Optimizing breast cancer treatment efficacy with intensity-modulated radiotherapy

: 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.

: 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.

: 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.

: 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.     

Intensity modulated radiation therapy (IMRT) reduces the dose to the contralateral breast when compared to conventional tangential fields for primary breast irradiation

Summary Purpose To determine the dose received by the contralateral breast during primary breast irradiation using IMRT compared to conventional tangential field techniques. Methods and materials Between March 2003 and March 2004, 83 patients with breast carcinoma were treated using 6, 10, or mixed 6/18 MV photons (65 with tangential IMRT technique and 18 with 3-dimensional technique using tangential fields with wedges) for primary breast irradiation following breast-conserving surgery. Paired thermoluminescent dosimeters (TLDs) were placed on each patient’s contralateral breast, 4 and 8 cm from the center of the medial border of the tangential field. The TLDs were left on the patient during a single fraction and then measured 24 h afterwards. Results The mean dose delivered with photons to the primary breast for all patients was 4999 cGy (SD=52) with a mean single fraction dose of 199 cGy (SD=8). The mean percent of the prescribed dose to the contralateral breast measured at the 4- and 8-cm positions were 7.19% (SD=2.28) and 4.63% (SD=2.12), respectively, for patients treated with IMRT compared to 11.22% (SD=2.73) and 10.70% (SD=3.44), respectively, for the patients treated with conventional tangential field techniques. This represented a 36% and 57% reduction at the 4 and 8-cm contralateral positions, respectively, in the mean dose to the contralateral breast using IMRT compared to 3-D technique which was statistically significant (p<0.0005, <0.0005, respectively). Conclusion Primary breast irradiation with tangential IMRT technique significantly reduces the dose to the contralateral breast compared to conventional tangential field techniques. *Presented in part of the 46th Annual Meeting of the American Society for Therapeutic Radiology and Oncology, Atlanta, GA, October 2004.     

Superficial doses in breast cancer radiotherapy using conventional and IMRT techniques: A film-based phantom study

Background and purpose

Superficial doses in radiotherapy are affected by the treatment technique. The implications for breast cancer treatments were evaluated.

Material and methods

Four treatment techniques relevant for breast cancer irradiation were evaluated; tangential standard, tangential IMRT, 7-field IMRT (arc-like field arrangement) and hybrid IMRT (an IMRT plan mixed with non-modulated fields). Only 6 MV photons were used. GafChromic EBT film was used for dose measurements at the surface, in the skin (0–5 mm depth) and in the superficial parts of CTV (5–10 mm depth) of an anthropomorphic thorax phantom.

Results

Only small differences in superficial doses were observed between tangential standard and tangential IMRT. Compared to the tangential standard plan, the surface and skin doses were reduced with the 7-field IMRT plan, on average by 20% and 5%, respectively, while hybrid IMRT reduced the surface and skin doses medially (by 44% and 8%, respectively) and increased the surface and skin dose laterally (by 40% and 15%, respectively). Minimum superficial CTV doses varied between regions, but were mainly between 90% and 95% of the target dose for all plans, only the hybrid IMRT plan resulted in a region with minimum dose below 90%.

Conclusions

Compared to tangential irradiation, skin sparing was achieved by the 7-field IMRT plan. The minimum dose in the superficial parts of the CTV was below 95% of the target dose for all plans investigated.     

Intensity modulated versus non-intensity modulated radiotherapy in the treatment of the left breast and upper internal mammary lymph node chain: a comparative planning study.

BACKGROUND AND PURPOSE: To compare and evaluate intensity modulated (IMRT) and non-intensity modulated radiotherapy techniques in the treatment of the left breast and upper internal mammary lymph node chain. MATERIALS AND METHODS: The breast, upper internal mammary chain (IMC), heart and lungs were delineated on a computed tomography (CT)-scan for 12 patients. Three different treatment plans were created: (1) tangential photon fields with oblique IMC electron-photon fields with manually optimized beam weights and wedges, (2) wide split tangential photon fields with a heart block and computer optimized wedge angles, and (3) IMRT tangential photon fields. For the IMRT technique, an inverse planning program (KonRad) generated the intensity profiles and a clinical three-dimensional treatment planning system (U-MPlan) optimized the segment weights. U-MPlan calculated the dose distribution for all three techniques. The normal tissue complication probabilities (NTCPs) for the organs at risk (ORs) were calculated for comparison. RESULTS: The average root mean square deviation of the differential dose-volume histogram of the breast planning target volume was 4.6, 3.9 and 3.5% and the average mean dose to the IMC was 97.2, 108.0 and 99.6% for the oblique electron, wide split tangent and IMRT techniques, respectively. The average NTCP for the ORs (i.e. heart and lungs) were comparable between the oblique electron and IMRT techniques (or=2%) for the ORs. CONCLUSIONS: The lowest NTCP values were found with the oblique electron and the IMRT techniques. The IMRT technique had the best breast and IMC target coverage.     

An improved breast irradiation technique using three-dimensional geometrical information and intensity modulation.

BACKGROUND AND PURPOSE: In spite of the complex geometry of the breast, treatment planning for tangential breast irradiation is conventionally performed using two-dimensional patient anatomy information. The purpose of this work was to develop a new technique which takes the three-dimensional (3D) patient geometry into account. MATERIALS AND METHODS: An intensity-modulated radiotherapy (IMRT) technique was developed based on the division of the tangential fields in four multi-leaf collimator (MLC) shaped segments. The shape of these segments was obtained from an equivalent path length map of the irradiated volume. Approximately 88% of the dose was delivered by two open fields covering the whole treated volume. Dose calculations for the IMRT technique and the conventional technique were performed for five patients, using computer tomography (CT) data and a 3D calculation algorithm. A planning target volume (PTV) and ipsilateral lung volume were delineated in these CT data. RESULTS: All patients showed similar equivalent path length patterns. Analysis of the dose distribution showed an improved dose distribution using the IMRT technique. The dose inhomogeneity in the PTV was 9.0% (range 6.4-11.4%) for the conventional and 7.6% (range 6.5-10.3%) for the IMRT technique. The mean lung dose was reduced for the IMRT technique by approximately 10% compared with the conventional technique. CONCLUSION: A new breast irradiation technique has been developed which improves the dose homogeneity within the planning target volume and reduces the dose to the lung. Furthermore, the IMRT technique creates the possibility to improve the field matching in case of multiple field irradiations of the breast and lymph nodes.     

Reduction of cardiac and lung complication probabilities after breast irradiation using conformal radiotherapy with or without intensity modulation.

PURPOSE: The main purpose of this work is to reduce the cardiac and lung dose by applying conformal tangential beam irradiation of the intact left breast with and without intensity modulation, instead of rectangular tangential treatment fields. The extension of the applicability of the maximum heart distance (MHD) to conformal tangential fields as a simple patient selection criterion, identifying patients for which rectangular and conformal tangential fields without intensity modulation will result in unacceptable normal tissue complication probability (NTCP) values for late cardiac mortality (e.g. >2%), was also investigated. MATERIALS AND METHODS: Three-dimensional treatment planning was performed for 17 left-sided breast cancer patients. Three different tangential beam techniques were compared: (1) optimized wedges without blocks, (2) optimized wedges with conformal blocks and (3) intensity modulation. Plans were evaluated using dose-volume histograms (DVHs) for the planning target volume (PTV), the heart and the lungs. NTCPs for radiation pneumonitis and late cardiac mortality were calculated using the DVH data. The MHD was measured for all rectangular (MHD(rectangular)) and conformal (MHD(conformal)) treatment plans. RESULTS: For all patients, on average, part of the PTV receiving a dose between 95 and 107% of the prescribed dose of 50Gy in 25 fractions of 2Gy was 90.8% (standard deviation (SD): 5.0%), 92.8% (SD: 3.5%) and 92.8% (SD: 3.6%) for the intensity modulation radiation therapy (IMRT), conformal and rectangular field treatment techniques, respectively. The NTCP for radiation pneumonitis was 0.3% (SD: 0.1%), 0.4% (SD: 0.4%) and 0.5% (SD: 0.6%) for the IMRT, conformal and rectangular field techniques, respectively. The NTCP for late cardiac mortality was 5.9% (SD: 2.2%) for the rectangular field technique. This value was reduced to 4.0% (SD: 2.3%) with the conformal technique. A further reduction to 2.0% (SD: 1.1%) could be accomplished with the IMRT technique. The NTCP for late cardiac mortality could be described as a second order polynomial function of the MHD. This function could be described with a high accuracy and was independent of the technique for which the MHD was determined (r(2)=0.88). In order to achieve a NTCP value for late cardiac mortality below 1, 2 or 3%, the MHD should be equal to or smaller than 11, 17 or 23 mm, respectively. If such a maximum complication probability cannot be accomplished, a treatment using the IMRT technique should be considered. CONCLUSIONS: The use of conformal tangential fields decreases the NTCP for late cardiac toxicity on average by 30% compared to using rectangular fields, while the tangential IMRT technique can further reduce this value by an additional 50%. The MHD can be used to estimate the NTCP for late cardiac mortality if rectangular or conformal tangential treatment fields are used.     

Skin-sparing radiation using intensity-modulated radiotherapy after conservative surgery in early-stage breast cancer: a planning study

PURPOSE: To evaluate the feasibility of skin-sparing by configuring it as an organ-at-risk (OAR) while delivering whole-breast intensity-modulated radiotherapy (IMRT) in early breast cancer. METHODS AND MATERIALS: Archival computed tomography scan images of 14 left-sided early-breast tumor patients who had undergone lumpectomy were selected for this study. Skin was contoured as a 4- to 5-mm strip extending from the patient outline to anterior margin of the breast planning target volume (PTV). Two IMRT plans were generated by the helical tomotherapy approach to deliver 50 Gy in 25 fractions to the breast alone: one with skin dose constraints (skin-sparing plan) and the other without (non-skin-sparing plan). Comparison of the plans was done using a two-sided paired Student t test. RESULTS: The mean skin dose and volume of skin receiving 50 Gy were significantly less with the skin-sparing plan compared with non-skin-sparing plan (42.3 Gy vs. 47.7 Gy and 12.2% vs. 57.8% respectively; p < 0.001). The reduction in skin dose was confirmed by TLD measurements in anthropomorphic phantom using the same plans. Dose-volume analyses for other OARs were similar in both plans. CONCLUSIONS: By configuring the skin as an OAR, it is possible to achieve skin dose reduction while delivering whole-breast IMRT without compromising dose profiles to PTV and OARs.     

Differential dosing of prostate and seminal vesicles using dynamic multileaf collimation

Purpose: We have investigated the potential of applying different doses to the prostate (PTV2) and prostate/seminal vesicles (PTV1) using multileaf collimation (MLC) for intensity modulated radiation therapy (IMRT). Current dose-escalation studies call for treatment of the PTV1 to 54 Gy in 27 fractions followed by 20 Gy minimum to the PTV2. A daily minimum PTV dose of 2 Gy using a 7-field technique (4 obliques, opposed laterals, and an ant-post field) is delivered. This requires monitor unit calculations, paper and electronic chart entry, and quality assurance for a total of 14 fields. The goal of MLC IMRT is to improve efficiency and deliver superior dose distributions. Acceptance testing and commissioning of the dynamic MLC (DMLC) option on a dual-energy accelerator was accomplished. Most of the testing was performed using segmental MLC (SMLC) IMRT with stop-and-shoot sequences built within the dynamic mode of the DMLC.

Methods and Materials: The MLC IMRT fields were forward planned using a three-dimensional treatment planning system. The 14 fields were condensed to 7 SMLC IMRT fields with two segments each. In this process, steps were created by moving the leaves to the reduced field positions. No dose (<0.01%) was delivered during this motion. The monitor units were proportioned according to the planned treatment weights. Film and ionization chamber dosimetry were used to analyze leaf positional accuracy and speed, output, and depth-dose characteristics. A geometric phantom was used for absolute and relative measurements. We obtained a volumetric computerized tomography (CT) scan of the phantom, performed 3D planning, and then delivered a single treatment fraction.

Results: The acceptance testing and commissioning demonstrated that the leaves move to programmed positions accurately and in a timely manner. We did find an 1 mm offset of the set leaf position and radiation edge (50%) due to the curved-end nature and calibration limitations. The 7-field SMLC IMRT treatment duplicated the 14-field static plan dose distribution with variations no greater than 1.5%.

Conclusions: The MLC IMRT approach will improve efficiency because the number of electronic and chart entries has decreased by a factor of 2. Portal images are able to capture the initial and final MLC segments. The question of differential daily dose to the prostate and seminal vesicles remains.     

Dosimetric analysis of a simplified intensity modulation technique for prone breast radiotherapy

PURPOSE: Prone-position breast radiotherapy (RT) has been described as an alternative technique to improve dose homogeneity for women with large, pendulous breasts. We report the feasibility and dosimetric analysis of a simplified intensity-modulated RT (IMRT) technique, previously reported for women in the supine treatment position, to plan prone-position RT to the intact breast. METHODS AND MATERIALS: Twenty patients with clinical Stage TisN0-T1bN1 breast cancer undergoing breast-conserving therapy underwent whole breast RT using a prone position technique. The treatment plans were developed using both conventional tangents and a simplified intensity-modulated tangential beam technique based on optimization of the intensity distributions across the breast. The plans were compared with regard to the dose-volume parameters. RESULTS: Dose heterogeneity within the breast planning target volume was significantly greater for the conventional tangent plans. Of 20 patients, 16 (80%) received maximal doses of > or =110% using the conventional tangents vs. only 1 (5%) using the IMRT plan. The isodose level encompassing 5% of the planning target volume was reduced from an average of 110% with conventional tangents to 105% with IMRT. The maximal dose within the planning target volume was reduced from an average of 114% with conventional tangents to 107% with IMRT. The greatest improvement was seen in the patients with the most pendulous breasts. CONCLUSION: An IMRT planning approach is feasible for prone-position breast RT and improves dose homogeneity, particularly in women with larger, pendulous breasts. Additional follow-up is necessary to determine whether the improvements in dose homogeneity impact acute toxicity and cosmetic outcome in this cohort of women who have historically suffered from poor cosmesis after breast-conserving therapy.     

Significant reductions in heart and lung doses using deep inspiration breath hold with active breathing control and intensity-modulated radiation therapy for patients treated with locoregional breast irradiation

PURPOSE: To evaluate the heart and lung sparing effects of moderate deep inspiration breath hold (mDIBH) achieved using an active breathing control (ABC) device, compared with free breathing (FB) during treatment with deep tangents fields (DT) for locoregional (LR) irradiation of breast cancer patients, including the internal mammary (IM) nodes (IMNs). To compare the DT-mDIBH technique to other standard techniques and to evaluate the dosimetric effect of intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: Fifteen patients (9 left-sided and 6 right-sided lesions) with Stages 0-III breast cancer underwent standard FB and ABC computed tomographic (CT) scans in the treatment position. A dosimetric planning study was performed. In FB, the 9 left-sided patients were planned with a 5-field technique where electron fields covering the IM region were matched to shallow tangents using wedges (South West Oncology Group [SWOG] protocol S9927 technique A). This method was compared with a 3-field DT technique covering the breast and the IMNs (SWOG S9927 technique B). Compensation with IMRT was then compared with wedges for each technique. For the 15 total patients, dosimetric planning using DT with IMRT was then reoptimized on the mDIBH CT data set for comparison. Dose-volume histograms for the clinical target volume (CTV) (including the IMNs), planning target volume (PTV), ipsilateral and contralateral breast, and organs at risk (OAR) were analyzed. In addition, normal tissue complication probabilities (NTCP) for lung and heart, mean lung doses, and the number of monitor units (MUs) for a 1.8 Gy fraction were compared. RESULTS: For the 9 left-sided patients, the mean percentage of heart receiving more than 30 Gy (heart V30) was lower with the 5-field wedged technique than with the DT wedged technique (6.8% and 19.1%, respectively, p < 0.004). For the DT technique, the replacement of wedges with IMRT slightly diminished the mean heart V30 to 16.3% (p < 0.51). The introduction of mDIBH to the DT-IMRT technique reduced the heart V30 by 81% to a mean of 3.1% (p < 0.0004). Compared with 5-field IMRT, DT-IMRT with mDIBH reduced the heart V30 for 6 of the 9 patients, entirely avoiding heart irradiation in 2 of these 6 patients. For DT-IMRT, mDIBH reduced the mean lung dose and NTCP to levels obtained with the 5-field IMRT technique. For the 15 patients planned with DT-IMRT in FB, the use of mDIBH reduced the mean percentage of both lungs receiving more than 20 Gy from 20.4% to 15.2% (p < 0.00007). With DT-IMRT, more than 5% of the contralateral breast received more than 10 Gy for 6 of the 9 left-sided patients in FB, 3 of those 9 patients in mDIBH, and only 1 of those 9 patients planned with 5 fields. The mean % of the PTV receiving more than 55 Gy (110% of the prescribed dose) was 36.4% for 5-field wedges, 33.4% for 5-field IMRT, 28.7% for DT-wedges, 12.5% for DT-IMRT, and 18.4% for DT-IMRT mDIBH. The CTV remained covered by the 95% isodose in all the DT plans but one (99.1% of the volume covered). DT-wedges required more MUs than DT-IMRT (mean of 645 and 416, respectively, p < 0.00004). CONCLUSION: mDIBH significantly reduces heart and lung doses when DT are used for LR breast irradiation including the IMNs. Compared with shallow tangents matched with electrons, DT with mDIBH reduces the heart dose (in most patients) and results in comparable lung toxicity parameters, but may increase the dose to the contralateral breast. IMRT improves dose homogeneity, slightly reduces the dose to the heart, and diminishes the number of MUs required.     

Intensity-modulated radiotherapy of breast cancer using direct aperture optimization.

BACKGROUND AND PURPOSE: To design a clinically reliable and efficient step-and-shoot IMRT delivery technique for the treatment of breast cancer using direct aperture optimization (DAO). Using DAO, segments are created and optimized within the same optimization process. PATIENTS AND METHODS: The DAO technique implemented in the Pinnacle treatment planning system, which is called direct machine parameter optimization (DMPO), was used to generate IMRT plans for twelve breast cancer patients. The prescribed dose was 50 Gy. Two DMPO plans were generated. The first approach uses DMPO only; the second technique combines DMPO with two predefined segments (DMPO(segm)), having shapes identical to the conventional tangential fields. The weight of these predefined segments is optimized simultaneously with DMPO. The DMPO plans were compared with normal two-step (TS) IMRT, creating segments after optimizing the intensity. RESULTS: Dose homogeneity within the target volume was 4.8+/-0.6, 4.3+/-0.5 and 3.8+/-0.5 Gy for the TS, DMPO and DMPO(segm) plans, respectively. Comparing the IMRT plans with an idealized dose distribution obtained using only beamlet optimization, the degradation of the dose distribution was less for the DMPO plans compared with the two-step IMRT approach. Furthermore, this degradation was similar for all patients, while for the two-step IMRT approach it was patient specific. CONCLUSIONS: An efficient step-and-shoot IMRT solution was developed for the treatment of breast cancer using DMPO combined with two predefined segments.     

Comparison of contralateral breast dose for various tangential field techniques in clinical radiotherapy

Contralateral breast (CLB) cancer is a rare but serious concern in radiotherapy. In this study, the CLB dose was measured using MOSFET dosimeter in 49 patients who underwent breast conservation surgery treated by different radiotherapy tangential field techniques, which included enhanced dynamic wedge (EDW), physical wedge, and intensity modulated radiation therapy (IMRT). The mean percent of the prescribed dose received by the contralateral areola in treatment technique using physical wedge (Cobalt), physical wedge (Linac), EDW, and IMRT were 4.27% (SD: 0.65), 3.61% (SD: 0.60), 3.38% (SD: 0.58), and 1.65% (SD: 0.24), respectively. There was a 29% CLB dose reduction at 3 cm from the medial tangential field border with IMRT compared to other wedged tangential field techniques. The study shows that the CLB dose could be reduced with IMRT or reducing or avoiding the medial wedge in conventional tangential field planning for breast cancer.     

The delivery of intensity modulated radiotherapy to the breast using multiple static fields.

BACKGROUND AND PURPOSE: To develop a method of using a multileaf collimator (MLC) to deliver intensity modulated radiotherapy (IMRT) for tangential breast fields, using an MLC to deliver a set of multiple static fields (MSFs). MATERIALS AND METHODS: An electronic portal imaging device (EPID) is used to obtain thickness maps of medial and lateral tangential breast fields. From these IMRT deliveries are designed to minimize the volume of breast above 105% of prescribed dose. The deliveries are universally-wedged beams augmented with a set of low dose shaped irradiations. Dosimetric and planning QA of this method has been compared with the standard, wedged treatment and the corresponding treatment using physical compensators. Several options for delivering the MSF treatment are presented. RESULTS: The MSF technique was found to be superior to the standard technique (P value=0.002) and comparable with the compensated technique. Both IMRT methods reduced the volume of breast above 105% dose from a mean value of 12.0% of the total breast volume to approximately 2.8% of the total breast volume. CONCLUSIONS: This MSF method may be used to reduce the high dose volume in tangential breast irradiation significantly. This may have consequences for long-term side effects, particularly cosmesis.     

A comparison of different intensity modulation treatment techniques for tangential breast irradiation

Purpose: Several intensity modulation (IM) treatment techniques for tangential breast irradiation were evaluated in terms of dose uniformity in the treated breast volume, contralateral breast dose, and treatment irradiation time.

Methods and Materials: Contralateral breast dose was measured via TLD chips, and the dose uniformity was calculated on two anthropomorphic phantoms. IM was applied to all beams or to the lateral-medial (LM) beam only. The techniques evaluated include (a) IM via “step & shoot” multileaf collimator (MLC), (b) IM via intensity modulator (compensator), (c) virtual wedge, and (d) physical wedge. A dose optimization algorithm was used for the first two techniques.

Results: Collimator-generated IM techniques (MLC-IM and the virtual wedge) produced 50% (average) less contralateral breast dose than the conventional two-wedge technique. When the compensator or the physical wedge was used, contralateral breast dose was reduced 30% (average) by leaving the ML beam open.

Conclusion: The treatments generated by dose optimization algorithm and delivered via the compensator and MLC techniques offered superior dose uniformity. Single-beam IM techniques in general use less irradiation time without significant degradation of dose uniformity. The MLC-IM technique in this study required the longest treatment irradiation time, while the virtual wedge and compensator IM techniques required the least.     

Breast-conserving radiation therapy using combined electron and intensity-modulated radiotherapy technique.

BACKGROUND AND PURPOSE: To explore the feasibility of a multi-modality breast-conserving radiation therapy treatment technique to reduce high dose to the ipsilateral lung and the heart when compared with the conventional treatment technique using two tangential fields. MATERIALS AND METHODS: An electron beam with appropriate energy was combined with four intensity modulated photon beams. The direction of the electron beam was chosen to be tilted 10-20 degrees laterally from the anteroposterior direction. Two of the intensity-modulated photon beams had the same gantry angles as the conventional tangential fields, whereas the other two beams were rotated 15-25 degrees toward the anteroposterior directions from the first two photon beams. An iterative algorithm was developed which optimizes the weight of the electron beam as well as the fluence profiles of the photon beams for a given patient. Two breast cancer patients with early-stage breast tumors were planned with the new technique and the results were compared with those from 3D planning using tangential fields as well as 9-field intensity-modulated radiotherapy (IMRT) techniques. RESULTS: The combined electron and IMRT plans showed better dose conformity to the target with significantly reduced dose to the ipsilateral lung and, in the case of the left-breast patient, reduced dose to the heart, than the tangential field plans. In both the right-sided and left-sided breast plans, the dose to other normal structures was similar to that from conventional plans and was much smaller than that from the 9-field IMRT plans. The optimized electron beam provided between 70 to 80% of the prescribed dose at the depth of maximum dose of the electron beam. CONCLUSIONS: The combined electron and IMRT technique showed improvement over the conventional treatment technique using tangential fields with reduced dose to the ipsilateral lung and the heart. The customized beam directions of the four IMRT fields also kept the dose to other critical structures to a minimum.     

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.     

Impact of IMRT and leaf width on stereotactic body radiotherapy of liver and lung lesions

PURPOSE: The present study explored the impact of intensity-modulated radiotherapy (IMRT) on stereotactic body RT (SBRT) of liver and lung lesions. Additionally, because target dose conformity can be affected by the leaf width of a multileaf collimator (MLC), especially for small targets and stereotactic applications, the use of a micro-MLC on "uniform intensity" conformal and intensity-modulated SBRT was evaluated. METHODS AND MATERIALS: The present study included 10 patients treated previously with SBRT in our institution (seven lung and three liver lesions). All patients were treated with 3 x 12 Gy prescribed to the 65% isodose level. The actual MLC-based conformal treatment plan served as the standard for additional comparison. In total, seven alternative treatment plans were made for each patient: a standard (actual) plan and an IMRT plan, both calculated with Helax TMS (Nucletron) using a pencil beam model; and a recalculated standard and a recalculated IMRT plan on Helax TMS using a point dose kernel approach. These four treatment plans were based on a standard MLC with 1-cm leaf width. Additionally, the following micro-MLC (central leaf width 3 mm)-based treatment plans were calculated with the BrainSCAN (BrainLAB) system: standard, IMRT, and dynamic arc treatments. For each treatment plan, various target parameters (conformity, coverage, mean, maximal, and minimal target dose, equivalent uniform doses, and dose-volume histogram), as well as organs at risk parameters (3 Gy and 6 Gy volume, mean dose, dose-volume histogram) were evaluated. Finally, treatment efficiency was estimated from monitor units and the number of segments for IMRT solutions. RESULTS: For both treatment planning systems, no significant difference could be observed in terms of target conformity between the standard and IMRT dose distributions. All dose distributions obtained with the micro-MLC showed significantly better conformity values compared with the standard and IMRT plans using a regular MLC. Dynamic arc plans were characterized by the steepest dose gradient and thus the smallest V(6 Gy) values, which were on average 7% smaller than the standard plans and 20% lower than the IMRT plans. Although the Helax TMS IMRT plans show about 18% more monitor units than the standard plan, BrainSCAN IMRT plans require approximately twice the number of monitor units relative to the standard plan. All treatment plans optimized with a pencil beam model but recalculated with a superposition method showed significant qualitative, as well as quantitative, differences, especially with respect to conformity and the dose to organs at risk. CONCLUSION: Standard conformal treatment techniques for SBRT could not be improved with inversely planned IMRT approaches. Dose calculation algorithms applied in optimization modules for IMRT applications in the thoracic region need to be based on the most accurate dose calculation algorithms, especially when using higher energy photon beams.