Conventional Tangential Fields Research Articles

Decreasing Skin Toxicity in Whole Breast Irradiation with Helical Tomotherapy IMRT

To decrease skin toxicity resulting from whole breast irradiation with Helical Tomotherapy IMRT. Patients treated with the Helical Tomotherapy IMRT planning yielded an average mean skin dose and maximum skin dose of about 85% and 102% of the prescribed dose respectively resulting in brisk erythema. Target volumes and dose parameters were in accordance to the NSABP B51 protocol guidelines using a breast PTV cropped 5mm from the skin surface. A unique treatment planning technique was designed to decrease the skin toxicity while delivering the desired dose to the breast PTV. We started by determining a tolerable skin dose while not compromising breast PTV coverage. This was determined by evaluating the skin dose of patients treated via conventional tangent fields using similar dose prescription. The conventional tangent fields yielded an average mean skin dose and maximum skin dose of about 70% and 100% of the prescribed dose respectively. These patients had G1 skin toxicity. The next step was to design a helical tomotherapy IMRT treatment planning technique that would deliver a comparable tolerable mean skin dose to the conventional tangent fields. This technique was implemented by utilizing a 3mm skin rind limiting the dose to a maximum point ≤ 95% and a mean of 70%-75% of the prescribed dose. Treatment plans were generated using the 3mm skin rind as an OAR and a Breast PTV at 6mm, 7mm and 8mm from the skin surface to mimic the coverage seen in the conventional tangential fields. The findings for the 3 groups were as followed: 6mm: The Breast PTV coverage was good with above 90% and 97.7% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 1.5% or 17.32cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 69.4% and a maximum dose of 90.1%. 7mm: The Breast PTV coverage was at 88.4% and 96.2% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 1.6% or 19.88cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 67.5% and a maximum dose of 86.6%. 8mm: The Breast PTV coverage was good with above 79.9% and 90% of the volume receiving 100% and 95% of the prescribed dose respectively. Only 2.2% or 26.16cc of the volume received 105% of the prescribed dose. The skin rind received a mean dose of 64.3% and a maximum dose of 79.6%. 5/7patients treated prior to this technique experienced G2 toxicity while none of the 13 patients treated with technique developed greater than G1 toxicity. With a Breast PTV cropped 6mm from skin surface a mean dose of 75% and a maximum dose of 95% was achieved in these 13 patients CONCLUSION: Adding the skin rind as an OAR allowed a reduction in skin dose without compromising coverage of the breast PTV with a breast PTV cropped 6mm from the skin surface.

Low doses to the heart in daily practice for treating left-sided breast cancer using accelerated partial-breast irradiation by multicatheter brachytherapy and deep-inspiration breath-hold using a SIB

PurposeThe aim of this study was to analyze the heart dose for left-sided breast cancer that can be achieved during daily practice in patients treated with multicatheter brachytherapy (MCBT) accelerated partial-breast irradiation (APBI) and deep-inspiration breath-hold (DIBH) whole-breast irradiation (WBI) using a simultaneous integrated tumor bed boost (SIB)—two different concepts which nonetheless share some patient overlap.Materials and methodsWe analyzed the nominal average dose (Dmean) to the heart as well as the biologically effective dose (BED) and the equivalent dose in 2‑Gy fractions (EQD2) for an α/β of 3 in 30 MCBT-APBI patients and 22 patients treated with DIBH plus SIB. For further dosimetric comparison, we contoured the breast planning target volume (PTV) in each of the brachytherapy planning CTs according to the ESTRO guidelines and computed tangential field plans. Mean dose (Dmean), EQD2 Dmean, and BED Dmean for three dosing schemes were calculated: 50 Gy/25 fractions and two hypofractionated regimens, i.e., 40.05 Gy/15 fractions and 26 Gy/5 fractions. Furthermore, we calculated tangential field plans without a boost for the 22 cases treated with SIB with the standard dosing scheme of 40.05 Gy/15 fractions.ResultsMCBT and DIBH radiation therapy both show low-dose exposure of the heart. As expected, hypofractionation leads to sparing of the heart dose. Although MCBT plans were not optimized regarding dose to the heart, Dmean differed significantly between MCBT and DIBH (1.28 Gy vs. 1.91 Gy, p < 0.001) in favor of MCBT, even if the Dmean in each group was very low. In MCBT radiation, the PTV–heart distance is significantly associated with the dose to the heart (p < 0.001), but it is not in DIBH radiotherapy using SIB.ConclusionIn daily practice, both DIBH radiation therapy as well as MCBT show a very low heart exposure and may thus reduce long term cardiac morbidity as compared to currently available long-term clinical data of patients treated with conventional tangential field plans in free breathing. Our analysis confirms particularly good cardiac sparing with MCBT-APBI, so that this technique should be offered to patients with left-sided breast cancer if the tumor-associated eligibility criteria are fulfilled.

Replacing Manual Planning of Whole Breast Irradiation With Knowledge-Based Automatic Optimization by Virtual Tangential-Fields Arc Therapy.

PurposeTo implement Knowledge Based (KB) automatic planning for right and left-sided whole breast treatment through a new volumetric technique (ViTAT, Virtual Tangential-fields Arc Therapy) mimicking conventional tangential fields (TF) irradiation.Materials and MethodA total of 193 clinical plans delivering TF with wedged or field-in-field beams were selected to train two KB-models for right(R) and left(L) sided breast cancer patients using the RapidPlan (RP) tool implemented in the Varian Eclipse system. Then, a template for ViTAT optimization, incorporating individual KB-optimized constraints, was interactively fine-tuned. ViTAT plans consisted of four arcs (6 MV) with start/stop angles consistent with the TF geometry variability within our population; the delivery was completely blocked along the arcs, apart from the first and last 20° of rotation for each arc. Optimized fine-tuned KB templates for automatic plan optimization were generated. Validation tests were performed on 60 new patients equally divided in R and L breast treatment: KB automatic ViTAT-plans (KB-ViTAT) were compared against the original TF plans in terms of OARs/PTVs dose-volume parameters. Wilcoxon-tests were used to assess the statistically significant differences.ResultsKB models were successfully generated for both L and R sides. Overall, 1(3%) and 7(23%) out of 30 automatic KB-ViTAT plans were unacceptable compared to TF for R and L side, respectively. After the manual refinement of the start/stop angles, KB-ViTAT plans well fitted TF-performances for these patients as well. PTV coverage was comparable, while PTV D1% was improved with KB-ViTAT by R:0.4/L:0.2 Gy (p < 0.05); ipsilateral OARs Dmean were similar with a slight (i.e., few % volume) improvement/worsening in the 15–35 Gy/2–15 Gy range, respectively. KB-ViTAT better spared contralateral OARs: Dmean of contralateral OARs was 0.1 Gy lower (p < 0.05); integral dose was R:5%/L:8% lower (p < 0.05) than TF. The overall time for the automatic plan optimization and final dose calculation was 12 ± 2 minutes.ConclusionsFully automatic KB-optimization of ViTAT can efficiently replace manually optimized TF planning for whole breast irradiation. This approach was clinically implemented in our institute and may be suggested as a large-scale strategy for efficiently replacing manual planning with large sparing of time, elimination of inter-planner variability and of, seldomly occurring, sub-optimal manual plans.

Contralateral breast dose with electronic compensators and conventional tangential fields – A clinical dosimetric study

Dose to the contralateral breast (CLB) from radiotherapy treatment has the potential to induce secondary breast cancer. Electronic tissue compensation (eComp) for breast cancer patients is one of the alternative methods to conventional 3D-conformal radiotherapy that eliminates the use of wedges. Several studies have investigated dose to the CLB using tangential fields involving wedges, intensity-modulated radiation therapy and volumetric modulated arc radiation therapy and various other techniques via treatment planning system calculations, Monte Carlo methods and phantoms. However, there are limited data published in assessing the actual dose received by the CLB from treatment with eComp-based tangential fields.In this study, the CLB dose for patients undergoing tangential field radiotherapy with eComp and enhanced dynamic wedged (standard) tangential fields was measured and compared to assess the CLB dose between the two methods. Measurements were conducted on a randomised trial of 40 patients, 20 of them had undergone standard planning, and the remaining 20 were treated with eComp. The mean surface dose measured with TLDs at 3cm from the medial tangential border for eComp and standard techniques was 10.04±1.37% and 10.14±2.05%, respectively for a prescription dose of 2.65Gy/fraction. The estimated dose at 1cm depth in tissue, measured with the use of perspex domes placed over the TLD at the same location, was 5.12±0.87% and 6.29±2.01% for eComp and standard, respectively.The CLB dose is dependent on the proximity of the medial tangential field edge to the contralateral breast and is patient-specific. The results of this study show that at 1cm depth, eComp technique delivers significantly less dose (p<0.05) to the CLB as compared to standard tangential fields. Furthermore, the surface dose measured for both eComp and standard are comparable indicating that the eComp-based tangential field technique does not contribute any excess dose to CLB when compared to standard tangential fields. The excess relative risk (ERR) for radiation-induced cancers for eComp was found to be 0.08, compared to 0.11 for standard tangential fields.

Hybrid volumetric-modulated arc therapy for postoperative breast cancer including regional lymph nodes: the advantage of dosimetric data and safety of toxicities.

ABSTRACTTo improve the homogeneity and conformity of the irradiation dose for postoperative breast cancer including regional lymph nodes, we planned Hybrid volumetric-modulated arc therapy (VMAT), which combines conventional tangential field mainly for the chest area and VMAT mainly for the supraclavicular area and marginal zone. In this study, we compared the dosimetric impact between traditional 3D conformal radiotherapy (3DCRT) and Hybrid VMAT and observed toxicities following Hybrid VMAT. A total of 70 patients indicated between October 2016 and December 2017 were included. The prescribed dose was 50 Gy/25 fractions. For the dosimetric impact, 3DCRT and Hybrid VMAT plans were compared in each patient with respect to the dosimetric parameters. Toxicities were followed using the Common Terminology Criteria for Adverse Events version 4.0. The median follow-up duration was 319 days. For the dosimetric impact, the homogeneity index (HI) and conformity index (CI) of PTV were significantly improved in the Hybrid VMAT plan compared with that in the 3DCRT plan (HI, 0.15 ± 0.07 in Hybrid VMAT vs 0.41 ± 0.19 in 3DCRT, P < 0.001; CI, 1.61 ± 0.44 in Hybrid VMAT vs 2.10 ± 0.56 in 3DCRT, P < 0.001). The mean irradiated ipsilateral lung dose was not significantly different in both plans (12.0 ± 2.4 Gy in Hybrid VMAT vs 11.8 ± 2.8 Gy in 3DCRT, P < 0.533). Regarding toxicity, there were no patients who developed ≥grade 3 acute toxicity and ≥grade 2 pneumonitis during the follow-up. Hybrid VMAT for postoperative breast cancer including regional lymph nodes was a reasonable technique that improved the homogeneity and conformity of the irradiation dose to the planning target volume while keeping the irradiation dose to organs at risk to a minimum.

Patient setup variations in computed tomography-based treatment planning for left-sided breast cancer using electronic portal images

Background and Aim: This study deals with isocentric variations along with the setup reproducibility and determines the random and systematic errors in a cohort of 25 (females) left-sided breast cancer patients treated with megavoltage X-rays using an online electronic portal imaging (EPI) protocol. Materials and Methods: This is a hospital-based cross-sectional observational study which was carried out on 25 female patients of carcinoma breast (left sided) who had undergone modified radical mastectomy. After completion of the planned chemotherapy, all patients underwent virtual three-dimensional (3D) computed tomography (CT) simulation, and an external beam radiotherapy treatment was planned on these 3D CT images on a treatment planning system (TPS) using two (coplanar)/conventional tangential fields for a total dose of 50 Gy in 25 fractions. Analysis of 150 EPIs determined changes in the treatment fields during setup of these 25 patients. The online assessment included setup deviations in all the three directions (anteroposterior [AP], superoinferior [SI], and mediolateral [ML]) and variations in central lung distance (CLD) during the first three fractions. Results: Random errors ranged from 1 to 5 mm for the chest wall (medial and lateral) tangential treatments and 1 mm for the anterior supraclavicular nodal field. Systematic errors ranged from 2.5 to 4.5 mm in the AP direction for the tangential fields and from 2.5 to 7.5 mm in the SI and Mediolateral directions for the anterior supraclavicular nodal field. For 25 (left-sided) patients, the CLD (TPS) was 20–30 mm, CLD (EPIs) was 25–40 mm showing variations of 5–10 mm, V20 was 1.0–6.0 Gy, maximum total lung dose was 43 Gy, V30 was 2.0–4.0 Gy, maximum heart dose was 52 Gy, and maximum spine dose was 45 Gy. Conclusions: Online assessment of patient position with matching of EPIs with digitally reconstructed radiographs is a useful method in evaluation of interfraction reproducibility of tangential fields in breast irradiation, thereby improving upon the quality of treatment delivery for our patient population.

94P Influence of different treatment planning techniques on radiation doses to the heart, left anterior descending coronary artery and lungs in the radiotherapy of left-sided breast cancer patients

Background Breast-conservingsurgery(BCS)followedbyradiotherapy(RT)tothe breastisnowanacceptablestandardofcareforthemajorityofwomenwithearly-stage breast cancer. But evidence has long been accumulating that RT doses to the heart can result in premature ischemic heart disease. In this study 3 different RT techniques were compared for heart, left anterior descending coronary artery (LAD) and lung doses in left breast cancer patients after breast-conserving surgery. Methods Three different plans were designed for each patient using conventional tangential fields, 6 + 18 MV combination beams, and filed-in-field (FIF) technique. These were compared in terms of doses to the planning target volume (PTV), ipsilateral lung, heart and LAD. Results Forty left breast cancer patients were included in this study. Mean PTV V95% was 95.74% for conventional, 90.45% for FIF and 87.89% for6 + 18 MV (p < 0.05). Meanleftlungdosewas 11.22 Gyfor FIF, 12.25 Gyfor6 + 18MV and 12.95Gyfor conventional (p < 0.05). Mean heart dose was 4.52 Gy for FIF, 4.85 Gy for 6 + 18MV and5.13Gyforconventional(p<0.05).MeanheartV5Gywas11.80%,12.02%and 13.23%(p<0.05),meanheartV25Gywas6.1%,6.35%and6.65%(p<0.05),andmean D2% for LAD was 40.06, 43.43 and 45.25 Gy (p < 0.01) in FIF, 6 + 18 MV and conventional techniques, respectively. Conclusions The results of our study indicated that the FIF and 6 + 18 MV combination techniques significantly reduced the doses received by the heart, LAD and left lung compared to conventional tangential fields, while FIF was superior in general to6 + 18 MV consideringthe above variables. Thelowerdosestothe organs at riskwere achieved in these plans with a small but statistically significant loss in PTV coverage. Clinical trial indentification 94-02-207-29322 Tehran University of Medical Sciences Legal entity responsible for the study Radiation Oncology Research Center, Tehran University of Medical Sciences Funding Tehran University of Medical Sciences Disclosure All authors have declared no conflicts of interest.

Postoperative radiotherapy following mastectomy for patients with left-sided breast cancer: A comparative dosimetric study

The purposes of this article were to compare the biophysical dosimetry for postmastectomy left-sided breast cancer using 4 different radiotherapy (RT) techniques. In total, 30 patients with left-sided breast cancer were randomly selected for this treatment planning study. They were planned using 4 RT techniques, including the following: (1) 3-dimensional conventional tangential fields (TFs), (2) tangential intensity-modulated therapy (T-IMRT), (3) 4 fields IMRT (4F-IMRT), and (4) single arc volumetric-modulated arc therapy (S-VMAT). The planning target volume (PTV) dose was prescribed 50Gy, the comparison of target dose distribution, conformity index, homogeneity index, dose to organs at risk (OARs), tumor control probability (TCP), normal tissue complication probability (NTCP), and number of monitor units (MUs) between 4 plans were investigated for their biophysical dosimetric difference. The target conformity and homogeneity of S-VMAT were better than the other 3 kinds of plans, but increased the volume of OARs receiving low dose (V5). TCP of PTV and NTCP of the left lung showed no statistically significant difference in 4 plans. 4F-IMRT plan was superior in terms of target coverage and protection of OARs and demonstrated significant advantages in decreasing the NTCP of heart by 0.07, 0.03, and 0.05 compared with TFs, T-IMRT, and S-VMAT plan. Compared with other 3 plans, TFs reduced the average number of MUs. Of the 4 techniques studied, this analysis supports 4F-IMRT as the most appropriate balance of target coverage and normal tissue sparing.

Dosimetric and clinical advantages of deep inspiration breath-hold (DIBH) during radiotherapy of breast cancer

BackgroundTo investigate the potential dosimetric and clinical benefits of Deep Inspiration Breath-Hold (DIBH) technique during radiotherapy of breast cancer compared with Free Breathing (FB).MethodsEight left-sided breast cancer patients underwent a supervised breath hold during treatment. For each patient, two CT scans were acquired with and without breath hold, and virtual simulation was performed for conventional tangential fields, utilizing 6 or 15 MV photon fields. The resulting dose–volume histograms were calculated, and the volumes of heart/lung irradiated to given doses were assessed. The left anterior descending coronary artery (LAD) mean and maximum doses were calculated, together with tumour control probability (TCP) and normal tissue complication probabilities (NTCP) for lung and heart.ResultsFor all patients a reduction of at least 16% in lung mean dose and at least 20% in irradiated pulmonary volumes was observed when DIBH was applied. Heart and LAD maximum doses were decreased by more than 78% with DIBH. The NTCP values for pneumonitis and long term cardiac mortality were also reduced by about 11% with DIBH. The NTCP values for pericarditis were zero for both DIBH and FB.ConclusionDelivering radiation in DIBH conditions the dose to the surrounding normal structures could be reduced, in particular heart, LAD and lung, due to increased distance between target and heart, and to reduced lung density.

Image-guided volumetric modulated arc therapy for breast cancer: a feasibility study and plan comparison with three-dimensional conformal and intensity-modulated radiotherapy

To test the feasibility of volumetric modulated arc therapy (VMAT) in breast cancer and to compare it with three-dimensional conformal radiotherapy (3D-CRT) as conventional tangential field radiotheraphy (conTFRT). 12 patients (Stage I, 8: 6 left breast cancer and 2 right breast cancer; Stage II, 4: 2 on each side). Three plans were calculated for each case after breast-conserving surgery. Breast was treated with 50 Gy in four patients with supraclavicular lymph node inclusion, and in eight patients without the node inclusion. Multiple indices and dose parameters were measured. V95% was not achieved by any modality. Heterogeneity index: 0.16 (VMAT), 0.13 [intensity-modulated radiotherapy (IMRT)] and 0.14 (conTFRT). Conformity index: 1.06 (VMAT), 1.15 (IMRT) and 1.69 (conTFRT). For both indices, IMRT was more effective than VMAT (p=0.009, p=0.002). Dmean and V20 for ipsilateral lung were lower for IMRT than VMAT (p=0.0001, p=0.003). Dmean, V2 and V5 of contralateral lung were lower for IMRT than VMAT (p>0.0001, p=0.005). Mean dose and V5 to the heart were lower for IMRT than for VMAT (p=0.015, p=0.002). The hypothesis of equivalence of VMAT to IMRT was not confirmed for planning target volume parameter or dose distribution to organs at risk. VMAT was inferior to IMRT and 3D-CRT with regard to dose distribution to organs at risk, especially at the low dose level. New technology VMAT is not superior to IMRT or conventional radiotherapy in breast cancer in any aspect.

A comparative dosimetric study for treating left-sided breast cancer for small breast size using five different radiotherapy techniques: conventional tangential field, filed-in-filed, Tangential-IMRT, Multi-beam IMRT and VMAT

Background and purposesTo compare the dosimetry for the left-sided breast cancer treatment using five different radiotherapy techniques.Materials and methodsTwenty patients with left sided breast cancer were treated with conservative surgery followed by radiotherapy. They were planned using five different radiotherapy techniques, including: 1) conventional tangential wedge-based fields (TW); 2) field-in-field (FIF) technique; 3) tangential inverse planning intensity-modulated radiation therapy (T-IMRT); 4) multi-field IMRT (M-IMRT); and 5) volumetric modulated arc therapy (VMAT). The CTV, PTV and OARs including the heart, the regions of coronary artery (CA), the contralateral breast, the left and right lung were delineated. The PTV dose was prescribed 50Gy and V47.5≥95%. Same dose constraint was used for all five plans. The planned volumetric dose of PTV and PRV-OARs were compared and analyzed.ResultsExcept VMAT (Average V47.5 was 94.72%±1.2%), all the other four plans were able to meet the V95% (V47.5) requirement. T-IMRT plan improved the PTV dose homogeneity index (HI) by 0.02 and 0.03 when compared to TW plan and VMAT plan, and decreased the V5, V10 and V20 of all PRV-OARs. However, the high dose volume (≥ 30Gy) of the PRV-OARs in T-IMRT plan had no statistically significant difference compared with the other two inverse plans. In all five plans, the dose volume of coronary artery area showed a strong correlation to the dose volume of the heart (the correlation coefficients were 0.993, 0.996, 1.000, 0.995 and 0.986 respectively).ConclusionCompared to other techniques, the T-IMRT technology reduced radiation dose exposure to normal tissues and maintained reasonable target homogeneity, VMAT is not recommended for left-sided breast cancer treatment. In five techniques, the dose-volume histogram (DVH) of the heart can be used to predict the dose-volume histogram (DVH) of the coronary artery.

Improvement of dose distribution with irregular surface compensator in whole breast radiotherapy.

Aim of this study was to compare the dosimetric aspects of whole breast radiotherapy (WBRT) between an irregular surface compensator (ISC) and a conventional tangential field technique using physical wedges. Treatment plans were produced for 20 patients. The Eclipse treatment planning system (Varian Medical Systems) was used for the dose calculation: For the physical wedge technique, the wedge angle was selected to provide the best dose homogeneity; for the ISC technique, the fluence editor application was used to extend the optimal fluence. These two treatment plans were compared in terms of doses in the planning target volume, the dose homogeneity index, the maximum dose, ipsilateral lung and heart doses for left breast irradiation, and the monitor unit counts required for treatment. Compared with the physical wedge technique, the ISC technique significantly reduced the dose homogeneity index, the maximum dose, the volumes received at 105% of the prescription dose, as well as reducing both the ipsilateral lung and heart doses (P < 0.01 for all comparisons). However, the monitor unit counts were not significantly different between the techniques (P > 0.05). Thus, the ISC technique for WBRT enables significantly better dose distribution in the planning target volume.

Second cancer incidence risk estimates using BEIR VII models for standard and complex external beam radiotherapy for early breast cancer.

To compare organ specific cancer incidence risks for standard and complex external beam radiotherapy (including cone beam CT verification) following breast conservation surgery for early breast cancer. Doses from breast radiotherapy and kilovoltage cone beam CT (CBCT) exposures were obtained from thermoluminescent dosimeter measurements in an anthropomorphic phantom in which the positions of radiosensitive organs were delineated. Five treatment deliveries were investigated: (i) conventional tangential field whole breast radiotherapy (WBRT), (ii) noncoplanar conformal delivery applicable to accelerated partial beast irradiation (APBI), (iii) two-volume simultaneous integrated boost (SIB) treatment, (iv) forward planned three-volume SIB, and (v) inverse-planned three volume SIB. Conformal and intensity modulated radiotherapy methods were used to plan the complex treatments. Techniques spanned the range from simple methods appropriate for patient cohorts with a low cancer recurrence risk to complex plans relevant to cohorts with high recurrence risk. Delineated organs at risk included brain, salivary glands, thyroid, contralateral breast, left and right lung, esophagus, stomach, liver, colon, and bladder. Biological Effects of Ionizing Radiation (BEIR) VII cancer incidence models were applied to the measured mean organ doses to determine lifetime attributable risk (LAR) for ages at exposure from 35 to 80 yr according to radiotherapy techniques, and included dose from the CBCT imaging. All LAR decreased with age at exposure and were lowest for brain, thyroid, liver, and bladder (<0.1%). There was little dependence of LAR on radiotherapy technique for these organs and for colon and stomach. LAR values for the lungs for the three SIB techniques were two to three times those from WBRT and APBI. Uncertainties in the LAR models outweigh any differences in lung LAR between the SIB methods. Constraints in the planning of the SIB methods ensured that contralateral breast doses and LAR were comparable to WBRT, despite their added complexity. The smaller irradiated volume of the ABPI plan contributed to a halving of LAR for contralateral breast compared with the other plan types. Daily image guided radiotherapy (IGRT) for a left breast protocol using kilovoltage CBCT contributed <10% to LAR for the majority of organs, and did not exceed 22% of total organ dose. Phantom measurements and calculations of LAR from the BEIR VII models predict that complex breast radiotherapy techniques do not increase the theoretical risk of second cancer incidence for organs distant from the treated breast, or the contralateral breast where appropriate plan constraints are applied. Complex SIB treatments are predicted to increase the risk of second cancer incidence in the lungs compared to standard whole breast radiotherapy; this is outweighed by the threefold reduction in 5 yr local recurrence risk for patients of high risk of recurrence, and young age, from the use of radiotherapy. APBI may have a favorable impact on risk of second cancer in the contralateral breast and lung for older patients at low risk of recurrence. Intensive use of IGRT increased the estimated values of LAR but these are dominated by the effect of the dose from the radiotherapy, and any increase in LAR from IGRT is much lower than the models' uncertainties.

Treatment of left sided breast cancer for a patient with funnel chest: Volumetric-modulated arc therapy vs. 3D-CRT and intensity-modulated radiotherapy

This case study presents a rare case of left-sided breast cancer in a patient with funnel chest, which is a technical challenge for radiation therapy planning. To identify the best treatment technique for this case, 3 techniques were compared: conventional tangential fields (3D conformal radiotherapy [3D-CRT]), intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT). The plans were created for a SynergyS® (Elekta, Ltd, Crawley, UK) linear accelerator with a BeamModulator™ head and 6-MV photons. The planning system was Oncentra Masterplan® v3.3 SP1 (Nucletron BV, Veenendal, Netherlands). Calculations were performed with collapsed cone algorithm. Dose prescription was 50.4 Gy to the average of the planning target volume (PTV). PTV coverage and homogeneity was comparable for all techniques. VMAT allowed reducing dose to the ipsilateral organs at risk (OAR) and the contralateral breast compared with IMRT and 3D-CRT: The volume of the left lung receiving 20 Gy was 19.3% for VMAT, 26.1% for IMRT, and 32.4% for 3D-CRT. In the heart, a D15% of 9.7 Gy could be achieved with VMAT compared with 14 Gy for IMRT and 46 Gy for 3D-CRT. In the contralateral breast, D15% was 6.4 Gy for VMAT, 8.8 Gy for IMRT, and 10.2 Gy for 3D-CRT. In the contralateral lung, however, the lowest dose was achieved with 3D-CRT with D10% of 1.7 Gy for 3D-CRT, and 6.7 Gy for both IMRT and VMAT. The lowest number of monitor units (MU) per 1.8-Gy fraction was required by 3D-CRT (192 MU) followed by VMAT (518 MU) and IMRT (727 MU). Treatment time was similar for 3D-CRT (3 min) and VMAT (4 min) but substantially increased for IMRT (13 min). VMAT is considered the best treatment option for the presented case of a patient with funnel chest. It allows reducing dose in most OAR without compromising target coverage, keeping delivery time well below 5 minutes.

Conventional radiotherapy of localized right side breast cancer after radical mastectomy: development of innovative “field in field” technique

Introduction: The aim of this paper is to study the distribution of the therapy dosage applied by a modified conventional “field in field” technique and compare it to the distribution of the dosage applied by the standard conventional technique.Methods: The study included ten patients with right side breast cancer, after they were exposed to radical mastectomy and chemotherapy. Radiotherapy dosage of TD 50 Gy in 25 fractions was applied to the anterolateral side of the right thoracic wall, with two opposite conventional tangential fields by the linear accelerator Elekta Synergy and the energy of 6 megavolts (MV). A delineation of the target volume (CTV – Clinical Target Volume) was done within conventional fields. At the XiO system for planning we included additional fields within the existing conventional fields, which was the so called “field in field” technique. On the basis of CTV the Dose Volume Histogram (DVH) was calculated for conventional and “field in field” plans. VD90%, VD95%, VD107%, VD115%, CI and HI were calculated for both techniques. Means were pared with the paired Student's t-test. The results were considered significantly different if p&lt;0.05.Results: VD90% and VD 95% were significantly higher for the “field in field” technique. Therefore, CI also favored the “field in field” technique (p=0.02). There was no difference in VD107% and VD115% between the compared groups. Consequently, there was no statistically significant difference in HI (1.13±0.03 vs.1.13±0.03, p=0.06).Conclusion: Conventional postoperative radiotherapy of localized right side breast cancer by “field in field” technique provides excellent coverage of the target volume by radiotherapy isodose.

Dosimetric evaluation of whole breast radiotherapy using field-in-field technique in early-stage breast cancer

The purpose of this study is to evaluate the dosimetric benefits of whole breast radiotherapy (WBRT) using the field-in-field technique compared with conventional tangential field radiotherapy with physical wedges for WBRT. In this planning study, 20 patients were included. For each patient, two different treatment plans were created for the entire treated breast. The dosimetric parameters of the planning target volume for dose evaluation and the organs at risk for each planning technique were compared. In the clinical outcome, acute skin toxicity for each treatment technique was compared. The field-in-field technique significantly reduced the maximum dose, the volumes receiving >107% of the prescription dose, and homogeneity index for the planning target volume for dose evaluation compared with the tangential field technique. For each dosimetry of the organs at risk, excluding the contralateral breast, the field-in-field technique significantly reduced the maximum dose and the volumes receiving >10, 30, and 50 Gy of the prescribed dose. The volume receiving <1 Gy of the prescription dose for the contralateral breast was significantly decreased using the field-in-field technique. In addition, the dose distribution using the field-in-field technique in the target volume was less sensitive to the effects of breast motion during normal breathing. In the clinical outcome, the field-in-field technique significantly reduced Radiation Therapy Oncology Group (RTOG) grade II acute skin toxicity compared with the tangential field technique (3.1 vs. 10.6%). WBRT using the field-in-field technique improved dose distribution in the treated breast and decreased RTOG grade II acute skin toxicity compared with conventional tangential field radiotherapy with physical wedges.

A Technique for Verification of Isocenter Position in Tangential Field Breast Irradiation

Treatment verification and reproducibility of the breast treatment portals play a very important role in breast radiotherapy. We propose a simple technique to verify the planned isocenter position during treatment using an electronic portal imaging device. Ten patients were recruited in this study and (CT) computed tomography-based planning was performed with a conventional tangential field technique. For verification purposes, in addition to the standard medial (F1) and lateral (F2) tangential fields, a field (F3) perpendicular to the medial field was used for verification of the treatment portals. Lead markers were placed along the central axis of the 2 defined fields (F1 and F3) and the separation between the markers was measured on the portal images and verified with the marker separation on the digitally reconstructed radiographs (DRRs). Any deviation will identify the shift in the planned isocenter position during treatment. The average deviation observed between the markers measured from the DRR and portal image was 1.6 and 2.1 mm, with a standard deviation of 0.4 and 0.9 mm for fields F1 and F3, respectively. The maximum deviation observed was 3.0 mm for field F3. This technique will be very useful in patient setup for tangential breast radiotherapy.

TH‐C‐M100E‐09: Assessment of Skin Dose for Breast Chest Wall Radiotherapy as a Function of Bolus Material

Purpose: Skin dose assessment to the chest wall is important to ensure sufficient dose to the near‐surface target volume without undue skin reaction. Bolus is often used for a portion of the treatment course, but removed if clinically necessary because of skin toxicity. This study quantifies changes to the surface dose as a function of bolus material for conventional and IMRT techniques using a thermoluminescent dosimeter (TLD) extrapolation technique. Methods and Materials: Three types of bolus materials (2mm solid, 2mm fine mesh, and 3.2mm large mesh aquaplasts) were compared with Superflab (Med‐Tec). Surface dose measurements were performed using the Attix (parallel‐plate) chamber in a flat solid water phantom with the bolus materials for 10×10 cm2 and 10×20 cm2 jaw fields at 00, 450 and 700 incident angles. The Attix chamber measurements were used to validate the TLD extrapolation technique (0.89, 0.38, 0.15 mm thicknesses). TLDs were used to measure the surface dose on an anthropomorphic phantom for conventional and IMRT tangential fields. Results: Surface dose increased with increasing angles and field sizes. Oblique incidence has a larger influence on the surface when no bolus is present (from 20% to 48% for 10×10 cm2). The skin dose of solid 2mm aquaplast was larger than that of fine mesh aquaplast (22% for 10×10cm2−00 incidence, and 11% for 10×10cm2−700 incidence). Compared to conventional tangential fields, the skin dose for IMRT decreased ∼5%. For the conventional tangential fields, skin doses of fine mesh, solid, and large mesh aquaplasts were 21%, 11% and 9% less than that of superflab, respectively. For IMRT fields, skin doses were 22%, 12% and 10% less than that of superflab, respectively. Conclusion: For chest wall radiotherapy, the bolus type can be selected to compromise near‐skin target dose vs skin tolerance dose for optimal clinical outcome.

SU‐FF‐T‐51: A Technique for Verification of Isocenter Position in Tangential Field Breast Radiotherapy

Breast irradiation is one of the most challenging problems in radiotherapy due to its complex shape of the target volume and its proximity to the surrounding normal structures. Proper implementation of the planned parameter during treatment is very essential, especially, verification of the planned isocenter position. Small deviations in the positioning of the patient with regard to the beam set up could have a relatively important impact on the treatment volume. Hence, treatment verification and reproducibility of the breast treatment portals is an important step in breast radiotherapy. A simple technique has been proposed in this study to verify the planned isocenter during treatment using electronic portal imaging device. Ten patients were recruited in this study and CT based planning was performed with conventional tangential field technique. For verification purpose, in addition to the standard medial (F1) and lateral (F2) tangential fields, a field (F3) perpendicular to the medial field was used for verification of the treatment portals. Lead markers were placed along the central axis of the two defined fields (F1 &amp; F3) and the separations between the markers were measured on the portal images and verified with the marker separation on the digitally reconstructed radiographs (DRRs). Any deviation will identify the shift in the planned isocenter position during treatment. The average deviation observed between the markers measured from the DRR and portal image was 1.6 mm and 2.1 mm with a standard deviation of 0.4 mm and 0.9 mm for field F1 and F3 respectively. The maximum deviation observed was 3 mm for field F3. This technique will be very useful in patient set‐up for tangential breast radiotherapy.

Comparison of Contralateral Breast Dose for Various Tangential Field Techniques in Clinical Radiotherapy

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