Invited review: tangential breast irradiation--rationale and methods for improving dosimetry

Anatomy-based prediction method for determining ipsilateral lung doses in postoperative breast radiation therapy assisted by diagnostic computed tomography images

Background

This study aimed to investigate whether ipsilateral lung doses (ILDs) could be predicted by anatomical indexes measured using diagnostic computed tomography (CT) prior to the planning stage of breast radiation therapy (RT).

Materials and methods

The thoracic diameters and the length of lines drawn manually were measured on diagnostic CT images. The parameters of interest were the skin maximum lung distance (sMLD), central lung distance (CLD), Haller index (HI), and body mass index (BMI). Lung dose-volume histograms were created with conformal planning, and the lung volumes receiving 5-40 Gy (V5-V40) were calculated. Linear regression models were used to investigate the correlations between the anatomical indexes and dose differences and to estimate the slope and 95% confidence intervals (CIs).

Results

A total of 160 patients who had undergone three-dimensional conformal RT after breast-conserving surgery were included. Univariable analysis revealed that the sMLD (p < 0.001), CLD (p < 0.001), HI (p = 0.002), and BMI (p < 0.001) were significantly correlated with the V20. However, multivariable analysis revealed that only the sMLD (slope: 0.147, p = 0.001, 95% CI: 0.162-0.306) and CLD (0.157, p = 0.005, 0.048-0.266) were strongly correlated with the V20. The p-value for the sMLD was the lowest among the p-values for all indexes, thereby indicating that the sMLD had the best predictive power for ILD.

Conclusions

sMLD and CLD are anatomical markers that can be used to predict ILD in whole breast RT. An sMLD > 20.5 mm or a CLD > 24.3 mm positively correlated with a high ILD.

Does breast composition influence late adverse effects in breast radiotherapy?

BACKGROUND

Large breast size is associated with increased risk of late adverse effects after surgery and radiotherapy for early breast cancer. It is hypothesised that effects of radiotherapy on adipose tissue are responsible for some of the effects seen. In this study, the association of breast composition with late effects was investigated along with other breast features such as fibroglandular tissue distribution, seroma and scar.

METHODS

The patient dataset comprised of 18 cases with changes in breast appearance at 2 years follow-up post-radiotherapy and 36 controls with no changes, from patients entered into the FAST-Pilot and UK FAST trials at The Royal Marsden. Breast composition, fibroglandular tissue distribution, seroma and scar were assessed on planning CT scan images and compared using univariate analysis. The association of all features with late-adverse effect was tested using logistic regression (adjusting for confounding factors) and matched analysis was performed using conditional logistic regression.

RESULTS

In univariate analyses, no statistically significant differences were found between cases and controls in terms of breast features studied. A statistically significant association (p < 0.05) between amount of seroma and change in photographic breast appearance was found in unmatched and matched logistic regression analyses with odds ratio (95% CI) of 3.44 (1.28-9.21) and 2.57 (1.05-6.25), respectively.

CONCLUSIONS

A significant association was found between seroma and late-adverse effects after radiotherapy although no significant associations were noted with breast composition in this study. Therefore, the cause for large breast size as a risk factor for late effects after surgery and optimally planned radiotherapy remains unresolved.

Comparison of plan optimization for single and dual volumetric-modulated arc therapy versus intensity-modulated radiation therapy during post-mastectomy regional irradiation

The aim of the present study was to investigate volumetric-modulated arc therapy (VMAT) with single arc (1ARC) and dual arc (2ARC), and intensity-modulated radiation therapy (IMRT), and to evaluate the quality and delivery efficiency of post-mastectomy regional irradiation. A total of 24 female patients who required post-mastectomy regional irradiation were enrolled into the current study, and 1ARC, 2ARC and IMRT plans were designed for each individual patient. The quality of these plans was evaluated by calculating the homogeneity index (HI), conformity index (CI) and specific volume dose to the ipsilateral lung, double lungs, contralateral breast, heart and spinal cord. For the delivery efficiency of these plans, the total treatment time (TTT) and the number of monitor units (MUs) were evaluated. The 1ARC and 2ARC VMAT plans exhibited significantly better HIs and CIs than IMRT. For dose-volume histogram analysis, 1ARC and 2ARC VMAT spared a more specific volume dose to the ipsilateral lung, double lungs, contralateral breast, heart and spinal cord than IMRT (P<0.05). A lower MU per 2.0-Gy fraction was required for 1ARC (539 MU) and 2ARC (608 MU) than for IMRT (1,051 MU). Thus, TTT was correspondingly reduced in 1ARC and 2ARC compared to IMRT (P<0.05). There was no significant dose-volume difference in all the organs at risk (OARs) between the 1ARC and 2ARC plans (P>0.05), and 2ARC VMAT displayed a better HI and CI than 1ARC VMAT (P<0.05). By contrast, 1ARC VMAT was superior to 2ARC VAMT with regard to MU and TTT (P<0.05). The 1ARC and 2ARC VMAT plans demonstrated significantly better dose distribution in a shorter treatment time than IMRT for post-mastectomy regional irradiation, and spared the majority of OARs without compromising target coverage. The results of the present study suggest that 2ARC VMAT may be an alternative to 1ARC in order to obtain a more optimal HI and CI.

Characterisation of 6MV and 10MV superficial build up dosimetry in tangential beam radiography

Introduction: Although tangential radiotherapy is one of the major treatments for breast cancer, little has been done to address the skin toxicity and general dose inhomogeneity experienced in patients with larger breasts that are treated with 6MV photons. From our understanding of radiation in tissue at depth, it is proposed that 10MV photons could have a clear role in such patients through improved dose distribution. However, a greater build up depth with 10MV could mean that this energy is unacceptable.

Aims: To quantify and characterise superficial build up dosimetry in tangential breast irradiation for 6MV and 10MV photons.

Methods: Using Thermoluminescent Dosimeters (TLD’S), a comparative study was carried out investigating dose at a range of superficial depths in a phantom irradiated by tangential fields. Each delivering 2Gy for 6MV and 10MV photons.

Results: There was a 0.10Gy difference in maximum dose over a depth of 10.8 mm between 6MV and 10MV photons, along with an average difference of dose at depth of 0.09Gy.

Conclusion: Evidence has been obtained that eliminates comprise to superficial tissue if 10MV photons are used. Furthermore, reinforcement towards a more homogenous dose distribution with 10MV photons has been established.

Randomised trial of standard 2D radiotherapy (RT) versus intensity modulated radiotherapy (IMRT) in patients prescribed breast radiotherapy

BACKGROUND

Radiation dose distributions created by two dimensional (2D) treatment planning are responsible for partial volumes receiving >107% of the prescribed dose in a proportion of patients prescribed whole breast radiotherapy after tumour excision of early breast cancer. These may contribute to clinically significant late radiation adverse effects.

AIM

To test three dimensional (3D) intensity modulated radiotherapy (IMRT) against 2D dosimetry using standard wedge compensators in terms of late adverse effects after whole breast radiotherapy.

METHODS

Three hundred and six women prescribed whole breast radiotherapy after tumour excision for early stage cancer were randomised to 3D IMRT (test arm) or 2D radiotherapy delivered using standard wedge compensators (control arm). All patients were treated with 6 or 10MV photons to a dose of 50Gy in 25 fractions to 100% in 5 weeks followed by an electron boost to the tumour bed of 11.1Gy in 5 fractions to 100%. The primary endpoint was change in breast appearance scored from serial photographs taken before radiotherapy and at 1, 2 and 5 years follow up. Secondary endpoints included patient self-assessments of breast discomfort, breast hardness, quality of life and physician assessments of breast induration. Analysis was by intention to treat.

RESULTS

240 (79%) patients with 5-year photographs were available for analysis. Change in breast appearance was identified in 71/122 (58%) allocated standard 2D treatment compared to only 47/118 (40%) patients allocated 3D IMRT. The control arm patients were 1.7 times more likely to have a change in breast appearance than the IMRT arm patients after adjustment for year of photographic assessment (95% confidence interval 1.2-2.5, p=0.008). Significantly fewer patients in the 3D IMRT group developed palpable induration assessed clinically in the centre of the breast, pectoral fold, infra-mammary fold and at the boost site. No significant differences between treatment groups were found in patient reported breast discomfort, breast hardness or quality of life.

CONCLUSION

This analysis suggests that minimisation of unwanted radiation dose inhomogeneity in the breast reduces late adverse effects. Incidence of change in breast appearance was statistically significantly higher in patients in the standard 2D treatment arm compared with the IMRT arm. A beneficial effect on quality of life remains to be demonstrated.

Analysis of non-genetic risk factors for adverse skin reactions to radiotherapy among 284 Breast Cancer patients

OBJECTIVES

We analyzed non-genetic risk factors for adverse skin reactions to irradiation at 4 collaborating Japanese institutions, to design future investigation into genetic risk factors for adverse skin reactions to irradiation in a multicenter setting.

METHODS

From April 2001, 284 breast cancer patients, who underwent radiotherapy with breast-conserving surgery, were enrolled from 4 collaborating institutions in Japan. We graded skin reactions according to international scoring systems. Clinical factors were tested against adverse effects.

RESULTS

Grade 1+ skin reactions were observed in 261 (92%) of the patients in less than 3 months, 118 (42%) at 3 months, and 29 (10%) at 6 months in the late phase. Univariate analysis of treatment risk factors (such as the use of a multi-leaf colimeter, wedge-filter, or immobilization device) for skin reactions revealed a significant association (p< 0.0001). After a variable selection procedure with logistic regression, the institution, operative procedure, and magnitude of photon energy remained significantly associated with acute skin reactions. Only the institution was an explanatory variable for skin reactions at 3 and 6 months in the final logistic model.

CONCLUSION

After stratification, substantial remaining variations in the occurrence of skin reactions of a given level suggested that individual genetic factors contribute markedly to individual radiosensitivity. Analysis of genetic factors associated with adverse effects would be possible by stratifying patients according to institution. Selection of eligible institutions, where appropriate treatment modalities could be performed, would also be possible when planning such a study.

Survey of tangential field planning and dose distribution in the UK: background to the introduction of the quality assurance programme for the START trial in early breast cancer

A background survey of UK breast radiotherapy techniques was performed prior to the introduction of the quality assurance programme for the Standardization of Radiotherapy (START) trial in breast cancer, a UK multicentre randomized trial of different dose fractionations for breast radiotherapy. Analysis of patient treatment plans was performed at this initial stage of the quality assurance programme to ensure eventual uniformity of treatment within the randomized trial and hence ensure reliable end results. As an integral part of this initial survey, three patient outlines of different size and shape were circulated between November 1997 and January 1998 to 56 UK radiotherapy centres. Dose distributions were produced according to the routine planning protocol of each department to provide information on treatment planning techniques. Criteria used for treatment plan production and the resultant dose distributions were analysed. The dose distributions varied between centres. Dose inhomogeneity of no more than 10% was achieved, on the central axis, for all chest wall and medium breast size plans. The number of larger breast size distributions exceeding a 10% dose gradient across the treatment volume was 54% (26). Most centres in the UK determine the breast dose distribution by planning on a two-dimensional contour taken along the central plane of the breast. Variation in the breast contour either side of this central plane is not taken into account. Care with plan optimization by selecting the most appropriate beam parameters can lead to an improvement in breast dosimetry.

Dose-position and dose-volume histogram analysis of standard wedged and intensity modulated treatments in breast radiotherapy

The aim of this work was to evaluate the positional distribution of dose in a concise manner and to analyse dose-histogram results in tangential breast radiotherapy in 300 patients, randomized to standard wedged or intensity modulated radiotherapy (IMRT), for future correlation with clinical outcome data. A simple method for analysing the dose-position relationship in the treatment volume was used to compare the spatial distribution of dose in patients. The breast was divided into equal thirds (upper, middle and lower) and dose was assessed using three dose bands; 95-105%, >105-110% and >110% of the prescription dose. The effect of using IMRT on the dosimetry was assessed from dose-volume histogram data using the following parameters: percentage of the target volume receiving a dose less than 95%, greater than 105%, either less than 95% or greater than 105% of that prescribed; the mean dose; and the maximum dose. Doses greater than 105% were predominantly in the upper and lower regions of the breast in the standard wedged treatment. 96% of these patients received doses greater than 105% in the upper region of the breast and 70% received doses greater than 105% in the lower breast. Only 4% of patients allocated IMRT received doses greater than 105% in either region. Analysis of dose-volume histogram data showed that IMRT reduced the volume receiving a dose greater than 105% by a mean of 10.7% (p= or <0.001); the mean change in the volume receiving a dose less than 95% was 0.2% (p=0.63). Average mean plan dose was 101.6% for standard treatment and 99.6% for IMRT (p<0.001 for each compared with 100.0% ideal). The mean value of maximum dose was reduced from 111% to 106% in the group of patients randomized to IMRT. A simple method for describing the relationship between dose and position in the breast, which is helpful for the effective correlation of dosimetry and clinical effects, is reported. Further, application of IMRT to the tangential field irradiation of the breast has been demonstrated to reduce high dose regions in both volume and dose level without compromising either minimum dose coverage or mean dose delivered to the breast.

Optimizing breast cancer treatment efficacy with intensity-modulated radiotherapy

PURPOSE

To present our clinical experience using intensity-modulated radiation therapy (IMRT) to improve dose uniformity and treatment efficacy in patients with early-stage breast cancer treated with breast-conserving therapy.

METHODS AND MATERIALS

A total of 281 patients with Stage 0, I, and II breast cancer treated with breast-conserving therapy received whole breast RT after lumpectomy using our static, multileaf collimator (sMLC) IMRT technique. The technical and practical aspects of implementing this technique on a large scale in the clinic were analyzed. The clinical outcome of patients treated with this technique was also reviewed.

RESULTS

The median time required for three-dimensional alignment of the tangential fields and dosimetric IMRT planning was 40 and 45 min, respectively. The median number of sMLC segments required per patient to meet the predefined dose-volume constraints was 6 (range 3-12). The median percentage of the treatment given with open fields (no sMLC segments) was 83% (range 38-96%), and the median treatment time was <10 min. The median volume of breast receiving 105% of the prescribed dose was 11% (range 0-67.6%). The median breast volume receiving 110% of the prescribed dose was 0% (range 0-39%), and the median breast volume receiving 115% of the prescribed dose was also 0%. A total of 157 patients (56%) experienced Radiation Therapy Oncology Group Grade 0 or I acute skin toxicity; 102 patients (43%) developed Grade II acute skin toxicity and only 3 (1%) experienced Grade III toxicity. The cosmetic results at 12 months (95 patients analyzable) were rated as excellent/good in 94 patients (99%). No skin telengiectasias, significant fibrosis, or persistent breast pain was noted.

CONCLUSION

The use of intensity modulation with our sMLC technique for tangential whole breast RT is an efficient method for achieving a uniform and standardized dose throughout the whole breast. Strict dose-volume constraints can be readily achieved resulting in both uniform coverage of breast tissue and a potential reduction in acute and chronic toxicities. Because the median number of sMLC segments required per patient is only 6, the treatment time is equivalent to conventional wedged-tangent treatment techniques. As a result, widespread implementation of this technology can be achieved with minimal imposition on clinic resources and time constraints.

A novel approach of dose mapping using a humanoid breast phantom in radiotherapy

A study of dose mapping techniques to investigate the dose distribution throughout a planned target volume (PTV) in a humanoid breast phantom exposed to a 6 MV photon beam similar to that of treatment conditions is described. For tangential breast irradiation using a 6 MV accelerator beam, the dose is mapped at various locations within the PTV using thermoluminescent dosemeters (TLDs) and radiographic films. An average size perspex breast phantom with the ability to hold the dosemeters was made. TLDs were exposed after packing them in various locations in a particular slice, as planned by the treatment planning system (TPS). To map the dose relative to the isocenter, films were exposed after tightly packing them in between phantom slices, parallel to the central axis of the beam. The dose received at every location was compared with the given dose as generated by the TPS. The mapped dose in each location in the isocentric slice from superficial to deep region was found to be in close agreement with the TPS generated dose to within +/-2%. Doses at greater depths and distant medial and lateral ends, however, were found to be lower by as much as 9.4% at some points. The mapped dose towards the superior region and closest inferior region from the isocenter was found to agree with those for TPS. Conversely, results for the farthest inferior region were found to be significantly different with a variance as much as 17.4% at some points, which is believed to be owing to the variation in size and shape of the contour. Results obtained from films confirmed this, showing similar trends in dose mapping. Considering the importance of accurate doses in radiotherapy, evaluating dose distribution using this technique and tool was found to be useful. This provides the opportunity to choose a technique and plan to provide optimum dose delivery for radiotherapy to the breast.

Cardiac and pulmonary doses and complication probabilities in standard and conformal tangential irradiation in conservative management of breast cancer

BACKGROUND AND PURPOSE

The clinical benefit of irradiating the intact breast after lumpectomy must be weighted against the risk of severe toxicity. We present a study on cardiac and pulmonary dose-volume data and the related complication probabilities of tangential breast irradiation having the following objectives: (1) to quantify the sparing of the organs at risk (ORs), the heart and the lung, achieved by three-dimensional (3-D) conformal tangential irradiation (CTI) as compared to standard tangential irradiation (STI); (2) to elucidate the uncertainty in radiation tolerance data; and (3) to analyse the relation between the amount of OR irradiated and the resulting morbidity risk.

MATERIAL AND METHODS

Computed tomography (CT)-based 3-D treatment plans of 26 patients prescribed to CTI of the intact breast were applied. Contour-based STI has been our routine treatment, and was reconstructed for all patients. Dose-volume data and normal tissue complication probability (NTCP) predictions from the probit and relative seriality models with several cardiac and pulmonary tolerance parameterizations were analysed and compared.

RESULTS AND CONCLUSIONS

A significant amount of normal tissues can be spared from radiation by using CT-based CTI, resulting in a 50% reduction of the average excess cardiac mortality risk in the left-sided cases. The risks for pericarditis and pneumonitis were too low to reveal any clinically significant difference between the treatments. For the STI set-up, a regression analysis showed that the excess cardiac mortality risk increased when larger parts of the heart were inside the fields. However, the different excess cardiac mortality and pneumonitis tolerance parameters resulted in statistically significant different NTCPs, which precluded the ability to accurately predict absolute NTCPs after tangential breast irradiation. Despite this uncertainty the different series of cardiac and pulmonary risk predictions were in relatively good agreement when small volumes of the ORs were irradiated. From the present data and without consideration of patient or organ motion, it therefore appears that tangential breast irradiation with less than 1 cm of the heart and 2-2.5 cm of the lung included inside the treatment fields will cause at most 1 per thousand risk for cardiac mortality and pulmonary morbidity. CT-based CTI should be considered, in particular for the left-sided cases, if these requirements cannot be met.

The use of a compensator library to reduce dose inhomogeneity in tangential radiotherapy of the breast

BACKGROUND AND PURPOSE

The dose variation throughout the volume of the breast from tangential fields can exceed 20% for large breasts. This is postulated to result in poor cosmesis [Radiother Oncol 16 (1989) 253], particularly at the inframammary fold, where the dose is highest. Compensators may be used to reduce this variation, but at the cost of the time to manufacture each unique compensator for the individual patients. This paper outlines the implementation and routine use of a library of reusable compensators.

MATERIALS AND METHODS

For the period of December 1999 to May 2001, 94 patients attending for breast radiotherapy received treatment using breast compensators calculated from multiple outlines measured using the Osiris system. The compensators manufactured for the early patients were added to a library for possible reuse by later patients. Of the 94 patients, 28 patients' compensators formed the library and 66 subsequent patients have been treated using compensators derived from the library. Selection of the most appropriate library compensator was determined from the analysis of the distribution of the calculated dose-volume histogram for the whole breast, excluding lung, penumbra and build-up regions. Once the library was complete, approximately 50% of all subsequent breast patients were treated with compensators (46% from the library and 4% with individual compensators). This represented a usage rate of 92% for the library compensators for those patients requiring compensation.

RESULTS

In all cases the compensators reduced the variation in the dose distribution. For example, the group treated with a library compensator demonstrated a mean reduction from 29 to 9% for the volume of breast tissue receiving more than 5% greater than the reference dose. If the same patients had been treated using their own individual compensators, the corresponding value would have been 7%. There is a small systematic, but negligible, difference in the two populations of dose variation for individual versus library compensators, but this difference (P=0.20) did not reach the level of statistical significance of P=0.05).

CONCLUSION

The method of creation and selection of library compensators has proved to be simple and reliable in practice. Every patient receiving radiotherapy for breast cancer is currently investigated under full software control to ascertain whether the use of a library compensator would be advantageous.

The role of biologically effective dose (BED) in clinical oncology

There are many clinical situations in which radiobiological considerations can be usefully applied and all clinicians should be aware of the potential benefits of developing a quantitative radiobiological approach to their practice. The concept of biologically effective dose (BED) in particular is useful for quantifying treatment expectations, but clinical oncologists should recognize that careful interpretation of modelling results is required before clinical decisions can be made and that there is a lack of reliable human parameters for application in some situations. Correct use of the BED concept will, in more complex treatment situations, sometimes involve the use of multiple parameters and BED calculations. Examples include: 1. Where the dose per fraction is being altered and it is possible that normal tissue tolerance may be compromised, calculations should include two or more alpha/beta ratio values, some being less than 3 Gy, in order to estimate the 'worst case scenario'. 2. A single one-point BED calculation will not be representative of the biological effect throughout a large planning target volume where there are significant 'hot spots'. Multiple BED evaluations are then indicated. 3. Where there are combinations of radiotherapy treatments or phases of treatments, these can be quantitatively assessed by the addition of BEDs, although the volume of tissue is not inherently included in the BED calculation and any high-dose region needs to be separately assessed as in point 2. 4. Allowance for tumour clonogen repopulation during therapy is required for some tumour types. 5. Different histological classes of cancers require the use of different alpha/beta ratios. Where there is reasonable doubt regarding this parameter, a suitable range should be used. The principles involved are illustrated by worked examples. Attention to detail and the examination of ranges of possible results should offer a safer guide to alternative dose fractionation schedules, although the ultimate choice will be tempered by clinical circumstances.

Laser scanning of patient outlines for three-dimensional radiotherapy treatment planning

In the planning of radiation treatments it is important to have a knowledge of the patient outline in order to correctly calculate the dose distribution that can be expected within the patient. This information is routinely obtained using x-ray computed tomography (CT). Although the CT data set is the ultimate data set, it can be impractical for economic and physical reasons. These impracticalities have been overcome using a commercial three dimensional (3D) laser scanning system. The system scans a laser line across the surface of the patient while a CCD camera views the patient from an offset angle. From a knowledge of the spatial orientation of the camera and the laser source, the system is able to detect the patient's surface and generate an equivalent 3D point cloud. Manipulation of 3D data sets allows the appropriate outlines of the patient to be obtained, that can then be used with the radiotherapy planning system. This has enabled the evaluation of 3D dose distributions for patients, and hence will allow the development of techniques for improving the uniformity of dose in breast treatments. The technique has no radiation overhead associated with it, is quick and is relatively cheap.

Determination of optimal radiation energy for different breast sizes using CT-simulator [correction of simulatior] in tangential breast irradiation

BACKGROUND

The purpose of this study is to determine and recommend the optimal radiation source according to breast size for tangential irradiation in breast conserving therapy.

METHODS

Twenty-eight patients treated at our department from January 1994 to January 1996 were studied. The dose distribution within the irradiated breast was calculated using a (60)Co-gamma ray and 6 MV-X ray. Then we compared 3-D dose distributions of the (60)Co-gamma ray and 6 MV-X ray in different-sized breasts. Three parameters (breast volume, chest wall separation, and breast height) were adopted as representative of breast size. We also examined correlations among the three parameters.

RESULTS

When the breast size was large (breast volume >400 cm(3), chest wall separation > 19.5 cm, or breast height > 6.5 cm), the average volume of normal tissue which received more than 110% of the isocenter dose ("hot spot") was significantly greater with the (60)Co-gamma ray than with the 6 MV-X ray (p < 0.05). A similar result was obtained with regard to hot spots in the clinical target volume. The cold area that received less than 95% of the isocenter dose was greater using a 6 MV-X ray when the breast size was small (breast volume <200 cm(3), chest wall separation <17.5 cm, or breast height <5.0 cm). However, the difference was not significant. There was a significant correlation between breast volume and chest wall separation (r =0.849, p <0.001). Breast volume and breast height were also significantly correlated (r =0.813, p <0.001).

CONCLUSIONS

Since breast volume and shape are different in each patient, the optimal energy should be selected for each case to obtain uniform dose distribution in breast-conserving therapy. Chest wall separation or breast height, which are measurable without a 3-D planning system, can substitute for breast volume as parameters for breast size. We recommend that the (60)Co-gamma ray not be used for treating large breasts, those with chest wall separation > or =19.5 cm or breast height > or =6.5 cm.

Influence of a vac-fix immobilization device on the accuracy of patient positioning during routine breast radiotherapy

Continued use of basic planning and treatment techniques, in contrast to the improved methods implemented at many other anatomical sites, has emphasized the need for improved breast dosimetry. Any future technique delivering a superior three-dimensional dose distribution will be of maximum benefit if set-up errors are minimized. To determine the influence of vacuum moulded bag (vac-fix) immobilization on routine breast radiotherapy, 17 patients received half their radiotherapy fractions using our standard breast board technique and half using a vac-fix device positioned on the breast board. Treatment accuracy and reproducibility were assessed for each technique using daily electronic portal imaging and were analysed in terms of random and systematic translational and rotational displacements of treatment fields with respect to corresponding simulation images. In addition, patients completed a short questionnaire aimed at determining which technique they preferred. Results showed that random errors for the two techniques did not differ significantly. Approximately 80% of random translations recorded were less than 3 mm and 80% of random rotations were less than 1.5 degrees. Systematic errors showed some improvement with the vac-fix system. In the anteroposterior direction, approximately 80% of systematic errors were less than 4 mm for both techniques, but in the superoinferior direction the 80% point was reduced from 5.0 mm for the standard set-up to 2.7 mm for treatment in vac-fix. For rotational systematic errors, the corresponding value dropped from 1.8 degrees for the standard set-up to 1.1 degrees in vac-fix. Therefore, for many patients, additional use of a vac-fix device improved the transfer of the planned set-up from simulator to treatment unit. Additionally, answers to the questionnaire indicated that patients generally favoured the vac-fix system over use of the breast board alone. In conclusion, however, introduction of vac-fix immobilization for all patients was not thought justified as the improvements demonstrated are not likely to be clinically significant with the present treatment technique.

Dosimetric improvements following 3D planning of tangential breast irradiation

PURPOSE

To evaluate the dosimetric difference between a simple radiation therapy plan utilizing a single contour and a more complex three-dimensional (3D) plan utilizing multiple contours, lung inhomogeneity correction, and dose-based compensators.

METHODS AND MATERIALS

This is a study of the radiation therapy (RT) plans of 85 patients with early breast cancer. All patients were considered for breast-conserving management and treated by conventional tangential fields technique. Two plans were generated for each patient. The first RT plan was based on a single contour taken at the central axis and utilized two wedges. The second RT plan was generated by using the 3D planning system to design dose-based compensators after lung inhomogeneity correction had been made. The endpoints of the study were the comparison between the volumes receiving greater than 105% and greater than 110% of the reference dose, as well as the magnitude of the treated volume maximum dose. Dosimetric improvement was defined to be of significant value if the volume receiving > 105% of one plan was reduced by at least 50% with the absolute difference between the volumes being 5% or greater. The dosimetric improvements in 49 3D plans (58%) were considered of significant value. Patients' field separation and breast size did not predict the magnitude of improvement in dosimetry.

CONCLUSION

Dose-based compensator plans significantly reduced the volumes receiving > 105%, >110%, and volume maximum dose.

Intensity modulation to improve dose uniformity with tangential breast radiotherapy: initial clinical experience

PURPOSE

We present a new technique to improve dose uniformity and potentially reduce acute toxicity with tangential whole-breast radiotherapy (RT) using intensity-modulated radiation therapy (IMRT). The technique of multiple static multileaf collimator (sMLC) segments was used to facilitate IMRT.

METHODS AND MATERIALS

Ten patients with early-stage breast cancer underwent treatment planning for whole-breast RT using a new method of IMRT. The three-dimensional (3D) dose distribution was first calculated for equally weighted, open tangential fields (i.e., no blocks, no wedges). Dose calculation was corrected for density effects with the pencil-beam superposition algorithm. Separate MLC segments were constructed to conform to the beam's-eye-view projections of the 3D isodose surfaces in 5% increments, ranging from the 120% to 100% isodose surface. Medial and lateral MLC segments that conformed to the lung tissue in the fields were added to reduce transmission. Using the beam-weight optimization utility of the 3D treatment planning system, the sMLC segment weights were then determined to deliver the most uniform dose to 100 reference points that were uniformly distributed throughout the breast. The accuracy of the dose calculation and resultant IMRT delivery was verified with film dosimetry performed on an anthropomorphic phantom. For each patient, the dosimetric uniformity within the breast tissue was evaluated for IMRT and two other treatment techniques. The first technique modeled conventional practice where wedges were derived manually without consideration of inhomogeneity effects (or density correction). A recalculation was performed with density correction to represent the actual dose delivered. In the second technique, the wedges were optimized using the same beam-weight optimization utility as the IMRT plan and included density correction. All dose calculations were based on the pencil-beam superposition algorithm.

RESULTS

For the sMLC technique, treatment planning required approximately 60 min. Treatment delivery (including patient setup) required approximately 8-10 min. Film dosimetry measurements performed on an anthropomorphic phantom generally agreed with calculations to within +/- 3%. Compared to the wedge techniques, IMRT with sMLC segments resulted in smaller "hot spots" and a lower maximum dose, while maintaining similar coverage of the treatment volume. A median of only 0.1% of the treatment volume received > or = 110% of the prescribed dose when using IMRT versus 10% with standard wedges. A total of 6-8 segments were required with the majority of the dose delivered via the open segments. The addition of the lung-block segments to IMRT was of significant benefit for patients with a greater proportion of lung parenchyma within the irradiated volume. Since August 1999, 32 patients have been treated in the clinic with the IMRT technique. No patient experienced RTOG grade III or greater acute skin toxicity.

CONCLUSION

The use of intensity modulation with an sMLC technique for tangential breast RT is an efficient and effective method for achieving uniform dose throughout the breast. It is dosimetrically superior to the treatment techniques that employ only wedges. Preliminary findings reveal minimal or no acute skin reactions for patients with various breast sizes.

Three-dimensional dose distribution of tangential breast irradiation: results of a multicentre phantom dosimetry study

BACKGROUND AND PURPOSE

One aspect of good radiotherapeutic practice is to achieve dose homogeneity. Dose inhomogeneities occur with breast tangent irradiation, particularly in women with large breasts.

MATERIALS AND METHODS

Ten Australian radiation oncology centres agreed to participate in this multicentre phantom dosimetry study. An Alderson radiation therapy anthropomorphic phantom with attachable breasts of two different cup sizes (B and DD) was used. The entire phantom was capable of having thermoluminescent dosimeters (TLD) material inserted at various locations. Nine TLD positions were distributed throughout the left breast phantom including the superior and inferior planes. The ten centres were asked to simulate, plan and treat (with a prescription of 100 cGy) the breast phantoms according to their standard practice. Point doses from resultant computer plans were calculated for each TLD position. Measured and calculated (planning computer) doses were compared.

RESULTS

The dose planning predictability between departments did not appear to be significantly different for both the small and large breast phantoms. The median dose deviation (calculated dose minus measured dose) for all centres ranged from 2. 3 to 5.3 cGy on the central axis and from 2.1 to 7.5 cGy for the off-axis planes. The highest absolute dose was measured in the inferior plane of the large breast (128.7 cGy). The greatest dose inhomogeneity occurred in the small breast phantom volume (median range 93.2-105 cGy) compared with the large breast phantom volume (median range, 100.1-107.7 cGy). There was considerable variation in the use (or not) of wedges to obtain optimized dosimetry. No department used 3D compensators.

CONCLUSION

The results highlight areas of potential improvement in the delivery of breast tangent radiotherapy. Despite reasonable dose predictability, the greatest dose deviation and highest measured doses occurred in the inferior aspects of both the small and large breast phantoms.

Biological equivalent dose assessment of the consequences of hypofractionated radiotherapy

PURPOSE

To investigate the changes in biological effective dose (BED) that occur in high-dose regions within a target volume when radiotherapy is hypofractionated.

METHODS AND MATERIALS

By comparing a standard prescription of 2 Gy per fraction that is matched to give the same BED as a hypofractionated schedule at a standard intersectional prescription point, the BED increments for late-tissue effects at a higher dose region within the planning target volume (PTV) are compared. The alternative approach of BED matching between a conventional and hypofractionated schedule at the high-dose region is also considered. The results are presented as a sequence of calculations that can be understood by practicing radiation oncologists and in graphical form.

RESULTS

The BED increment at the high-dose region is marginally increased by hypofractionation, although the latter effect is relatively small: up to 5% additional BED due to hypofractionation for a 20% increase in physical dose when the prescribed fraction size is 6-7 Gy. BED matching for late effects between a conventional and hypofractionated schedule at the high-dose region produces lower BED values throughout the remaining PTV, but at the expense of a reduced tumor control BED.

CONCLUSION

Clinical trials that use BED isoeffect matching for late reacting tissue effects to design a hypofractioned test schedule should include comprehensive calculations of the likely BED in high-dose regions.

Evaluation of compensation in breast radiotherapy: a planning study using multiple static fields

PURPOSE

A method that uses electronic portal imaging to design intensity-modulated beams for compensation in breast radiotherapy was implemented using multiple static fields in a planning study. We present the results of the study to verify the algorithm, and to assess improvements to the dosimetry.

METHODS AND MATERIALS

Fourteen patients were imaged with computed tomography (CT) and on a treatment unit using an electronic portal imager. The portal imaging data were used to design intensity-modulated beams to give an ideal dose distribution in the breast. These beams were implemented as multiple static fields added to standard wedged tangential fields. Planning of these treatments was performed on a commercial treatment planning system (Target 2, IGE Medical Systems, Slough, U.K.) using the CT data for each patient. Dose-volume histogram (DVH) analysis of the plans with and without multileaf collimator (MLC) compensation was carried out. This work has been used as the basis for a randomized clinical trial investigating whether improvements in dosimetry are correlated with the reduction of long-term side effects from breast radiotherapy.

RESULTS

The planning analysis showed a mean increase in target volume receiving 95-105% of prescribed dose of 7.5% (range -0.8% to 15.9%) when additional MLC compensation was applied. There was no change to the minimum dose for all 14 patient data sets. The change in the volume of breast tissue receiving over 105% of prescribed dose, when applying MLC compensation, was between -1.4% and 11.9%, with positive numbers indicating an improvement. These effects showed a correlation with breast size; the larger the breast the greater the amount of improvement.

CONCLUSIONS

The method for designing compensation for breast treatments using an electronic portal imager has been verified using planning on CT data for 14 patients. An improvement was seen in planning when applying MLC compensation and this effect was greater the larger the breast size.

Reducing cardiac dose in post-operative irradiation of breast cancer patients: the relative importance of patient positioning and CT scan planning

Left-sided post-operative radiotherapy fields for the treatment of breast cancer inevitably encompass the heart within the treatment volume, resulting in late mortality which may negate the cause-specific survival advantage of the therapy. The effect of positioning was studied in 11 patients with left-sided tumours and five with right-sided tumours receiving routine post-operative radiotherapy to the breast or chest wall as part of primary therapy for breast cancer. Using the same arrangement of glancing fields for each patient treatment position, the optimum patient positioning resulted in a reduction in cardiac dose compared to our standard patient treatment position. On the left side the reduction in mean cardiac dose was 60% (p < 0.001) and the reduction in maximum dose was 32% (p < 0.001); on the right it was 17% and 31%, respectively. The volume of cardiac tissue irradiated was also reduced for all patients. Using this optimum treatment position, cardiac dose was investigated in a further 10 patients with left-sided tumours and our standard glancing field set-up was compared with 3-dimensional planning. A further reduction of 12% in the mean cardiac dose was achieved. 5 of 10 patients had a further small reduction of 4.6% in the maximum dose and one patient had a further reduction in maximum dose of 58%. In conclusion, sophisticated radiotherapy planning can reduce cardiac doses, but optimum patient positioning is of greater importance. The general application of such relatively simple measures could have a significant positive effect on overall survival from breast cancer.

An assessment of the number of CT slices necessary to plan breast radiotherapy

AIMS

The aim of this study was to evaluate the number of CT slices required to produce satisfactory dose distribution for tangential field irradiation of the chest wall and breast and to assess correlation of this with the volume of breast tissue treated. Forty-six patients underwent a CT scan of the thorax. An optimized plan was produced by assessing dose distribution on the central axis (CAX) slice only. This plan was then recalculated using the entire CT data set without any changes to the beam parameters. A separate optimized plan was generated using the CAX slice and two slices indicative of the upper and lower level of the field. This three-slice plan was then calculated using the entire CT data set. Finally an optimized 3D plan was generated using the entire CT data set. The different planning methods were compared using dose-volume histograms (DVH). Dose inhomogeneity was defined as any treatment volume outside the ICRU 50 dose distribution recommendations.

RESULTS

Fifty-two percent of single-slice plans and 21% of three-slice plans (when assessed volumetrically) had greater volumes of breast tissue outside the ICRU 50 report guidelines suggesting that better homogeneity could be achieved by assessing a greater number of slices. Seventy-nine percent of three-slice plans showed no homogeneity improvement if the plan was calculated with the entire 3D data set.

CONCLUSIONS

We conclude that a single-slice plan is unsatisfactory in providing sufficient information about the dose variation across the treatment volume and that ideally a 3D plan with DVHs should be produced. If the required data is unavailable then a minimum of three slices should be used as an approximation. We also propose a software tool for treatment planning systems, which calculates the percentage of the total PTV having dose outside the ICRU 50 radiation dose distribution homogeneity guideline range.

A correlation between residual radiation-induced DNA double-strand breaks in cultured fibroblasts and late radiotherapy reactions in breast cancer patients

BACKGROUND AND PURPOSE

Prediction of late normal tissue reactions to radiotherapy would permit tailoring of dosage to each patient. Measurement of residual DNA double strand breaks using pulsed field gel electrophoresis (PFGE) shows promise in this field. The aim of this study was to test the predictive potential of PFGE in a group of retrospectively studied breast cancer patients.

MATERIALS AND METHODS

Thirty nine patients, treated uniformly for breast cancer 9-15 years previously, with excision of the tumour and radiotherapy to the breast and drainage areas, were assessed clinically using the LENT SOMA scale, and a 5-mm punch biopsy taken from the buttock. Fibroblast cell strains were established and used to study residual DNA double strand breaks, using PFGE.

RESULTS

There were significant correlations between the DNA assay results and the fibrosis score (r(s) = 0.46; P = 0.003), the combined fibrosis and retraction score (r(s) = 0.45, P = 0.004) and the overall LENT score (r(s) = 0.43; P = 0.006). Using polychotomous logistic regression, the fibroblast DNA assay result was an independent prognostic factor for fibrosis severity.

CONCLUSIONS

There is a relationship between residual radiation-induced DNA damage in fibroblasts and the severity of the late normal tissue damage seen in the patients from whom the cells were cultured.

The use of compensators to optimise the three dimensional dose distribution in radiotherapy of the intact breast

BACKGROUND AND PURPOSE

Dose heterogeneity in tangential breast irradiation has been shown to be as high as 20% and may lead to problems in local control and cosmesis. In this study, dose heterogeneity in three dimensions (3D) in the breast irradiated with wedged tangential beams is assessed and the improvement which can be made by the use of individualised two dimensional (2D) compensators is established. The compensation required is calculated in two ways: (I) by an iterative technique giving a uniform dose on a plane through the isocentre normal to the central axis of each beam, and (II) by inverse planning using an optimisation technique based on simulated annealing.

MATERIALS AND METHODS

A total of 17 patients with histologically proven T0-3, N0, N1, M0 breast cancer undergoing breast irradiation following wide local excision, were CT scanned using contiguous 1 cm slices from approximately 2 cm superior to 2 cm inferior of the irradiated volume. The dose distributions are determined using a 3D algorithm that calculates primary and scatter dose separately using a differential scatter air ratio method and corrects both for the presence of heterogeneities. The iterative technique achieves a dose variation of better than 0.5% on the plane through the isocentre with compensation on both beams. Compensation for the lateral beam only is calculated using the optimisation technique in order to minimise the scatter dose to the contralateral breast. The optimisation algorithm minimises the dose variance over the target and sets upper dose limits for the lung and the remainder of the irradiated volume.

RESULTS

For the group of patients the average dose heterogeneity in 3D using wedges is 12% (range 8-17%), which reduces to 8% (5-16%) using compensation on a plane and to 5% (4-7%) using the optimisation technique.

CONCLUSIONS

Inverse planning is normally used for complex radiotherapy techniques but when applied to tangential breast irradiation, can reduce the dose heterogeneity through the breast as a whole to as little as 4%, with potential benefits in local control and cosmesis.

Acute and late morbidity of using a breast positioning ring in women with large/pendulous breasts

PURPOSE

To assess acute and late effects of radiation therapy in women with breast cancer treated with a breast positioning ring.

MATERIALS AND METHODS

Fifty-six patients with large and/or pendulous breasts were irradiated using a breast positioning ring. The incidence of acute morbidity was correlated with patient weight and breast 'size'. Cosmesis was scored at > or = 1 year following radiation therapy by the patients. Dose changes in the buildup region under the ring were measured using a computer-controlled scanning system.

RESULTS

Moist desquamation (MD) occurred in 60.7% (34/56) of patients treated with the breast ring. The incidence of MD was more common in patients with larger breasts (P = 0.08), the severity necessitating a treatment interruption in 5 out of 56 (9%) patients. Cosmesis at > or = 1 year following radiation therapy was scored as > or = good by all patients. The surface dose under the ring was approximately 85% of the Dmax dose.

CONCLUSIONS

The incidence or severity of acute MD in patients treated with a breast positioning ring appears high in patients with large pendulous breasts, and might be related in part, to the increased skin dose due to the positioning ring. To date, there appears to be no significant late normal tissue effects in patients treated with the positioning ring. Additional follow up is needed to assess the long-term consequences of the ring on cosmesis.

Patterns of dose variability in radiation prescription of breast cancer

PURPOSE

Comparison of radiation outcome of various treatment protocols is difficult due to the variability of dose prescription. A retrospective analysis of the pattern and intercomparison of dose prescriptions is presented for the treatment of breast cancer.

MATERIALS AND METHODS

To represent the clinical practice for breast irradiation with tangential fields, commonly used prescription points were chosen that lie on the perpendicular bisector of the chest wall separation (s) that represents the breast apex height (h). These points are located at 1.5 cm from the posterior beam edge, at the chest wall-lung interface (2-3 cm), at distances of h/3 and h/2, and at the isocenter. One hundred consecutive patients treated with intact breast following excisional biopsy were used in this study. For analysis, treatment planning was carried out without lung correction with a 6 MV beam for all patients, even though some of the patients were treated with high energy beams for dose uniformity. Dose distributions were optimized with wedges and beam weights to provide a symmetrical dose distribution on the central axis plane. The statistical analyses of the different parameters, s, h, maximum dose, and doses at various prescription points were carried out.

RESULTS

The maximum dose (hot spot) in breast varied from +5% to +27% above the prescribed dose among the patient population. The hot spot was directly related to s, and appeared to be independent of h and the ratio h/s. Among 55%, 40%, and 5% of the patients, the magnitude of the hot spot was 5-10%, 10-15%, and >15%, respectively. Except for the magnitude of the hot spot, the doses at various prescription points were independent of the breast size. For a prescription point at h/3 or at the lung-chest wall interface, the dose variation within +/- 1% is observed for 90% of the patient population. On the other hand, the average dose variation is about +/- 3% among other protocols with dose prescription point varying up to the h/2 point. With the prescription point at the isocenter, an average and maximum variation of 4-5% and 11% were observed, respectively. The maximum dose inhomogeneity for some patients was significantly higher, i.e. up to +27% even without the lung correction.

CONCLUSIONS

A wide variation in prescription dose is observed among the different treatment protocols commonly used in breast treatment. For a total dose of 46-50 Gy delivered at 2 Gy/fraction to the breast, the prescribed dose may vary between 50 and 55 Gy and the hot spot dose per fraction may range between 2.3 and 2.5 Gy depending on the protocol and breast size. Thus dose normalization at hot spot and the isocenter should be discouraged unless the total dose to the breast is modified. A uniform definition of dose prescription for breast treatment is greatly required for intercomparison of clinical data.