-induced osteogenesis.

Animals↗
PubMed2002

Alpha-tricalcium phosphate hydrolysis to octacalcium phosphate: effect of sodium polyacrylate.

Alpha-Tricalcium phosphate (alpha-TCP) hydrolysis into octacalcium phosphate (OCP) has been investigated in phosphoric acid solution at different concentrations of sodium polyacrylate (NaPA). The hydrolysis process has been followed by powder X-ray diffraction, infrared absorption and scanning electron microscopy analyses. In the absence of the polyelectrolyte, alpha-TCP undergoes a complete transformation into OCP in 24 h. The presence of polyacrylate in solution inhibits the hydrolysis so that a NaPA concentration of 0.5 microm is sufficient to lengthen the time required to complete the hydrolysis to 4 days. The variation of Ca2+ concentration in the soaking solution suggests that the transformation occurs through alpha-TCP dissolution followed by OCP precipitation. The delayed OCP nucleation and growth in the presence of polyacrylate implies a preferential adsorption of the polyelectrolyte on the growing OCP crystals, which induces an anisotropic reduction of the coherence lengths of the perfect crystalline domains.

Acrylic Resins↗
PubMed2002

Production and evaluation of biodegradable composites based on PHB-PHV copolymer.

In recent years, emphasis in biomaterials engineering has moved from materials that remain stable in the biological environment to materials that can degrade in the human body. Biodegradable materials are designed to degrade gradually and be replaced eventually by newly formed tissue in the body. In this investigation, two particulate bioactive ceramics, i.e., hydroxyapatite (HA) and tricalcium phosphate (TCP), were incorporated into polyhydroxybutyrate-polyhydroxyvalerate (PHB-PHV), which is a biodegradable copolymer. to produce new biomaterials for potential medical applications. All raw materials were commercially available and they were characterised prior to composite production. HA/PHB-PHV and TCP/PHB-PHV composites containiing up to 30 vol% of the bioceramics were produced through an established procedure. Compounded and compression moulded materials were evaluated using various techniques including thermogravimatric analysis, scanning electron microscopy, differential scanning calorimetry and dynamic mechanical analysis. The results showed that intended compositions of composites had been achieved and bioceramic particles were well distributed in the polymer. The degradation temperature of PHB-PHV was significantly reduced by the incorporation of bioceramics, while the melting temperature was slightly affected by the addition of bioceramics. The crystallinity of PHB-PHV was also varied with the presence of HA or TCP particles. The storage modulus and loss modulus of the composites increased with the increase in HA or TCP content. Composites containing the highest percentage of bioceramics exhibited the highest stiffness. Preliminary in vitro study indicated enhanced ability of the composites to induce the formation of bone-like apatite on their surfaces.

Apatites↗
PubMed1997

Hydrolysis and phase transition of alpha-tricalcium phosphate.

Increasing attention has been paid in recent years to alpha-tricalcium phosphate (alpha-TCP), which is used as the main constituent of calcium phosphate bioactive bone cements and biphasic calcium phosphate ceramics. Its hydrolysis and conversion into apatite phase may play an important role in new bone formation in vivo. In this experiment, alpha-TCP powder was made and immersed in deionized water. The morphology change and phase composition were analysed before and after immersion. Based on the results of hydrolysis, a formula for the converted apatite-TCP phase containing lattice water was put forward and a partial structural model along the hydroxyl column was proposed.

Biocompatible Materials↗
PubMed1997

Degradation behaviour of a new bioceramic: Ca2P2O7 with addition of Na4P2O7.10H2O.

A newly produced bioceramic, beta-Ca2P2O7 with addition of Na4P2O7.10H2O (SDCP), has been implanted into the femoral condyle of rabbits. Within 6 weeks after implantation, most of the bioceramic is replaced by new woven bone. On the contrary, block from hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP), which are osteoconductible, do not resorb within a short period of time. We believe that the biodegradable behaviour of SDCP may occur in two steps. The first and most important step is the digestion of particles and migration of the particles by phagocytosis. The object of this study is to examine the change in morphologies, chemical compositions and crystal structure of SDCP after soaking in distilled water for a certain period of time. The SDCP ceramic was also co-cultured with leucocytes to observe how the SDCP particles were digested by the leucocytes, so that the mechanism of biodegradable behaviour of SDCP ceramic in vivo might be clarified. Four types of sintered calcium phosphate ceramics were tested in the experiment: SDCP, pure beta-Ca2P2O7 (DCP), HA and beta-TCP. They wee soaked in distilled water at 37 degrees C for up to 30 days. The microstructure and morphology of crystals deposited on the surface were observed using scanning electron microscopy. Sodium, calcium and phosphorus ion contents in the supernatant solution were detected by atomic absorption analysis and ion coupled plasma. In summary, HA and DCP showed no significant evidence of dissolution in distilled water. In static distilled water, calcium ions may be released from beta-TCP into solution during the initial 7 days and then converted into HA by reprecipitation. The results showed that the SDCP was firstly dissolved into small grains or fragments by the solution. The small fragments should be so small as to be digested by the phagocytes in a physiological environment.

Animals↗
PubMed1997

Osteoclastic resorption of calcium phosphate ceramics with different hydroxyapatite/beta-tricalcium phosphate ratios.

To study the influence of calcium phosphate ceramic solubility on osteoclastic resorption, neonatal rabbit bone cells were cultured for 2 days on hydroxyapatite (HA), beta-tricalcium phosphate (beta-TCP) and two types of biphasic calcium phosphate (BCP) with HA/beta-TCP ratios of 25/75 and 75/25. Solubility was regulated by varying the ratio of less-soluble HA and more-soluble beta-TCP. After removal of stromal cells by pronase E treatment, ceramic surfaces were observed by scanning electron microscopy. Osteoclasts resorbed BCP most extensively, with an HA/beta-TCP ratio of 25/75, producing typical lobulated, zig-zag track-like resorption lacunae. On pure beta-TCP, which had the highest solubility in acid, osteoclasts formed smaller discontinuous island-like lacunae. The resorption pattern may have been modified by the large number of calcium ions released into the acidic microenvironment at the osteoclast-ceramic interface. No resorption lacunae were found on the other specimens. The extent of osteoclastic resorption of calcium phosphate ceramics might, to a certain degree, be proportional to solubility, although this was not the case when solubility was very high. It would appear that ceramic solubility influences osteoclast resorption activity.

Animals↗
PubMed1998

Biological evaluation of biphasic calcium phosphate ceramic vertebral laminae.

An artificial vertebral lamina with a dense inside surface and porous outside part, fabricated with a biphasic calcium phosphate (70% hydroxyapatite/30% tricalcium phosphate) (HA-TCP) ceramic (abbr. CVL), was evaluated by animal experiments. The animal experiments showed that at half a month postoperation, no bone formation occurred on the macropore surfaces of the implants, however, fibrous connective tissues and blood vessels had grown into the macropores, contributing to the early fixation of the CVLs. The degradation of TCP phase was detected through X-ray diffraction (XRD); in the meanwhile, needle-like and plate-like crystals were found in the materials through scanning electron microscopy (SEM), and infrared spectroscopy (IR) observations showed that the carbonate apatites similar to bone apatites began to occur in the materials. At one month postoperation, the degradation of the TCP phase became moderate, new bone began to grow into the porous structures of the implants, and further degradation of the implants provided rich Ca and P ions for new bone formation. The newly formed bone in the macropores of the implants increased with implantation time. At one year postoperation, the implant was completely fused with natural bone on the interfaces between them, new bone had grown into most of the porous structures of the implants, and a natural bone tissue layer formed on the inside surface of the artificial vertebral lamina. The new bone tissue layer played a more effective role in protecting the spinal cord and improving the spinal stability in the later implantation time.

Animals↗
PubMed1998

Dissolution behaviour of calcium phosphate coatings obtained by laser ablation.

Pulsed laser deposited calcium phosphate coatings on titanium alloy have been tested under simulated physiological conditions in order to evaluate the changes in morphology, composition and structure. The coatings were deposited under different conditions to obtain different crystalline structures, ranging from amorphous and mixed crystalline phases to pure crystalline hydroxyapatite (HA). The coated samples were immersed in a Ca-free Hank's balanced salt solution for up to 5 days. Characterization of the coatings was performed by X-ray diffraction, scanning electron microscopy and Fourier-transform Raman spectroscopy before and after immersion. Their dissolution behaviour was also monitored through their mass loss and calcium release. Coatings of pure HA preserve their morphology and structure during the exposure time in solution. In multiphasic coatings, consisting of HA with tetracalcium phosphate (TetraCP) or beta-tricalcium phosphate (beta-TCP) with a-tricalcium phosphate (alpha-TCP), microporosity is induced by the complete dissolution of TetraCP or gamma-TCP. Amorphous calcium phosphate coatings totally dissolve.

Alloys↗
PubMed1999

Hydrolysis of alpha-tricalcium phosphate in NaF solutions.

Controlling the incorporation of Na and fluoride in apatite-based dental restoratives and analogs of bone formed under physiologic conditions may be desirable in controlling their long-term in vivo responses. Formation of these analogs was investigated. Hydrolysis of alpha-tricalcium phosphate (alpha-TCP) was carried out at physiologic temperature in NaF solutions and the solids product(s) were analyzed. alpha-TCP hydrolysis was complete within 48 h and the only solid products identified were apatites. Changes in solution chemistry were determined at 48 h and 4 weeks. Na and Ca concentrations were determined by spectrometric methods, P and F concentrations were determined by ion chromatography; pH values were obtained. The extent of fluoride and sodium incorporation in the apatites formed varied depending on the NaF concentration of the solution. Both increased with increasing NaF concentration. Apatite compositions ranged from Ca9.06(HPO4)0.94(PO4)5.06OH1.06 for hydrolysis in water to Ca9.28Na0.56(HPO4)(x)(PO4)(6-x)F0.920Hy for hydrolysis in 0.1 M NaF solution. The proportions of PO4, HPO4 and OH in Na- and F-containing apatites are indeterminate but obey the equation (y = constant+x). The (Ca+Na)/P ratio of the apatite formed by alpha-TCP hydrolysis in 0.1M NaF approaches 1.67 indicating the vacant Ca sites become almost completely filled by the Na ions. The surface areas of these apatites initially remain constant with increasing NaF concentrations; at elevated concentrations apatite surface areas decrease with increasing NaF concentration. This is consistent with the removal of Na from solution by its incorporation in the apatites, not by its adsorption onto their surfaces.

Adsorption↗
PubMed2000

Acute and chronic life cycle toxicity of acenaphthene and 2,4,6-trichlorophenol to the midge Paratanytarsus parthenogeneticus (Diptera: Chironomidae).

The acute and life cycle toxicities of acenaphthene and 2,4,6-trichlorophenol (2,4,6-TCP) were evaluated using the parthenogenic dipteran larva, Paratanytarsus parthenogeneticus, of the family Chironomidae. Static 48 h acute toxicity tests employed third instar larvae, and the flow-through 20-day life cycle tests were initiated with eggs. No acute lethal effect was observed in the saturated concentration (2.1 mg/l) of acenaphthene in water, and the median lethal concentration of 2,4,6-TCP was approximately 40 mg/l. In the life cycle toxicity test with acenaphthene, hatchability of the midge was affected by 50% at an exposure concentration of approximately 0.17 mg/l. The median effective concentration for larval, pupal and adult development was found between 0.06 and 0.07 mg/l, respectively, and these were significantly lower than the effective concentration for hatching success. With regard to 2,4,6-TCP toxicity, the median effective concentration for midge hatchability was 4.23 mg/l. The larval development, pupal formation and adult emergence, however were impeded at 1.60, 1.46 and 1.33 mg/l, respectively. Each level was noticeably lower than the median effective concentration for hatchability. The concentrations for each compound that interfered with the development to fourth instar, pupa and adult were not significantly different. These results indicate that larval developments after hatching were the most sensitive stages and affected the success of midge growth.

Acenaphthenes↗
PubMed2000

A quantitative treatment planning study evaluating the potential of dose escalation in conformal radiotherapy of the oesophagus.

BACKGROUND AND PURPOSE: This study aims to evaluate the reduction in radiation dose to normal thoracic structures through the use of conformal radiotherapy techniques in the treatment of oesophageal cancer, and to quantify the resultant potential for dose escalation. MATERIALS AND METHODS: Three different CT-derived treatment plans were created and compared for each of ten patients. A two-phase treatment with conventional straight-edged fields and standard blocks (CV2), a two-phase conformal plan (CF2), and a three-phase conformal plan where the third phase was delivered to the gross tumour only (CF3), were considered for each patient. Escalated dose levels were determined for techniques CF2 and CF3, which by virtue of the conformal field shaping, did not increase the mean lung dose. The resulting increase in tumour control probability (TCP) was estimated. RESULTS: A two-phase conformal technique (CF2) reduced the volume of lung irradiated to 18 Gy from 19.7+/-11.8 (1 SD) to 17.1+/-12.3% (P=0.004), and reduced the normal tissue complication probability (NTCP) from 2.4+/-4.0 to 0.7+/-1.6% (P=0.02) for a standard prescribed dose of 55 Gy. Consequently, technique CF2 permitted a target dose of 59.1+/-3.2 Gy without increasing the mean lung dose. Technique CF3 facilitated a prescribed dose of 60.7+/-4.3 Gy to the target, the additional 5 Gy increasing the TCP from 53. 1+/-5.5 to 68.9+/-4.1%. When the spinal cord tolerance was raised from 45 to 48 Gy, technique CF3 allowed 63.6+/-4.l Gy to be delivered to the target, thereby increasing the TCP to 78.1+/-3.2%. CONCLUSIONS: Conformal radiotherapy techniques offer the potential for a 5-10 Gy escalation in dose delivered to the oesophagus, without increasing the mean lung dose. This is expected to increase local tumour control by 15-25%.

Adult↗
PubMed2002

Definition of gross tumor volume in lung cancer: inter-observer variability.

BACKGROUND AND PURPOSE: To determine the inter-observer variation in gross tumor volume (GTV) definition in lung cancer, and its clinical relevance. MATERIALS AND METHODS: Five clinicians involved in lung cancer were asked to define GTV on the planning CT scan of eight patients. Resulting GTVs were compared on the base of geometric volume, dimensions and extensions. Judgement of invasion of lymph node (LN) regions was evaluated using the ATS/LCSG classification of LN. Clinical relevance of the variation was studied through 3D-dosimetry of standard conformal plans: volume of critical organs (heart, lungs, esophagus, spinal cord) irradiated at toxic doses, 95% isodose volumes of GTVs, normal tissue complication probabilities (NTCP) and tumor control probabilities (TCP) were compared for evaluation of observer variability. RESULTS: Before evaluation of observer variability, critical review of planning CT scan led to up- (two cases) and downstaging (one case) of patients as compared to the respective diagnostic scans. The defined GTVs showed an inter-observer variation with a ratio up to more than 7 between maximum and minimum geometric content. The dimensions of the primary tumor had inter-observer ranges of 4.2 (transversal), 7.9 (cranio-caudal) and 5.4 (antero-posterior) cm. Extreme extensions of the GTVs (left, right, cranial, caudal, anterior and posterior) varied with ranges of 2.8-7.3 cm due to inter-observer variation. After common review, only 63% of involved lymph node regions were delineated by the clinicians (i.e. 37% are false negative). Twenty-two percent of drawn in lymph node regions were accepted to be false positive after review. In the conformal plans, inter-observer ranges of irradiated normal tissue volume were on average 12%, with a maximum of 66%. The probability (in the population of all conformal plans) of irradiating at least 95% of the GTV with at least 95% of the nominal treatment dose decreased from 96 to 88% when swapping the matched GTV with an unmatched one. The average (over all patients) inter-observer range in NTCP varied from 5% (spinal cord) to 20% (ipsilateral lung), whereas the maximal ranges amounted 16% (spinal cord) to 45% (heart). The average TCP amounted 51% with an average range of 2% (maximally 5%) in case of matched GTVs. These values shifted to 42% (average TCP) with an average range of 14% (maximally 31%) when defining unmatched GTVs. Four groups of causes are suggested for the large inter-observer variation: (1) problems of methodology; (2) impossible differentiation between pathologic structures and tumor; or (3) between normal structures and tumor, and (4); lack of knowledge. Only the minority of these can be resolved objectively. For most of the causal factors agreements have to be made between clinicians, intra- and inter-departmentally. Some of the factors will never be unequivocally solved. CONCLUSIONS: GTV definition in lung cancer is one of the cornerstones in quality assurance of radiotherapy. The large inter-observer variation in GTV definition jeopardizes comparison between clinicians, institutes and treatments.

Carcinoma, Non-Small-Cell Lung↗
PubMed1997

Potential advantages of protons over conventional radiation beams for paraspinal tumours.

BACKGROUND AND PURPOSE: Conformal treatment planning with megavoltage X-rays and protons was studied in an attempt to determine if there are advantage of boost therapy with protons instead of X-rays for a patient with a tumour growing around the cervical spinal cord. MATERIALS AND METHODS: A patient with a Ewing sarcoma was selected for the model study. The proton boost plan was realised with a six beam patched technique. Several X-ray boost techniques were planned, some not yet practically realisable. The techniques giving the best dose distributions and the best tumour control probabilities in the absence of significant late toxicity were looked for. The boost techniques were added to two large lateral X-ray beams covering the planning target volume (PTV) and the main risk organ, the spinal cord. The evaluation was made with two biological models, i.e. the tumour control probability (TCP) model, proposed by Webb and Nahum (Webb, S. and Nahum, A.E. A model for calculating tumour control probability in radiotherapy including the effect of inhomogeneous distributions of dose and clonogenic cell density. Phys. Med. Biol. 38: 653-666, 1993), and the normal tissue complication probability (NTCP) model, first derived by Lyman (Lyman, J.T. Complication probability as assessed from dose-volume histograms. Radiat. Res. 104: s13-s19, 1985). RESULTS: The comparison showed small but clear advantages of protons for the boost. At 1% NTCP in the spinal cord, the calculated TCP was on average 5% higher. However, depending on the values of the parameters chosen in the biological models, the gain for protons varied from 0-10%. The smallest gains were seen in radiosensitive tumours for which the TCP was close to 100% with any of the techniques and in radioresistant tumours for which neither technique resulted in any appreciable probability of local cure. CONCLUSION: Protons appear to have therapeutic advantages over conventional radiotherapy in tumours with relatively high radiosensitivity situated close to the spinal cord.

Adult↗
PubMed1999

A comparison of coplanar four-field techniques for conformal radiotherapy of the prostate.

BACKGROUND AND PURPOSE: Conformal radiotherapy of the prostate is an increasingly common technique, but the optimal choice of beam configuration remains unclear. This study systematically compares a number of coplanar treatment plans for four-field irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV). MATERIALS AND METHODS: A variety of four-field coplanar treatment plans were created for PO and PSV volumes in each of ten patients. Plans included a four-field 'box' plan, a symmetric plan having bilateral anterior and posterior oblique fields, a plan with anterior oblique and lateral fields, a series of asymmetric plans, and a three-field plan having anterior and bilateral fields for comparison. Doses of 64 and 74 Gy were prescribed to the isocentre. Plans were compared using the volume of rectum irradiated to greater than 50% (V50), 80% (V80) and 90% (V90) of the prescribed dose. Tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) for the rectum, bladder and femoral heads were also evaluated. Femoral head dose was limited such that less than 10% of each femoral head received 70% of the prescribed dose. RESULTS: For the PO group, the optimal plan consisted of anterior oblique and lateral fields (Rectal V80 = 23.8+/-5.0% (1 SD)), while the box technique (V80 = 26.0+/-5.8%) was less advantageous in terms of rectal sparing (P = 0.001). Similar results were obtained for the PSV group (Rectal V80 = 43.9+/-5.0% and 47.3+/-5.5% for the two plan types, respectively, P = 0.001). The three-field plan was comparable to the optimal four-field plan but gave higher superficial body dose. With dose escalation from 64 to 74 Gy, the mean TCP for the optimal plan rose from 52.0+/-2.8% to 74.1+/-2.0%. Meanwhile, rectal NTCP for the optimal plan rose by 3.5% (PO) or 8.4% (PSV), compared to 4.7% (PO) or 10.1% (PSV) for the box plan. CONCLUSIONS: For PO volumes, a plan with gantry angles of 35 degrees, 90 degrees, 270 degrees and 325 degrees offers a high level of rectal sparing and acceptable dose to the femoral heads for all patients, while for PSV volumes, the corresponding plan has gantry angles of 20 degrees, 90 degrees , 270 degrees and 340 degrees. Using these plans, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in anticipated rectal NTCP.

Algorithms↗