Dosimetric consequences of adapting the craniocaudal isocenter distance to daily patient position in craniospinal irradiation using volumetric modulated arc therapy.

PURPOSE: In craniospinal irradiation, two or three isocenter groups along the craniocaudal axis are required to cover the long treatment target. Adapting the isocenter distance according to daily deviations in patient position is challenging because dosimetric hot or cold spots may occur in the field junction. The aim of this study was to quantify the effect of adapting the isocenter distance to patient position on the dose distribution of the field overlap region in craniospinal irradiation using partial-arc volumetric modulated arc therapy. METHODS: The magnitude of isocenter distance deviations in craniocaudal direction was quantified by registering the setup images of 204 fractions of 12 patients to the planning images. The dosimetric effect of these deviations was determined by shifting the isocenters of the original treatment plan and calculating the resulting dose distribution. RESULTS: On fraction-level, deviations larger than 3 mm caused more than 5 percentage point changes in the doses covering 2% (D2%) and 98% (D98%) of the junction volume in several patients. On treatment course-level, the changes in D2% and D98% of the junction volume were less than 5 percentage points in all cases except for one patient. CONCLUSIONS: Craniocaudal isocenter distance adaptation can be conducted provided that the mean isocenter distance deviation over the treatment course is within 3 mm.

Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy.

AIM: Traditional radiotherapy treatment techniques of the breast are insensitive for deformations and swelling of the soft tissue. The purpose of this study was to evaluate the dose changes seen with tissue deformations using different image matching methods when VMAT technique was used, and compare these with tangential technique. METHODS: The study included 24 patients with breast or chest wall irradiations, nine of whom were bilateral. In addition to planar kV setup imaging, patients underwent weekly cone-beam computed tomography (CBCT) imaging to evaluate soft tissue deformations. The effect of the deformations was evaluated on VMAT plans optimized with 5-mm virtual bolus to create skin flash, and compared to standard tangential plans with 2.5 cm skin flash. Isocenter positioning using 2D imaging and CBCT were compared. RESULTS: With postural changes and soft tissue deformations, the target coverage decreased more in the VMAT plans than in the tangential plans. The planned V90% coverage was 98.3% and 99.0% in the tangential and VMAT plans, respectively. When tattoo-based setup and online 2D match were used, the coverage decreased to 97.9% in tangential and 96.5% in VMAT plans (P < 0.001). With automatic CBCT-based image match the respective coverages were 98.3% and 98.8%. In the cases of large soft tissue deformations, the replanning was needed for the VMAT plan, whereas the tangential plan still covered the whole target volume. CONCLUSIONS: The skin flash created using an optimization bolus for VMAT plans was in most cases enough to take into account the soft tissue deformations seen in breast VMAT treatments. However, in some cases larger skin flash or replanning were needed. The use of 2D match decreased the target coverage for VMAT plans but not for FinF plans when compared to 3D match. The use of CBCT match is recommended when treating breast/chest wall patients with VMAT technique.

Improving the reproducibility of voluntary deep inspiration breath hold technique during adjuvant left-sided breast cancer radiotherapy.

BACKGROUND: Adjuvant radiotherapy (RT) of left-sided breast cancer (LSBC) with voluntary deep inspiration breath hold (vDIBH) technique reduces the cardiac dose. In this study, the effect of marker block position and the efficacy of breath hold level (BHL) correction based on lateral kV setup images are evaluated to improve the daily reproducibility. MATERIAL AND METHODS: A total of 148 consecutive LSBC patients treated with vDIBH RT were included in this study. The real-time position management (RPM) marker block was placed on the abdominal wall in 63 patients (group A) and on the sternum in 85 patients (group S). Acquired 900 (group A) + 1040 (group S) orthogonal image pairs were retrospectively analyzed. The actual BHL was determined from the lateral kV images. The height of the BHL gating window in RPM was corrected if errors of the actual BHL exceeded 4 mm. Setup margins were calculated for the chest wall and for bony surrogates of the lymph node regions. RESULTS: The sternal marker block reduced the random residual errors in the actual BHL (p < 0.05). The BHL correction was required for 26/63 patients in group A and for 26/85 patients in group S. Correction of the BHL window significantly reduced both the systematic and the random residual error in both groups. In patients with lymph node irradiation, the effect of both marker placement and BHL window correction was significant in the superior-inferior direction. Correction of the BHL reduced the mean cardiac dose by 0.5 Gy (p < 0.01) in group A and 0.6 Gy (p < 0.05) in group S. CONCLUSIONS: Reproducibility of the BHL can be improved by placing the marker block on the sternum and correcting the height of the BHL window based on lateral kV setup images. Acquisition of lateral kV images in the first 3 fractions and once a week during RT is recommended.

A novel arc geometry setting for pelvic radiotherapy with extensive nodal involvement.

The aim of this study was to find optimal planning approach for large planning targets with complicated geometry requiring wide field openings. The study presents a novel approach for arc geometry design for pelvic targets with extensive nodal involvement. A total of 15 patients with anorectal carcinoma or vulvar cancer were selected retrospectively. For each patient, one seven-field IMRT plan and three VMAT plans were calculated: one with two 360° arcs with no limitations for the field size (VMATw); one with two asymmetrically field-size-restricted 360° arcs (VMATr); and the proposed novel approach which consisted of one 360° arc with the field size restricted to the central PTV, and another arc divided into two 180° arcs, restricting the field sizes with the focus on the lymph nodes. The techniques were compared in terms of PTV coverage (VPTV(95%)), dose maximum (D(max)), dose conformity index (CI), homogeneity index (HI), and organs at risk doses. The proposed novel approach with one full and two half arcs tended to have better PTV coverage (VPTV(95%) = 97% ± 2%, compared to 95% ± 3%, 95% ± 3%, and 97% ± 2% in VMATw, VMATr, and 7f-IMRT, respectively) and lower maxima (D(max) = 107% ± 1%, compared to 110% ± 3%, 110% ± 4%, and 110% ± 4% in VMATw, VMATr, and 7f-IMRT, respectively); and lower or equal organs at risk doses. The superiority of the proposed technique (CI = 1.16 ± 0.05, HI = 9 ± 2) was more pronounced compared with the VMATw plans (CI = 1.41 ± 0.10, paired t-test p < 0.001; HI = 12 ± 2, p < 0.001), but the proposed technique was slightly better also in comparison with the VMATr plans (CI = 1.21 ± 0.07, p < 0.001; HI= 11 ± 4, p = 0.015) and 7f-IMRT plans (CI = 1.18 ± 0.03, p = 0.016; HI = 10 ± 2, p = 0.215). Radiotherapy treatment planning for large and complicated treatment volumes benefits not only from restricting the field size but also from careful field design that considers PTV geometry. This optimizes multileaf collimator movements, leading to better dose conformity and homogeneity.

Treatment accuracy without rotational setup corrections in intracranial SRT.

The aim of this study was to evaluate the impact of actual rotational setup errors on dose distributions in intracranial stereotactic radiotherapy (SRT) with different alternatives for treatment position selection. A total of 38 SRT fractions from 18patients were retrospectively evaluated with rotational setup errors obtained from actual treatments. The planning computed tomography (CT) images were rotated according to online cone-beam CT (CBCT) images and the dose distribution was recalculated to the rotated CT images using three different patient positionings derived from: 1) an automatic 6D match neglecting rotation correction (Auto6D); 2) an automatic 3D match (Auto3D); and 3) a manual 3D match from actual treatment (Treat3D). The mean conformity index (CI) was 0.92 for the original plans and 0.91 for the Auto6D plans. The mean CI decreased significantly (p < 0.01) to 0.78 and 0.80 for the Auto3D and the Treat3D plans, respectively. The mean minimum dose of the planning target volume (PTVmin) was 91.9% of the prescribed dose for the original plans and 92.1% for the Auto6D plans, while for the Auto3D and the Treat3D plans PTVmin decreased significantly (p < 0.01) to 78.9% and 80.2%, respectively. No significant differences were seen between the Auto6D and the original treatment plans in terms of the dose parameters. However, the Auto3D and the Treat3D plans were statistically significantly inferior (p < 0.01) to the Auto6D and the original plans. In addition, a significant negative correlation (p < 0.01, |r| > 0.38) was found in the Auto3D and the Treat3D cases between the rotation error and CI, PTVmin or minimum dose of gross tumour volume. In SRT, a treatment plan of comparable quality to 6D rotation correction can be achieved by using 6D registration without a rotational correction in the selection of patient positioning. This was demonstrated for typical rotation errors seen in clinical practice.

Dosimetric effect of rotational setup errors in volumetric modulated arc therapy and field-in-field treatment of left-sided breast cancer.

Setup errors are an important factor in the dosimetric accuracy of radiotherapy delivery. In this study, we investigated how rotational setup errors influence the dose distribution in volumetric modulated arc therapy (VMAT) and tangential field-in-field (FiF) treatment of left-sided breast cancer with supraclavicular lymph node involvement in deep inspiration breath hold. Treatment planning computed tomography images and radiotherapy plans of 20 patients were collected retrospectively for the study. Rotational setup errors up to 3° were simulated by rotating the planning images, and the resulting dosimetric changes were calculated. With rotational setup errors up to 3°, the median decrease of V95% to clinical target volume was less than 0.8 percentage point in both VMAT and FiF plans. The dose distribution of the heart and left anterior descending artery was more stable with respect to rotations in VMAT plans compared to FiF plans. Correction of ≥1° setup errors is recommended due to increased doses to the heart and left anterior descending artery after 1° setup errors.

Validation of HDR brachytherapy doses in the treatment of keloid scars using the egs_brachy Monte Carlo application.

Objective. Radiotherapy is a well-known alternative in the treatment of keloid scars to reduce the recurrence of scars. The purpose of this study was to investigate the feasibility and accuracy of dose delivered from a high-dose-rate (HDR) afterloaders in keloid scar brachytherapy using Monte Carlo (MC) simulations and measurements.Approach. Treatment doses and central axis dose profiles were measured using radiophotoluminescence dosimeters and radiochromic films, respectively, with two HDR afterloaders, both using an Ir-192 source, in a phantom made of solid water and polycarbonate sheets. The nominal treatment dose calculated by the AAPM Task Group No. 43 (TG-43) dose model was set to 8.5 Gy at a distance of 0.5 cm laterally from the middle of the source line located in a plastic applicator simulating a 15 cm long surgically removed scar treatment with 30 equally spaced (0.5 cm) source positions. The dose profiles were measured at three different distances from the applicator and the absolute doses at four points at different distances. MC simulations were performed using the egs_brachy, which is based on EGSnrc code system.Main results. The measured and simulated dose profiles match well, especially at 10.0 mm (difference <1%) and 15.0 mm depths (difference <4%), and with a small dose difference at 5.0 mm depth (difference <4%). Point dose measurements agreed well in the dose maximum area (difference <7%) with the simulated dose profiles, although the largest difference near the edge of the profile was <30%. The dose differences between the TG-43 dose model and the MC simulation were small (differences <4%).Significance. Simulated and measured dose levels at a depth of 0.5 cm showed that the nominal treatment dose can be achieved with the utilized setup. The measurement results of the absolute dose agree well with the corresponding simulation results.

The robustness of prostate radiotherapy for patients with hip prosthesis.

The aim of this study was to investigate prostate radiotherapy techniques for the patients with hip prosthesis in 4 different field setups. Volumetric Modulated Arc Therapy (VMAT) technique was used in 4 different cases: (1) using full VMAT arcs (VMAT_F); (2) same arcs as in case 1 but with avoidance sectors (VMAT_ASEC); (3) as case 2 but with the addition of a lateral static field through the prosthesis (VMAT_ASEC+STAT); (4) as in case 1 but with an automated structure avoidance option to avoid irradiation through the prosthesis (VMAT_ASTR). Fifteen previously treated prostate patients were retrospectively selected to this study. Treatment plans were created for all patients using all 4 techniques. The potential prosthesis misalignment in the treatment setup was modeled by moving the prosthesis 0.5, 1.0, and 1.5 cm ventrally and dorsally and recalculating the plans in each case. For VMAT_ASEC, the dose parameters for organs at risk were the highest and the dose coverage of the target volume was the poorest when compared to the other techniques. For VMAT_ASEC+STAT, the movement of the prosthesis changed the target dose distribution the most. VMAT_F and VMAT_ASTR fulfilled the planning criteria the best, even when the prosthesis was misaligned. VMAT_F radiated through the prosthesis more than VMAT_ASTR and increased the dose near the prosthesis surface when compared to VMAT_ASTR. VMAT_ASTR and VMAT_F were the most robust techniques for the patients with the hip prosthesis considering plan quality and the effect of positioning errors. The increased prosthesis surface dose with VMAT_F and possible dose calculation uncertainties favors the use of VMAT_ASTR.

The robustness of VMAT radiotherapy for breast cancer with tissue deformations.

To investigate the near-surface doses and target coverage in modulated arc radiotherapy (RT) of the breast or chest wall in two treatment planning systems (TPS) in the presence of soft tissue deformations. This retrospective study consisted of 10 breast cancer patients with axillary lymph node inclusion. For each case, five RT plans were created: (1) tangential 3D conformal field-in-field (FinF) technique; (2) 200° to 240° arcs with optimization bolus (OB) in Eclipse (EB); (3) 243° to 250° arcs with an 8-mm OB in Monaco (MB); (4) 243° to 250° arcs with automatic skin flash tool (ASF) in Monaco TPS (MA); (5) 243° to 250° arcs with both ASF and OB in Monaco (MAB). Soft tissue deformation was simulated by editing CT-images with 4-, 8-, and 12-mm swelling and recalculating the dose. The increasing swelling from 0 to 12 mm caused the coverage (V95%) in clinical target volume to decrease from 96% ± 2% to 90% ± 6% for the FinF plans. For volumetric-modulated arc therapy (VMAT), the coverage decreased from 99% ± 1% to 92% ± 4% in the EB plans, and from 97% ± 1% to 68% ± 8%, 85% ± 6%, and 86% ± 5% for MA, MB, and MAB, respectively. The mean dose in the surface extending from 0 to 3 mm from the skin decreased on average 5%, 17%, 20%, 15%, and 8% in FinF, EB, MA, MB, and MAB, respectively. In the Monaco plans, the use of an OB(+ASF) provided better target coverage and lower dose maxima despite of tissue swelling than the ASF alone. With modulated arc therapy, we recommend the use of an OB instead of or in addition to the ASF. The use of 8 mm OB with VMAT plans is robust to account deformations extending outside up to 8mm. If soft tissue deformation is larger than 8 mm, the need for replanning should be evaluated.

Contralateral tissue sparing in lymph node-positive breast cancer radiotherapy with VMAT technique.

The objective of this study was to modify volumetric modulated arc therapy (VMAT) design for breast irradiation with axillary lymph node involvement to enhance normal tissue sparing while maintaining good planning target volume (PTV) coverage. Four VMAT plans were generated retrospectively for 10 patients with breast cancer for comparison. First, 2 partial arcs with an avoidance sector (Pavoid) for the lung and the heart were created. Second, a split-arc design with 2 partial arcs was used, changing the collimator angle by splitting the arcs in the middle, resulting in 4 partial arcs (Psplit). Third, the arc angles in the Psplit were modified to emphasize tangential directions, corresponding to the avoidance sector in Pavoid, resulting in 2 lateral and 2 anterior partial arcs. Furthermore, a fifth arc was added to ensure the coverage of axillary lymph nodes (Ptang). Fourth, one of the anterior arcs was removed to limit the number of arcs during treatment (Ptang-1). PTV coverage was the highest in Psplit with a V90%(PTV) of 98.4 ± 0.6%. Also the dose homogeneity and conformity were the best (p < 0.02) in Psplit, and a smaller high-dose volume was distributed to the ipsilateral lung, heart, and humeral head, than in the other designs. In Ptang and Ptang-1, the PTV coverage was acceptable with V90%(PTV) of 97.9 ± 0.8% and 98.0 ± 0.8%, respectively, and low-dose volumes in normal tissue were smaller compared with Psplit. The removal of 1 partial arc from Ptang (Ptang-1) did not have a significant effect on dose parameters. In Pavoid, the contralateral breast and lung volumes of low-dose level were the smallest. However, the PTV coverage was reduced (V90% = 97.0 ± 1.6%), and the heart, ipsilateral lung, and humeral head received significantly higher doses than in other designs. The modified split-arc methods Ptang and Ptang-1, emphasizing tangential directions, were close to the original split-arc method in PTV coverage while reducing the dose to the healthy tissues distant from the PTV. Ptang-1 is seen as a favorable treatment option over Ptang with less treatment time.

Optimal selection of optimization bolus thickness in planning of VMAT breast radiotherapy treatments.

The aim of this study was to find an optimal optimization skin flash thickness in volumetric modulated arc radiotherapy of the breast in consideration of soft tissue deformations during the treatment course. Ten breast radiotherapy patients with axillary lymph node inclusion were retrospectively planned with volumetric modulated arc radiotherapy technique. The plans were optimized with the planning target volume (PTV) extending outside the skin contour by 0, 5, 7, and 10 mm; and with optimization boluses of 3 or 5 mm on the extended PTV. The final dose was calculated without the bolus. The plans were compared in terms of PTV homogeneity and conformity, and dose minima and maxima. The doses to organs at risk were also evaluated. The doses were recalculated in real patient geometries based on cone beam computed tomography (CBCT) images captured 3 to 6 times during each patient's treatment course. The optimization to the PTV without the PTV extension resulted in the best CTV coverage in the original plans (V95% = 98.0% ± 1.2%). However, when these plans were studied in real CBCT-based patient geometries, the CTV V95% was compromised (94.6% ± 8.3%). In addition, for the surface (4 mm slap inside the PTV 4 mm below the body contour) dose V95% was reduced from the planned 74.7% ± 7.5% to the recalculated 65.5% ± 11.5%. Optimization with an 8-mm bolus to a PTV with 5-mm extension was the most robust choice to ensure the CTV and surface dose coverage (recalculated V95% was 95.2% ± 6.4% and 74.6% ± 8.4%, respectively). In cases with the largest observed deformations, even a 10-mm PTV extension did not suffice to cover the target. Optimization with a 5-mm PTV extension and an 8-mm optimization bolus improved the surface dose and slightly improved the CTV dose when compared to no extension plans. For deformations over 1 cm, no benefit was seen in PTV extensions and replanning is recommended. Frequent tangential and CBCT imaging should be used during treatment course to detect potential large anatomical changes.

Monte Carlo investigation on the effect of air gap under bolus in post-mastectomy radiotherapy.

OBJECTIVES: To investigate the dosimetric effect of air gaps under bolus on skin dose for left-sided post-mastectomy radiotherapy with loco regional involvement. METHODS: Eight patients were planned retrospectively with volume modulated arc therapy (VMAT) and conventional static Field-in-Field (FinF) methods. Three different setups were applied for the 5-mm bolus over the chest wall having 0, 5 or 10 mm air gap under the bolus. The dose calculation was performed using Monte Carlo (MC) simulation. In addition, Analytic Anisotropic Algorithm (AAA) was used to demonstrate the differences observed in clinical setting. RESULTS: The investigated air gaps under the bolus had minimal effect on surface dose for FinF plans (relative difference ≤ 2.6%), whereas for VMAT plans the surface dose decreased 13.6% when compared to the case with no air gap. In both FinF and VMAT, the largest differences between AAA and MC were seen at the surface where AAA underestimated the dose by 1.5 Gy (p < 0.05) on average; while the dose in the target volume excluding the surface was relatively similar being on average 0.3 Gy (p > 0.05) larger with AAA than with MC calculations. CONCLUSIONS: The surface dose was significantly lower with VMAT technique than with FinF technique. Possible air gaps under the bolus reduced the surface dose significantly further for VMAT but not for FinF treatments, which may have clinical impact on recurrence rate. AAA was shown to underestimate the surface dose when compared to MC calculation.

Dosimetric comparison of surface mould HDR brachytherapy with VMAT.

INTRODUCTION: The aim of this study was to investigate the dosimetric differences between surface mould high-dose-rate (HDR) brachytherapy and external beam volumetric-modulated arc therapy (VMAT) for two treatment sites. METHODS: Previously treated HDR brachytherapy surface mould scalp (n = 4) and lower leg (n = 3) treatments were retrospectively analysed. The VMAT plans were optimised using an additional 3-mm setup margin on the clinical target volume (CTV) of the previously treated HDR plans. The HDR plans were calculated and normalised using the TG-43 formalism and recalculated with Acuros BV (AC). RESULTS: On average, the mean brain and normal tissue doses were reduced by 44.8% and 27.4% for scalp and lower leg VMAT cases, respectively, when compared to AC calculated HDR plans. For VMAT plans, the average dose to a 1-mm thick skin structure deep to the target volume was not any lower than that in AC HDR plans. On average, the CTV coverage was 13.8% and 9.6% lower for scalp cases with AC dose calculation than with TG-43 and 8.3% and 5.3% lower for lower leg cases if 0- or 1-cm backscatter material was applied above the catheters, respectively. CONCLUSIONS: VMAT is a feasible treatment option in the case of extensive skin malignancies of the scalp and lower leg. Uncertainties related to delivered dose with HDR brachytherapy when using the TG-43 dose calculation model or possible air gaps between the mould and skin favour the use of VMAT. The potential soft tissue deformation needs to be considered if VMAT is used.

Dosimetric evaluation of modern radiation therapy techniques for left breast in deep-inspiration breath-hold.

PURPOSE: The dosimetric differences between four radiation therapy techniques for left sided whole breast irradiation were evaluated side by side in the same patient population. METHODS: Radiotherapy treatment plans were retrospectively created with Accuray TomoDirect (TD), Elekta Volumetric Modulated Arc Therapy (E-VMAT), Varian RapidArc (RA) and Field-in-field (FinF) technique for 20 patients, who had received left breast irradiation during deep-inspiration breath-hold. Dose characteristics of planning target volume and organs at risk were compared. RESULTS: The E-VMAT, TD and RA treatment plans had higher target coverage (V95%) than FinF plans (97.7-98.3% vs. 96.6%). The low-dose spillage to contralateral breast and lung was smaller with FinF and TD (mean 0.1 and 0.3 Gy) compared to E-VMAT and RA (mean 0.6 and 0.9 Gy). E-VMAT, RA and TD techniques were more effective than FinF in sparing left anterior descending artery (mean 4.0, 4.2 and 4.7 Gy vs. 6.1 Gy, respectively). CONCLUSIONS: In whole breast irradiation TD, E-VMAT and RA plans generated in this study achieved higher dose coverage and sparing of organs from the high dose in the vicinity of the PTV. The advantage of calculated FinF plans is the lowest dose on contralateral organs. The choice of the technique used should be weighted by each institution taking into account the dose characteristics of each technique and its fit with patient anatomy bearing in mind the increased workload of using modulated techniques and the increased beam on time.

The robustness of dual isocenter VMAT radiation therapy for bilateral lymph node positive breast cancer.

PURPOSE: To investigate the use of dual isocenters for VMAT planning in patients with lymph node positive synchronous bilateral breast cancer (BBC) compared to a single isocenter option. METHODS: Treatment plans of 11 patients with lymph node positive BBC were retrospectively analyzed using two different VMAT planning techniques: dual-isocenter split-arc VMAT plans (Iso2) were compared with mono-isocenter VMAT plans (Iso1). For Iso2 plans, PTV dose was investigated after introducing ±2 and ±5 mm couch shift errors between the two isocenters in the lateral, longitudinal and vertical direction. RESULTS: For both techniques the planning aims for PTV coverage and OARs were met. The mean dose for the bilateral lungs and heart was reduced from 11.3 Gy and 3.8 Gy to 10.9 Gy (p < .05) and 3.6 Gy (p < .05), respectively, for Iso2 plans when compared to Iso1 plans. Positive statistically significant correlation (rho = 0.76, p = .006) was found between PTV volume and D2ccPTV for Iso1 plans. No clinically significant change was seen in the D98CTV or D2ccPTV after the 2 and 5 mm errors were introduced between isocenters for Iso2 plans. CONCLUSIONS: The split arc method was shown to be a feasible treatment technique in the case of synchronous BBC for both mono and dual isocenter techniques. The dose parameters were slightly favoring dual-isocenter option instead of mono-isocenter. The dual-isocenter method was shown to be a robust treatment option in the presence of ≤5 mm errors in the shifts between the two isocenters.

Importance of deformable image registration and biological dose summation in planning of radiotherapy retreatments.

The purpose of this study is to evaluate the effect of nonrigid and fractionation-corrected dose summation on total doses in radiotherapy and to demonstrate the benefits of such dose summation on clinical decision-making for planning of retreatments. Dose summation of organs at risk (OARs) was investigated for 3 clinical cases with need of retreatment to the same site: head and neck, brain, and mediastinum. Three different summation methods over old and new radiotherapy treatment plans are presented and compared: (1) rigid raw sum with rigid registration of the planning images and direct dose summing; (2) deformable raw sum with deformable image registration and direct dose summing; and (3) deformable biological sum with deformable registration and takes into account the dose per fraction in biological manner in certain critical organs. In 2 cases, a user-defined dose downscaling is applied to take into account the time between the treatments and the healing from the radiation-induced effects. Of the 3 summation methods presented, the deformable biological sum was considered to offer the most biologically plausible account of the treatment. There were remarkable differences between near-maximum doses (D0.1cc) and dose-volume histogram (DVH) curves for OARs between different summation methods. The differences between deformable raw sum and rigid raw sum D0.1cc doses are in the range from -8 Gy to 2 Gy. Similarly, the deviation was from -14 Gy to 5 Gy for the deformable biological sum compared with the rigid raw sum. These differences come from incorrect summation of doses in the rigid raw sum case, and from the dose per fraction effect in biological summation. We conclude that computing the 3-dimensional deformable biological summation could be a valuable tool for treating patients with complex retreatments. It has the potential to assist the oncologist in refining plans for maximally curative doses while respecting appropriate tissue tolerances.

Treatment plan dosimetric impact after catheter stretch during multi-catheter interstitial breast brachytherapy.

PURPOSE: Nylon 6/6 interstitial brachytherapy catheters may stretch when exposed to moisture, mechanical tension, and body temperature. The purpose of this study is to evaluate the magnitude of catheter stretch during a course of multi-catheter interstitial breast brachytherapy for nylon 6/6 treatment catheters, and to assess the impact this has on treatment plan dosimetry. MATERIAL AND METHODS: Catheters were exposed to water at 37°C for six days and the internal catheter length change (ΔL_W) was measured daily. Additionally, the measured internal catheter length change (ΔL_P), performed prior to each treatment fraction, for seven interstitial breast brachytherapy patients (total of 76 catheters) were retrospectively analyzed. The maximum length change seen in ΔL_P and ΔL_W were introduced as a source positional error to retrospective treatment plans, and treatment plan dosimetry was analyzed. RESULTS: ΔL_W and ΔL_P were on average +4.0% and +1.6% of the catheter lengths in water or tissue after 48 hours. Weak correlation was seen between the average ΔL_P per catheter and both the catheter length within tissue (ρ = 0.36, p = 0.0007), and the mid-catheter depth in tissue (ρ = 0.42, p < 0.0001). The D90CTV decreased 1.5% (p < 0.05) and 8.2% (p < 0.05) when the ΔL_P and ΔL_W were introduced to the initial plans. CONCLUSIONS: Nylon 6/6 catheters stretch during a course of multi-catheter interstitial breast brachytherapy treatment. The observed stretch may affect treatment plan dosimetry, if the catheter internal length is only measured immediately after the insertion. Additional catheter length checks are recommended to verify the actual catheter internal length during the treatment.

The validity of Acuros BV and TG-43 for high-dose-rate brachytherapy superficial mold treatments.

PURPOSE: The purpose of this work is to validate the Acuros BV dose calculation algorithm for high-dose-rate (HDR) brachytherapy superficial mold treatments in the absence of full scatter conditions and compare this with TG-43 dose calculations. We also investigate the impact of additional back scatter material (bolus) applied above surface molds to the dose distributions under the mold. METHODS AND MATERIALS: The absorbed dose at various depths was compared for simulations performed using either TG-43 or Acuros BV dose calculations. Parameter variations included treatment area, thickness of the bolus, and surface shape (flat or spherical). Film measurements were carried out in a flat phantom. RESULTS: Acuros BV calculations and film measurements agreed within 1.5% but were up to 15% lower than TG-43 dose calculations when no bolus was applied above the treatment catheters. The difference in dose at the prescription depth (1 cm below the central catheter) increased with increasing treatment area: 3.3% difference for a 3 × 3.5 cm2 source loading area, 7.4% for 8 × 9 cm2, and 13.4% for 18 × 19 cm2. The dose overestimation of the TG-43 model decreased when bolus was added above the treatment catheters. CONCLUSIONS: The TG-43 dosimetry formalism cannot model surface mold treatments in the absence of full scatter conditions within 5% for loading areas larger than approximately 5 × 5 cm2. The TG-43 model results in an overestimation of the delivered dose, which increases with treatment area. This confirms the need for model-based dose calculation algorithms as discussed in TG-186.

A new split arc VMAT technique for lymph node positive breast cancer.

PURPOSE: To investigate different volumetric modulated arc therapy (VMAT) field designs for lymph node positive breast cancer patients when compared to conventional static fields and standard VMAT designs. METHODS: Nineteen breast cancer patients with lymph node involvement (eleven left and eight right sided) were retrospectively analyzed with different arc designs. Proposed split arc designs with total rotations of 2×190° and 2×240° were compared to conventional field in field (FinF) and previously published non-split arc techniques with the same amount of total rotations. RESULTS: All VMAT plans were superior in dose conformity, when compared to the FinF plans. Split arc design decreased significantly ipsilateral lung dose and heart V5Gy for both left and right sided cases, when compared to non-split VMAT designs. For left sided cases no significant differences were seen in contralateral lung mean dose or V5Gy between different VMAT designs. For right sided cases the contralateral lung dose V5Gy was significantly higher in split VMAT group, when compared to non-split VMAT designs. The contralateral breast dose V5Gy increased significantly for split VMAT plans for both sides, when compared to non-split VMAT designs or FinF plans. CONCLUSIONS: The proposed split VMAT technique was shown to be superior to previously published non-split VMAT and conventional FinF techniques significantly reducing dose to the ipsilateral lung and heart. However, this came with the expense of an increase in the dose to the contralateral breast and for right-sided cases to the contralateral lung.

Troponin T-release associates with cardiac radiation doses during adjuvant left-sided breast cancer radiotherapy.

BACKGROUND: Adjuvant radiotherapy (RT) for left-sided breast cancer increases cardiac morbidity and mortality. For the heart, no safe radiation threshold has been established. Troponin T is a sensitive marker of myocardial damage. Our aim was to evaluate the effect of left-sided breast cancer RT on serum high sensitivity troponin T (hscTnT) levels and its association with cardiac radiation doses and echocardiographic parameters. METHODS: A total of 58 patients with an early stage, left-sided breast cancer or ductal carcinoma in situ (DCIS) who received adjuvant breast RT without prior chemotherapy were included in this prospective, non-randomized study. Serum samples were taken before, during and after RT. An increase of hscTnT >30 % was predefined as significant. A comprehensive 2D echocardiograph and electrocardiogram (ECG) were performed before and after RT. Dose-volume histograms (DVHs) were generated for different cardiac structures. RESULTS: The hscTnT increased during RT from baseline in 12/58 patients (21 %). Patients with increased hscTnT values (group A, N = 12) had significantly higher radiation doses for the whole heart (p = 0.02) and left ventricle (p = 0.03) than patients without hscTnT increase (group B, N = 46). For the left anterior descending artery (LAD), differences between groups A and B were found in volumes receiving 15 Gy (p = 0.03) and 20 Gy (p = 0.03) Furthermore, after RT, the interventricular septum thickened (p = 0.01), and the deceleration time was prolonged (p = 0.008) more in group A than in group B. CONCLUSIONS: The increase in hscTnT level during adjuvant RT was positively associated with the cardiac radiation doses for the whole heart and LV in chemotherapy-naive breast cancer patients. Whether these acute subclinical changes increase the risk of excessive long-term cardiovascular morbidity or mortality, will be addressed in the follow-up of our patients.