Biomedical subjects

R Calandrino

Publications and source records attributed to R Calandrino.

At least 19 recordsLinked to original sources

PubMed1998

Dose calculation and dosimetry tests for clinical implementation of 1D tissue-deficit compensation by a single dynamic absorber.

BACKGROUND AND PURPOSE: In this study the possibilities for implementing 1D tissue-deficit compensation techniques by a dynamic single absorber were investigated. This research firstly involved a preliminary examination on the accuracy of a pencil beam-based algorithm, implemented for irregularly shaped photon beams in our 3D treatment planning system (TPS) (Cadplan 2.7, Varian-Dosetek Oy), in calculating dose distributions delivered in ID non-uniform fields. Once the reliability of the pencil beam (PB) algorithm for dose calculations in non-uniform beams was verified, we proceeded to test the feasibility of tissue-deficit compensation using our single absorber modulator. As an example, we considered a mantle field technique. MATERIALS AND METHODS: To evaluate the accuracy of the method employed in calculating dose distributions delivered in 1D non-uniform fields, three different fluence profiles, which could be considered as a small sample representative of clinically relevant applications, were selected. The incident non-uniform fluences were simulated by the sum of simple blocked fields (i.e. with rectangular 'strip' blocks, one per beam) properly weighed by the 'modulation factors' Fi, defined in each interval of the subdivided profile as the ratio between the desired fluence and the open field fluence. Depth dose distributions in a cubic phantom were then calculated by the TPS and compared with the corresponding doses (at 5 and 10 cm acrylic depths) delivered by the single absorber modulation system. In the present application, the absorber speed profile able to compensate for the tissue deficit along the cranio-caudal direction and then homogenizing the dose distribution on a 'midline' isocentric plane with sufficient accuracy can be directly derived from anatomic data, such as the SSDs (source-skin distances) along the patient contour. The compensation can be verified through portal dosimetry techniques (using a traditional port film system). RESULTS: The technique was tested in isocentric conditions on the humanoid RANDO phantom in a clinically suitable situation. The agreement between expected/calculated and measured incident/exit dose profiles was found to be within 4%, with deviations generally around 1-2%. As for the PB accuracy investigation for dose calculations in non-uniform fields, calculated versus measured dose profiles were found to be in good agreement, indicating a satisfactory accuracy of the method employed for dose calculation in 1D non-uniform photon beams. A better performance should be expected if the incident fluences could be directly inserted in the TPS. CONCLUSIONS: The results show that the proposed technique should be sufficiently reliable for clinical application. The main advantages are its simplicity and the possibility of application on Linacs which have no complex options for dynamic control of collimators.

Algorithms↗

PubMed1998

Intra- and inter-observer variability in contouring prostate and seminal vesicles: implications for conformal treatment planning.

BACKGROUND AND PURPOSE: Accurate contouring of the clinical target volume (CTV) is a fundamental prerequisite for successful conformal radiotherapy of prostate cancer. The purpose of this study was to investigate intra- and inter-observer variability in contouring prostate (P) and seminal vesicles (SV) and its impact on conformal treatment planning in our working conditions. MATERIALS AND METHODS: Inter-observer variability was investigated by asking five well-trained radiotherapists of contouring on CT images the P and the SV of six supine-positioned patients previously treated with conformal techniques. Short-term intra-observer variability was assessed by asking the radiotherapists to contour the P and SV of one patient for a second time, just after the first contouring. The differences among the inserted volumes were considered for both intra- and inter-observer variability. Regarding intra-observer variability, the differences between the two inserted contours were estimated by taking the relative differences in correspondence to the CT slices on BEV plots (antero-posterior and left-right beams). Concerning inter-observer variability, the distances between the internal and external envelopes of the inserted contours (named projected diagnostic uncertainties or PDUs) and the distances from the mean inserted contours (named mean contour distances or MCDs) were measured from BEV plots (i.e. parallel to the CT slices). RESULTS: Intra-observer variability was relatively small (the average percentage variation of the volume was approximately 5%; SD of the differences measured on BEV plots within 1.8 mm). Concerning inter-observer variability, the percentage SD of the inserted volumes ranged from 10 to 18%. Differences equal to 1 cm in the cranio-caudal extension of P + SV were found in four out of six patients. The largest inter-observer variability was found when considering the anterior margin in the left-right beam of P top (MCD = 7.1 mm, 1 SD). Relatively high values for MCDs were also found for P bottom, for the posterior and lateral margins of P top (2.6 and 3.1 mm, respectively, I SD) and for the anterior margin of SV (2.8 mm, 1 SD). Relatively small values were found for P central (from 1.4 to 2.0 mm, 1 SD) and the posterior margin of SV (1.5 mm, 1 SD). CONCLUSIONS: The application of larger margins taking inter-observer variability into account should be taken into consideration for the anterior and the lateral margins of SV and P top and for the lateral margin of P. The impact of short-term intra-observer variability does not seem to be relevant.

Humans↗

PubMed1997

Comparing 3-, 4- and 6-fields techniques for conformal irradiation of prostate and seminal vesicles using dose-volume histograms.

BACKGROUND AND PURPOSE: Comparing some isocentric coplanar techniques for conformal irradiation of prostate and seminal vesicles. MATERIALS AND METHODS: Five conformal techniques have been considered: (A) a 3-fields technique with an antero-posterior (AP) field and two lateral (LAT-LAT) 30 degrees wedged fields; (B) a 3-fields technique with an AP field and two oblique posterior (OBL) 15 degrees wedged fields with relative weights of 0.8, 1 and 1, respectively; (C) a 4-fields technique (AP-PA and LAT-LAT); (D) a 6-fields technique (LAT-LAT and four OBL at gantry angles 45 degrees, 135 degrees, 235 degrees and 315 degrees) with all the fields having the same weight; (E) the same 6-fields technique with lateral fields double-weighted with respect to the oblique fields. The conformal plans have been simulated on 12 consecutive patients (stages B and C) by using our 3D treatment planning system (Cadplan 2.7). The contours of the rectum, the bladder and the left femoral head were outlined together with the clinical target volume (CTV) which included the prostate and the seminal vesicles. A margin of 10 mm was added to define the planning target volume (PTV) through automatic volume expansion. Then a 7 mm margin between the PTV and block edges was added to take the beam penumbra into account. Dose distributions were normalised to the isocentre and the reference dose was considered to be 95% of the isocentre dose. Dose-volume histograms and dose statistics of the rectum, the bladder and the left femoral head were collected for all plans. For the rectum and the bladder the mean dose (Dm) and the fraction of volume receiving a dose higher than the reference dose (V95) were compared. For the femoral head, the mean dose together with the fraction of volume receiving a dose higher than 50% (V50) were compared. RESULTS: Differences among the techniques have been found for all three considered organs at risk. When considering the rectum, technique A is better than the others both when considering Dm and V95 (P = 0.002), while technique D is the worst when considering Dm (P < 0.002) and is also worse than techniques A, E (P = 0.002) and C (P = 0.003) when considering V95. Technique E is the best when considering the bladder mean dose (P = 0.002 against A and D, P < 0.01 against B and C) and technique C is the worst (P < 0.012). No relevant differences were found for the bladder V95. In the femoral heads, techniques A and E are worse than B, C and D (P < 0.003) when considering Dm and V50. Moreover, techniques B and D are better than C (P < 0.004) when considering V50. CONCLUSIONS: There is no technique that is absolutely better than the others. Technique A gives the best sparing of the rectum; the bladder is better spared with technique E. These results are reached with a worse sparing of the femoral heads which should be carefully taken into account.

Femur Head↗

PubMed1997

Detection of systematic errors in external radiotherapy before treatment delivery.

The execution of an independent control of monitor units (MU) and dose distribution calculation, together with a check of the data reported in the treatment chart is an effective tool in strongly reducing the occurrence of systematic errors before treatment delivery. In this paper we report the results of the analysis of 6272 controls (about 5000 patients) registered over more than 5 years; 70 serious errors (producing a deviation larger than 5% from the prescribed daily dose) and 147 minor errors were detected and corrected before the start of the treatment. The error rate was found to be strongly operator-dependent (serious error rate ranging from 0.3 to 2.5% when considering different operators). A time-trend analysis showed a significant reduction of serious errors, i.e. 1.5% in the period from September 1991 to April 1994 compared to 0.9% in the period from April 1994 to November 1996. However, even if the double check was highly effective in revealing human errors, three serious systematic errors (errors occurring during the calculation/planning/transcription phases) escaped the control and were detected by diode in vivo dosimetry during the period October 1994 to November 1996 (in 650 patients controlled).

Humans↗

PubMed1997

Variations of tumor control and rectum complication probabilities due to random set-up errors during conformal radiation therapy of prostate cancer.

BACKGROUND AND PURPOSE: The effect of random set-up errors on tumor control probability (TCP) and rectum complication probability (NTCP) on 3D conformal treatment planning of prostate cancer has been investigated by applying the convolution method originally proposed by Leong (Leong, J. Implementation of random positioning error in computerized radiation treatment planning systems as a result of fractionation. Phys. Med. Biol. 32: 327-334, 1987). MATERIALS AND METHODS: The combined influence of the standard deviation of the random shifts probability distribution (sigma) of the dose and of the Beam's-eye-view margin (M) between the clinical target volume (CTV) and the edge of the blocks have been investigated in two patients. RESULTS AND CONCLUSIONS: Random set-up error has been found to decrease TCP (for a typical 70 Gy CTV mean dose) by up to 6% for a 1 cm margin (sigma = 7 mm). When M is equal to or larger than 1.5 cm, no relevant effects on TCP are obtained. Maximum acceptable TCP values (corresponding to a rectum NTCP equal to 5%) have been derived and the dependence on sigma and M has been investigated.

Humans↗

PubMed1997

Optimizing the movement of a single absorber for 1D non-uniform dose delivery by (fast) simulated annealing.

A new simplified technique for 1D non-uniform dose delivery using a single dynamic absorber, driven by a computer system, has been recently proposed together with a simple analytic algorithm. This technique uses an optimized 'stepped' absorber's speed profile and the generated fluence profile is an approximation of the desired radiation beam. In the case of non-uniform beam profiles with multiple maxima/minima, the original proposed 'stepping algorithm' has some limitations and produces a too rough approximation of the desired profiles. In order to increase the agreement between desired and generated profiles, more sophisticated optimization schemes are required. In this paper we have applied a variant of simulated annealing (SA) as a statistical optimization algorithm to further investigate the possibilities and the limits of the single-absorber technique in the field of 1D intensity modulation. In the current application the cost function used is the mean square root of the percentage differences between desired and generated profiles, the absorber's resting times have been chosen as optimization variables and at each iteration just one variable is randomly changed, adding an incremental 'grain'. A Cauchy generating function is used, different cooling schedules are evaluated; constraints related to our apparatus are introduced and starting annealing parameters are set after some initial optimization tests. The method is tested in reproducing theoretical non-uniform beams, by comparing desired modulated fluence profiles with calculated fluence profiles obtainable with the single absorber after the derivation of optimized speed profiles by the proposed SA approach. The results of these simulations show that the application of the SA method optimizes the single absorber's performance and that clinically important modulated beams useful for conformal radiotherapy can be accurately reproduced.

Algorithms↗

PubMed1997

Monitor unit calculation in 6 MV irregularly shaped beams--accuracy in clinical practice.

The results of an investigation of the accuracy of monitor unit (MU) calculation in clinical shaped beams are presented. Measured doses at the reference depth on the beam central axis (isocentre) or on a beam axis representative of the irradiated area (when the isocentre lies under a block or near the edges of the block's shadow) were compared with the expected doses when calculating MUs, by applying different methods normally used in clinical practice. Empirical (areas weighted, Wrede) and scatter summation (Clarkson) methods as well as a pencil-beam based algorithm were applied. 40 irregular fields (6 MV X-rays, CLinac, Varian 6/100), divided into six categories, were considered. Dose measurements were performed with a NE2571 ionization chamber in an acrylic 30 x 30 x 30 cm3 phantom. The depths in acrylic were converted into water-equivalent depths through a correction factor derived from TMR measurements. The method of dose measurements in acrylic was found to be sufficiently accurate for the purpose of this study by comparing expected and measured doses in open square and rectangular fields (mean deviation +0.2%, SD = 0.5%). Results show that all the considered methods are sufficiently reliable in calculating MUs in clinical situations. Mean deviations between measured and expected dose values are around 0 for all the methods; standard deviations range from 1% for the Wrede method to 0.75% for the pencil-beam method. The differences between expected and measured doses were within 1% for about 3/4 of the fields when calculating MUs with all the considered methods. Maximum deviations range from 1.6% (pencil-beam) to 3% (Wrede). Slight differences among the methods of MU calculation were revealed within the different categories of blocked fields analysed. The surprising agreement between measured and expected dose values obtained by using empirical methods (area weighted and Wrede) is probably due to the fact that the reference points were positioned in a "central" region of the unblocked areas.

Algorithms↗

PubMed1996

On-line exit dose profile measurements by a diode linear array.

The possibility of using a commercial diode linear array (BMS Schuster Inc.) in on-line portal dosimetry has been investigated. The system is composed of 88 equispaced diodes (distance between diodes, 0.5 cm; detection area, 2.5 x 2.5 mm2). The ability to measure exit dose profiles has been demonstrated by comparing relative exit dose profiles measured by an ionization chamber (NE 2571) with 'portal' profiles measured by the diode array on a number of homogeneous and inhomogeneous phantoms in 6 MV x-ray beams (from a Clinac Varian 6/100). The influence of the variation of the scattered radiation at the exit level with respect to the detector level has been discussed and investigated by varying the air gap (from 0 to 80 cm for a homogeneous phantom and from 0 to 25 cm for inhomogeneous phantoms) as well as the field width. A good agreement (maximum difference 3.8%; 2.5% when the array was positioned in contact with the phantoms) between 'portal' profiles and exit dose profiles in both homogeneous and inhomogeneous phantoms has been found if the array-phantom distance is kept below 7.5 cm. Results indicate that the system should be suitable for applications in transit dosimetry.

Air↗

PubMed1995

Dynamic beam modulation by using a single computer-controlled absorber.

The authors have developed an apparatus able to generate ID intensity-modulated beams, using only one moving absorber within the irradiation field. A procedure for deriving optimized absorber-speed profiles in order to produce the desired fluence/dose profiles has been suggested. Experimental tests show that the system should be sufficiently reliable in reproducing modulated beam profiles of different shape: expected relative doses against measured relative doses have been found to be in agreement in a number of situations within 3% using a nonfocused device. A better agreement should be expected using a focused apparatus (which is currently being developed). Beam modulation by single absorber cannot modulate the beam fluence in any was one wishes, due to physical constraints, which depend on the absorber and field widths and on the shape of the desired fluence profile. However, the authors show that this simple and low-cost tool could offer, with a sufficient degree of accuracy, the possibility of modulating the beam fluence with a high degree of versatility. In particular, a procedure or performing tissue-missing compensation by single-absorber dynamic beam modulation is suggested. Moreover, 'strongly' modulated beam profiles can be created, showing that this simple technique could also have some interesting applications in the field of conformal radiotherapy by non-uniform dose delivery.

Algorithms↗

PubMed1994

Skin-sparing reduction effects of thermoplastics used for patient immobilization in head and neck radiotherapy.

Skin-sparing benefits derived from the use of megavoltage photon beams can be strongly reduced when filters are inserted between the source and the patient. The use of plastic masks for immobilizing the patient is the most important cause of this reduction in head and neck treatments. The influence of thermoplastics, commercially available for patient immobilization systems (Orfit Raycast (Luxilon Ind. Co.), Posicast (Sinmed bv) and Optimold (WFR Aquaplast Corp.)), on the patient skin dose value has been investigated by using an NE2534 'Markus' chamber. Indicative measurements with moulded masks (carried out with 2-mm Orfit and 3.2-mm Optimold layers) show significant differences between masks moulded with the two thermoplastics.

Acrylic Resins↗

PubMed1994

Cable-induced effects on plane-parallel ionization chamber measurements in large clinical electron beams.

The interaction between photon or electron fields and cables of ionization chambers induces the flow of leakage currents affecting the measured signal; this "cable effect" is particularly important when large electron and photon fields are used, i.e., when large portions of cable are irradiated. Therefore it is more interesting to investigate cable-induced effects when ionization chambers are used for clinical situations where large fields are used, for example, total body and total skin electron irradiations (TSEI). In TSEI fields these effects are particularly important. Cable and connector effects using an NE2534 Markus chamber in total skin irradiation conditions with different electron energies (from 1.6 to 4.5 MeV) have been investigated. These effects are significant and show that for TSI dosimetry it is vital to take them into account.

Electrons↗

PubMed1993

Development of a computer-controlled moving bar (CCMB) conformal technique for neck irradiation.

The development of an original conformal technique for neck cancer is in progress in our Institute. This technique uses a computer-controlled moving bar (CCMB): a portion of a blocking bar rotates during the rotation of the gantry in a 2 pi arc field in order to shield the spinal cord over the whole irradiated volume. This technique should solve in a relatively simple way some problems for different clinical situations when cervical node irradiation is required together with the primary tumor. The technique has been tested in an acrylic cylindrical phantom and in the humanoid RANDO phantom for two different irradiation conditions (neck completely bent and partially aligned).

Head and Neck Neoplasms↗

PubMed1993

Exit dose measurements by portal film dosimetry.

Portal in vivo dosimetry is a very attractive tool for patient dose measurements because of the large amount of information that portal film systems can easily collect, once positioned at the exit surface of the patient. The first step in the verification of the reliability of portal films as in vivo dosimeters is the evaluation of the agreement between exit patient dose profiles and optical density profiles measured on the portal film. We checked the possibilities for exit dose measurements of a commercial portal film system (Film Kodak X-Omat V and Localization Kodak Cassette) verifying the agreement between relative exit doses (measured by ionization chamber and film dosimetry, calculated by our treatment planning system (Cadplan Dosetek)) and relative optical densities on portal films in cubic homogeneous and inhomogeneous, cylindrical and humanoid phantoms. In particular, a good agreement (mean difference in absolute value: 2%) between optical densities and calculated exit doses for the Rando phantom were found, once the optical densities values are corrected for an inverse square correction factor, taking into account the variation of the profile of the phantom.

Absorptiometry, Photon↗

PubMed1993

Human errors in the calculation of monitor units in clinical radiotherapy practice.

Human mistakes are an important source of error in all steps of radiotherapy planning and their incidence should be investigated. As has been recognized by different authors and by the ICRU [4], the human error rate in the calculation of monitor units (MU) is relatively high. At our institute, we measured the human error rate in the calculation of MU by an independent check of the calculation. From September 1991 to June 1992 we identified and corrected 17 serious errors (deviation from the prescribed dose > or = 5%) over 890 controls (1.9%) (daily dose errors). We also found a serious global dose error rate (i.e. the errors induced on the total reference dose for the complete course of the treatment) of 1.3% (9/685) during the period November 1991-June 1992. These values suggest the importance of human errors in the calculation of MU and also confirm the validity of the independent check of MU calculation as one of the simplest ways of avoiding erroneous dose delivery by incorrect calculation of MU.

Humans↗

PubMed1993

[Human errors in the calculation of the Monitor Unit in radiotherapy].

Human mistakes are a major source of error from the definition to the execution of a treatment planning. An unrevealed serious human error can cause therapy to fail therefore it is of fundamental importance to eliminate serious human errors during MU calculation. In this work the human error incidence in MU calculation is evaluated by an independent check. The investigation refers to 1,926 controls collected in about 18 months. Serious daily errors rate (errors causing a 5%, or higher, discrepancy on the daily reference dose) was 1.4% (27/1926). Serious global errors incidence (errors causing a 5%, or higher, discrepancy on the total reference dose) was 0.9% (15/1,731). The data show that the human error in MU calculation is not negligible; they also indicate the value of the independent control of MU, which is an important tool for quality assurance in radiotherapy (like in vivo dosimetry and portal imaging.

Bias↗

PubMed1992

[Dosimetric problems and their solution in the preparation of a 6-dual-field total-skin technique].

The six-field total skin electron irradiation (TSEI) technique needs an accurate preliminary dosimetric study. The American Association Physics in Medicine (AAPM) defined a dosimetric protocol that recommends the careful dosimetry of the horizontal, the dual and the six-dual fields by using both a cubic and a cylindrical phantoms. In our Institute, in a TSEI development program, we carried out the preliminary dosimetry according to AAPM criteria. We also investigated some dosimetric problems--e.g., the so-called "cable effect", which takes place when the detector cable in a TSEI field is not well shielded, polarity effects and photon contamination. As to the "cable effect", it is especially marked with the Markus NE2534 chamber; moreover, this effect, if not considered, can lead to overestimation of X-rays contamination.

Calibration↗

PubMed1992

[Conformal technics by the movement of bars in pendular fields. 1. Prototype realization and the possible applications].

The growing interest for conformal radiotherapy originates from the need of giving the prescribed dose to the target volume, by sparing, at the same time, surrounding healthy tissues and organs. More dose to the target volume with respect to the healthy tissues always increases the curative possibilities of the treatment. However, the development of conformal techniques implies an increased complexity of the treatment and the solution of many technical and dosimetric problems. In our Institute we are developing new conformal techniques, based on the use of moving bars driven by a computer-controlled system in arc therapy. This paper refers to the conclusion of the preliminary part of our work: a movement (translating or rotating) of bars in arc therapy seems to have good chances to tailor dose distribution in a relatively simple way. We realized two mechanical systems driven by computer for translating and rotating movements of a bar. The two techniques have been tested by TLD and film dosimetry on acrylic phantoms. We present the results of these tests, and describe technical problems and the clinical possibilities of this method.

Equipment Design↗

PubMed1992

[Conformal technics by the movement of bars in pendular fields. 2. The dosimetric aspects].

The development of conformal techniques by movement of bars in pendular fields requires a careful examination of many physical and dosimetric problems: bar-critical organ synchronization problems, dose calculation problems, and problems relative to the "shadow effect". The use of a bar in an arc field, causes to a slow gradient of dose between shielded zone and target volume with a loss of homogeneity in dose distribution. This effect is well known ("shadow effect") and depends on the fact that different points spend different times beyond the bar's shadow. In this work the problem is investigated in the case of moving bar technique, mainly for dose calculation possibilities; then the possibility is analyzed of optimizing dose distribution by means of filters whose profile can be calculated for simple geometric conditions (fixed bar on the isocenter without considering the profile of the patient). These filters will be made in our Institute and they will be tested in various conditions, for both fixed bars and moving bars in arc fields.

Equipment Design↗