Accelerated partial breast irradiation using 3D conformal radiotherapy: toxicity and cosmetic outcome.

PURPOSE: The aim of this paper is to analyze the incidence of acute and late toxicity and cosmetic outcome in breast cancer patients submitted to breast conserving surgery and three-dimensional conformal radiotherapy (3D-CRT) to deliver accelerated partial breast irradiation (APBI). METHODS AND MATERIALS: 84 patients were treated with 3D-CRT for APBI. This technique was assessed in patients with low risk stage I breast cancer enrolled from September 2005 to July 2011. The prescribed dose was 34/38.5 Gy delivered in 10 fractions twice daily over 5 consecutive days. Four to five no-coplanar 6 MV beams were used. In all CT scans Gross Tumor Volume (GTV) was defined around the surgical clips. A 1.5 cm margin was added by defining a Clinical Target Volume (CTV). A margin of 1 cm was added to CTV to define the planning target volume (PTV). The dose-volume constraints were followed in accordance with the NSABP/RTOG protocol. Late toxicity was evaluated according to the RTOG grading schema. The cosmetic assessment was performed using the Harvard scale. RESULTS: Median patient age was 66 years (range 51-87). Median follow-up was 36.5 months (range 13-83). The overall incidence of acute skin toxicities was 46.4% for grade 1 and 1% for grade 2. The incidence of late toxicity was 16.7% for grade 1, 2.4% for grade 2 and 3.6% for grade 3. No grade 4 toxicity was observed. The most pronounced grade 2 late toxicity was telangiectasia, developed in three patients. Cosmetics results were excellent for 52%, good for 42%, fair for 5% and poor for 1% of the patients. There was no statistical correlation between toxicity rates and prescribed doses (p = 0.33) or irradiated volume (p = 0.45). CONCLUSIONS: APBI using 3D-CRT is technically feasible with very low acute and late toxicity. Long-term results are needed to assess its efficacy in reducing the incidence of breast relapse.

Radio hyperthermia for re-treatment of superficial tumours.

PURPOSE: Relapse remains an unsolved problem for previously radio-treated patients. Our purpose is to evaluate the role of radio-hyperthermia (RT-HT) in the retreatment of superficial recurrences. MATERIALS AND METHODS: From 1998 to 2007, 51 patients affected by four histological types (breast recurrences (group A), melanoma recurrences (group B), head and neck recurrences (group C), and others (group D)) of 76 superficial lesions, were enrolled at Mauriziano Hospital at the Research Institute of Cancer Care Candiolo (IRCC) in Turin. All patients had previously undergone RT except 6 patients of group B. The total mean retreatment dose was 31.8 Gy (20-60 Gy), while the mean of HT sessions was 5 (1 to 8), temperature ranged from 38.5 degrees C (T min) to 44 degrees C (T max). RESULTS: Acute cutaneous toxicity was 77.6% G1, 22.4% G2, none for G3. Forty-five days later we observed: for group A 65.9% complete response (CR), 29.5% partial response (PR), 4.5% non-response (NR); for group B 33.3% CR, 25% PR and 41.7% NR; for group C 40% CR, 13.3% PR, 46.7% NR, for group D 60% CR and 40% NR. 18 months later group A presented 72.7% local control (LC), 20.5% stable disease (SD) and 6.8% non-control (NC), group B 50% LC, 16,7% SD and 33.3% NC, group C 33.3% LC, 40% SD and 26.7% NC, group D 40% LC and 60% NC. Early response, size of lesions < or =3 cm, T max > or =42 degrees C and RT doses > or =40 Gy were predictive outcome factors. CONCLUSIONS: We confirmed that radio-hyperthermia is useful in re-irradiation with a very high patient compliance.

The behavior of several microionization chambers in small intensity modulated radiotherapy fields.

The aim of this work is to compare different ion chambers available for dose measurements in small fields used in intensity modulated radiotherapy. Some dosimetric aspects, related to these small radiation fields, i.e., lack of electronic lateral equilibrium and steep dose region, must be evaluated, in order to obtain an accurate technique implementation. Furthermore, the size of the sensitive volume of the chambers compared with the mapping of the beams or segments needs consideration. If the size of the chamber is too large for the flatness of the field, the measurement can deviate from the expected absorbed dose at a point. We propose a comparison of various dosimetric values between different microionization chambers with respect to a smaller dosimeter, such as the diamond detector.

PC-aided assessment of the thermal performances of a MW applicator for oncological hyperthermia.

The thermal performances of an MW oncological hyperthermic (OH) system have been assessed with a PC-aided procedure. Measurements were performed on a muscle-equivalent phantom. Between the applicator and the phantom a water bolus was interposed which, to simulate real OH treatments, could be connected to a forced cooling water circulation system. Direct thermal measurements of temperatures and SAR (using the 'short pulse technique') and simulation by numerical modelling were performed, both aiming at describing the 3-D thermal field inside the phantom. Accuracy and manageability of the automated procedure proved suitable for characterization and quality assurance of MW applicators in clinical hyperthermia and encourage further efforts towards the development of computerized treatment simulations in OH.

Effective penumbra and scalloping effect: a dosimetric study in multifield radiotherapy with multileaf collimator for prostate cancer treatment.

AIMS AND BACKGROUND: The aim of the study was to test whether the multileaf collimator can be used to replace divergent alloy blocks for field shaping and to evaluate the dosimetric impact of the scalloping effect and the effective penumbra in multifield isocentric configurations routinely used at our department to treat early stage prostate tumor in supine patients. Deviations between measurements and treatment planning system calculations are also discussed in order to estimate the accuracy of effective penumbra calculations carried out by the software in the presence of blocks or a multileaf collimator. METHODS: The multileaf collimator installed on a dual energy (6 and 18 MV) linear accelerator Varian CLINAC 2100 C/D is an add-on component positioned below the standard jaws, with 40 computer-controlled opposed pairs of tungsten leaves. Transmission, effective penumbra and scalloping measurements were performed with films placed at different depths in a (30 x 30 x 20 cm3) acrylic phantom. A laser scanning photodensitometer was used to obtain the optical density and the relative dose profile. Effective penumbra and scalloping effect measured data were tested on a software phantom; the phantom, automatically performed with the treatment planning system, was a regular parallelepiped measuring 30 x 30 x 20 cm3 and the acrylic electronic density value. RESULTS: For one multileaf collimator-shaped field, the width of effective penumbra was about 2 mm wider than penumbra for cerrobend blocks, at a 45 degrees angle between leaf motion direction and the field edge. Collimator rotation, automatically performed by the treatment planning system, by minimizing the sum of over- and underblocked areas, reduces the differences between the multileaf collimator and blocks. The differences between measured and treatment planning system calculated data were within the treatment planning system dose calculation accuracy limits, as recommended in ICRU Report No. 42. CONCLUSIONS: Penumbra and, for the multileaf collimator, scalloping effect values seem to depend on the gantry angle, i.e., on the fields path of entry. The values for even fields are higher than the those for odd fields, because the dose gradient at the target edges is steeper for a single field than for two opposite fields, and the interplay of doses from the individual beams increases the distance between the isodose levels. Therefore, in order to reduce scalloping and effective penumbra values, it would be better to rotate the collimators, above all in even-number field techniques. In particular, the six-field technique, used mostly in prostate treatment, shows the same effective penumbra values with the multileaf collimator, with proper collimator rotation, and in blocked fields.

[Measures of specific absorption rate (SAR) in microwave hyperthermic oncology and the influence of the dynamic bolus on clinical practice]. / Misure di deposizione di potenza nell'ipertermia oncologia con microonde e influenza del bolus dinamico nella pratica clinica.

AIM: The bolus (silicon + deionized water) is used in order to achieve a good electromagnetic match between the biological tissue and the applicator surface and to locally modify the skin temperature, to regulate it based on the patient's sensitivity. Therefore, it is very important to know the electromagnetic power deposition and how the bolus can induce a variation in the thermal map, both superficially and deeply. The aim of this study is to evaluate the applicator characteristics in the same conditions as those indicated by the ESHO guidelines for clinical practice and to investigate the penetration depth in the absence and in the presence of a very effective circulating bolus. The first condition is used by the manufacturer to characterize MW applicator while the second condition is used by medical equipes delivering HT treatments. MATERIAL AND METHODS: The specific absorption rate (SAR) generated by a microwave planar applicator (H2, CFMA, Istok,Russia) operating at 433 MHz connected with the hyperthermic equipment ALBA (Restek, Italy) was studied in a muscle-equivalent polyacrilamide phantom. IsoSAR lines were detected on a liquid crystal sheet with a video camera. Images analysis was performed using the graphic software Paint Shop Pro 6. This method allows to evaluate PD in the phantom under the plane of MW applicator. The hyperthermic equipment ALBA is used in the Radiotherapy Unit of the Mauriziano Umberto I Hospital in Turin for both oncologic and psychiatric treatments. RESULTS AND DISCUSSION: The actual pattern of measured SAR mainly depends on the applicator and the phantom characteristics, but also the thickness and the efficiency of the bolus inserted between the applicator and the patient's skin have been shown to affect the results. In this study the penetration depth was measured on 5 applicator sections both with non circulating bolus (static) and with circulating bolus (dynamic). The penetration depth is reduced with the dynamic bolus with respect to the static bolus in all sections, and specifically: in section I it is reduced from 19.46 +/- 1.49 mm to 17.22 +/- 0.71 mm; in section II from 38.17 +/- 4.77 mm to 26.91 +/- 1.48 mm; in section III from 39.81 +/- 3.24 mm to 30.38+/- 4.56 mm; in section IV from 42.12 +/- 1.67 mm to 33.11 +/- 1.89 mm; and finally in section V from 39.83 +/- 4.14 mm to 31.064 +/- 1.57 mm. The above reduction ranges between 11.5 and 29 % with an average value of 21.64 % Our results suggest that different conditions at the interface between bolus and phantom resulting from the use of a dynamic or static bolus produce considerable changes on the heated volume dimension and on the SAR local pattern. The effect of the convective heat losses due to the circulating bolus' assessed by our measurements is not negligible and should be taken into account when evaluating the SAR distribution before clinical treatments. CONCLUSIONS: To disregard the heat losses due to a circulating bolus in MW applicator characterization can severely affect the SAR estimation. This may have serious consequences on clinical applications, since the temperature in the heated lesion can be lower than expected, and the clinical effectiveness of the therapeutical session can be therefore severely reduced. Since at the moment inexpensive and accurate non-invasive temperature monitoring systems are not available, a sound knowledge of the PD of the MW applicator is of primary importance for clinical applications and for a treatment plan allowing to deliver customized treatment to each patient.

[Dosimetric characterization of a multileaf collimator]. / Caratterizzazione dosimetrica di un collimatore multilamellare.

INTRODUCTION: We studied the dosimetric characteristics of a multileaf collimator (MLC) installed on a dual energy accelerator with 6 and 18 MV photon beams in the Radiotherapy Department of Mauriziano Umberto I Hospital in Turin initiating its use in clinical practice. In particular, measurements included transmission through and between the leaves and at the junction under closed-leaves, central axis percentage depth dose, output factors and effective penumbra. MATERIAL AND METHODS: The MLC installed on the dual energy (6 and 18 MV) linear accelerator Varian Clinac 2100 C/D used in our radiotherapy department is an add-on component positioned below the standard jaws; it consists of 40 computer-controlled opposed pairs of 5 cm thick tungsten leaves, each projecting a 1 cm width at the isocenter, and it provides a maximum treatment field of 40 x 40 cm2 at 100 cm SAD. Transmission, penumbra and scalloping values were measured with the standard radiographic film routinary used in our department. A laser scanning photodensitometer (WP102, Wellhofer) with a 450 microns spot was used to obtain the optical density and the relative dose profile. Radiographic films had been calibrated with an ionization chamber, by irradiating samples to known doses; this calibration was used to correct the film scanner readings to dose. Percentage depth doses were also measured in an automatic water phantom (WP600, Wellhofer) for irregular fields defined by either MLC or alloy blocks, in order to test the differences in the build-up region due to the presence of the acrylic accessory tray. Measured and calculated output factors were compared for some irregular fields defined by the MLC. This comparison tested the algorithm accuracy of our Treatment Planning System 3D CadPlan 3.1.1 Varian-Dosetek. RESULTS AND DISCUSSION: For both energies, approximately 2% of the incident radiation on the MLC is transmitted and an additional 0.5% leakage occurs between adjacent leaves. The leakage under closed-leaves junction is remarkable: about 25-33%. Relative depth dose curves are similar for two fields shaped by either MLC or conventional jaws. Skin dose with MLC-shaped field is less (3.5%) than the one with cerrobend block-shaped fields. The monitor unit calculation procedure used in our treatment planning system can be applied to the MLC (the difference is less than 1%). Effective penumbra in MLC-shaped irregular fields is on the average 11 mm, which is slightly wider (2-3 mm) than the conventional cerrobend blocks penumbra. Effective penumbra increases with depth, field width and leaves positioning. CONCLUSIONS: The MLC, if properly used (collimator rotation, jaws and leaves position, high number of fields), can be applied to conformal radiotherapy with good results. The MLC is better than conventional cerrobend blocks both to improve the treatment reproducibility and accuracy, and relative to dosimetric characteristics like dose transmission and skin dose. The use of MLC to modulate beam fluence (IMRT) will permit to modify beam intensity for improved shaping of the treated volume and to overcome the static therapy dosimetric limitations.

Perfusion and thermal field during hyperthermia. Experimental measurements and modelling in recurrent breast cancer.

Recurrences of malignant tumours in the chest wall are proposed as a valuable model of tissue mainly perfused by small size vessels (the so-called 'phase III' vessels). Invasive thermal measurements have been performed on two patients affected by cutaneous metastasis of malignant tumours during hyperthermic sessions. Thermal probes were inserted into catheters implanted into the tissue at different depths. In one of the catheters a probe connected with laser-Doppler equipment was inserted to assess blood perfusion in the tumour periphery. The perfusion was monitored throughout the sessions, and a noticeable temporal variability was observed. The effect of the perfusion on the thermal map in the tissue was evaluated locally and the 'effective conductivity' of the perfused tissue was estimated by means of the numerical integration of the 'bio-heat' equation. The tumour temperature, at the site where the perfusion probe is located, can be predicted by the numerical model provided two free parameters, alpha and beta, are evaluated with a fitting procedure. Alpha is related to the effective conductivity and beta to the SAR term of the bio-heat equation. The model aimed at estimating the 'effective conductivity' K(eff) of the perfused tissue, and average values of K(eff) of 0.27 +/- 0.03 W m(-1) degrees C(-1) in Patient 1 and of 0.665 +/- 0.005 W m(-1) degrees C(-1) in Patient 2 were obtained throughout the treatment. However, when the average temperature in a larger tumour volume is to be predicted but only a single, 'local' measurement of the perfusion is available and is assumed to be representative for the whole region, the model results are far less satisfactory. This is probably due to the fact that changes of blood perfusion throughout hyperthermic sessions occur to different extents within the tumour volume, and the differences in perfusion cannot be ignored. The above result suggests that, in addition to the 'temperature map', also a 'perfusion map' within the heated volume should be monitored routinely throughout hyperthermic sessions.