Skin dose in chest wall radiotherapy with bolus: a Monte Carlo study.

Monte Carlo simulations are used to investigate skin dose resulting from chest wall radiotherapy with bolus. A simple model of a female thorax is developed, which includes a 2 mm-thick skin layer. Two representative 6 MV source models are considered: a tangents source model consisting of a parallel opposed pair of medial and lateral fields and subfields, and an arc source model. Tissue equivalent (TE) boluses (thicknesses of 3, 5 and 10 mm) and brass mesh bolus are considered. Skin dose distributions depend on incident photon obliquity: for tangents, radiation is incident more obliquely, resulting in longer path lengths through the bolus and higher skin dose compared to the arc source model in most cases. However, for thicker TE boluses, attenuation of oblique photons becomes apparent. Brass bolus and 3 mm TE bolus result in similar mean skin dose. This relatively simple computational model allows for consideration of different bolus thicknesses, materials and usage schedules based on desired skin dose and choice of either tangents or an arc beam technique. For example, using a 5 mm TE bolus every second treatment would result in mean skin doses of 89% and 85% for tangents and the arc source model, respectively. The hot spot metric D[Formula: see text] would be 103% and 99%, respectively.

Electron modulated arc therapy (EMAT) using photon MLC for postmastectomy chest wall treatment I: Monte Carlo-based dosimetric characterizations.

PURPOSE: To study the dosimetric properties of electron arc beams delivered by photon-beam multi-leaf collimators (pMLC) in electron modulated arc therapy (EMAT) for postmastectomy chest wall treatments. METHODS: Using the Monte Carlo method, we simulated a 2100EX Varian linear accelerator and verified the beam models in a water tank. Dosimetric characterizations were performed on cylindrical water phantoms of elliptical bases with various field sizes, arc ranges and source-to-surface distances (SSDs) for 6, 9 and 12 MeV beam energy. RESULTS: The arc beam has a higher bremsstrahlung dose than the static beam at the isocenter due to crossfire, but choosing a field size greater than 5 cm effectively reduces the bremsstrahlung dose. The depths of the 90% maximum dose located at 1.7, 2.8 and 4.1 cm for 6, 9 and 12 MeV, respectively, are similar to those of the static beams and independent of the field size and arc range. CONCLUSION: Based on the study, we recommend using the 5 cm field width for electron arc beams considering both bremsstrahlung dose at the isocenter and the arc profile penumbra. To ensure sufficient PTV edge coverage, we recommend a field length extension of at least 4 cm from PTV's edge for all beam energies and an arc extension of around 7°, 5°, and 5° for beam energies 6, 9, and 12 MeV, respectively. These dosimetric characterizations are the basis of pMLC-delivered EMAT treatment planning for postmastectomy chest wall patients.

Assessment of Setup Accuracy Using Anatomical Landmarks for Breast and Chest Wall Irradiation With Surface Guided Radiation Therapy.

PURPOSE: This study aimed to determine setup accuracy using anatomic landmarks for breast irradiation with and without surface guided radiation therapy (SGRT) and assess setup time with SGRT. METHODS AND MATERIALS: This study included 115 patients with 1945 treatment fractions. Patients were treated with 4 techniques: tangents, tangents using deep-inspiration breath hold, and tangents with regional nodal irradiation with and without deep-inspiration breath hold. A total of 915 portal verification images were analyzed to determine setup errors for the skin, chest wall (CW), and heart. Setup error at each landmark was defined as the mean and maximum distances between the projected planning structure and the delineated structure on the portal image. Setup time for each fraction was determined using 2 recorded time outs: one upon the patient entering the treatment room and another before radiation beam on. RESULTS: Setup errors for the skin were significantly reduced with SGRT for all 4 treatment techniques (P < .001). On average, the mean and maximum errors for the skin decreased from 3.5 mm to 2.3 mm (P < .001) and from 7.6 mm to 5.6 mm (P < .001), respectively. Setup errors for the CW were not significantly different for tangent treatments, but significantly different for locoregional treatments. For all patients, the average mean and maximum errors for the CW were reduced from 3.1 mm to 3.0 mm (P = .21) and from 6.1 mm to 5.5 mm (P = .001), respectively. No significant change in setup errors for the heart was observed. Setup times with SGRT were slightly longer (P < .01), and the average setup time increased from 5.4 to 6.3 minutes. CONCLUSIONS: Using anatomic landmarks, we confirm that SGRT improved patient setup accuracy with a slight, but clinically nonsignificant increase in setup time.

A Phase 2 Study of 2 Weeks of Adjuvant Whole Breast/Chest Wall and/or Regional Nodal Radiation Therapy for Patients With Breast Cancer.

PURPOSE: To report the results in terms of feasibility and early toxicity of hypofractionated adjuvant whole breast/chest wall and/or regional nodal radiation therapy for patients with breast cancer. METHODS AND MATERIALS: From June 2013 to October 2014, 50 patients with breast cancer after mastectomy or after breast conservation surgery (BCS) were prospectively included. The institutional ethics committee approved the study, which was registered with ClinicalTrials.gov (ClinicalTrials.gov identifier no. NCT02460744). Treatment planning was performed using a simulator with 2 tangential fields to the breast/chest wall and an incident field to the supraclavicular fossa. The radiation dose delivered was 34 Gy in 10 fractions within 2 weeks, followed by a boost of 10 Gy in 5 fractions within 1 week for patients who underwent BCS. Acute skin toxicities were recorded during and after treatment according to the Radiation Therapy Oncology Group acute radiation toxicity scoring criteria. The primary objective was to obtain estimates of the acute toxicity rates and cosmetic outcomes that could be used to design a subsequent phase III comparative study. Acute skin and late toxicities were recorded during and after treatment. Cosmetic outcomes were assessed before and after treatment and during the regular follow-up period. A cost/benefit analysis was also performed and compared with that for standard treatment of 35 Gy in 15 fractions within 3 weeks. RESULTS: The median follow-up was 39 months (range 14-48). The mean age was 51 years (range 26-75). A left-sided tumor was present in 25 patients (50%). Total mastectomy with axillary clearance was performed in 40 (80%) and BCS in 10 (20%) patients. Acute grade 2 and 3 skin toxicity was seen in 16 (32%) and 1 (2%) patient, respectively. In the BCS patients, grade 2 skin and subcutaneous toxicity was seen in 2 (20%) and 1 (10%) patient, respectively. Grade 2 edema was seen in 1 patient (10%). The cosmesis was excellent or good in 8 (80%) and fair or poor in 2 (20%) patients. The cost/benefit analysis revealed significantly less financial burden on the patients with 2 weeks of treatment. Disease-free and overall survival at 3 years was 94% and 96%, respectively. CONCLUSIONS: Hypofractionated radiation therapy within 2 weeks appears to be feasible for patients with breast cancer and was associated with acute and late skin toxicity profiles similar to those observed with 3 weeks of treatment. The financial burden on the patient and family could be reduced with 2 weeks of treatment. Long-term follow-up data and a prospective comparative study are needed to strengthen these results. Hypofractionation might help radiation centers worldwide to meet the increasing need for radiation for breast cancer, especially in developing countries where resources are limited and patients must travel long distances for treatment.

Quantitative assessment of radiation dose and fractionation effects on normal tissue by utilizing a novel lung fibrosis index model.

BACKGROUND: Normal lung tissue tolerance constitutes a limiting factor in delivering the required dose of radiotherapy to cure thoracic and chest wall malignancies. Radiation-induced lung fibrosis (RILF) is considered a critical determinant for late normal tissue complications. While RILF mouse models are frequently approached e.g., as a single high dose thoracic irradiation to investigate lung fibrosis and candidate modulators, a systematic radiobiological characterization of RILF mouse model is urgently needed to compare relative biological effectiveness (RBE) of particle irradiation with protons, helium-, carbon and oxygen ions now available at HIT. We aimed to study the dose-response relationship and fractionation effect of photon irradiation in development of pulmonary fibrosis in C57BL/6 mouse. METHODS: Lung fibrosis was evaluated 24 weeks after single and fractionated whole thoracic irradiation by quantitative assessment of lung alterations using CT. The fibrosis index (FI) was determined based on 3D-segmentation of the lungs considering the two key fibrosis parameters affected by ionizing radiation i.e., a dose/fractionation dependent reduction of the total lung volume and increase of the mean lung density. RESULTS: The effective dose required to induce 50% of the maximal possible fibrosis (ED 50 ) was 14.55 ± 0.34Gy and 27.7 ± 1.22Gy, for single and five- fractions irradiation, respectively. Applying a deterministic model an α/ß = 4.49 ± 0.38 Gy for the late lung radiosensitivity was determined. Intriguingly, we found that a linear-quadratic model could be applied to in-vivo log transformed fibrosis (FI) vs. irradiation doses. The LQ model revealed an α/ß for lung radiosensitivity of 4.4879 Gy for single fraction and 3.9474 for 5-fractions. Our FI based data were in good agreement with a meta-analysis of previous lung radiosensitivity data derived from different clinical endpoints and various mouse strains. The effect of fractionation on RILF development was further estimated by the biologically effective dose (BED) model with threshold BED (BED Tr ) = 30.33 Gy and BED ED50  = 61.63 Gy, respectively. CONCLUSION: The systematic radiobiological characterization of RILF in the C57BL/6 mouse reported in this study marks an important step towards precise estimation of dose-response for development of lung fibrosis. These radiobiological parameters combined with a large repertoire of genetically engineered C57BL/6 mouse models, build a solid foundation for further biologically individualized risk assessment of RILF and functional RBE prediction on novel of particle qualities.

Dosimetric feasibility of using tungsten-based functional paper for flexible chest wall protectors in intraoperative electron radiotherapy for breast cancer.

Intraoperative electron radiotherapy (IOERT), which is an accelerated partial breast irradiation method, has been used for early-stage breast cancer treatment. In IOERT, a protective disk is inserted behind the target volume to minimize the dose received by normal tissues. However, to use such a disk, the surgical incision must be larger than the field size because the disk is manufactured from stiff and unyielding materials. In this study, the applicability of newly developed tungsten-based functional paper (TFP) was assessed as an alternative to the existing protective disk. The radiation-shielding performance of the TFP was verified through experimental measurements and Monte Carlo simulations. Percentage depth dose curves and lateral dose profiles with and without TFPs were measured and simulated on a dedicated IOERT accelerator. The number of piled-up TFPs was changed from 1 to 40. In the experimental measurements, the relative doses at the exit plane of the TFPs for 9 MeV were 42.7%, 9.2%, 0.2%, and 0.1% with 10, 20, 30, and 40 TFPs, respectively, whereas those for 12 MeV were 63.6%, 27.1%, 8.6%, and 0.2% with 10, 20, 30, and 40 TFPs, respectively. Slight dose enhancements caused by backscatter radiation from the TFPs were observed at the entrance plane of the TFPs at both beam energies. The results of the Monte Carlo simulation indicated the same tendency as the experimental measurements. Based on the experimental and simulated results, the radiation-shielding performances of 30 TFPs for 9 MeV and 40 TFPs for 12 MeV were confirmed to be acceptable and close to those of the existing protective disk. The findings of this study suggest the feasibility of using TFPs as flexible chest wall protectors in IOERT for breast cancer treatment.

Revision of orthovoltage chest wall treatment using Monte Carlo simulations.

PURPOSE: Given the high local control rates observed in breast cancer patients undergoing chest wall irradiation by kilovoltage x-rays, we aimed to revisit this treatment modality by accurate calculation of dose distributions using Monte Carlo simulation. METHODS AND MATERIAL: The machine components were simulated using the MCNPX code. This model was used to assess the dose distribution of chest wall kilovoltage treatment in different chest wall thicknesses and larger contour or fat patients in standard and mid sternum treatment plans. Assessments were performed at 50 and 100 cm focus surface distance (FSD) and different irradiation angles. In order to evaluate different plans, indices like homogeneity index, conformity index, the average dose of heart, lung, left anterior descending artery (LAD) and percentage target coverage (PTC) were used. Finally, the results were compared with the indices provided by electron therapy which is a more routine treatment of chest wall. RESULT: These indices in a medium chest wall thickness in standard treatment plan at 50 cm FSD and 15 degrees tube angle was as follows: homogeneity index 2.57, conformity index 7.31, average target dose 27.43 Gy, average dose of heart, lung and LAD, 1.03, 2.08 and 1.60 Gy respectively and PTC 11.19%. Assessments revealed that dose homogeneity in planning target volume (PTV) and conformity between the high dose region and PTV was poor. To improve the treatment indices, the reference point was transferred from the chest wall skin surface to the center of PTV. The indices changed as follows: conformity index 7.31, average target dose 60.19 Gy, the average dose of heart, lung and LAD, 3.57, 6.38 and 5.05 Gy respectively and PTC 55.24%. Coverage index of electron therapy was 89% while it was 22.74% in the old orthovoltage method and also the average dose of the target was about 50 Gy but in the given method it was almost 30 Gy. CONCLUSION: The results of the treatment study show that the optimized standard and mid sternum treatment for different chest wall thicknesses is with 50 cm FSD and zero (vertical) tube angle, while in large contour patients, it is with 100 cm FSD and zero tube angle. Finally, chest wall kilovoltage and electron therapies were compared, which revealed that electron therapy produces a better dose distribution than kilovoltage therapy.

PERSONALISED BODY COUNTER CALIBRATION USING ANTHROPOMETRIC PARAMETERS.

Current calibration methods for body counting offer personalisation for lung counting predominantly with respect to ratios of body mass and height. Chest wall thickness is used as an intermediate parameter. This work revises and extends these methods using a series of computational phantoms derived from medical imaging data in combination with radiation transport simulation and statistical analysis. As an example, the method is applied to the calibration of the In Vivo Measurement Laboratory (IVM) at Karlsruhe Institute of Technology (KIT) comprising four high-purity germanium detectors in two partial body measurement set-ups. The Monte Carlo N-Particle (MCNP) transport code and the Extended Cardiac-Torso (XCAT) phantom series have been used. Analysis of the computed sample data consisting of 18 anthropometric parameters and calibration factors generated from 26 photon sources for each of the 30 phantoms reveals the significance of those parameters required for producing an accurate estimate of the calibration function. Body circumferences related to the source location perform best in the example, while parameters related to body mass show comparable but lower performances, and those related to body height and other lengths exhibit low performances. In conclusion, it is possible to give more accurate estimates of calibration factors using this proposed approach including estimates of uncertainties related to interindividual anatomical variation of the target population.

Concomitant Imaging Dose and Cancer Risk in Image Guided Thoracic Radiation Therapy.

PURPOSE: Kilovoltage cone beam computed tomography (CT) (kVCBCT) imaging guidance improves the accuracy of radiation therapy but imposes an extra radiation dose to cancer patients. This study aimed to investigate concomitant imaging dose and associated cancer risk in image guided thoracic radiation therapy. METHODS AND MATERIALS: The planning CT images and structure sets of 72 patients were converted to CT phantoms whose chest circumferences (Cchest) were calculated retrospectively. A low-dose thorax protocol on a Varian kVCBCT scanner was simulated by a validated Monte Carlo code. Computed doses to organs and cardiac substructures (for 5 selected patients of various dimensions) were regressed as empirical functions of Cchest, and associated cancer risk was calculated using the published models. The exposures to nonthoracic organs in children were also investigated. RESULTS: The structural mean doses decreased monotonically with increasing Cchest. For all 72 patients, the median doses to the heart, spinal cord, breasts, lungs, and involved chest were 1.68, 1.33, 1.64, 1.62, and 1.58 cGy/scan, respectively. Nonthoracic organs in children received 0.6 to 2.8 cGy/scan if they were directly irradiated. The mean doses to the descending aorta (1.43 ± 0.68 cGy), left atrium (1.55 ± 0.75 cGy), left ventricle (1.68 ± 0.81 cGy), and right ventricle (1.85 ± 0.84 cGy) were significantly different (P<.05) from the heart mean dose (1.73 ± 0.82 cGy). The blade shielding alleviated the exposure to nonthoracic organs in children by an order of magnitude. CONCLUSIONS: As functions of patient size, a series of models for personalized estimation of kVCBCT doses to thoracic organs and cardiac substructures have been proposed. Pediatric patients received much higher doses than did the adults, and some nonthoracic organs could be irradiated unexpectedly by the default scanning protocol. Increased cancer risks and disease adverse events in the thorax were strongly related to higher imaging doses and smaller chest dimensions.

Adjustment of chest wall thickness of voxel phantom for numerical efficiency calibration of lung counters.

A modification method was implemented to adjust the chest wall thickness of human voxel phantom for the purpose of numerical efficiency calibration of lung counters. This method was based on two basic mathematical morphology operations (dilation and erosion) and combined with proper structure elements. The voxel model of LLNL torso phantom was used as a reference to validate the modification process. The chest wall was mathematically modified from the starting phantom with no overlay plate to the target with an overlay plate of 24-mm thickness. The influences of different structure elements on detection efficiency were discussed. When diamond or square structure elements were used, the calculated efficiency was overestimated or underestimated by ∼40 % for 17.5-keV photons, compared with that of target phantom. In contrast, it was shown a good agreement with a deviation of <3 % when the hybrid structure elements were adopted. A similar adjustment method can be used for 3D modification of human voxel phantom to keep the body's anatomical geometry without distortion during the adjustment process.

Preclinical assessment of comfort and secure fit of thermobrachytherapy surface applicator (TBSA) on volunteer subjects.

A thermobrachytherapy surface applicator (TBSA) was developed for simultaneous heat and brachytherapy treatment of chest wall (CW) recurrence of breast cancer. The ability to comfortably secure the applicator over the upper torso relative to the CW target throughout treatment is assessed on volunteers. Male and postmastectomy female volunteers were enrolled to evaluate applicator secure fit to CW. Female subjects with intact breast were also enrolled to assess the ability to treat challenging cases. Magnetic resonance (MR) images of volunteers wearing a TBSA over the upper torso were acquired once every 15 minutes for 90 minutes. Applicator displacement over this time period required for treatment preplanning and delivery was assessed using MR visible markers. Applicator comfort and tolerability were assessed using a questionnaire. Probability estimates of applicator displacements were used to investigate dosimetric impact for the worst-case variation in radiation source-to-skin distance for 5 and 10 mm deep targets spread 17 × 13 cm on a torso phantom. Average and median displacements along lateral and radial directions were less than 1.2 mm over 90 minutes for all volunteers. Maximum lateral and radial displacements were measured to be less than 1 and 1.5 mm, respectively, for all CW volunteers and less than 2 mm for intact breast volunteers, excluding outliers. No complaint of pain or discomfort was reported. Phantom treatment planning for the maximum displacement of 2 mm indicated < 10% increase in skin dose with < 5% loss of homogeneity index (HI) for -2 mm uniform HDR source displacement. For +2 mm uniform displacement, skin dose decreased and HI increased by 20%. The volunteer study demonstrated that such large and uniform displacements should be rare for CW subjects, and the measured variation is expected to be low for multifraction conformal brachytherapy treatment.

Lung counting: comparison of detector performance with a four detector array that has either metal or carbon fibre end caps, and the effect on mda calculation.

This study described the performance of an array of high-purity Germanium detectors, designed with two different end cap materials-steel and carbon fibre. The advantages and disadvantages of using this detector type in the estimation of the minimum detectable activity (MDA) for different energy peaks of isotope (152)Eu were illustrated. A Monte Carlo model was developed to study the detection efficiency for the detector array. A voxelised Lawrence Livermore torso phantom, equipped with lung, chest plates and overlay plates, was used to mimic a typical lung counting protocol with the array of detectors. The lung of the phantom simulated the volumetric source organ. A significantly low MDA was estimated for energy peaks at 40 keV and at a chest wall thickness of 6.64 cm.

Minimising contralateral breast dose in post-mastectomy intensity-modulated radiotherapy by incorporating conformal electron irradiation.

PURPOSE: To assess the potential benefit of incorporating conformal electron irradiation in intensity-modulated radiotherapy (IMRT) for loco-regional post-mastectomy RT. PATIENTS AND METHODS: Ten consecutive patients that underwent left-sided mastectomy were selected for this comparative planning study. Three-dimensional conformal radiotherapy (3D-CRT) photon-electron dose plans were compared to photon-only IMRT (IMRT(p)) and photon IMRT with conformal electron irradiation (IMRT(p/e)). The planning target volume (PTV) was prescribed 50 Gy and included the chest wall and the internal mammary and supra-clavicular lymph node regions. It was attempted to minimise dose delivered to heart, lungs and contralateral breast (CB), while maintaining adequate PTV coverage. RESULTS: All plans complied with objectives for PTV coverage. IMRT(p/e) eliminated volumes receiving 70 Gy (V70) that were present in 3D-CRT at the junction of photon and electron beams. Both IMRT strategies reduced heart V30 significantly below 3D-CRT levels. Mean heart dose with IMRT(p/e) was the lowest and was equal to that with 3D-CRT. Minimising heart dose with IMRT(p) resulted in irradiated CB volumes much larger than that with 3D-CRT. With IMRT(p/e), CB dose was only slightly increased when compared to 3D-CRT. Mean lung dose values were similar for IMRT and 3D-CRT. With IMRT, lung V20 was smaller, whereas V5 values for heart, lung and CB were higher than those with 3D-CRT. CONCLUSIONS: Incorporation of conformal electron irradiation in post-mastectomy IMRT(p/e) enables a heart dose reduction which can only be obtained with IMRT(p) when allowing large irradiated volumes in the contralateral breast.

Skin dose study of chest wall treatment with tomotherapy.

PURPOSE: The tangential-beam technique frequently presents challenges in homogeneity of radiation dose to the target. To ensure an adequate dose to the skin, a bolus is often used. Tomotherapy has already been shown to improve target conformity and homogeneity in other disease sites. Because of the tangential delivery technique and lack of flattening filter in TomoTherapy accelerators, we hypothesize that during chest wall irradiation using tomotherapy, the skin dose will be adequate without bolus. MATERIALS AND METHODS: This study compares the dosimetric differences between tomotherapy chest wall irradiation and traditional linear accelerator-based tangential-beam technique. Tomotherapy treatment plans with and without bolus were compared with tangentialbeam plans. Plans were also generated for phantom studies, and point doses were measured using MOSFET dosimetry to verify the adequate skin dose. Monte Carlo simulations of static beams of both techniques were performed, and dosimetry was compared. RESULTS: Monte Carlo simulations and measurements confirmed that beams from tomotherapy deliver a higher skin dose than a standard linear accelerator. Skin dose also increases with the incident angle of the beams. CONCLUSION: Because of the characteristics of the tomotherapy beam and delivery technique, chest wall treatment plans from tomotherapy showed adequate skin dose [more than 75% of prescribed planning target volume (PTV) dose] even without bolus.

Modulated electron radiotherapy treatment planning using a photon multileaf collimator for post-mastectomized chest walls.

BACKGROUND AND PURPOSE: To evaluate the feasibility of using a photon MLC (xMLC) for modulated electron radiotherapy treatment (MERT) as an alternative to conventional post-mastectomy chest wall (CW) irradiation. A Monte Carlo (MC) based planning system was developed to overcome the inaccuracy of the 'pencil beam' algorithm. MC techniques are known to accurately calculate the dose distributions of electron beams, allowing the explicit simulation of electron interactions within the MLC. MATERIALS AND METHODS: Four real clinical CW cases were planned using MERT which were compared with the conventional electron treatments based on blocks and by a straightforward approach using the MLC, and not the blocks (as an intermediate step to MERT) to shape the same segments with SSD between 60 and 70 cm depending on PTV size. MC calculations were verified with an array of ionization chambers and radiochromic films in a solid water phantom. RESULTS: Tests based on gamma analysis between MC dose distributions and radiochromic film measurements showed an excellent agreement. Differences in the absolute dose measured with a plane-parallel chamber at a reference point were below 3% for all cases. MERT solution showed a better PTV coverage and a significant reduction of the doses to the organs at risk (OARs). CONCLUSION: MERT can effectively improve the current electron treatments by obtaining a better PTV coverage and sparing healthy tissues. More directly, block-shaped treatments could be replaced by MLC-shaped non-modulated segments providing similar results.

Comparison of conventional inserts and an add-on electron MLC for chest wall irradiation of left-sided breast cancer.

BACKGROUND: Collimation of irregularly shaped clinical electron beams is currently based on electron inserts made of low melting point alloys. The present investigation compares a conventional electron applicator with insert and add-on eMLC-based dose distributions in the postoperative chest wall irradiation of left-sided breast cancer. MATERIAL AND METHODS: Voxel Monte Carlo++ (VMC++) calculated dose distributions related to electron fields were compared with 10 left-sided breast cancer patients after radical mastectomy. The prescription dose was 50 Gy at a build-up maximum. The same dose was prescribed for the ipsilateral axillary, parasternal and supraclavicular lymph nodes that were treated with photons and calculated with a pencil beam algorithm. The insert beams were shaped with 1.5 cm thick Wood's metal electron inserts in an electron applicator of a Varian 2100 C/D linac. Doses for the eMLC-shaped beams were calculated for an eMLC prototype with 2 cm thick and 5 mm wide steel leaves. The same collimator-to-surface distance (CSD) of 5.8 cm was used for both collimators. RESULTS: The mean PTV dose was slightly higher for the eMLC plans (50.7 vs 49.5 Gy, p<0.001, respectively). The maximum doses assessed by D5% for the eMLC and insert were 60.9 and 59.1 Gy (p<0.001). The difference was due to the slightly higher doses near the field edges for the eMLC. The left lung V20 volumes were 34.5% and 34.0% (p<0.001). There was only a marginal difference in heart doses. DISCUSSION: Despite a slight increase of maximum dose in PTV the add-on electron MLC for chest wall irradiation results in practically no differences in dose distributions compared with the present insert-based collimation.

Psychological assessment of women on an early breast screening program after radiotherapy to the chest wall for childhood cancer.

AIMS AND BACKGROUND: This study investigates the psychological status in a population of female patients who received chest irradiation for a childhood cancer and were screened for second primary breast cancer. METHODS: Sixty-eight consecutive such young women were included. Compilation of the Crown-Crisp Index questionnaire was requested and 49/68 patients accepted to fill it in; 14 women in the sample had children (28%). RESULTS: Twenty-seven of 49 patients achieved a normal score, whereas in 22 the score was slightly above the normal range in at least one scale. Pathological scores were more frequent among the women without children. CONCLUSION: Quality of life in this series of long-term survivors does not seem to be severely affected by previous treatment for cancer nor by the concern for the onset of a second primary malignancy.

Assessment of skin dose for breast chest wall radiotherapy as a function of bolus material.

Skin dose assessment for chest wall radiotherapy is important to ensure sufficient dose to the surface target volume without excessive skin reaction. This study quantified changes to the surface doses as a function of bolus material for conventional and intensity modulated radiation therapy (IMRT) tangential fields. Three types of bolus materials (2 mm solid, 2 mm fine mesh and 3.2 mm large mesh Aquaplast) were compared with Superflab. Surface dose measurements were performed using an Attix parallel plate chamber in a flat solid water phantom at 0 degrees , 45 degrees and 70 degrees incident angles. Over-response correction factors were applied to the Attix chamber results for different incident angles. Surface dose measurements on an anthropomorphic phantom were done using a thermoluminescent dosimeter extrapolation method. Dose characteristics of Superflab and solid Aquaplast were within 2% of solid water material. No significant differences (within 3%) in the surface dose were found between conventional and IMRT tangential techniques. The bolus effect was large for chest wall tangential radiotherapy, with up to an 82% increase using 2 mm fine mesh Aquaplast. The dosimetric effect of different Aquaplast materials has been quantified in this work. These materials can be used to create a custom bolus with potentially better reproducibility of placement.

Dosimetric effect of respiratory motion in external beam radiotherapy of the lung.

BACKGROUND AND PURPOSE: To study the effect of breathing motion on gross tumor volume (GTV) coverage for lung tumors using dose-volume histograms and relevant dosimetric indices. PATIENTS AND METHODS: Treatment plans were chosen for 12 patients treated at our institution for lung carcinoma. GTV volumes of these patients ranged from 1.2 to 97.3 cm(3). A margin of 1-2 cm was used to generate the planning target volume (PTV). Additional margins of 0.6-1.0 cm were added to the PTV when designing treatment portals. For the purposes of TCP calculation, the prescription dose was assumed to be 70 Gy to remove the effects of prescription differences. Setup error was incorporated into the evaluation of treatment plans with a systematic component of sigma(RL) = 0.2 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.3 cm and a random component of sigma(RL) = 0.3 cm, sigma(AP) = 0.3 cm, and sigma(SI) = 0.3 cm. Breathing motion was incorporated into these plans based on an independent analysis of fluoroscopic movies of the diaphragm for 7 patients. The systematic component of breathing motion (sigma(RL) = 0.3 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.6 cm) was incorporated into the treatment plans on a slice by slice basis. The intrafractional component of breathing motion (sigma(RL) = 0.3 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.6 cm) was incorporated by averaging the dose calculation over all displacements of the breathing cycle. Each patient was simulated 500 times to discern the range of possible outcomes. The simulations were repeated for a worst case scenario which used only breathing data with a large diaphragmatic excursion, both with and without intrafractional breathing motion. RESULTS: Dose to 95% of the GTV (D95), volume of the GTV receiving 95% of the prescription dose (V95) and TCP changed an average of -1.4+/-4.2, -1.0+/-3.3, and -1.4+/-3.8%, respectively, with the incorporation of normal breathing effects. In the worst case scenario (heavy breathers), D95 and V95 changed an average of -9.8+/-10.1 and -8.3+/-11.3%, respectively, and TCP changed by -8.1+/-9.1%. GTVs with volumes greater than 60 cm(3) showed stronger sensitivity to breathing especially if the shape was non-ellipsoidal. In the normal breathing case, the probability of a decrease in D95, V95, or TCP of a magnitude greater than 10% is less than 4%, and in the worse case scenario this probability is approximately 30-40% with intrafractional breathing motion included, and less than 10% with intrafractional breathing motion not included. CONCLUSIONS: With the PTV margins routinely used at our center, the effects of normal breathing on coverage are small on the average, with a less than 4% chance of a 10% or greater decrease in D95, V95, or TCP. However, in patients with large respiration-induced motion, the effect can be significant and efforts to identify such patients are important.