Breast IMRT Research Articles

Independent validation of genes and polymorphisms reported to be associated with radiation toxicity: a prospective analysis study.

Several studies have reported associations between radiation toxicity and single nucleotide polymorphisms (SNPs) in candidate genes. Few associations have been tested in independent validation studies. This prospective study aimed to validate reported associations between genotype and radiation toxicity in a large independent dataset. 92 (of 98 attempted) SNPs in 46 genes were successfully genotyped in 1613 patients: 976 received adjuvant breast radiotherapy in the Cambridge breast IMRT trial (ISRCTN21474421, n=942) or in a prospective study of breast toxicity at the Christie Hospital, Manchester, UK (n=34). A further 637 received radical prostate radiotherapy in the MRC RT01 multicentre trial (ISRCTN47772397, n=224) or in the Conventional or Hypofractionated High Dose Intensity Modulated Radiotherapy for Prostate Cancer (CHHiP) trial (ISRCTN97182923, n=413). Late toxicity was assessed 2 years after radiotherapy with a validated photographic technique (patients with breast cancer only), clinical assessment, and patient questionnaires. Association tests of genotype with overall radiation toxicity score and individual endpoints were undertaken in univariate and multivariable analyses. At a type I error rate adjusted for multiple testing, this study had 99% power to detect a SNP, with minor allele frequency of 0·35, associated with a per allele odds ratio of 2·2. None of the previously reported associations were confirmed by this study, after adjustment for multiple comparisons. The p value distribution of the SNPs tested against overall toxicity score was not different from that expected by chance. We did not replicate previously reported late toxicity associations, suggesting that we can essentially exclude the hypothesis that published SNPs individually exert a clinically relevant effect. Continued recruitment of patients into studies within the Radiogenomics Consortium is essential so that sufficiently powered studies can be done and methodological challenges addressed. Cancer Research UK, The Royal College of Radiologists, Addenbrooke's Charitable Trust, Breast Cancer Campaign, Cambridge National Institute of Health Research (NIHR) Biomedical Research Centre, Experimental Cancer Medicine Centre, East Midlands Innovation, the National Cancer Institute, Joseph Mitchell Trust, Royal Marsden NHS Foundation Trust, Institute of Cancer Research NIHR Biomedical Research Centre for Cancer.

Doses to internal organs for various breast radiation techniques - implications on the risk of secondary cancers and cardiomyopathy

BackgroundBreast cancers are more frequently diagnosed at an early stage and currently have improved long term outcomes. Late normal tissue complications induced by adjuvant radiotherapy like secondary cancers or cardiomyopathy must now be avoided at all cost. Several new breast radiotherapy techniques have been developed and this work aims at comparing the scatter doses of internal organs for those techniques.MethodsA CT-scan of a typical early stage left breast cancer patient was used to describe a realistic anthropomorphic phantom in the MCNP Monte Carlo code. Dose tally detectors were placed in breasts, the heart, the ipsilateral lung, and the spleen. Five irradiation techniques were simulated: whole breast radiotherapy 50 Gy in 25 fractions using physical wedge or breast IMRT, 3D-CRT partial breast radiotherapy 38.5 Gy in 10 fractions, HDR brachytherapy delivering 34 Gy in 10 treatments, or Permanent Breast 103Pd Seed Implant delivering 90 Gy.ResultsFor external beam radiotherapy the wedge compensation technique yielded the largest doses to internal organs like the spleen or the heart, respectively 2,300 mSv and 2.7 Gy. Smaller scatter dose are induced using breast IMRT, respectively 810 mSv and 1.1 Gy, or 3D-CRT partial breast irradiation, respectively 130 mSv and 0.7 Gy. Dose to the lung is also smaller for IMRT and 3D-CRT compared to the wedge technique. For multicatheter HDR brachytherapy a large dose is delivered to the heart, 3.6 Gy, the spleen receives 1,171 mSv and the lung receives 2,471 mSv. These values are 44% higher in case of a balloon catheter. In contrast, breast seeds implant is associated with low dose to most internal organs.ConclusionsThe present data support the use of breast IMRT or virtual wedge technique instead of physical wedges for whole breast radiotherapy. Regarding partial breast irradiation techniques, low energy source brachytherapy and external beam 3D-CRT appear safer than 192Ir HDR techniques.

Phase III Study Comparing Prone Accelerated Whole Breast IMRT with a Daily vs. a Weekly Tumor Bed Boost: Interim Analysis Results

This prospective randomized trial is comparing hypofractionated (15 fraction) prone whole breast IMRT either with a daily concomitant boost to the tumor bed (Formenti et al, JCO 2007) or with a weekly Friday boost (FB), which may have a radiobiological advantage by counteracting tumor repopulation occurring over the weekend break. This trial is designed to test the hypothesis that toxicity, local control and cosmetic results are comparable in the two arms. We are reporting the results of a planned interim analysis for the acute toxicity endpoint. Stage 0-II breast cancer patients after lumpectomy with negative margins (>1 mm), and sentinel/axillary lymph node dissection were eligible. Patients were stratified by menopausal status and chemotherapy prior to radiation. Patients were CT scanned in the prone position on a specially designed prone table. Arm 1: Patients received 15 daily fractions of 2.7 Gy, Mon-Fri to the breast with a daily concomitant boost of 0.5 Gy to the tumor bed. Total dose: 40.5 Gy to the breast, 48.0 Gy to the tumor bed. Arm 2 (FB): Patients received 15 daily fractions of 2.7 Gy Mon-Fri to the breast with a Fri boost of 2.0 Gy to the tumor bed with Cone-beam CT. Total dose: 40.5 Gy to the breast, 46.5 Gy to the tumor bed, based on BED calculations. Interim analysis evaluated the study's primary endpoint of acute toxicity ≥ grade 2 occurring within 60 days after treatment. Between 3/2009 - 2/2010, 118 patients have enrolled to this protocol: 60 patients randomized to Arm 1 and 58 to Arm 2 FB. CTCAE v3.0 defined radiation dermatitis was evaluated in 55 patients of Arm 1 at a median 69 days post-treatment (range, 34-288), and in 52 patients on Arm 2 FB at a median of 76 days (range, 36-281). Erythema grade I: 50 (86%) Arm 1, 49 (91%) Arm 2. Grade II: 8 (14%) Arm 1, 4 (7%) Arm 2. Grade III: 1 (2%) Arm 2. Edema grade I: 19 (83%) Arm 1, 18 (86%) Arm 2. Grade II: 3 (13 %), 1 (4%). Grade III 1 (4%). There was no statistical difference between the two arms in RT-related acute toxicity. Interim analysis of the acute toxicities of patients enrolled on a Phase III randomized trial assessing concomitant vs. weekly (Friday) boost demonstrates equivalence between the two regimens. The trial continues accrual to 400 total patients (200 per arm) as planned.

A Comparison of Quality of Life for Early Stage Breast Cancer Examining Whole Breast IMRT versus Accelerated Partial Breast Irradiation

A Comparison of Quality of Life for Early Stage Breast Cancer Examining Whole Breast IMRT versus Accelerated Partial Breast Irradiation

SU‐GG‐T‐205: Limitations of Delta4 IMRT QA for Large Field Sizes

Purpose: Pre‐treatment QA of IMRT plans are critical to uphold patient safety. Given that IMRT plans are becoming more prevalent in radiation oncology it is important to exam the limitations of current IMRT QA devices. Current IMRT QA devices use a 2D array of detectors to examine IMRT QA plans, and 3D analysis is lacking. The Delta4 is a relatively new IMRT QA device, that can perform 3D plan analysis, however the field size limitations of the device are unknown. We herein examine the abilities of the Delta4 to perform IMRT QA on 80 IMRT plans on various treatment sites. Methods and Materials: Clinical IMRT plans from an in‐house TPS, PlanUNC, were retrospectively examined to determine the field size limitation on the Delta4. 20 IMRT plans for each of the following sites were examined: head and neck (H&N), prostate, breast, and pelvis. We determined if the entire intensity map could be measured using the Delta4 based upon the treatment field size using the suggested isocentric set‐up. We also determined which treatment field intensity maps with large field sizes could be completely measured using isocenter shifts for the Delta4. Results: Using the Delta4, 6 H&N, 20 prostate, and 3 pelvis IMRT QA plans were deliverable. Due to large field sizes 14 H&N, and 17 Pelvis plans required a shift to complete measure the dose fluence. All 20 breast IMRT QA plans were deliverable on the Delta4, however all fields were prescribed a table kick out, which greatly increased the time required to measure the plans. Conclusions: The 20cm × 20cm field size of the Delta4 limits its ability to measure large treatment fields using the isocentric set‐up. However shifting the device can increase the detector size, but also decreases IMRT QA efficiency.

Effect of collimator and couch angle change on breast IMRT dose distributions

Intensity‐modulated tangential photon beams for breast cancer treatment can improve the dose uniformity significantly throughout the whole breast and reduce the dose to the lung and the heart when compared to the conventional technique. Before the first treatment, patient setup may require a change on the collimator angle and/or the couch angle based on the chest wall coverage according to the port films. The objective of this work is to investigate the effects of the collimator and the couch angle change on the dose distribution for breast cancer treatment using intensity‐modulated tangential photon beams, and to determine the clinical acceptable range of the angle change for routine treatment. Ten breast cases treated with intensity‐modulated tangential photon beams were analyzed in this study. Patient‐specific CT data and the radiation therapy planning (RTP) files obtained from our in‐house Monte Carlo based breast IMRT treatment planning system were used for IMRT dose recalculation with collimator or couch angle changes. The isodose distributions and DVHs were compared with the original plans, and the effects of the collimator and couch angle change to breast IMRT dose distributions were evaluated. Our results show that a 4° change in the collimator angle or the couch angle did not affect the dose distribution significantly and it is acceptable in the clinic for patient treatment.PACS number: 87.10.Rt

SU‐FF‐T‐106: Does Intrafraction Motion Increase Dose to the Inframammary Fold Areas in Whole Breast Treatment Using Direct Machine Parameter Optimization IMRT?

Purpose: Dosimetric uncertainties in the inframmamary fold due to intrafraction breast motion are major clinical concerns for treating large or irregularly shaped breast patients as skin break‐downs commonly occurred near the regions during the course of the treatment. Direct Machine Parameter Optimization (DMPO) IMRT has been well reported for whole breast treatments. The purpose of this study is to investigate whether intrafraction motion affects skin sparing for patients treated with this technique. Method and Materials: A pair of open tangential beams (6 MV) combined with a maximum of 20 DMPO segments of mixed photon energies (6 or 18 MV) was used to create DMPO IMRT plan for a large shaped breast case which was then benchmarked against a standard wedge‐pair plan. In order to constrain the dose to the inframamary fold, a region‐of‐interest starting near the inferior border and extending 3–4 cm superiorly was contoured. Using recorded intrafraction breast movements obtained from an image‐tracked CyberKnife system, transformed treatment plans were created while scaling the average time patterns from the CyberKnife treatment to simulate DMPO IMRT delivery. Results: Transformed DMPO plans received lower dose (90.6±3.1)% to the inframammary region compared to the original DMPO plan (96.0%). V100% for the PTV was slightly reduced from the original 97.5% to 95.0±1.5%. The treatment planning effort and delivery efficiency of DMPO IMRT were found to be similar to the wedge‐pair technique. However, the DMPO method significantly reduced the maximum dose and improved the overall dose uniformity to the inframmamary region. Conclusions: DMPO is an effective and efficient planning technique in skin sparing particularly in the inframammary fold areas for the whole breast IMRT treatments. Our study found no negative impact on such advantage due to intrafraction patient's breathing motion. In addition, the PTV dose coverage was also found to be insensitive to such motion.

A Two Year Comparison of Quality of Life for Early Stage Breast Cancer Patients Treated with Whole Breast IMRT with and without Chemotherapy

A Two Year Comparison of Quality of Life for Early Stage Breast Cancer Patients Treated with Whole Breast IMRT with and without Chemotherapy

Whole Breast IMRT Using Inverse Planning: Optimizing Dose Homogeneity With Preferential Sparing of Normal Tissues

Whole Breast IMRT Using Inverse Planning: Optimizing Dose Homogeneity With Preferential Sparing of Normal Tissues

The Minimal Dosimetric Benefit of Breast IMRT as Compared to Using a Small Number of Forward Planned MLC Segments Does Not Justify the Cost

The Minimal Dosimetric Benefit of Breast IMRT as Compared to Using a Small Number of Forward Planned MLC Segments Does Not Justify the Cost

Evaluation of an Adaptive Diffusion Smoothing Technique to Improve Delivery Efficiency in Accelerated Partial Breast IMRT

Evaluation of an Adaptive Diffusion Smoothing Technique to Improve Delivery Efficiency in Accelerated Partial Breast IMRT

Is an Additional Margin for Respiratory Motion Necessary When Utilizing IMRT for Breast Radiotherapy?

IMRT has greatly enhanced our ability to conform dose to target structures while minimizing dose to normal tissues. This improved conformality mandates that targets be clearly defined and target motion be critically assessed. We set out to analyze breast motion due to respiration using 4D CT scans for women undergoing IMRT breast radiotherapy at Fox Chase Cancer Center (FCCC) and to determine whether our current margins are adequate to cover the entire breast in all phases of the respiratory cycle during normal quiet breathing. 20 women, 10 with left breast cancer and 10 with right breast cancer, who were simulated for breast radiotherapy at FCCC underwent a free breathing 4D CT scan. An average intensity projection scan (ave) was constructed from the 4D dataset. The 4D scan was analyzed in detail in order to identify the two phases of the respiratory cycle which represented the extremes of respiration during normal quiet breathing–maximum inspiration (MI) and maximum expiration (ME). The breast, ipsilateral lung and, for left-sided breast cancers, the heart, were contoured on the average scan as well as on the two phases mentioned above. Breast motion was measured on the 4D scan in three planes: axial, sagittal and coronal. The axial motion was measured at the chest wall, the coronal motion was measured at the inframammary fold and the sagittal motion was measured at the breast surface. These landmarks represented the points of maximum motion observed on the 4D scan in each plane. In order to assess the coverage of the breast and the doses to the normal structures at the extremes of the respiratory cycle, IMRT plans were generated for the ave scan as well as for the MI and ME phases. The IMRT plan generated from the ave scan was used to treat the patient. Each IMRT plan was then analyzed and compared using the parameters which are used to evaluate all breast IMRT plans at FCCC. For the 20 patients analyzed, the mean motion in the axial direction was 1.9 mm (range 0–4 mm), in the coronal direction was 0.7 mm (range 0–2 mm) and in the sagittal direction was 2.0 mm (range 0–4 mm). For 7 patients, the sagittal motion was greatest and for 8 patients, the axial motion was the greatest. For all but 1 patient, the coronal motion was the least. PTVs were defined as breast tissue plus 2 cm superiorly and inferiorly and 7 mm posteriorly. Dose volume parameters were analyzed for the first 10 patients. The median PTV volume for the ave scan was 748 cc, for the MI phase was 733 cc and for the ME phase was 728 cc. The V95 for the PTV for the ave plan 98.4% vs. 96.3% for the MI plan and 96.5% for the ME plan. (The FCCC goal for the V95 is ≥95%). None of the other dose-volume parameters analyzed (V100, V105, D99, D1, mean dose to PTV, min dose to PTV and max dose to PTV) were significantly different between the ave and the MI and ME plans. The V20 for the lung was also analyzed and was not significantly different between the ave, MI and ME plans. 4D CT simulation is unnecessary for breast radiotherapy treatment planning, as the motion of the breast is minimal during normal quiet breathing. The present IMRT methods being utilized at our institution are sufficient and no additional margin to account for respiratory motion is necessary.

TH-E-M100E-02: Superiority of Equivalent Uniform Dose (EUD)-Based Optimization for Breast and Chest Wall IMRT

Purpose: To investigate whether IMRT optimization based on generalize equivalent uniform dose1 (gEUD) objectives for target volumes and organs at risk (OAR) alike can lead to superior plans as opposed to multiple dose-volume (DV) based objectives plans, for intact breast and postmastectomy chest wall (CW) cancer. Methods and Materials: Four IMRT plans with six or seven coplanar 6-MV beams were prepared for a number of chest wall and breast CA patients (10 patients). The first three plans utilized our standard in-house physician-set of DV objectives (phys-plan), gEUD-based objectives for the OARs (gEUD-plan), and multiple, “very stringent”, DV objectives for each OAR and PTV (DV-plan), respectively. The fourth was only beam fluence optimized plan (FO-plan), without segmentation and utilized the same objectives as in the DV-plan. The latter plan was to be used as an “optimum” benchmark without the effects of the segmentation for deliverability. Various dosimetric quantities, such as mean dose (Dmean) for heart, contralateral breast, and contralateral lung; and V20 (volume of organ receiving 20Gy) for the ipsilateral lung were employed to evaluate our results. Results: For all patients in this study, we have seen that the gEUD-based plans allow greater sparing of the OARs while maintaining excellent target coverage. The use of gEUD allows selective optimization of the dose for each OAR and results in a truly individualized treatment plan. Conclusions: gEUD requires a smaller number of parameters for optimization and allows exploration of a much wider space of solutions, thereby making it easier for the optimization system to balance competing requirements in search of a better solution. Thus, gEUD optimization can be used to search for or evaluate plans of different DVHs with the same gEUDs. This method can be efficiently used in routine clinical IMRT treatment planning.

WE‐D‐AUD‐06: In Vivo EPID Dosimetry for Large Scale Clinical IMRT Verification

Purpose: To introduce 2D in vivo EPID dosimetry as a tool for IMRT verification in the clinic for all curative patients (about 2000/year) before the end of 2007; meanwhile replacing pre‐treatment dosimetry, reducing workload and improving efficiency. Method and Materials: EPID images are acquired per segment, and by means of a back‐projection algorithm converted to dose distributions in a plane intersecting the isocenter, perpendicular to the beam axis. In this plane, a 2D field‐by‐field comparison is performed between the back‐projected EPID and planned dose distributions, using the γ‐evaluation method with 3%/3mm of maximum dose as criteria. For each field the mean γ, maximum 1% γ, percentage of points in agreement, and the isocenter dose difference are reported. These numbers are fed into a decision rule setting limits on the approval of a treatment plan. Results: Currently, treatment plans of prostate, rectum, skull and liver cancer patients are already validated based on in vivo EPID measurements; for the other patient groups in vivo dosimetry is being introduced. Statistics for a group of 152 prostate patients, each having 3–5 EPID measurements thus filtering out random uncertainties, show an average mean γ‐value per patient of 0.41, and an average isocenter dose difference of −1.5% between EPID and plan. Clinically relevant errors were detected in four prostate plans, and these plans were replaced. Preliminary results for head&neck, breast and lung IMRT treatments show the feasibility of the method for these sites but inhomogeneity corrections need to be refined to improve accuracy. Conclusions: For a variety of treatment sites, 2D in vivo EPID dosimetry is now clinically used, or will be introduced soon, for IMRT verification of all curative patients. In this way, an efficient and accurate routine procedure has been developed for routine purposes providing the radiotherapy chain with an extra safety net.

SU-FF-T-266: Intensity Modulated Radiotherapy of Breast Cancer Using Direct-Machine-Parameter-Optimization

Purpose: To design an efficient step-and-shot IMRT technique for breast CA and compare the results with other established treatment planning techniques. Methods and Materials: The technique was based on a modified Direct Machine Parameter Optimization (DMPO) method, where some of the inversely optimized segments were adjusted by the user in order to allow for skin “fall-off”. During DMPO, the optimized fluence was converted into segments where the segment shape and weight became part of the optimization; thereby, forcing segments that did not satisfy the requirements to be discarded. A set of 20 breast CA patients was used to develop the technique and compare it with a 3D-conformal with optimized wedges and a forward-optimized technique with manually defined segments. Results: Dose distribution and DVH analysis of all patient plans resulted superior PTV coverage with better dose homogeneity and lower lung and heart doses for our IMRT technique, compared to the two other techniques. The number of segments can be controlled by the user and the resulted MUs for delivery are less that those needed for the 3D-conformal with optimized wedges technique. Conclusions: DMPO can be effectively used on a routine breast IMRT treatment planning since it allows the user to modify the number and shapes of selected segments quickly and efficiently. Thus, this method solves the issue of patient and PTV setup uncertainty and motion by allowing the creation of “fall-off” defined by the user, on patient-to-patient basis. The technique can be easily extended to 4-field plans were the two anterior and posterior oblique fields are added for more complex PTVs. Dose uniformity to the PTV (due to the electronic compensation) and lower doses to the lungs and heart are the major advantages of our method.

SU-FF-T-379: Significance of Artificial Critical Structure (ACS) in Inverse Planning for Partial Breast Irradiation Treatment

Purpose: The purpose of this study was to investigate influence of artificial critical structure (ACS) in sparing ipsilateral lung volume doses during partial breast IMRT treatment. Introduction: In partial breast irradiation (PBI) techniques, the goal has been to limit dose around lumpectomy cavity, and sparing critical structures as ipsilateral lung and skin. Mammosite and 3-D treatment modalities have been used to achieve this goal. However, the role of inverse treatment planning was never investigated for reducing the doses to lung. Dosimetric plans were reviewed to justify IMRT role in PBI. Methods and Materials In late 2006, we investigated role of IMRT for partial breast irradiation in patients found unsuitable for mammosite treatment.During the investigation our major concern was excessive dose to ipsilateral lung volume. The lung volume doses were significantly reduced by introducing artificial critical structure between lumpectomy cavity & lung volume. Total eight patient's dosimetry was reviewed retroactively to study influence of ACS. IMRT plans were compared for ipsilateral lung DVH with and without ACS, and these results were further compared with published DVH for lung using 3-D* treatment plans. Dose prescription in all the modalities was 34 Gy in 10 Fractions, prescribed at 10 mm from lumpectomy cavity volume. Results: Dosimetry plans (Corvus V6.2, Nomos Inc.) for eight PBI patients were reviewed. Ipsilateral lung volumes were compared for 17 Gy dose volumes. IMRT plans without ACS indicated 17 Gy lung volumes of 6% to 14.5%, median 7.5 %, while plans with ACS indicated volumes of 0.5 to 6.5%, median 2.8%. The published data for 3-D* plans indicated 17 Gy dose volumes of 1% to 12%, median 5%. Conclusions: The DVH analysis indicated improved DVH for ipsilateral lung with ACS using IMRT. The results were superior to established 3-D technique.

TH-E-M100J-04: Quantitative Assessment of Tissue Toxicity in Breast Cancer Radiation Therapy Using Spectrophotometry and Ultrasonic Tissue Characterization Imaging

Purpose: To investigate a novel combination of two non-invasive techniques, spectrophotometry and ultrasound tissue characterization (UTC) imaging, to quantitatively evaluate breast tissue toxicity in radiation treatment. Method and Materials: Skin and soft tissue injury are the most common toxicities of breast cancer radiation therapy. There is currently no objective means of measuring breast tissue injury in the clinic. We investigated the combination of Spectrophotometry and UTC imaging to examine radiation toxicity. A spectrophotometer (Mexameter® MX) was used to measure the radiation damage to the skin surface and an ultrasound scanner (Ultrasonix® with 14-MHz probe) was utilized to measure the soft tissue changes. Six imaging parameters were computed to quantitatively measure toxicity: melanin, erythema, skin thickness, UTC slope, intercept and midband value. Subjective clinical assessment of toxicity was done by a radiation oncologist. Statistical analysis was performed to correlate spectrophotometer and UTC findings with clinical assessments (RTOG clinical toxicity scale). To date, twelve breast cancer patients were enrolled. All patients received a standard course of radiation: the whole breast received 50–50.4 Gy followed by an electron boost of 10–16 Gy at the lumpectomy site. Each patient received a series of spectrophotometer and ultrasound scans prior to, during and post radiation treatment. Results: Twenty-eight spectrophotometer and ultrasound scans were performed. The contra-lateral (untreated) breast scans showed good accuracy and reproducibility. Our spectrophotometer and UTC evaluations were consistent with the clinical breast toxicity assessments. We observed significant patient variations. During six-week radiation treatment, patient melanin increases were between 5 to 20%, erythema increases varied from 0% to 100%. Conclusion: The combination of spectrophotometer and UTC provides effective means of assessing radiation damage to the skin and the underlying breast tissue respectively. This tool becomes increasingly valuable as we evaluate new strategies for breast cancer radiation therapy, such as partial breast IMRT and MammoSite.

SU‐FF‐T‐431: Uncertainties in Superficial Dose From Helical Tomotherapy Delivery Due to Target Localization Errors

Purpose: To quantitate shallow‐depth dose calculation accuracy for IMRT breast treatment plans created with Tomotherapy system and to estimate the dose errors caused by setup errors. Methods: A cylindrical solid water phantom with radiochromic film was used for this purpose. The split phantom can hold a film in coronal or sagittal planes. A 5cm thick PTV was contoured by extending it to the surface of the phantom. A plan was optimized to treat the superficial PTV while limiting the dose to the surrounding critical structures. To evaluate the setup uncertainties multiple phantom plans were generated by shifting the phantom 5, 10 and 20 mm to right and up (7, 14, and 28mm distance) and simulated doses were compared against the measured doses. The 3D dose matrices from TPS for no‐shift and shifted phantom plans were exported in DICOM and were analyzed in MatLab. Doses from eleven transverse slices were analyzed to estimate the dose differences in the shifted phantom plans. Shifted phantom plan dose distributions were transposed back onto the patient PTV and computed dose difference histograms (DDHs) in the PTV volume. Results: The planning system overestimated the shallow‐depth dose by as much as 14%, but was smaller than 3% at depths greater than 5mm. PTV DDHs for no and 7 mm shifts showed <5% dose differences, while for 14 mm, the dose differences were ⩽10% and were very large for the 28 mm shift. Conclusion: Tomotherapy planning system computes the shallow‐depth dose within 14% accuracy at 1.0 mm and better than 3% for depths greater than 5mm. Setup errors ⩽7mm showed negligible dose errors, consistent with the use of image‐guided therapy. Large shifts were required to induce large dose errors in the PTV. Conflict of Interest: This work supported in part by Tomotherapy, Inc.

A Forward-planning Solution for the IMPORT HIGH Breast IMRT Trial

A Forward-planning Solution for the IMPORT HIGH Breast IMRT Trial

Effect of respiratory motion on the delivery of breast radiotherapy using SMLC intensity modulation

This study evaluates the effects of respiratory motion on breast radiotherapy delivered using segmented multileaf collimator (SMLC) intensity modulation. An anthropomorphic breast phantom was constructed of polystyrene plates between which radiographic films were inserted. The phantom was mounted on a moving platform to simulate one-dimensional sinusoidal oscillation with variable amplitude and frequency. The motion effect on two breast IMRT techniques, a beamlet-based plan created using the Corvus treatment planning system and an aperture-based plan, was evaluated via film comparison. Motion-induced differences in the treatment region are generally within +5%, with the exception of the posterior field edge and the apex of the breast in the Corvus IMRT plan. Considering the experimental uncertainty arising from the setup and film dosimetry, this result indicates that respiratory motion-induced dose variations are generally relatively insignificant. It appears that the anterior hot spots observed in the Corvus IMRT plan result from the high intensity fluence delivered to the "virtual bolus" area which must be created during the planning process in order to provide "flash" for the respiratory motion. The potential magnitude of such effects resulting from the interplay between fluence modulation and patient motion are unique to the individual planning system and planning technique, as well as the delivery equipment and technique. Such effects should be carefully investigated prior to the implementation of IMRT for breast radiotherapy.