Dose Distribution In Target Volume Research Articles

Comparison of Percentage Depth Doses with the Published Data for Co-60 Radiotherapy Machine at a Regional Cancer Hospital

In external beam radiation therapy, the percentage depth dose (PDD) is a main factor for estimation of patient’s dose and dose distribution in target volume, therefore its accurate estimation is important. The purpose of this article is to compare PDDs with the published PDDs of different authors along central axis at different depths and field sizes for cobalt-60 (Co-60) radiotherapy machine at a regional cancer hospital Pakistan. A dedicated water phantom was used for estimation of PDDs at different depths and different field sizes, for Theratron phoenix Co-60 machine. It was observed that for 10×10 cm2 filed size of Co-60 beam mean percent variation in measured PDDs and published PDDs by different authors was -0.29% to 1.13%, which was within acceptable limit of ± 2%. However, for one author who used semi-empirical equation for PDDs calculation, the mean percent variation between measured PDDs and that of the author was -3.23%, 4.69% and 5.88% for 10×10 cm2, 25×25 cm2 and 30×30 cm2 field sizes of Co-60 beam respectively, which were within acceptable limit of ±10%. A noticeable increase in PDDs was observed with increase of the field size at given depth which shows obvious contribution of secondary scattered radiation. Also measured PDDs were well matched with that of published PDDs of most of the authors i.e. ± 2%, but the measured PDDs were moderately matched with that of PDDs for only one author for some field sizes and some depths i.e. ±10%, which need to be rectified by taking more such data.

Dosimetric comparison between stereotactic body radiotherapy and carbon-ion radiation therapy for prostate cancer.

Prostate cancer rates have been steadily increasing in recent years. As high-precision radiation therapy methods, stereotactic body radiation therapy (SBRT) and carbon-ion radiation therapy (CIRT) have unique advantages. Analyzing the dosimetric differences between SBRT and CIRT in the treatment of localized prostate cancer can help provide patients with more accurate, individualized treatment plans. We selected computed tomography positioning images and the contours of target volumes of 16 patients with localized prostate cancer who received radiotherapy. We delineated the organs at risk (OARs) on the CyberKnife (CK) treatment planning system (TPS) MultiPlan4.0, which were imported into the CIRT uniform scanning TPS HIMM-1 ci-Plan. Two treatment plans, SBRT and CIRT, were designed for the same patient, and we used SPSS 22.0 for the statistical analysis of data. Both SBRT and CIRT plans met the prescribed dose requirements. In terms of target volume exposure dose, D2 (P<0.001), D5 (P<0.001), D50 (P<0.001), D90 (P=0.029), D95 (P<0.001), D98 (P<0.001), and Dmean (P<0.001) under SBRT were significantly higher than those under CIRT; the conformity index (CI) under SBRT was significantly better than that under CIRT (P<0.001); the target volume coverage rate (V95%) and dose homogeneity index (HI) under CIRT were significantly better than those under SBRT (P<0.001). In terms of OAR exposure dosage, the Dmax of the bladder and rectum under SBRT was significantly lower than that under CIRT (P<0.001), but Dmean was in the other direction; the exposure dose of the intestinal tract under CIRT was significantly lower than that under SBRT (P<0.05); Dmax of the femoral head under CIRT was significantly lower than that under SBRT (P<0.05), and there was no statistical difference between them at other doses. In this study, we found that when CIRT was used for treating localized prostate cancer, the dose distribution in target volume was more homogeneous and the coverage rate was higher; the average dose of OARs was lower. SBRT had a better CI and higher dose in target volume; the dose hotspot was lower in OARs. It is important to comprehensively consider the dose relationship between local tumor and surrounding tissues when selecting treatment plans.

Impact of dose distribution on rotational setup errors in radiotherapy for prostate cancer.

This study aimed to assess the impact of rotational setup errors on the target volume's dose distribution during radiotherapy for prostate cancer. A 6D robotic couch was used to describe the rotational setup error, and the dosage change in the target volume was analyzed using the planning evaluation factors. Treatment plans for three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and volumetric modulated arc radiotherapy (VMAT) were established after contouring the target volume and surrounding normal tissues on tomography obtained from the humanoid phantom. A 6D robotic couch was employed in the radiation room to describe the rotational setup errors of ±1° to ±5° in roll, yaw, and pitch, and cone beam computed tomography (CBCT) images were obtained. Furthermore, the dose distribution was extracted from the 3DCRT, IMRT, and VMAT treatment plans, dose mapping was performed on CBCT that depicts the rotational setup error. Target coverage(TC) decreased by 0.39% to 2.17% in roll, 0.43% to 2.59% in yaw, and 0.70% to 4.12% in pitch, respectively. In the comparison using the Radiation Therapy Oncology Group (RTOG) protocol criteria, when the rotational setup error of VMAT pitch was -2° or more, more than +1°, a target coverage of 95% or lower was shown, indicating the greatest effect among rotational setup errors. Furthermore, in 3DCRT, IMRT, and VMAT, the rotational setup error showed the greatest effect in pitch, and the dose change was larger in VMAT than in 3DCRT and IMRT. Therefore, specific rotational error due to pitch during radiotherapy for prostate cancer requires special consideration. Moreover, the more sophisticated and complex algorithms, such as VMAT, applied, the greater the dose change of target coverage due to rotational error; therefore, caution is required.

Tomotherapy: Comparison of Hi-ART, Tomo-HD, and Radixact.

Aim In this study, we compared three generations of tomotherapy (Hi-ART, Tomo-HD, and Radixact). This is to study the difference among tomotherapy systems in terms of dose distribution to planning target volume and organs at risk, and irradiation time. Materialsand methods The treatment planning CT and contour information used were seven cases of rectum cancer pre-operative irradiation. The contour information used was the planning target volume, and the organs at risk were set as the bladder and body. Optimization was conducted at each planning station using the parameters that were actually used in a clinical setting.The prescribed radiation dose was 25 Gy in fivefractions and normalized at the isodose line, covering 95% of the planning target volume. Results There were no significant differences in planning target volume among the three models. Meanwhile,Hi-ART had a significantly higher dose than Tomo-HD and Radixact at body D50%.Radixact shortened the irradiation time by approximately 15% compared to Hi-ART/Tomo-HD. Conclusion Planning target volume dose distribution of tomotherapy devices was not different.Radixactrequired a significantly shorter time than Hi-ART and Tomo-HD.

Role of MRI-Based Functional Imaging in Improving the Therapeutic Index of Radiotherapy in Cancer Treatment.

Advances in radiation technology, such as intensity-modulated radiation therapy (IMRT), have largely enabled a biological dose escalation of the target volume (TV) and reduce the dose to adjacent tissues or organs at risk (OARs). However, the risk of radiation-induced injury increases as more radiation dose utilized during radiation therapy (RT), which predominantly limits further increases in TV dose distribution and reduces the local control rate. Thus, the accurate target delineation is crucial. Recently, technological improvements for precise target delineation have obtained more attention in the field of RT. The addition of functional imaging to RT can provide a more accurate anatomy of the tumor and normal tissues (such as location and size), along with biological information that aids to optimize the therapeutic index (TI) of RT. In this review, we discuss the application of some common MRI-based functional imaging techniques in clinical practice. In addition, we summarize the main challenges and prospects of these imaging technologies, expecting more inspiring developments and more productive research paths in the near future.

Evaluation of set-up errors and estimation of set-up margin during external beam radiation therapy of prostate cancer using electronic portal imaging device (EPID)

AbstractAim:In radiation therapy, accurate dose distribution in target volume requires accurate treatment setup. The set-up errors are unwanted and inherent in the treatment process. By achieving these errors, a set-up margin (SM) of clinical target volume (CTV) to planning target volume (PTV) can be determined. In the current study, systematic and random set-up errors that occurred during prostate cancer radiotherapy were measured by an electronic portal imaging device (EPID). The obtained values were used to propose the optimum CTV-to-PTV margin in prostate cancer radiotherapy.Materials and methods:A total of 21 patients with prostate cancer treated with external beam radiation therapy (EBRT) participated in this study. A total of 280 portal images were acquired during 12 months. Gross, population systematic (Σ) and random (σ) errors were obtained based on the portal images in Anterior–Posterior (AP), Medio-Lateral (ML) and Superior–Inferior (SI) directions. The SM of CTV to PTV were then calculated and compared by using the formulas presented by the International Commission on Radiation Units and Measurements (ICRU) 62, Stroom and Heijmen and Van Herk et al.Results:The findings showed that the population systematic errors during prostate cancer radiotherapy in AP, ML and SI directions were 1·40, 1·95 and 1·94 mm, respectively. The population random errors in AP, ML and SI directions were 2·09, 1·85 and 2·29 mm, respectively. The SM of CTV to PTV calculated in accordance with the formula of ICRU 62 in AP, ML and SI directions were 2·51, 2·68 and 3·00 mm, respectively. And according to Stroom and Heijmen, formula were 4·23, 5·19 and 5·48 mm, respectively. And Van Herk et al. formula were 4·96, 6·17 and 6·45 mm, respectively.Findings:The SM of CTV to PTV in all directions, based on the formulas of ICRU 62, Stroom and Heijmen and van Herk et al., were equal to 2·73, 4·98 and 5·86 mm, respectively; these values were obtained by averaging the margins in all directions.

Estimation of radiation-induced second cancer risk associated with the institutional field matching craniospinal irradiation technique: A comparative treatment planning study

To estimate and compare the lifetime attributable risk (LAR) of radiation-induced second cancer (SC) in pediatric medulloblastoma patients planned with institutional 3D conformal field matching method, gap junction method and Intensity Modulated Radiotherapy (IMRT). The epidemiological studies on childhood cancer survivors reported that long-term cancer survivors who received radiotherapy are at a significantly increased risk for the development of SC. Hence, the increased concern to predict the SC risk for long-term survivors. In addition to institutional field matching planning method, IMRT and gap junction methods were created for ten pediatric medulloblastoma patients. The risk estimates were made based on the site-specific cancer risk coefficient provided by the BEIR VII committee according to the organ equivalent dose for various critical organs. Also, plans were compared for target volume dose distribution and dose received by critical organs. When compared to the gap junction method, the IMRT and institutional field matching method were superior in normal tissue sparing and dose conformity. However, highly significant volume of low dose associated with IMRT was the main concern for the SC risk. The accumulated LAR for all the critical organs with 3D conformal gap junction and IMRT method was 23-25% while for the 3D conformal field matching method it was 21%. The LAR associated with the institutional field matching technique was substantially lower. As this method is highly robust and easy to set up, it can be a better choice of a craniospinal irradiation technique where 3DCRT is the only choice of treatment.

Dosimetric Comparison of Sequential Versus Simultaneous-integrated Boost in Early-stage Breast Cancer Patients Treated With Breast-conserving Surgery.

To compare simultaneous-integrated boost (SIB) versus sequential-boost (SB) delivered in the context of whole-breast irradiation (WBI) via volumetric-modulated arc therapy (VMAT) and helical-tomotherapy (HT). Planning target-volume (PTV) dosimetric parameters and organs at risk (OAR) were analyzed for SB plan (50 Gy plus 16 Gy boost) and SIB plan (50.4 Gy WBI and 64.4 Gy tumor bed boost) in VMAT and HT techniques. Conformity and homogeneity for target-volume doses were better in HT plans compared to VMAT plans. There were no significant differences in ipsilateral lung doses between VMAT and HT plans for SB/SIB techniques, except for a significantly higher lung V5 value with VMAT-SB, and lung V13 value with HT-SIB technique. HT provided a statistically significant decrease in contralateral lung mean V5. The SIB technique showed better target-volume dose distribution in both HT and VMAT plans, and better sparing heart in HT compared to the SB technique.

Expert consensus on computed tomography-assisted three-dimensional-printed coplanar template guidance for interstitial permanent radioactive 125I seed implantation therapy.

Interstitial permanent radioactive seed implantation delivers a high local dose to tumors and sharply drops off at surrounding normal tissues. Radioactive seeds implanted via ultrasound or computed tomography (CT) guidance are minimally invasive and facilitate quick recovery. Transrectal ultrasound-guided 125I seed implantation assisted by a transperineal plane template is standard for early-stage prostate carcinoma, with a highly consistent target volume dose distribution. The postplan dose evaluation is consistent with the preplan evaluation. Until now, there was no workflow for seed implantation elsewhere in the body, and it was difficult to effectively preplan for seed implantation because of patients' position changes, organ movement, and bone structure interference. Along with three-dimensional (3D) printing techniques and seed implantation planning systems for brachytherapy, coplanar and X Y axis coordinate templates were created, referred to as 3D-printed coplanar templates (3D-PCT). 125I seed implantation under CT guidance with 3D-PCT assistance has been very successful in some carcinomas. Preplanning was very consistent with postplanning of the gross tumor volume. All needles are kept parallel for 3D-PCT, with no coplanar needle rearrangement. No standard workflow for 3D-PCT-assisted seed implantation exists at present. The consensus topics for CT-assisted guidance compared to 3D-PCT-assisted guidance for seed implantation are as follows: Indications for seed implantation, preplanning, definition of radiation doses and dosimetry evaluation, 3D-PCT workflow, radiation protection, and quality of staff. Despite current data supporting 125I seed implantation for some solid carcinomas, there is a need for prospectively-randomized multicenter clinical trials to gather strong evidence for using 125I seed implantation in other solid carcinomas.

A Hybrid Electron and Photon IMRT Planning Technique in Vulvar Cancer

IMRT is increasingly used instead of 3DCRT in vulvar cancer. Critical structures around the target volumes can be spared with IMRT technique, but normal tissue integral dose (NTID) may increase due to increased number of beams. In this study we aimed to produce homogeneous dose distribution in target volumes while decreasing the NTID and critical organ doses in the vicinity. The 3DCRT, IMRT, and hybrid electron-IMRT treatment plans of seven patients with the diagnosis of vulvar cancer were performed using the Eclipse 8.9 TPS. The dose DVHs of techniques were compared for target volume and critical structures. Also, NTID was calculated for each treatment plan. The prescribed dose was 5040 cGy in 28 fractions. When hybrid plan was performed 70% of dose was given with electron beams and 30% with IMRT. Female Alderson rando phantom, TLD, and Gafchromic EBT3 film calculations were used for dosimetric analyses. Treatment plan comparisons were made by using D95%, Dmax, Dmean, and D5% of PTV (Table 1). Both IMRT plans were resulted in a significantly higher D95% compared to 3DCRT technique; however, there was no difference between IMRT and hybrid electron-IMRT techniques. Dmean and D5% were significantly improved with hybrid electron-IMRT techniques compared to sole IMRT techniques. For the 3DCRT, IMRT, and hybrid electron-IMRT techniques, the volume received ≥40 Gy (V40) for bladder were 95%, 39.4%, and 34.4%; V40 for rectum were 54.8%, 32.8%, and 28.4%; V35 for bowel were 42.2%, 41.8%, and 36%; V50 for femoral head were 3%, 3.1%, and 2.5%, respectively. NTID was compared based on the body-PTV Dmean and were calculated as 1221 cGy, 1404 cGy, and 1288 cGy for 3DCRT, IMRT and hybrid electron-IMRT technique, respectively (p = 0.018). The percent difference between TPS and TLD calculations were between 0.9%-13%. For EBT3 film measurements, this ratio is between 0.2%-4.2%. Hybrid electron-IMRT technique produced the lowest doses in the critical organs. Additionally, NTID values were significantly lower with hybrid electron-IMRT technique than the IMRT technique. All these values were confirmed dosimetrically. We think that hybrid electron-IMRT technique should be the preferred technique for patients with vulvar cancer.Abstract 3588; Table 1D95%, Dmax, Dmean, D5% and p values of PTV for 3DCRT, IMRT, and hybrid electron-IMRT techniquesTechniqueD95%DmaxDmeanD5%3DCRT4713.15459.45066.85295IMRT4936.55496.75094.55212.4p value0.0280.2370.3980.0283DCRT4713.15459.45066.85295Hybrid electron-IMRT4914.755935145.55329.5p value0.0180.0180.0910.398IMRT4936.55496.75094.55212.4Hybrid electron-IMRT4914.755935145.55329.5p value0.6120.0910.0280.018 Open table in a new tab

Dosimetric effects of target volume delineation with metal clip and seroma, alone or in combination, on external-beam partial breast irradiation: a study based on four-dimensional computed tomography

Objective To evaluate the dosimetric effects of target volume delineation with metal clip and seroma, alone or in combination, on external-beam partial breast irradiation (EB-PBI) based on four-dimensional computed tomography (4DCT). Methods Twenty female patients undergoing EB-PBI from 2009 to 2013 were enrolled as subjects. The gross tumor volumes (GTVS), GTVC, GTVS, and GTVC+ S, were delineated on 4DCT images at 10 phases using metal clip, seroma, and both of them, respectively. The GTVS on 4DCT images at 10 phases were fused to generate the internal gross tumor volumes (IGTVS), IGTVC, IGTVS, and IGTVC+ S. The planning target volumes (PTVS), PTVC, PTVS, and PTVC+ S, were obtained via expansion of margin by 15 mm. The three-dimensional conformal radiotherapy plans were made by one physician based on PTVC, PTVS, and PTVC+ S on end-inhalation images. The target volume, homogeneity index (HI), conformity index (CI), and doses to organs at risk were compared between the three groups. Results The C+ S group had the largest IGTV, PTV, and the ratio of PTV to diseased breast volume, which was followed by the C group and the S group (all P 0.05). Conclusions The volume variation caused by target volume delineation on 4DCT images based on different references has little impact on dose distribution in target volume. However, it has substantial impact on radiation doses to the ipsilateral normal breast and lung. Key words: External-beam partial breast irradiation; Tmography, X-ray computed, four-dimensional; Surgical clips; Seroma; Target determination

Effect of amplitude of respiratory movements on dose distribution of static intensity-modulated radiotherapy

Objective To study the effect of amplitude of respiratory movements on dose distribution of static intensity-modulated radiotherapy (IMRT), and to provide a basis for dose correction against respiratory movements. Methods A two-dimensional matrix driven by the QUASAR program-controlled respiratory movement instrument was used to simulate human respiratory movements in the head/foot direction. The dose distribution was evaluated on the isocenter plane with different amplitudes of respiratory movements. The Verisoft software and absolute dose analysis were used to analyze dose distribution, percentage errors of absolute dose, and passing rates of radiation field for both collected data and planned dose distribution. Results In spite of little effect on dose distribution in target volume, respiratory movements increased the dose outside the marginal target volume along the movement direction. When the respiratory amplitude was lower than 6 mm, the passing rate of γ distribution met the requirement of clinical dose verification; when the respiratory amplitude was larger than 8 mm, the passing rate of γ distribution was reduced with the increasing respiratory amplitude and fell below the clinical standard. Conclusions Respiratory movements have a blurring effect on static IMRT. It is possible to introduce some compensation methods to static IMRT in the treatment of tumor with periodic respiratory movements. The normal tissue at the edge of target volume along the respiratory movement direction is exposed to a higher radiation dose than expected. Therefore, the radiation dose for the normal tissue around target volume should be made as low as possible in the radiotherapy plan. For the patients with relatively large respiratory amplitude, action should be taken to lower respiratory amplitude and elevate the radiation dose in target volume. Key words: respiratory movement amplitude; static intensity modulated radiotherapy; dose distribution; QUASAR program-controlled respiratory movement instrument

Challenges and differences in external radiation therapy for retinoblastoma: from standard techniques to new developments.

The purpose of this study is to calculate the treatment plans and to compare the dose distributions and dose-volume histograms (DVH) for 6 external radiotherapy techniques for the treatment of retinoblastoma as well as intensity-modulated radiotherapy (IMRT) and fractionated stereotactic radiotherapy (Cyberknife). Treatment plans were developed using 6 techniques, including an en face electron technique (ET), an anterior and lateral wedge photon technique (LFT), a 3D conformal (6 fields) technique (CRT), an inverse plan IMRT, tomotherapy, and conventional focal stereotactic external beam radiotherapy with Cyberknife (SBRT). Dose volume analyses were carried out for each technique. All techniques except electron provided similar target coverage. When comparing conformal plan with IMRT and SBRT, there was no significant difference in planning target volume dose distribution. The mean volume of ipsilateral bony orbit received more than 20 Gy, a suggested threshold for bone growth inhibition. The V20 Gy was 73% for the ET, 57% for the LFT, 87% for the CRT, 65% for the IMRT, 66% for the tomotherapy, and 2.7% for the SBRT. This work supports the potential use of IMRT and SBRT to spare normal tissues in these patients.

Effects of Setup Errors on Dose Distribution for Tangential Wedge Field and Field-in-Field Techniques During Breast Irradiation

This study is aimed to evaluate the effects of setup errors on dose distribution for target volume and healthy tissue within the irradiated volume and also critical surrounding organs for breast radiotherapy (RT) using both the tangential field and the field-in-field (FIF) technique. Ten patients with breast cancer were enrolled. For each patients two plans were generated; tangential field plan and FIF-plan. The setup errors were simulated for a series of displacements of ±5 mm and ±10 mm in superior-inferior (x-axis), medial-lateral (y-axis), and anteriorposterior (z-axis) directions and dose volume comparisons were made both between and within groups. The most prominent changes were observed in setup errors at z-axis. In wedge plan, 10-mm setup error at the +z axis caused a significant decrease in tumor coverage compared with the plan with no setup error (96.5% vs. 99.2%; p= 0.01). The 5 and 10 mm setup errors at the +z-axis resulted in significantly higher healthy tissue doses in wedge plans compared with FIF plans. The setup errors along z-axis had a significant effect on the dose distribution for target volume and also to the lungs. The setup error in the isocenter should be kept strictly below 5 mm.

SU‐E‐T‐432: Dosimetric Computation of Cyberknife SBRT Plans for Treatment of Kidney and Adrenal Gland

Purpose: It is well‐accepted that Monte Carlo algorithm (MCA) methods are superior to Ray‐Tracing algorithm (RTA), i.e., effective path length (EPL), methods for computing radiation dose, especially for structures with heterogeneous tissue compositions. In this study, the differences of dose distribution in target volumes (kidneys and adrenal glands) and adjacent organs at risk (OARs) were evaluated while the treatment plans were computed using MCA and RTA for Cyberknife™ stereotactic body radiotherapy (SBRT). Methods: A total of 14 renal tumor (10 kidney and 4 adrenal gland) patients who had prescriptions in the range of 24Gy–48Gy (mean=42Gy) were selected. Treatment plans were computed using RTA and MCA in Cyberknife MultiPlan™ (version‐3.5.2). First, dose was calculated using RTA and then was recomputed using MCA, keeping total MU the same. Liver, heart, stomach, spleen, bowel, and contralateral kidney were considered as OARs. Dosimetric parameters considered for the target and OARs were minimum dose, mean dose, and maximum point dose. Additionally, dose delivered to 95% and 5% of the target volumes were evaluated. Dose computed with two algorithms were compared and statistically analyzed using two‐tailed t‐tests. Results: This study revealed that differences (average) in mean dose (0.79Gy), maximum dose (2.02Gy), 95% (0.76Gy) and 5% (0.83Gy) of target coverage dose were not statistically significant (p‐value&gt;0.05). Differences in minimum dose (average=0.04–3.75Gy) to OARs exhibited significance (p‐value&lt; 0.05), though differences in minimum dose to target volumes (average=1.14Gy) showed no significant difference (p‐value&gt;0.05). Conclusion: Although Monte‐Carlo is more accurate compared to Ray‐Tracing for dosimetric computation, especially tumors in heterogeneous tissue composition, dose computation and delivery using MCA are quite involved due to additional computational time and associated patient‐specific quality assurance. This study indicated that both RTA and MCA are almost equally effective as dosimetric computation methods for renal tumors, and RTA can be used without compromising dosimetric accuracy.

PD-0278: Effect of lateral scatter on dose distribution for target volume near skin in Ir-192 HDR Brachytherapy

PD-0278: Effect of lateral scatter on dose distribution for target volume near skin in Ir-192 HDR Brachytherapy

SU‐E‐T‐822: Dosimetric Comparison of Intensity Modulated Radiotherapy Modes for Breast Cancer after Radical Mastectomy: Forward IMRT vs. IMRT

Purpose: To evaluate the dose distribution of target volume and normal tissues in forward intensity modulated radiotherapy (f‐IMRT) and inverse intensity modulated radiotherapy (IMRT) plans for breast cancer after radical mastectomy. Methods: Ten patients with breast cancer who received radical mastectomy were enrolled in this study. On each patientˈs CT images the supraclavicular, chest wall and internal mammary areas were delineated. F‐IMRT and IMRT plans were performed for each patient. The prescription dose was 50 Gy in 25 fractions. F‐IMRT plans for the supraclavicular and the chest wall area using 6 MV X‐ray irradiation; internal mammary area with 9‐12 MeV electron irradiation, according to the three regions of dose adjust the doses of cold and hot fit. The supraclavicular, chest wall and internal mammary area were considered as a whole target in the IMRT plans, using 6 MV X‐ray. The dose‐volume parameters of target volume and normal tissues, CI and HI of f‐IMRT and IMRT plans were analyzed, using paired t‐test. Results: The target volume coverage of f‐IMRT plans were similar to that of the IMRT plans (93% and 94.5%). The mean CI and mean HI were 0.67±0.02/1.18±0.02 in f‐IMRT and 0.75±0.03/1.14±0.01 in IMRT (P&lt;0.05). The differences of V10, V20, V25, V30 and Dmean of ipsilateral lung were not statistically significant. However, the V15 of ipsilateral lung in IMRT was 4.5% less than that in f‐IMRT, which was statistically significant (P&lt;0.05). There was no significant difference in Dmean and V30 of heart, Dmean of contralateral lung and contralateral breast between two modes. Conclusions: Compared with f‐IMRT, IMRT plans resulted in better conformal dose distribution and homogeneity, with comparable target volume coverage and sparing of lung, heart and contralateral breast.

SU‐E‐T‐685: Selection of the Optimized Source for Brachytherapy Treatment of Tongue Cancer Using Dose Distribution Simulation by MCNP4C

Purpose: Among different kinds of oral cavity cancers, the frequency of tongue cancer occurrence is more significant. Brachytherapy is the most common method to cure tongue cancers. The objective of this study is to asses the dose distribution around long sources which use in tongue brachytherapy, comparing different radioisotopes as brachytherapy sources, measuring the homogeneity of delivered dose to treatment volume and also comparing mandible dose and dose of tongue in the regions near the mandible with and without using shield. Methods: The Monte Carlo code MCNP4C was used for simulation. Tongue, mandible, sources like Ir‐192, Cs‐137, Ra‐226, Au‐198, In‐111, Ba‐131, guide gutters and lead shield were simulated. The accuracy of simulation was verified by comparing the results with experimental data. The position of sources was determined by Paris system. Dose distribution around sources assessed by surfer software and compared with each other. Results: The percentages of mandible dose reduction with use of 2 mm Pb shield for Ir‐192, Cs‐137, Ra‐226, Au‐198, In‐111, Ba‐131 were: 35.4%, 20.1%, 86.6%, 32.24%, 75.6%, and 36.8%. The tongue dose near the mandible with use of shield did not change significantly. The dose homogeneity from the most to least was obtained from these sources: Cs‐137, Au‐198, Ir‐192, Ba‐131, In‐111 and Ra‐226. Conclusions: According to results of this study Ir‐192 and Cs‐137 were the best sources for tongue brachytherapy because of homogenous dose distribution in target volume and less time they required for delivering prescribed dose. Au‐198 and Ba‐131 had the same performance by Ir‐192 but they required more time to deliver the prescribed dose. Ra‐226 and In‐111 had the most reduction of mandible dose but they required much more time to deliver prescribed dose and they had more dose inhomogeneity in target volume so that they were not suitable sources for tongue brachy therapy.

Comparison between intensity modulated radiotherapy (IMRT) and 3D tangential beams technique used in patients with early-stage breast cancer who received breast-conserving therapy

Background The most often found complications in patients with breast cancer who received radiotherapy are cardiac and pulmonary function disorders and development of second malignancies. Aim To compare the intensity modulated radiotherapy with the 3D tangential beams technique in respect of dose distribution in target volume and critical organs they generate in patients with early-stage breast cancer who received breast-conserving therapy. Materials and methods A dosimetric analysis was performed to assess the three radiotherapy techniques used in each of 10 consecutive patients with early-stage breast cancer treated with breast-conserving therapy. Radiotherapy was planned with the use of all the three techniques: 3D tangential beams with electron boost, IMRT with electron boost, and intensity modulated radiotherapy with simultaneous integrated boost. Results The use of the IMRT techniques enables more homogenous dose distribution in target volume. The range of mean and median dose to the heart and lung was lower with the IMRT techniques in comparison to the 3D tangential beams technique. The range of mean dose to the heart amounted to 0.3–3.5 Gy for the IMRT techniques and 0.4–4.3 for the tangential beams technique. The median dose to the lung on the irradiated side amounted to 4.9–5 Gy for the IMRT techniques and 5.6 Gy for the 3D tangential beams technique. Conclusion The application of the IMRT techniques in radiotherapy patients with early-stage breast cancer allows to obtain more homogenous dose distribution in target volume, while permitting to reduce the dose to critical organs.

Does Patient Positioning Affect Radiotherapy Dose Distribution in Target Volumes and Organs at Risk: Assessment in Parotid Tumor

Does Patient Positioning Affect Radiotherapy Dose Distribution in Target Volumes and Organs at Risk: Assessment in Parotid Tumor