Forward Intensity-modulated Radiotherapy Research Articles

Dosimetric Comparison of Different Dose Calculation Algorithms in Postmastectomy Breast Cancer Patients Using Conformal Planning Techniques.

The aim of the current study was to compare three different dose-calculating algorithms, i.e., superposition (SP), fast SP (FSP), and convolution (CV), for breast cancer patients treated with intensity-modulated radiotherapy (IMRT) and field-in-Field forward plan IMRT (FiF-FP-IMRT). The current retrospective study involved 100 postmastectomy breast cancer patients who were given radiotherapy using IMRT and FiF-FP-IMRT planning techniques. All the initially SP-calculated plans were recalculated with the same monitor units for FSP and CV algorithm without change in any of the other planning parameters. The isodose distribution and various plan evaluating parameters, for example, conformity index (CI), homogeneity index, and uniformity index target volume and normal structure doses were compared and analyzed for all the different algorithm calculated plans. In the IMRT plans, all the target and normal structure dose-volume parameters showed a significant difference between all the three different algorithms with P < 0.05. In the FiF-FP-IMRT plans, CV algorithm showed a significant difference in most of the target and normal structure dose-volume parameters. Among quality indexes, only CI showed a significant difference between all the algorithms in both the planning techniques. R50 showed a significant difference with the CV algorithm in both the planning techniques. The change in the dose calculation algorithm resulted in dosimetric changes which must be evaluated by the medical physicists and oncologists while evaluating treatment plans. In the current study with breast patients, the results obtained for target and normal structure doses using the CV algorithm are overestimated as compared to SP and FSP algorithms, producing variable results in air and bony normal structures. However, the ipsilateral lung V5 parameter and the ipsilateral humeral head mean dose were found to be underestimated by the CV algorithm as compared to the SP and FSP algorithm in both the planning techniques.

Dosimetric comparison of different intensity-modulated radiotherapy techniques for whole-breast irradiation of right-breast cancer

PurposeThis study compared the dosimetric parameters of field-in-field forward intensity-modulated radiotherapy (FIF-IMRT) and fixed-field inversely optimized intensity-modulated radiotherapy (FFIO-IMRT) for the whole-breast irradiation of patients undergoing right-breast lumpectomy. Material and methodsA total of 30 patients with pT1-2N0M0 right-breast invasive ductal carcinoma were enrolled in this study. Two different treatment plans, i.e., FIF-IMRT and FFIO-IMRT, were designed for each patient. The dosimetric parameters of the two treatment plans were compared including ipsilateral lung and heart, conformity index (CI), and the homogeneity index (HI) of the planning target volume (PTV). ResultsFixed-field inversely optimized intensity-modulated radiotherapy was found to significantly improve CI (83.302% vs. 60.146%) and HI (11.837% vs. 19.280%), and significantly reduced V25 (18.038% vs. 19.653%) and V30 (15.790% vs. 18.492%) of the ipsilateral lung. It also significantly increased V5 (69.791% vs. 32.615%) of the ipsilateral lung and V5 (61.579% vs. 3.829%), V10 (14.130% vs. 0.381%), V20 (1.843% vs. 0.051%), and Dmean (5.211Gy vs. 1.870Gy) of the heart. ConclusionRegardless of improving the conformity and homogeneity of PTV and reducing the ipsilateral lung irradiation volume at high doses, FFIO-IMRT significantly raised the ipsilateral lung irradiated volume at low doses, as well as the irradiation volume and mean radiation doses to the heart. This limits its use in patients with early-stage right breast cancer.

Dosimetric evaluation of hybrid and volumetric-modulated arc therapy plan for left-sided chest wall irradiation in MONACO treatment planning system.

Radiation induced toxicities in heart and lungs are diminishes the survival rate of cancer patients. The purpose of this study is to evaluate the dosimetric parameters of hybrid plans for chest wall irradiation of left breast carcinoma patients using Monaco treatment planning system and compare with the volumetric-modulated arc therapy (VMAT) treatment plans. Materials and Methods: Fifteen carcinoma left breast patients were randomly selected to evaluate the advantage of hybrid plan over VMAT. Hybrid plans were generated with 70% and 30% dose contribution from forward intensity-modulated radiotherapy and VMAT, respectively, whereas VMAT had been done with full prescription. Conformity and homogeneity indices were evaluated for target coverage between hybrid and VMAT plans. Hybrid plan has proved its superiority over VMAT in terms of better organ at risk sparing and lesser low dose spillage and at the same time providing comparable target coverage. In low-dose spectrum, VMAT showed higher dose-volume than the hybrid plan. The maximum variation was found to be 44.75% at 7 Gy and the minimum dose difference was observed at 1 Gy (6.02%). Conclusion: This study suggests that the hybrid plan could be a better option for left-sided chest wall irradiation in regular clinical practice.

Unintended dose to the lower axilla in adjuvant radiotherapy for breast cancer: Differences between tangential beam and VMAT

Background and purposeTo evaluate dosimetric differences in unintended dose to the lower axilla between 3D-standard (3DCRT), tangential beam forward intensity modulated radiotherapy (F-IMRT) and volumetric modulated arc therapy (VMAT). The objective is to evaluate whether results of clinical trials, such as the ACOSOG-Z011 trial, that evaluated omission of axillary clearance can be extrapolated towards more conformal techniques like VMAT. Materials and methodsTwenty-five consecutive patients treated with whole breast radiotherapy alone (WBRT) using a F-IMRT technique were identified. Three additional plans were created for every patient: one plan using a single 270° arc (VMAT 1x270°), another using two small ≤90° opposing arcs (VMAT 2x < 90°) and thirdly a 3DCRT plan without F-IMRT. Axillary levels I-II were contoured after the treatment plans were made. ResultsThe volume of the axilla level I that was covered by the 50% isodose (V50%) was significantly higher for VMAT 2x < 90° (71.3 cm3, 84% of structure volume, p < 0.001) and VMAT 1x270° (68.8 cm3, 81%, p < 0.01) compared to 3DCRT (60.3 cm3, 71%) and F-IMRT (60.8 cm3, 72%). The V50% to the axilla level II, however, was low for all techniques: 12.3 cm3 (12%); 8.9 cm3 (9%); 4.3 cm3 (4%); 4.4 cm3 (4%) for VMAT 2x < 90°, VMAT 1x270°, 3DCRT, F-IMRT, respectively. For the higher doses (V90% and above), no clinically relevant differences were seen between the different modalities. ConclusionWBRT treatments with VMAT do not lead to a significant reduction of the unintended axillary dose in comparison with a tangential beam setup. Hence, concerning tumor control, VMAT can be applied to clinical situations similar to the Z0011 trial. The intermediate axillary dose is higher with VMAT, but the clinical consequence of this difference on toxicity is unknown.

Suggested Template Plan for Forward Intensity Modulated Radiotherapy in Head and Neck Cancer Patients

Background: We aimed to achieve full tumor control during every fraction with head and neck cancer patients using 3DCRT treatment technique. Method: We divided 16 head and neck cancer patients into two groups to deliver radiotherapy doses of 66Gy and intensity modulated radiotherapy (IMRT) 70Gy. We applied 3DCRT plan as a forward IMRT plan for each patient with coplanar beams arrangement technique designed with angles of (0o, 60o, 90o, 180o (or around 175o and 185o), 270o and 300o).We assessed the plans according to DVHs and satisfactory dose distributions. Results: Based on the overall evaluation of the two groups (16 cases), we achieved an accepted dose distribution for PTVs and OARs dose; simulating IMRT inverse plans dose distribution. Conclusion: Using such a mono-isocenteric plan, we were able to achieve a perfect uniform dose distribution for PTVs up to 70Gy, while sparing critical organs. This template could be used in countries with no access to forward IMRT planning.

Is 5 mm breath-hold window (BHW) sufficient to treat carcinoma left breast patients post-conservative surgery: a comparative study using forward intensity-modulated radiotherapy (FIMRT) and volumetric modulated arc therapy (VMAT)

AbstractPurpose:The purpose of the study was to evaluate the impact of changes in breathing pattern inside the breath-hold window (BHW) during deep inspiration breath hold treatment for carcinoma left breast patients post-conservative surgery.Methods:Ten patients of carcinoma left breast post-conservative surgery were prospectively selected. Three sets of CT plain images were acquired, one with 5 mm deep inspiration BHW (DIBHR) and the other one with 1 mm BHW matching the lower threshold (DIBHL) and the third one with 1 mm BHW matching the upper threshold (DIBHH) as DIBHR. For all patients, forward intensity-modulated radiotherapy (FIMRT) and volumetric modulated arc therapy (VMAT) plans were generated in the 5 mm BHW CT series and the same plan being copy and pasted in other series. Target volume doses and critical structure doses were tabulated.Results:Planning target volume coverage was adequate and no significant differences were found in any CT series. Significant differences noted in average left lung V5%, V10% and V18% doses between DIBHR versus DIBHH (p values = 0·0461, 0·0283 and 0·0213, respectively) and DIBHL versus DIBHH (p values = 0·0434, 0·0484 and 0·0334, respectively) for FIMRT plans and V18% doses in DIBHR versus DIBHH (p = 0·0067) in VMAT. No differences in heart and apex of heart doses were found. Left anterior descending artery (LAD) mean doses were significant in DIBHL versus DIBHR, DIBHR versus DIBHH and DIBHL versus DIBHH (p = 0·0012, 0·0444 and 0·0048, respectively) series for FIMRT plans and DIBHR versus DIBHH and DIBHL versus DIBHH (p = 0·0341, 0·0001) for VMAT plans.Finding:The changes in the breathing pattern inside DIBH window level cause some variation in LAD doses and no other significant differences in any parameters noted, so care should be taken while treating patients with preexisting cardiac conditions.

&lt;p&gt;Postmastectomy radiotherapy using three different techniques: a retrospective evaluation of the incidental dose distribution in the internal mammary nodes&lt;/p&gt;

ObjectiveTo evaluate the incidental coverage dose to the internal mammary nodes (IMN) in patients treated with postmastectomy radiotherapy (PMRT) and its relationship with the treatment plan.Patients and methodsWe retrospectively analyzed 138 patients undergoing PMRT and divided them into three groups: three-dimensional conformal radiotherapy (3D-CRT), field-in-field forward intensity-modulated radiotherapy (F-IMRT), and inverse intensity-modulated radiotherapy (I-IMRT). The IMN were contoured according to the Radiation Therapy Oncology Group consensus and not included in the planning target volume. We analyzed incidental IMN dose coverage and its relationship with the lung and heart.ResultsThe mean dose (Dmean) to the IMN was 32.85 Gy for all patients, and the dose delivered to the IMN showed no differences in 3D-CRT, F-IMRT, and I-IMRT (33.80, 29.65, and 32.95 Gy, respectively). In addition, 10.42%, 2.04%, and 9.76% of patients achieved ≥45 Gy with 3D-CRT, F-IMRT, and I-IMRT, respectively. No differences were evident among the three treatment plans regarding IMN dose in the first three intercostal spaces (ICS1–3). The Dmean, V20, V30, V40, and V50 of ICS2 and ICS3 were superior to those of ICS1 for all three plans. For 3D-CRT, a moderate positive correlation was evident between the Dmean to the IMN and the Dmean to the heart. For F-IMRT and I-IMRT, positive correlations were evident between the Dmean of the IMN and the Dmean and V20 of the lung.ConclusionThe mean incidental dose to the IMN for IMRT (F-IMRT and I-IMRT) and 3D-CRT after modified radical mastectomy was insufficient to treat subclinical disease. A substantial dose was delivered to the IMN in some patients. Higher incidental doses to the IMN were associated with a higher heart mean dose for 3D-CRT and a higher dose to the lung for IMRT. Future prospective studies should further explore subgroups that do not require IMN irradiation.

Dose prescription point in forward intensity-modulated radiotherapy of breast and head/neck cancers.

In the forward intensity-modulated radiotherapy (FIMRT) technique of treatment planning, the isocenter cannot fulfill the requirements of the International Commission on Radiation Units and Measurements (ICRU) reference point. This study aimed to propose dose prescription points to be used in breast and head/neck cancer patients treated using the FIMRT technique. Two-hundred patients with head/neck (n = 100) and breast (n = 100) cancers were selected. Treatment plans involved using the FIMRT technique. The suggested reference points (SRPs) for dose prescription were placed at selected locations in the lateral neck site and the tangential site in breast and head/neck cancer patients, respectively. Next, doses at the SRPs (DSRPs) were compared to the planning treatment volume (PTV)-equivalent uniform dose (EUD) and mean dose in the PTV (Dmean) extracted from dose-volume histograms. The differences between DSRPs and Dmean for the PTVs were less than 2% in 78 cases and less than 1% in 28 cases. The DSRPs were comparable with the EUD in both types of PTVs; moreover, paired t test analyses indicated that the SRP doses and PTV EUD were statistically similar (p > 0.05). In 116 cases, the discrepancy between DSRP and EUD was less than 2% and less than 1% in 74 cases. The SRPs satisfy the ICRU requirement that the reference point dose should be clinically relevant and representative of the dose throughout the PTV. A consensus on the definition of the reference point is expected to lead to accurate inter-comparison between results from different treatment centers, facilitating the optimization of treatment procedures.

Reproducible deep-inspiration breath-hold irradiation with forward intensity-modulated radiotherapy for left-sided breast cancer significantly reduces cardiac radiation exposure compared to inverse intensity-modulated radiotherapy.

To investigate the objective utility of our clinical routine of reproducible deep-inspiration breath-hold irradiation for left-sided breast cancer patients on reducing cardiac exposure. Free-breathing and reproducible deep-inspiration breath-hold scans were evaluated for our 10 consecutive left-sided breast cancer patients treated with reproducible deep-inspiration breath-hold. The study was based on the adjuvant dose of 50 Gy in 25 fractions of 2 Gy/fraction. Both inverse and forward intensity-modulated radiotherapy plans were generated for each computed tomography dataset. Reproducible deep-inspiration breath-hold plans with forward intensity-modulated radiotherapy significantly spared the heart and left anterior descending artery compared to generated free-breathing plans based on mean doses - free-breathing vs reproducible deep-inspiration breath-hold, left ventricle (296.1 vs 94.5 cGy, P = 0.005), right ventricle (158.3 vs 59.2 cGy, P = 0.005), left anterior descending artery (171.1 vs 78.1 cGy, P = 0.005), and whole heart (173.9 vs 66 cGy, P = 0.005), heart V20 (2.2% vs 0%, P = 0.007) and heart V10 (4.2% vs 0.3%, P = 0.007) - whereas they revealed no additional burden on the ipsilateral lung. Reproducible deep-inspiration breath-hold and free-breathing plans with inverse intensity-modulated radiotherapy provided similar organ at risk sparing by reducing the mean doses to the left ventricle, left anterior descending artery, heart, V10-V20 of the heart and right ventricle. However, forward intensity-modulated radiotherapy showed significant reduction in doses to the left ventricle, left anterior descending artery, heart, right ventricle, and contralateral breast (mean dose, 248.9 to 12.3 cGy, P = 0.005). The mean doses for free-breathing vs reproducible deep-inspiration breath-hold of the proximal left anterior descending artery were 1.78 vs 1.08 Gy and of the distal left anterior descending artery were 8.11 vs 3.89 Gy, whereas mean distances to the 50 Gy isodose line of the proximal left anterior descending artery were 6.6 vs 3.3 cm and of the distal left anterior descending artery were 7.4 vs 4.1 cm, with forward intensity-modulated radiotherapy. Overall reduction in mean doses to proximal and distal left anterior descending artery with deep-inspiration breath-hold irradiation was 39% (P = 0.02) and 52% (P = 0.002), respectively. We found a significant reduction of radiation exposure to the contralateral breast, left and right ventricles, as well as of proximal and especially distal left anterior descending artery with the deep-inspiration breath-hold technique with forward intensity-modulated radiotherapy planning.

Comparison of incidental irradiation dose to the internal mammary nodes among I-IMRT, F-IMRT, and 3DCRT after breast-conserving surgery

Objective To explore the dosimetric variance in incidental irradiation to the internal mammary nodes among inverse intensity-modulated radiotherapy (I-IMRT), forward intensity-modulated radiotherapy (F-IMRT), and three-dimensional conformal radiotherapy (3DCRT) after breast-conserving surgery, and to provide a basis for deciding whether to spare the internal mammary nodes in clinical treatment. Methods A total of 84 patients undergoing breast-conserving surgery were enrolled as subjects. The internal mammary nodes in the first three intercostal spaces were contoured. Three radiotherapy plans were designed for each patient. The internal mammary nodes were not included in the planning target volume. Comparison was made among the three plans. The results were compared using Wilcoxon signed rank test. Results The I-IMRT, F-IMRT, and 3DCRT plans had similar median Dmean values for the internal mammary nodes, which were 2740.2, 2973.9, and 2951.4 cGy, respectively. The analyses of the three individual intercostal spaces showed that there was no difference in Dmean for the first intercostal space or the second intercostal space between the three plans; For the third intercostal space, however, I-IMRT had a significantly higher Dmean than 3DCRT and F-IMRT. The analyses of the three individual plans showed that for each plan, the Dmean was the highest in the third intercostal space, followed by the second intercostal space and the first intercostal space. Conclusions All the three plans fail to attain an adequate prescribed dose to cure subclinical disease, and there is no significant difference among the three plans. Therefore, it is risky to exclude the internal mammary nodes using any one of the three radiotherapy techniques for patients with clinical indications for internal mammary nodes radiation. In the combination therapy including chemotherapy, endocrine therapy, and targeted therapy, however, further follow-up is needed to determine whether the incidental irradiation dose to the internal mammary nodes could meet clinical requirement. Key words: Breast-conserving postoperative radiotherapy; Internal mammary lymph node region; Incidental irradiated dose; Treatment planning comparison

95P Radiotherapy (RT) for breast cancer patients- clinical implementation of the first ever Tomotherapy-H in a tertiary cancer centre in India

Background The first ever Tomotherapy-H system in India became operational in Feb 2016 in our hospital, Health care global enterprises, a tertiary level cancer care centre. In order to implement Tomotherapy as a routine technique to treat breast cancers we under took dosimetric comparison of helical Tomotherapy plans and five field forward planning intensity modulated radiotherapy (IMRT) plans. Methods We compared the Helical Tomotherapy plans with IMRT plans of the first 10 patients with early breast cancer who underwent adjuvant RT using helical Tomotherapy technique in our centre between February 2016 and June 2016. The treatment planning objectives were to cover 95% of the planning target volume (PTV) using a 95% isodose (V95 >/= 95%), with a minimum of 90% isodose covering 100% of PTV (V100 >/= 90%) and no more than 10% ofPTV to receive 110% (V110 <10%). The heart and lungs were contoured as organs at risk (OAR) and doses received were recorded in both the planning techniques. Results All patients were females with four right and six left sided cancers. Seven patients had undergone breast conserving surgery and three had mastectomy. When we compared the forward planning IMRT plans with Helical Tomotherapy plans, we found thattheadvantageofusingHelicalTomotherapyincludedsignificantlybettercoverage forV95(p<0.000),V100(p<0.000)andmedianV110was0.06%and0.14%in Helical Tomotherapy and IMRT plans respectively. Helical Tomotherapy plans had lower dose to ipsilateral lung (V35 P < 0.01) and lower median dose to the heart (Tomotherapy=8.2andIMRT=9Gy).Therewasimprovedcoverageoftheplanning target volume, including the regional nodes, without any field junction problems. None ofthepatientshadanymorethangrade1 skintoxicityandgrade1 oesophagitis. Conclusions Helical Tomotherapy, compared to forward planning IMRT for breast cancer treatment, demonstrated better target coverage and sparing ofOARs. The treatment was well tolerated with minimal toxicity. Long term toxicity is yet to be established by continued follow up ofthese patients in late side effects clinics. Legal entity responsible for the study Health Care Global Enterprises Funding Health Care Global Enterprises Disclosure All authors have declared no conflicts ofinterest.

Three-Dimensional Breast Radiotherapy and the Elective Radiation Dose at the Sentinel Lymph Node Site in Breast Cancer.

BackgroundSeveral trials are presently randomizing clinically node-negative breast cancer patients treated with breast-conserving therapy (BCT) to sentinel lymph node biopsy (SLNB) or watchful waiting. We aimed to investigate the elective radiation dose at the sentinel lymph node (SLN) site while evaluating two techniques for SLN localization, in breast cancer patients treated with lumpectomy and three-dimensional (3D) whole-breast radiotherapy.MethodsThe SLN site of consecutive Tis-2N0 breast cancer patients undergoing lumpectomy and forward intensity-modulated whole-breast radiotherapy was determined by the location of the hotspot on preoperative single-photon emission computed tomography (SPECT)/computed tomography (CT) and by a surgical clip placed at the removed SLN(s) during SLNB. The radiation dose at the SLN site was subsequently determined on the postoperative radiotherapy planning CT. An elective radiation dose to the SLN site was defined as at least 95 % of the breast dose.ResultsOf the 42 included patients, the mean percentage of the breast dose on the SLN site was 90 % (standard deviation 26, range 7–132, median 99), with a non-significant difference between the two techniques (surgical clip or SPECT/CT) (p = 0.608). In 32/42 patients (76 %) the SLN site received an elective radiation dose.ConclusionsA surgical clip placed at the removed SLN(s) during SLNB proved to be an adequate method of determining the radiation dose at the SLN site when compared with using SPECT/CT. With the use of 3D radiotherapy, the site of the SLN is treated with an elective radiation dose in the majority of patients who are treated with BCT.

Forward and inverse-planned intensity-modulated radiotherapy (IMRT) in the CHHiP trial: A comparison of dosimetry and normal tissue toxicity.

37 Background: CHHiP (CRUK/06/016) is a multicentre randomised controlled trial investigating the use of hypofractionated radiotherapy dose schedules for treatment of localised prostate cancer. RT treatment employs a complex target volume treated with either a multi-segment “forward” plan or inverse-planned intensity-modulated radiotherapy (IMRT). This study compares dose-volume histogram (DVH) and toxicity data for rectum and bladder for the two planning techniques. Methods: Three hundred thirty seven patients (230 forward-planned [F]; 107 inverse-planned [I]) with prospectively collected 2 year toxicity and DVH data for rectum and bladder dose constraints were included. Patients were paired for comparison by matching on (1) rectum and prostate + seminal vesicle PTV volumes for the rectal dose comparison (53 matched pairs available); and (2) bladder and prostate-alone PTV volumes for bladder dose comparison (61 matched pairs). For the toxicity comparison patients were additionally matched on randomised dose schedule. Results: Forward-planned patients had significantly larger volumes of rectum irradiated to 50 to 70Gy and bladder at 50 to 60Gy. In contrast, inverse-planned patients had significantly larger volumes of bladder irradiated to 74 Gy. Acute bowel toxicity (G2+ toxicity within 18 weeks of start of RT) was significantly worse in forward-planned patients (27/53 [52%] F vs 11/53 [21%] I; Mann-Whitney p=0.0002). There were no significant differences in acute urinary symptoms. Late toxicity was rare in both planning groups with only two patients (0 F; 2 I) reporting RTOG G2+ bowel/bladder effects at 24 months. Considering LENTSOM data, there was a suggestion of less late bowel toxicity in the inverse group (G1+ at 18 months: 16/53 (30%) F vs. 6/53 (11%) I; p=0.008). Patient reported outcomes of bowel habits showed no consistent differences between planning methods, although there was a tendency for worse urinary function scores in the inverse group at 12 months. Conclusions: Both planning techniques were associated with low late toxicity. Significant differences were found between DVHs from forward and inverse plans. There were some associations between DVH differences and normal tissue effects; these resolved by 2 years. Clinical trial information: CRUK/06/016.

Prone breast forward intensity-modulated radiotherapy for Asian women with early left breast cancer: factors for cardiac sparing and clinical outcomes

Since December 2009, after breast-conserving surgery for Stage 0–I cancer of the left breast, 21 women with relatively pendulous breasts underwent computed tomography prone and supine simulations. The adjuvant radiotherapy was 50 Gy in 25 fractions to the left breast alone. Four plans—conventional wedged tangents and forward intensity-modulated radiotherapy (fIMRT) in supine and prone positions—were generated. fIMRT generated better homogeneity in both positions. Prone position centralized the breast tissue by gravity and also shortened the breast width which led to better conformity in both planning techniques. Prone fIMRT significantly reduced doses to left lung, Level I and Level II axilla. The mean cardiac doses did not differ between positions. Among the four plans, prone fIMRT produced the best target dosimetry and normal organ sparing. In subgroup analysis, patients with absolute breast depth > 7 cm in the prone position or breast depth difference > 3 cm between positions had significant cardiac sparing with prone fIMRT. Sixteen patients with significant cardiac sparing in prone position were treated using prone fIMRT and the others using supine fIMRT. All patients received a supine electron tumor bed boost of 10 Gy in 5 fractions. No patients developed Grade 2 or worse acute or late toxicities. There was no difference in the number of segments or beams, monitor units, treatment time, or positioning reproducibility between prone and supine positions. At a median follow-up time of 26.8 months, no locoregional or distant recurrence or death was noted.

Evaluation of dosimetric variance in forward intensity modulated radiotherapy of the breast based on 4D CT and 3D CT during free breathing

To explore the dosimetric variance in forward intensity modulated radiotherapy (IMRT) based on 4D CT and 3D CT after breast conserving surgery. Seventeen patients after breast conserving surgery underwent 3D CT simulation scans followed by respiration-synchronized 4D CT simulation scans at free breathing state. The treatment plan constructed using the end inspiration (EI) scan was then copied and applied to the end expiration (EE), and 3D scans and dose distribution were calculated separately. Dose-volume histograms (DVHs) parameters for the CTV, PTV, ipsilateral lung and heart were evaluated and compared. The CTV volume difference was biggest between T0 and 3D CT, and the volume difference was 4.10 cm(3). Mean dose of PTV at EE was lower than that at EI (P = 0.019), but there were no statistically significant difference between 3D and EI, EE (all P > 0.05). The homogeneity index (HI) at EI, EE, 3D plans were 0.149, 0.159 and 0.164, respectively, and a significant difference was only between EI and EE (P = 0.039). The highest conformal index (CI) was at EI phase (P < 0.05), and there was no significant difference between EE and 3D (P = 0.758). The V(40) and V(50) of ipsilateral lung at EE phase were lower than that at EI (P < 0.05). There were no significant differences in all the indexes for heart (P > 0.05). The breast deformation during respiration may be disregarded in whole breast IMRT. PTV dose distribution is significantly changed between EI and EE phases, and the differentiation of the lung high dose area between EI and EE phases may be induced by thorax expansion. 3D treatment planning is sufficient for whole breast forward IMRT, but 4D CT scans assisted by respiratory gating ensures more precise delivery of radiation dose.

The dosimetric study of the targets and organs at risk in whole breast forward intensity-modulated radiotherapy during free breathing based on 4DCT

Objective To explore the correlation between the respiration-induced clinical target volume (CTV) motion and volume variation and the dosimetric variation of planning target volume (PTV) and organs at risk (OAR) during free-breathing (FB) with whole breast intensity-modulated radiotherapy (IMRT).Methods Seventeen patients with breast conserving surgery underwent respiration-synchronized four-dimentional computed tomography (4DCT) simulation scans on the state of FB.The treatment plan was constructed using the end-inspiration phase scan,then copied and applied to the other respiratory phases.The dose distribution was calculated separately to evaluate the dose-volume histograms parameters for the PTV,ipsilateral lung and heart.Results During FB,the CTV motion vector was (2.09 ±0.74) mm,and the volume variation was (3.05 ± 0.94) ％.There was no correlation between the volume variation of CTV and dosimetric variation of PTV/OAR ( r =-0.390 -0.480,P =0.182 -0.775 ).In anteroposterior (AP),superoinferior (SI) and vector directions,the CTV movement correlated well with the PTV mean dose,conformal index,and the lung volume receiving high dose (V20,V30,V40,and V50;r=-0.975-0.791,P =0.000 -0.041 ).In SI and vector directions,the CTV displacement only correlated with the heart volume receiving ＞ 5 Gy ( V5 ) ( r =-0.795,0.687,P =0.006,0.028 ).The lung volume variation and the lung volume receiving high dose correlated reasonably well (r=0.655 -0.882,P=0.001-0.04 0).The heart volume variation only correlated with the V5 of heart (r =-0.701,P =0.024).Conclusions During free-breathing,the effect of breast volume variation can be ignored for whole breast IMRT,and whole breast IMRT assisted with breath-hold may improve the accuracy of dose delivery during radiotherapy. Key words: Radiotherapy,whole breast; Radiotherapy,intensity-modulated; Dosimetry

Evaluation of dosimetric variance in whole breast forward intensity modulated radiotherapy based on 4D CT and 3D CT.

e13530 Background: To explore and compare the dosimetric variance in forward intensity modulated radiotherapy (IMRT) based on 4D CT and 3D CT after breast conserving surgery. Methods: Seventeen patients after breast conserving surgery underwent the 3D CT simulation scans followed by respiration-synchronized 4D CT simulation scans on the state of free breathing. The treatment plan constructed using the end inspiration (EI) scan was then copied and applied to the end expiration (EE) and 3D scans and the dose distribution was calculated separately. Dose–volume histograms (DVHs) parameters for the CTV, PTV, ipsilateral lung (IPSL) and heart were evaluated and compared. Results: The CTV volume amplitude was 11.93 ± 28.64 cm3, and volume of the CTV receiving 95%, 100%, and 103% prescription dose among different scans were all differed by &lt; 0.4%. Mean PTV dose at EE was lower than EI (t = 2.87, p = 0.011), but there were no statistice significance between 3D CT scan and EI, EE scans (t = 1.06, -1.59; p = 0.304, 0.132). The homogeneity index (HI) at EI, EE, 3D plans were 0.156 ± 0.02, 0.162 ± 0.02, 0.161 ± 0.02, respectively, and difference only between EI and EE (t = -2.56, p = 0.021). The highest conformal index (CI) was at EI phase (t = 4.55, 2.70; p = 0.000, 0.016), and there was no significant difference between EE and 3D (t = 0.04, p = 0.967). The V20, V30, V40, V50 and Dmean of IPSL at EE phase were lower than EI (t = 2.39~5.54, p = 0.000~0.030). There were no significant differences in all the indexes for heart (t = -1.77~1.40, p = 0.128~0.693). Conclusions: The breast deformation during respiration may be disregarded in whole breast IMRT; PTV dose distribution was changed significantly between EI and EE phase, and the differentiation of the lung high dose area between EI and EE phase may induced by thorax expansion. 3D treatment planning is sufficient for whole breast forward IMRT, but 4D CT scans assist with respiratory gating ensure precise delivery of radiation dose.

Dosimetric research on intensity-modulated arc radiotherapy planning for left breast cancer after breast-preservation surgery

Intensity-modulated radiotherapy (IMRT) has played an important role in breast cancer radiotherapy after breast-preservation surgery. Our aim was to study the dosimetric and implementation features/feasibility between IMRT and intensity-modulated arc radiotherapy (Varian RapidArc, Varian, Palo Alto, CA). The forward IMRT plan (f-IMRT), the inverse IMRT, and the RapidArc plan (RA) were generated for 10 patients. Afterward, we compared the target dose distribution of the 3 plans, radiation dose on organs at risk, monitor units, and treatment time. All 3 plans met clinical requirements, with RA performing best in target conformity. In target homogeneity, there was no statistical significance between RA and IMRT, but both of homogeneity were less than f-IMRT's. With regard to the V5 and V10 of the left lung, those in RA were higher than in f-IMRT but were lower than in IMRT; for V20 and V30, the lowest was observed in RA; and in the V5 and V10 of the right lung, as well as the mean dose in normal-side breast and right lung, there was no statistically significance difference between RA and IMRT, and the lowest value was observed in f-IMRT. As for the maximum dose in the normal-side breast, the lowest value was observed in RA. Regarding monitor units (MUs), those in RA were higher than in f-IMRT but were lower than in IMRT. Treatment time of RA was 84.6% and 88.23% shorter than f-IMRT and IMRT, respectively, on average. Compared with f-IMRT and IMRT, RA performed better in target conformity and can reduce high-dose volume in the heart and left lung—which are related to complications—significantly shortening treatment time as well. Compared with IMRT, RA can also significantly reduce low-dose volume and MUs of the afflicted lung.

5037 POSTER A Dosimetric Comparison of Inverse Intensity-modulated Radiotherapy and Forward Intensity-modulated Radiotherapy for Breast Cancer After Radical Mastectomy

5037 POSTER A Dosimetric Comparison of Inverse Intensity-modulated Radiotherapy and Forward Intensity-modulated Radiotherapy for Breast Cancer After Radical Mastectomy

Forward planned intensity modulated radiotherapy (IMRT) for whole breast postoperative radiotherapy. Is it useful? When?

The purpose was to compare the dosimetric results observed in 201 breast cancer patients submitted to tangential forward intensity‐modulated radiation therapy (IMRT) with those observed in 131 patients treated with a standard wedged 3D technique for postoperative treatment of whole breast, according to breast size and supraclavicular node irradiation. Following dosimetric parameters were used for the comparison: Dmax,Dmin,Dmean,V95% and V107% for the irradiated volume; Dmax,Dmean,V80% and V95% for the ipsilateral lung; Dmax,Dmean,V80% and V95% for the heart. Stratification was made according to breast size and supraclavicular (SCV) nodal irradiation. As respect to irradiated volume, a significant reduction of V107% (mean values: 7.0±6.6 versus 2.4±3.7,p<0.001) and Dmax (mean % values:111.2±2.7 versus 107.7±6.3,p<0.001), and an increase of Dmin (mean % values: 65.0±17.4 versus 74.9±12.9,p<0.001) were observed with forward IMRT. The homogeneity of dose distribution to target volume significantly improved with forward IMRT in all patient groups, irrespective of breast size or supraclavicular nodal irradiation. When patients treated with supraclavicular nodal irradiation were excluded from the analysis, forward IMRT slightly reduced V80% (mean values: 3.7±2.6 versus 3.0±2.4,p=0.03) and V95% (mean values 1.9±1.8 versus 1.2%±1.5;p=0.001) of the ipsilateral lung. The dose to the heart tended to be lower with IMRT but this difference was not statistically significant. Tangential forward IMRT in postoperative treatment of whole breast improved dosimetric parameters in terms of homogeneity of dose distribution to the target in a large sample of patients, independent of breast size or supraclavicular nodal irradiation. Lung irradiation was slightly reduced in patients not undergoing to supraclavicular irradiation.PACS numbers: 87.53.Kn; 87.55.de