Dosimetric effects of saline- versus water-filled balloon applicators for IORT using the model S700 electronic brachytherapy source.

PURPOSE: The Xoft Axxent Electronic Brachytherapy System (Xoft, Inc., San Jose, CA) is a viable option for intraoperative radiation therapy (IORT) treatment of early-stage breast cancer. The low-energy (50-kVp) X-ray source simplifies shielding and increases relative biological effectiveness but increases dose distribution sensitivity to medium composition. Treatment planning systems typically assume homogenous water for brachytherapy dose calculations, including precalculated atlas plans for Xoft IORT. However, Xoft recommends saline for balloon applicator filling. This study investigates dosimetric differences due to increased effective atomic number (Zeff) for saline (Zeff = 7.56) versus water (Zeff = 7.42). METHODS: Balloon applicator diameters range from 3 to 6 cm. Monte Carlo N-Particle software is used to calculate dose at the surface (Ds) of and 1 cm away (D1cm) from the water-/saline-filled balloon applicator using a single dwell at the applicator center as a simple estimation of the dosimetry and multiple dwells simulating the clinical dose distributions for the atlas plans. RESULTS: Single-dwell plans show a 4.4-6.1% decrease in Ds for the 3- to 6-cm diameter applicators due to the saline. Multidwell plans show similar results: 4.9% and 6.4% Ds decrease, for 4-cm and 6-cm diameter applicators, respectively. For the single-dwell plans, D1cm decreases 3.6-5.2% for the 3- to 6-cm diameter applicators. For the multidwell plans, D1cm decreases 3.3% and 5.3% for the 4-cm and 6-cm applicators, respectively. CONCLUSIONS: The dosimetric effect introduced by saline versus water filling for Xoft balloon applicator-based IORT treatments is ∼5%. Users should be aware of this in the context of both treatment planning and patient outcome studies.

Resident-reported brachytherapy experience in ACGME-accredited radiation oncology training programs.

PURPOSE: To describe resident-reported experience in brachytherapy in Accreditation Council of Graduate Medical Education-accredited radiation oncology training programs over the last 5 years. METHODS AND MATERIALS: Archived reports of Accreditation Council of Graduate Medical Education final resident case logs from the last 5 years were reviewed and summarized. Brachytherapy was categorized according to the dose rate (low dose rate vs. high dose rate), technique (interstitial vs. intracavitary), and primary tumor site. Linear regression was used to test for trends. RESULTS: The mean number of total brachytherapy procedures performed per resident in the last 5 years has decreased from 80.8 in 2006-2007 to 71.0 in 2010-2011, but the trend is not statistically significant. The average number of intracavitary procedures has remained steady. The average resident experience with interstitial brachytherapy has decreased in a statistically significant manner. The average number of interstitial procedures has decreased by 25%. CONCLUSIONS: The average number of interstitial procedures reported by residents has decreased by 25%. The community charged with training residents in interstitial brachytherapy should consider methods to ensure that residents obtain sufficient experience in the future.

A dosimetric comparison between the supine and prone positions for three-field intact breast radiotherapy.

PURPOSE: Supine tangential radiotherapy for the intact breast is a standard component of breast conservation management; a supraclavicular (SCV) field can be added for patients at high risk for nodal failure. Treatment in the prone position has demonstrated improvements in lung sparing, but has been limited to early-stage patients in whom radiation to only the breast was indicated. We sought to investigate the dosimetric feasibility of treating women in the prone position, using a 3-field monoisocentric technique. METHODS: A total of 10 patients previously simulated supine and prone were selected for replanning. The heart, ipsilateral breast, contralateral breast, and axillary/SCV lymph node regions were contoured in accordance with Radiation Therapy Oncology Group guidelines. The 3-field monoisocentric plans were created for both the supine and prone scans. Target coverage, homogeneity, and organ at risk sparing were examined. RESULTS: Both plans achieved acceptable coverage of the breast. The mean percentage of the breast receiving at least 95% of the prescription dose (V95%) were similar in the prone and supine positions, 89.3% versus 90.7% (P = 0.29). Mean V95% of the level 3 axilla and SCV were 93.8% versus 97.0% prone versus supine (P = 0.16). The percentage of ipsilateral lung receiving >20 Gy was substantially reduced from 21.2% supine to 9.3% prone (P = 0.001). CONCLUSION: Three-field radiotherapy in the prone position appears to be dosimetrically equivalent to supine treatment with respect to target coverage, but the prone position decreases lung dose.

Helical tomotherapy delivery of an IMRT boost in lieu of interstitial brachytherapy in the setting of gynecologic malignancy: feasibility and dosimetric comparison.

Interstitial brachytherapy is an important means by which to improve local control in gynecologic malignancy when intracavitary brachytherapy is untenable. Patients unable to receive brachytherapy have traditionally received conventional external beam radiation alone with modest results. We investigated the ability of Tomotherapy (Tomotherapy Inc., Madison, WI) to replace interstitial brachytherapy. Six patients were selected. The planning CT of each patient was contoured with the planning target volume (PTV), bladder, rectum, femoral heads, and bowel. Identical contour sets were exported to Tomotherapy and Nucletron PLATO (Nucletron B.V., Veenendaal, The Netherlands). With Tomotherapy, the PTV was prescribed 31 Gy in 5 fractions to 90% of the volume. With PLATO, 600 cGy × 5 fractions was prescribed to the surface of the PTV. Dose delivered was normalized to 2 Gy fractions (EQD2) and added to a hypothetical homogenous 45-Gy pelvic dose. Tomotherapy achieved a D90 of 87 Gy EQD2 versus 86 Gy with brachytherapy. PTV dose was more homogeneous with tomotherapy. The dose to the most at-risk 2 mL of bladder and rectum with Tomotherapy was of 78 and 71 Gy EQD2 versus 81 and 75 Gy with brachytherapy. Tomotherapy delivered more dose to the femoral heads (mean 1.23 Gy per fraction) and bowel. Tomotherapy was capable of replicating the peripheral dose achieved with brachytherapy, without the PTV hotspots inherent to interstitial brachytherapy. Similar maximum doses to bowel and bladder were achieved with both methods. Excessive small bowel and femoral head toxicity may result if previous pelvic irradiation is not planned accordingly. Significant challenges related to interfraction and intrafraction motion must be overcome if treatment of this nature is to be contemplated.

Experience with an electronic brachytherapy technique for intracavitary accelerated partial breast irradiation.

OBJECTIVES: Phase IV study evaluated the safety and device performance of an electronic brachytherapy system (Axxent Electronic Brachytherapy System) as adjuvant therapy for early-stage breast cancer. METHODS: Patients were > or =50 years of age and had completely resected invasive ductal carcinoma or ductal carcinoma in situ (<2.0 cm), with N0 M0 and negative microscopic margins of > or =1 mm. The balloon applicator was placed in a closed cavity with a balloon surface to skin distance of > or =7 mm. The prescribed dose was 3.4 Gy/fraction prescribed to 1 cm beyond the balloon surface twice daily (BID) for 10 fractions. RESULTS: Of 65 patients consented, 21 (32%) were not eligible for treatment, and 44 (68%) were treated, with 6-months follow-up in 43 and 1-year follow-up in 36. The prescribed radiation treatment was successfully delivered in 42/44 (95.4%) patients; one was unsuccessful due to a controller issue and the other declined the final fraction following a balloon deflation. Side effects were as anticipated and generally manageable. Four CTCAE v3 grade 3 toxicities were reported: blistering (1), breast tenderness (1), and moist desquamation (2); all have resolved. The most common grade 2 toxicity was erythema. There were no device-related serious adverse events. CONCLUSIONS: Early experience demonstrates that the electronic brachytherapy system performed as expected. Electronic brachytherapy has similar acute toxicity profiles to other high dose rate approaches for accelerated partial breast irradiation and offers the convenience of having the treatment in an unshielded room.

Variation in post-surgical lumpectomy cavity volume with delay in initiation of breast irradiation because of chemotherapy.

PURPOSE: The addition of a radiotherapy boost has been shown to improve local control in breast conservation therapy. Three dimensional planning provides more accurate targeting of the operative bed than clinical setup using the lumpectomy scar. However, contraction of the lumpectomy cavity over time may have implications for the volume of tissue included in the boost field. METHODS AND MATERIALS: The clinical variables and treatment planning volumes for patients receiving whole-breast radiotherapy at a single institution between July 1, 2006, and December 31, 2007 were analyzed retrospectively. RESULTS: Of the 93 patients identified, 29 received chemotherapy (CTX) and 64 did not; CTX was sequenced before radiotherapy in all patients. Patients receiving CTX were more likely to have higher T and N stage and a longer interval between definitive breast surgery and radiation. The lumpectomy specimens of women receiving CTX trended toward being larger than those of women not receiving CTX (113.4 cm(3) vs. 74.6 cm(3), p = 0.08). Despite this, the volume of the lumpectomy cavity measured on computed tomography was smaller in patients receiving CTX (9.1cm(3) vs. 16.8 cm(3), p = 0.02), as was the volume of the planning target volume (56.6 cm(3) vs. 79.9 cm(3), p = 0.02). CONCLUSIONS: Patients receiving CTX were at higher risk for local recurrence. However, as a result of lumpectomy bed contraction, these patients received a boost to a smaller volume than patients not receiving CTX. This finding is counterintuitive and supports re-evaluation of the optimal size of the boost field. In addition, these results may have implications for patients treated with partial breast irradiation.

Tomotherapy and multifield intensity-modulated radiotherapy planning reduce cardiac doses in left-sided breast cancer patients with unfavorable cardiac anatomy.

PURPOSE: For patients with left-sided breast cancers, radiation treatment to the intact breast results in high doses to significant volumes of the heart, increasing the risk of cardiac morbidity, particularly in women with unfavorable cardiac anatomy. We compare helical tomotherapy (TOMO) and inverse planned intensity modulated radiation therapy (IMRT) with three-dimensional conformal radiotherapy using opposed tangents (3D-CRT) for reductions in cardiac volumes receiving high doses. METHODS AND MATERIALS: Fifteen patients with left-sided breast cancers and unfavorable cardiac anatomy, determined by a maximum heart depth (MHD) of >or=1.0 cm within the tangent fields, were planned for TOMO and IMRT with five to seven beam angles, in addition to 3D-CRT. The volumes of heart and left ventricle receiving >or=35 Gy (V35) were compared for the plans, as were the mean doses to the contralateral breast and the volume receiving >or=20 Gy (V20) for the ipsilateral lung. RESULTS: The mean MHD was 1.7 cm, and a significant correlation was observed between MHD and both heart and left ventricle V35. The V35s for IMRT (0.7%) and TOMO (0.5%) were significantly lower than for 3D-CRT (3.6%). The V20 for IMRT (22%) was significantly higher than for 3D-CRT (15%) or TOMO (18%), but the contralateral breast mean dose for TOMO (2.48 Gy) was significantly higher than for 3D-CRT (0.93 Gy) or IMRT (1.38 Gy). CONCLUSIONS: Both TOMO and IMRT can significantly reduce cardiac doses, with modest increases in dose to other tissues in left-sided breast cancer patients with unfavorable cardiac anatomy.

Radiation recall reaction with docetaxel administration after accelerated partial breast irradiation with electronic brachytherapy.

PURPOSE: Accelerated partial breast irradiation (APBI) offers several advantages over whole breast irradiation. Electronic brachytherapy may further reduce barriers to breast conserving therapy by making APBI more available. However, its toxicity profile is not well characterized. METHODS AND MATERIALS: A 60-year-old woman was treated with APBI using Axxent (Xoft, Sunnyvale, CA) electronic brachytherapy. One month after APBI, a cycle of docetaxel and cyclophosphamide was given. Within 3 weeks, the patient developed an ulcerative radiation recall reaction in the skin overlying the lumpectomy cavity. To investigate this toxicity, the skin dose from electronic brachytherapy was compared with the dose that would have been delivered by an iridium-192 ((192)Ir) source. Additionally, a dose equivalent was estimated by adjusting for the increased relative biologic effectiveness (RBE) of low energy photons generated by the electronic source. RESULTS: Using electronic brachytherapy, the skin dose was 537cGy per fraction compared with 470cGy for an (192)Ir source. Given an RBE for a 40kV source of 1.28 compared with (192)Ir, the equivalent dose at the skin for an electronic source was 687cGy-equivalents, a 46% increase. CONCLUSIONS: We present a case of an ulcerative radiation recall reaction in a patient receiving APBI with electronic brachytherapy followed by chemotherapy. Our analysis shows that the use of electronic brachytherapy resulted in the deposition of significantly higher equivalent dose at the skin compared with (192)Ir. These findings suggest that standard guidelines (e.g., surface-to-skin distance) that apply to (192)Ir-based balloon brachytherapy may not be applicable to electronic brachytherapy.

Case report and dosimetric analysis of an axillary recurrence after partial breast irradiation with mammosite catheter.

Partial breast irradiation (PBI) was designed in part to decrease overall treatment times associated with whole breast radiation therapy (WBRT). WBRT treats the entire breast and usually portions of the axilla. The goal of PBI is to treat a smaller volume of breast tissue in less time, focusing the dose around the lumpectomy cavity. The following is a case of a 64-year-old woman with early-stage breast cancer treated with PBI who failed regionally in the ipsilateral axilla. With our dosimetric analysis, we found that the entire area of this axillary failure would have likely received at least 45 Gy if WBRT had been used, enough to sterilize microscopic disease. With PBI, this area received a mean dose of only 2.8 Gy, which raises the possibility that this regional failure may have been prevented had WBRT been used instead of PBI.

A dosimetric comparison of three-dimensional conformal, intensity-modulated radiation therapy, and MammoSite partial-breast irradiation.

PURPOSE: Limited information is available comparing target volume and normal tissue dosimetry with the different techniques of partial breast irradiation (PBI). We present results of a dosimetric comparison of single catheter, balloon-based brachytherapy using the MammoSite catheter (BRT), 3D conformal radiation therapy (3DCRT), and intensity-modulated radiation therapy (IMRT). METHODS AND MATERIALS: Fifteen patients were treated using the BRT device. With the use of CT scans with balloons in inflated and deflated states, plans were developed for each patient using each of the methods of PBI, for a total of 45 plans. The plans were then compared using the below dosimetric parameters. RESULTS: The mean V100 was 95%, 92%, and 94% for the BRT, 3DCRT, and IMRT techniques, respectively. The mean ipsilateral breast V50 was 29%, 56%, and 46% (p < 0.0001) and the mean ipsilateral lung V30 was 5%, 7%, and 2% (p < 0.001 for IMRT vs. others) for the BRT, 3DCRT, and IMRT methods, respectively. For the 10 patients with left-sided breast tumors, the mean heart V5 was 12%, 4%, and 1% for the BRT, 3DCRT, and IMRT methods, respectively (p < 0.01). CONCLUSIONS: With increasing interest in PBI, our data may help clinicians individualize patient treatment decisions.

Monte Carlo calculations of output factors for clinically shaped electron fields.

We report on the use of the EGS4/BEAM Monte Carlo technique to predict the output factors for clinically relevant, irregularly shaped inserts as they intercept a linear accelerator's electron beams. The output factor for a particular combination--energy, cone, insert, and source-to-surface distance (SSD)--is defined in accordance with AAPM TG-25 as the product of cone correction factor and insert correction factor, evaluated at the depth of maximum dose. Since cone correction factors are easily obtained, we focus our investigation on the insert correction factors (ICFs). An analysis of the inserts used in routine clinical practice resulted in the identification of a set of seven "idealized" shapes characterized by specific parameters. The ICFs for these shapes were calculated using a Monte Carlo method (EGS4/BEAM) and measured for a subset of them using an ion chamber and well-established measurement methods. Analytical models were developed to predict the Monte Carlo-calculated ICF values for various electron energies, cone sizes, shapes, and SSDs. The goodness-of-fit between predicted and Monte Carlo-calculated ICF values was tested using the Kolmogorov-Smirnoff statistical test. Results show that Monte Carlo-calculated ICFs match the measured values within 2.0% for most of the shapes considered, except for few highly elongated fields, where deviations up to 4.0% were recorded. Predicted values based on analytical modeling agree with measured ICF values within 2% to 3% for all configurations. We conclude that the predicted ICF values based on modeling of Monte Carlo-calculated values could be introduced in clinical use.

Three-dimensional photon dosimetry: a comparison of treatment of the intact breast in the supine and prone position.

PURPOSE: To compare the adequacy of target coverage, dose homogeneity, and volume of normal tissue irradiated in treatment of the intact breast in the supine and prone position. METHODS AND MATERIALS: Fifteen patients with early breast cancer who presented for treatment to the intact breast after excisional biopsy were studied. A specially designed device was used for the prone setup to displace the contralateral breast away from the tangential field borders. Treatment planning computed tomography was performed for each patient in both the supine and prone positions. Dosimetric data were obtained in both positions and isodose distributions were calculated for each patient in both positions. RESULTS: The volume of breast receiving greater than 5% of the prescribed dose was significantly less in the prone position. Medial wedges were either not used or their angles were reduced for all patients in the prone position compared with the supine position. The average volume of lung receiving >10 Gy and >20 Gy was significantly less in the prone positions. The volume of heart irradiated at critical dose levels did not vary consistently in the prone and supine positions. The integral dose delivered to the contralateral breast was not significantly different. CONCLUSION: Treatment of the intact breast in the prone position may result in improved dose homogeneity within the target volume as well as sparing of normal lung compared with treatment in the conventional supine position.