Dose Distribution For Treatment Research Articles

Impact of geometrical uncertainties on 3D CRT and IMRT dose distributions for lung cancer treatment

To quantify the effect of set-up errors and respiratory motion on dose distributions for non-small cell lung cancer (NSCLC) treatment. Irradiations of 5 NSCLC patients were planned with 3 techniques, two (conformal radiation therapy (CRT) and intensity modulated radiation therapy (IMRT1)) with a homogeneous dose in the planning target volume (PTV) and a third (IMRT2) with dose heterogeneity. Set-up errors were simulated for gross target volume (GTV) and organs at risk (OARs). For the GTV, the respiration was also simulated with a periodical motion around a varying average. Two configurations were studied for the breathing motion, to describe the situations of free-breathing (FB) and respiration-correlated (RC) CT scans, each with 2 amplitudes (5 and 10 mm), thus resulting in 4 scenarios (FB_5, FB_10, RC_5 and RC_10). Five thousand treatment courses were simulated, producing probability distributions for the dosimetric parameters. For CRT and IMRT1, RC_5, RC_10 and FB_5 were associated with a small degradation of the GTV coverage. IMRT2 with FB_10 showed the largest deterioration of the GTV dosimetric indices, reaching 7% for Dmin at the 95% probability level. Removing the systematic error due to the periodic breathing motion was advantageous for a 10 mm respiration amplitude. The estimated probability of radiation pneumonitis and acute complication for the esophagus showed limited sensitivity to geometrical uncertainties. Dmax in the spinal cord and the parameters predicting the risk of late esophageal toxicity were associated to a probability up to 50% of violating the dose tolerances. Simulating the effect of geometrical uncertainties on the individual patient plan should become part of the standard pre-treatment verification procedure.

A Pre-optimised Dosimetry System using a Rigid Applicator for Intracavitary Treatment of Cervical Carcinoma

Aims Tumour control and complication risk have been major concerns in the treatment of cervical carcinoma. A review of dose distribution for intracavitary treatment of cervical carcinoma revealed that modification of the Manchester dosimetry system is necessary for cases of narrow-sized vagina. A revised dosimetry system was introduced in the present study, with the objective of optimising the dose coverage for the parametrium while minimising the bladder and rectum dosage by restricting the rectal dose so as not to exceed 75% of the brachytherapy prescription dose. Materials and methods A suitable-sized applicator was selected according to the patient's anatomy. The revised system is optimised based on the fixed geometry of the applicator. The system was therefore predefined and the distribution of the treatment dose already determined before application. The revised system was applied to 135 cases, involving 540 applications. The clinical outcome in terms of local tumour control and complication rates is reported. The differences between the revised system and the Manchester system in terms of dose coverage for the parametrium and the rectum dose were compared. Results The results showed that higher rectal and parametrial dosages were obtained with the Manchester system as compared with the revised system. Our study showed that over 50% of our patients would have received a rectal dose close to 100% of the point A dose if the Manchester system was applied, whereas it was restricted to below 75% using the revised system. Using the revised system, the significance of the parametrial dosage coverage in relation to local control was assessed: the mean dose to the rectum and the bladder as a percentage of point A was 65.7 ± 5% (range 50–85%) and 66.4 ± 14% (range 29–116%), respectively. The 5-year actuarial local failure-free survival rates were 90, 92.9, 86.8, 100, 69.7 and 0% for stages IB, IIA, IIB, IIIA, IIIB and IV ( P < 0.0001), respectively. The 3-year actuarial complication rates (grade 3/4) for proctitis and cystitis were 1.4 and 0.5%, respectively. The dosage coverage for the parametrium was found to be significant ( P = 0.029) in relation to local control for early-stage disease. Conclusions The favourable local tumour control and low complication rates shown by our results indicate that the revised system presents an optimal dose distribution, particularly for the application of small ovoids, whereas morbidity was reduced to a lower level without compromising local control.

MO‐D‐ValA‐02: Patient Motion Modeling &amp; Treatment Adaptation

Patient anatomical variation during the radiotherapy course can be modeled using a stochastic process. In this process, spatial position of each subvolume in patient organs of interest is defined as a random vector described using a probability distribution function (pdf). Two main parameters, the mean and the standard deviation, of the pdf have been historically used to characterize patient anatomical variation during the radiation treatment. It has been demonstrated that treatment dose distribution in an organ of interest can be evaluated approximately using these two parameters alone, without the full knowledge of organ motion distribution. The approximation is, however, dependent on the scale of the standard deviation as well as the number of treatment delivery fractions. It is straightforward to estimate these two parameters if patient anatomical variation process is stationary. In this case, the two parameters are constants or time‐invariance during the treatment course. However, the estimation will be relatively difficult if patient anatomical variation process is non‐stationary.Patient anatomical variation in radiotherapy can be systematically managed using image feedback adaptive treatment technique. The fundamental difference between adaptive treatment technique and other image‐guided techniques is the use of patient‐specific treatment information. Adaptive technique intends to use all patient‐specific dose information ‐ including what has been delivered in the previous treatments, what can be delivered at the present treatment, and what would be delivered in future treatments ‐ in the design of treatment plan. Therefore, treatment plan designed in adaptive radiotherapy is called 4D adaptive plan, which is in principle a treatment control law to manage treatment process. Mathematically, treatment control law is a spatial mapping from the parameter space of patient variation to the parameter space of treatment delivery control, which can be determined including the patient variation in the planning optimization or inverse planning. The objectives in adaptive planning optimization are constructed based on a selection of control strategies that could be either the online or the offline with one control action, multiple actions or continue actions. Selection of control strategy and number of control actions is, of course, dependent on the nature of patient variation process as well as the estimation uncertainties, and has to be determined considering also the clinical practice.The lecture will provide an overview of the models and characteristics of patient anatomical variation process during the radiotherapy, the 4D dose summation methodology and the strategies of adaptive treatment process.Educational Objectives:1. Understand the characteristics and dynamic model for patient anatomical variation during the course of radiotherapy.2. Understand the model and methodology of 4D dose summation.3. Understand the options of control strategy for image guided adaptive radiation treatment.

SU‐DD‐A2‐06: The Effect of Respiratory Rate and Radiation Timing On Dose Coverage in Dynamic Breast IMRT

Purpose: IMRT has been shown to be capable of delivering plans with desirable homogeneous dose distribution for breast cancer treatment. However, the dose distribution may be influenced by interplay between dynamic MLC and respiratory motion. The purpose of this study was to investigate the impact of respiratory rate and radiation timing on the dose distribution of breast dynamic IMRT. Method and Materials: Using similar setup configuration, a helical CT and 4DCT image sets for six breast cancer patients were collected and contoured. Dynamic IMRT plans were designed using the helical CT images. The planned MLC sequence was segmented according to the respiratory phases with a series of respiratory rates (7.5–30/min) and radiation timing (evenly distributed in respiratory cycles). The segmented dynamic MLC sequences were applied to the radiation fields on the corresponding 4DCT phases. A program was developed to calculate the cumulative dose distribution from all the phases. Results: For normal breathing rates (15–20/min), the dose coverage didn't change significantly regardless of radiation starting time. The change of target V90 was less than 2%. However, for extremely slow respiratory rates (7.5–10/min), the dose distribution and V90 changed significantly depending on the radiation timing. The change of target V90 was more than 10%. There was no significant dose coverage change for the underlying heart regardless respiratory rate or radiation timing. Conclusions: For breast patients treated with dynamic IMRT, if the respiratory rate of the patient is within the “normal” range then the impact of such respiration on dose coverage of the target was found to be statistically insignificant. However, the dose distribution may change significantly when patient has a slow breathing rate. Respiratory gating may be required to obtain satisfactory dose coverage for such cases. There was no significant dose distribution change for heart regardless respiratory rate or radiation timing.

SU‐FF‐T‐440: Treatment Table Induced Dose Perturbation in An IMRT Treatment

Purpose: Treatment table support bars create problems in treatment planning and delivery. It is a complex issue for the case of IMRT with multiple and varying size beamlets. Methodology to account for the dose perturbation due to the presence of the table support in IMRT treatments is presented. Method and Materials: Five patients were planned with 7‐beam IMRT using a posterior field and six other fields spaced at equal gantry angles. Treatment plans were optimized to produce suitable dose distributions for patient treatment. Plans were imported to solid phantom for dose verification. Treatment plan verification with ion chamber and film was carried out with and without bar. A mathematical weighted dose calculation is presented based on the equation: Dose = TD * [(MU‐ ΣMUij*T)/MU)], where TD is total prescribed dose, MU is total monitor unit from all beams, MUij is monitor unit in ith beam and jth beamlet that is blocked through the bar, and T is the measured transmission factor through bar. T was measured at 90 cm SSD at a depth of 10 cm for all photon energy and a film profile was taken. Results: Measured transmission through the center of the Siemens table bar for 6 MV and 18 MV was found to be 72.9% and 78.8% respectively. Even though IMRT beamlets pass through the bar, the dosimetric effect is minimal. Measured and calculated doses through bar for all clinical cases show agreement within ±4.5%, which is within the limits of the IMRT criterion. Conclusion: IMRT planning and treatment should be coordinated carefully to avoid passage of the beam through treatment table supports to avoid underdosage of the target area. However, in an accidental situation, methodology presented here provides simple and accurate dose estimates for an IMRT treatment.

SU‐FF‐T‐327: Monte Carlo Dose Calculations in Homogeneous and Heterogeneous Media: A Comparison Between the PMCEPT Code and the MCNP5, EGS4, DPM Codes and Measurements

The Monte Carlo method for high‐energy photon and charged particle transport is the most accurate means for predicting dose distributions in radiation treatment of patients. Owing to rapid development of computer hardware and network technologies the use of this method is not restricted only to big research centers any more. A new parallel Monte Carlo electron and photon transport (PMCEPT) code [Kum and Lee, J. Kor. Phys. Soc. 47 (2005) 716] for calculating electron and photon beam doses has been developed based on a three dimensional geometry defined by computerized tomography (CT) images and implemented on the Beowulf PC cluster. The PMCEPT code was validated on the homogeneous and multi‐layered targets for megavoltage electron beams by comparing with the results of experiments and calculations from conventional Monte Carlo codes of the MCNP5, EGS4, and DPM. The computing time of the PMCEPT code was approximately twenty times faster than that of MCNP5 on the IBM ThinkPad X40 (laptop) with 1.2‐GHz CPU and 512‐MB ram memory operated by RedHat Linux 9. The PMCEPT results in general agreed well with others in homogeneous and heterogeneous media within a maximum of 2–3 % error. At the conference, we will show various benchmark results for the PMCEPT. This work was supported, in part, by the SRC/ERC program of MOST/KOSEF (grant number: R11‐1999‐054).

TU‐C‐ValB‐10: Rectal Dose Variation in Image Guided Radiation Therapy of Prostate Cancer

Purpose/Objective: To investigate the change in rectal dose during the treatment course for prostate IMRT with image‐guidance. Materials &amp; Methods: Ten prostate cancer patients treated with IMRT were included in this study. Each patient was administered an enema prior to CT‐ and MRI simulations. MR and CT were fused for target delineation. IMRT treatment planning was performed on the CT image. Prostate motion during the treatment course was corrected using a CT‐on‐Rails system. Rectal contours were generated on both simulation CT images and subsequent treatment CT images. IMRT plans were generated based on our clinical acceptance criterion. The subsequent treatment CT images for each patient from the CT‐on‐Rails system were used to recompute the patient dose distributions with the same leaf sequences used for treatment. The isocenter was shifted relative to the simulation CT, as required by the protocol, to ensure appropriate target coverage. The rectal doses based on the subsequent treatment CT were compared with the original doses planned on the simulation CT scans using our clinical acceptance criteria. Results: Based on ten patients with 84 treatment CT sets, 14% of the subsequent treatment dose distributions did not meet our criterion of V40 &lt; 35% (V40=36%∼50%), and 7% did not meet our criterion of V65&lt;17% (V65=18%∼36%). The inter‐fractional rectal volume variation is significant for some patients. The minimum changes in rectum volume are between 31 and 39.8cc while the maximum changes are between 50.2 and 161.7 cc. In general, IMRT planning with an empty rectum results in better subsequent treatment dose distributions to the rectum. Conclusions: Due to the large inter‐fractional variation of the rectal volume it is more favorable to plan prostate IMRT based on an empty rectum.

236 Impact of geometrical uncertainties on 3D-CRT and IMRT dose distributions for lung cancer treatment

236 Impact of geometrical uncertainties on 3D-CRT and IMRT dose distributions for lung cancer treatment

SU-FF-T-379: Biological Radial Dose Functions for Brachytherapy Sources

Purpose: Brachytherapy is often used in combination with external-beam-radiotherapy to deliver a tumoricidal dose, while respecting critical organ tolerances. Its biological equivalence to an external beam dose fractionation has conventionally been considered via only the prescribed dose, preventing the 3D summation of brachytherapy and external beam dose distributions. We investigate a methodology that calculates a brachytherapy dose distribution biologically equivalent to an external beam dose fractionation schedule using a commercial treatment-planning system that has only conventional brachytherapy dose calculation models. Method and Materials: Dose distributions from high-dose-rate (HDR) brachytherapy treatments, including point-source, line-source, planar, and intracavitary gynecological implants were converted to their biological equivalents for corresponding external beam dose fractionations using the linear quadratic equation and an α/β ratio of 10. The radial-dose-function (RDF) values of an Ir-192 source were modified (BRDF) to yield these biologically-equivalent dose distributions using the conventional dose calculation formalism. Use of this formalism was demonstrated by planning an IMRT treatment of cervical cancer constrained by delivered HDR dose distributions. Results: The BRDFs of HDR Ir-192 treatments vary as a function of external beam dose fractionations, the α/β ratio used, and implant geometry. BRDF's dependence on implant geometry is due to the nonlinearity of the linear-quadratic equation. BRDF's have non-unitary values at 1 cm from the source, depending on the equivalence of prescribed external beam and brachytherapy doses. Comparisons between the biological-equivalent dose distributions and the approximations obtained using BRDF showed excellent agreement. Conclusion: A method is proposed to allow calculation of biologically-equivalent brachytherapy dose distribution in commercial treatment planning systems. Preliminary studies using the BRDF demonstrated its usefulness in the IMRT treatment planning when constrained by delivered brachytherapy dose distribution. The process can also be used to review brachytherapy implant dose distributions at conventional external-beam fractionation schedules.

Treatment planning of stereotactic radiotherapy for solitary lung tumor

To analyze the stereotactic radiotherapy (SRT) plans in terms of internal target volume (ITV) and organs at risk (OARs). Treatment planning and dose distributions were analyzed using dose-volume histograms (DVHs) of ITV and OARs in 37 patients, who were treated for a solitary lung tumor with SRT. The stereotactic body frame (SBF) was used for immobilization and accurate setup. Prescription dose was 48 Gy in four fractions at the isocenter. Use of SBF limits the extent of the noncoplanar beam directions to prevent a collision with the Linac gantry. DVH analyses showed that the homogeneity index, defined as the ratio of maximum and minimum dose to ITV, ranged from 1.03 to 1.25 (mean, 1.12). The volume irradiated with 20 Gy or more (V(20)) of the lung ranged from 0.3 to 11.6% (mean, 4.4%) of the whole lung volume. The maximum dose to the other OARs ranged from 0 to 11.8 Gy (mean, 0.5-2.7) per fraction. No clinically significant complications were encountered. Despite the limitation of the beam arrangement, a homogeneous target dose distribution, while avoiding high doses to normal tissues, was obtained.

Monte Carlo assessment of boron neutron capture therapy for the treatment of breast cancer

For a large number of women who are diagnosed with breast cancer every year the avail able treatment options are effective, though physically and mentally taxing. This work is a starting point of a study of the efficacy of boron neutron capture therapy as an alternative treatment for HER-2+ breast tumors. Using HER-2-specific monoclonal anti bodies coupled with a boron-rich oligomeric phosphate diester, it may be possible to deliver sufficient amounts of 10B to a tumor of the breast to al low for selective cell destruction via irradiation by thermal neutrons. A comprehensive computational model (MCNP) for thermal neutron irradiation of the breast is described, as well as the results of calculations made using this model, in order to determine the optimum boron concentration within the tumor for an effective boron neutron capture therapy treatment, as compared with traditional X-ray radiotherapy. The results indicate that a boron concentration of 50-60 mg per gram of tumor tissue is optimal when considering treatment times, dose distributions and skin sparing. How ever these results are based upon best-guess assumptions that must be experimentally verified.

A comparison of forward and inverse planned conformal, multi segment and intensity modulated radiotherapy for the treatment of prostate and pelvic nodes

Background and purpose Full inverse planned intensity modulated radiotherapy (IMRT) may be indicated to treat concave targets like prostate and pelvic nodes, because concave dose distributions cannot be generated with conformal radiotherapy (CRT). We investigated whether this concave dose distribution can be produced using simplified forward planned multi segment radiotherapy (MSRT). Patients and methods CRT, MSRT and IMRT dose distributions were calculated and compared for five patients treated in our current IMRT prostate and pelvic node dose escalation trial. The same beam arrangement was used for CRT, MSRT and IMRT, increasing the number of segments. The MSRT concave dose distribution was realised regarding left and right pelvic nodes as two separate targets. The IMRT dose distribution had been used to treat the patients using a step and shoot delivery. Results Contrary to CRT, forward planned MSRT concave dose distributions had improved target coverage at lower or equivalent bowel doses than inverse planned IMRT. The five MSRT beams had a maximum of three segments per beam. Both lateral beams had two segments to deliver the two dose levels to prostate and nodes. The posterior field needed a third segment to avoid using a central block. The two anterior oblique beams needed a third segment to account for the different beam weighting because the nodes were irradiated partially using four and partially using five beams. Inverse planned IMRT used up to 15 segments in any one beam, with an average of 11.4 per beam. Conclusions Concave dose distributions for prostate and pelvic node treatment were generated using forward planned multi segment techniques. The plans met clinical constraints used in our IMRT protocol. MSRT presented a significant advantage over both CRT and IMRT.

Radiation-induced changes of brain tissue after radiosurgery in patients with arteriovenous malformations: correlation with dose distribution parameters

purpose To investigate the correlation of radiation-induced changes of brain tissue after radiosurgery in patients with cerebral arteriovenous malformations (AVMs) with treatment planning and dose distribution parameters. Methods and materials The data from 73 AVM patients with complete follow-up information who underwent stereotactic linear accelerator radiosurgery at our institution between 1993 and 1998 were analyzed. Patients were treated with 11–14 noncoplanar fields shaped by a micromultileaf collimator. A median dose of 19 Gy (range, 13.3–22 Gy) was prescribed to the 80% isodose, which completely encompassed the target. Patients were followed at 3-month intervals the first year and then every 6 months with MRI and neurologic examinations. No patient developed radiation necrosis. The end point of radiation-induced tissue changes on follow-up neuroimaging (i.e., edema, blood–brain barrier breakdown [BBBB], and edema and/or BBBB combined) was evaluated. Each end point was further differentiated into four levels with respect to the extent of the image change (i.e., small, intermediate, large, and very large). The correlation of each end point was investigated for several treatment planning parameters, including prescribed dose and the absolute size of the AVM target volume. In addition, a number of dose–volume variables were calculated from each patient's dose distribution in the brain, including the mean dose to a specified volume of 16 and 20 cm 3 that was given the highest dose (Dmean16 and Dmean20, respectively), and the absolute and percentage of brain volume (including the AVM target) receiving a dose of at least 8, 10, and 12 Gy (V8–V12, and V8 rel–V12 rel, respectively). These parameters were also determined excluding the AVM target volume from the considered volume (subscript “excl”). The correlation of all treatment planning and dose–volume parameters with outcome was assessed in univariate Cox proportional hazards models. The results were assessed by p values (statistical significance for p ≤0.05), residual deviance (ResDev) of the fits, and odds ratios. Results The prescribed dose was not predictive of outcome ( p >0.05 for all end points). The AVM target volume correlated significantly with large edema, as well as large edema and/or BBBB. V12 and Dmean20 were significantly associated with all end points, except very large edema and large BBBB. Patients with V12 of 27.6 cm 3 (Dmean20 of 18.9 Gy) had a 2.8-fold (fourfold) higher risk of developing edema and/or BBBB with large extent than those with V12 of 4.2 cm 3 (Dmean20 of 8.4 Gy). For all end points, V12 rel correlated worse with outcome compared with V12 (e.g., end point of large edema and/or BBBB: ResDev = 85.8 and 86.5 for V12 and V12 rel, respectively). Excluding the AVM target volume from the considered irradiated volume led to only small changes in the resulting correlations (e.g., end point of small edema and/or BBBB: ResDev = 99.0 and 98.7 for V12 and V12 excl, respectively, and ResDev = 96.1 and 96.1 for Dmean20 and Dmean20 excl, respectively). Throughout the analysis, V8-V12, Dmean20, and Dmean16 yielded similar results and none of these parameters could be favored over the others. Conclusion Radiation-induced changes of brain tissue after AVM radiosurgery can be well predicted by single dose distribution parameters that are a function of both dose and volume. These can be used to quantify dose–volume response relations. Studies of this nature will eventually help to improve our current understanding of the mechanisms leading to radiation-induced tissue changes after AVM radiosurgery and to optimize radiosurgery treatment planning.

The effect of Monte Carlo statistical uncertainties on the evaluation of dose distributions in radiation treatment planning

This paper discusses the effect of statistical uncertainties present in Monte Carlo (MC) calculated dose distributions on the evaluation of a ‘cost function’ that expresses the suitability of a treatment plan for the intended treatment. The mathematical derivations given are valid for any ‘well-behaved’ cost function. The validity of the general expressions is demonstrated using numerical examples. It is shown that random dose uncertainties lead to statistical and systematic uncertainties on the cost function. The balance between the two types of uncertainty and the desired accuracy on the cost function presents a clear criterion for the maximum acceptable MC dose uncertainties. It is demonstrated that it is possible to remove the systematic cost function uncertainty. Finally, it is shown that when the dose distribution is close to a true optimum, MC calculations of the cost function converge to the true result as one over the number of particles simulated, i. e. much faster than the individual dose uncertainties.

A technique to re-establish dose distributions for previously treated brain cancer patients in external beam radiotherapy

Tumor recurrences or new tumors may develop after irradiation of local lesion(s) in the brain, and additional radiotherapy treatments are often needed for previously treated patients. It is critical to re-establish the dose distributions delivered during the previous treatment in the current patient geometry, so that the previous dose distributions can be accurately taken into consideration in the design of the current treatment plan. The difficulty in re-establishing the previous treatment dose distributions in the current patient geometry arises from the fact that the patient position at the time of reirradiation is different from that at the previous treatment session. Simple re-entry of the previous isocenter coordinates, gantry, and couch and collimator angles into the new treatment plan would result in incorrect beam orientations relative to the new patient anatomy, and therefore incorrect display of the previous dose distributions on the current patient anatomy. To address this issue, a method has been developed so that the previous dose distributions can be accurately re-established in the framework of the current brain treatment. The method involves 3 matrix transformations: (1) transformation of beams from machine coordinate system to patient coordinate system in the previous treatment; (2) transformation of beams from patient coordinate system in the previous treatment to patient coordinate system in the current treatment; and (3) transformation of beams from patient coordinate system in the current treatment to machine coordinate system. The transformation matrices used in the second transformation are determined by registration using a mutual information-based algorithm with which the old and new computed tomography (CT) scan sets are registered automatically without human interpretation. A series of transformation matrices are derived to calculate the isocenter coordinates, the gantry, couch, and collimator angles of the beams for the previous treatment in the current patient geometry, and the previous dose distributions are re-established on the current CT images. The method has been proven to be successful and robust.

721 Poster Monte Carlo based study of the influence of double-focusing on dose distribution in IMRT treatments

721 Poster Monte Carlo based study of the influence of double-focusing on dose distribution in IMRT treatments

Electron beam process validation for sterilization of complex geometries

The application of low-energy electrons for the disinfection of containers of complex geometries has been limited due to their inability to efficiently penetrate the rigid walls. Most three-dimensional applications have been evaluated using higher energy processors with bulk or through-the-wall treatment. This work has been directed to the validation of electron disinfection of interior surfaces by injecting electrons through the open-mouth of the container. Both direct thin-film dosimetric mapping of the interior and exterior dose distributions for in-line treatment have been conducted and compared with the results of Monte Carlo modeling utilizing 10 6 or more source electron histories. Sterilizer characterization and model assumptions are described and the advantages of the modeling technique for process parameter optimization discussed.

Critical appraisal of treatment techniques based on conventional photon beams, intensity modulated photon beams and proton beams for therapy of intact breast

Purpose: To analyse different treatment techniques with conventional photon beams, intensity modulated photon beams, and proton beams for intact breast irradiation for patients in whom conventional irradiation would cause potentially dangerous lung irradiation. Material and methods: Five breast cancer patients with highly concave breast tissue volume around the lung were considered at planning level in order to assess the suitability of different irradiation techniques. Three-dimensional dose distributions for conventional two-field tangential photon treatment, two-field intensity modulated radiotherapy (IMRT), three-field non-IMRT, three-field IMRT, and single-field proton treatment were investigated, aiming at assessing the possibility to reduce lung irradiation below risk levels. Analysis of dose–volume histograms and related physical and biological parameters (significant minimum, maximum and mean doses, conformity indexes and equivalent uniform dose (EUD)) for planned target volume (PTV) and lung was carried out. Dose plans were compared with the conventional two-field tangential photon technique. Results: PTV coverage was comparable for non-IMRT and IMRT techniques (EUD from 47.1 to 49.4 Gy), and improved with single-field proton treatment (EUD=49.8 Gy). Lung irradiation was reduced, in terms of mean dose, with three-field (9.5 Gy) and proton technique (3.5 Gy), with respect to the conventional two-field treatment (12.9 Gy); also a reduction of the lung volume irradiated at high doses was observed. Better results could be achieved with protons. In addition, cardiac irradiation was also reduced with those techniques. Conclusions: Geometrically difficult breast cancer patients could be irradiated with a three-field non-IMRT technique thus reducing the dose to the lung which is proposed as standard for this category of patients. Intensity modulated techniques were only marginally more successful than the corresponding non-IMRT treatments, while protons offer excellent results.

Dosimetry with radiochromic films: a document scanner technique, neutron response, applications

The possibility of reading radiochromic films by the employment of a document scanner and associated software was explored. Dosimetric characteristics, such as the sensitivity of the technique, reproducibility in dose assessment, minimum detectable dose, film uniformity, OD variation with time, variation of OD due to multiple scans, polarity of the analyzing light, fast neutron response and thermal neutron yield were investigated. The technique was used to measure dose distributions in stereotactic radiotherapy, orthovoltage treatment and neutron capture therapy.

Application of enhanced dynamic wedge to stereotactic radiotherapy

Stereotactic radiotherapy has developed into a useful treatment technique in which conformal dose distributions can be delivered with precision and accuracy. In some cases, the position of the target volume relative to surrounding critical structures demands careful evaluation of fixed beam paths so that dose to these critical structures can be minimized. Micromultileaf collimators aid in conforming dose to the target volume but may not allow adjustment of an individual beam’s intensity (intensity modulation) in an effort to achieve dose uniformity throughout the treatment volume. Enhanced dynamic wedge (EDW) is demonstrated to be a valuable tool in improving the dose distribution in stereotactic radiotherapy treatments in which these fixed, conformal fields must be used due to constraints in beam trajectories. Four cases are presented which show the potential for gain in dose uniformity with the addition of EDW. These cases represent typical applications of EDW to conformal stereotactic radiotherapy.