Leonard H. Kim

Active breathing control (ABC) for Hodgkin’s disease: reduction in normal tissue irradiation with deep inspiration and implications for treatment☆

PURPOSE Active breathing control (ABC) temporarily immobilizes breathing. This may allow a reduction in treatment margins. This planning study assesses normal tissue irradiation and reproducibility using ABC for Hodgkins disease. METHODS AND MATERIALS Five patients underwent CT scans using ABC obtained at the end of normal inspiration (NI), normal expiration (NE), and deep inspiration (DI). DI scans were repeated within the same session and 1-2 weeks later. To simulate mantle radiotherapy, a CTV1 was contoured encompassing the supraclavicular region, mediastinum, hila, and part of the heart. CTV2 was the same as CTV1 but included the whole heart. CTV3 encompassed the spleen and para-aortic lymph nodes. The planning target volume (PTV) was defined as CTV + 9 mm. PTVs were determined at NI, NE, and DI. A composite PTV (comp-PTV) based on the range of NI and NE PTVs was determined to represent the margin necessary for free breathing. Lung dose-mass histograms (DMH) for PTV1 and PTV2 and cardiac dose-volume histograms (DVH) for PTV3 were compared at the three different respiratory phases. RESULTS ABC was well-tolerated by all patients. DI breath-holds ranged from 34 to 45 s. DMHs determined for PTV1 revealed a median reduction in lung mass irradiated at DI of 12% (range, 9-24%; n = 5) compared with simulated free-breathing. PTV2 comparisons also showed a median reduction of 12% lung mass irradiated (range, 8-28%; n = 5). PTV3 analyses revealed the mean volume of heart irradiated decreased from 26% to 5% with deep inspiration (n = 5). Lung volume comparisons between intrasession and intersession DI studies revealed mean variations of 4%. CONCLUSION ABC is well tolerated and reproducible. Radiotherapy delivered at deep inspiration with ABC may decrease normal tissue irradiation in Hodgkins disease patients.

Continuous arc rotation of the couch therapy for the delivery of accelerated partial breast irradiation: a treatment planning analysis.

PURPOSE We present a novel form of arc therapy: continuous arc rotation of the couch (C-ARC) and compare its dosimetry with three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT) for accelerated partial breast irradiation (APBI). C-ARC, like VMAT, uses a modulated beam aperture and dose rate, but with the couch, not the gantry, rotating. METHODS AND MATERIALS Twelve patients previously treated with APBI using 3D-CRT were replanned with (1) C-ARC, (2) IMRT, and (3) VMAT. C-ARC plans were designed with one medial and one lateral arc through which the couch rotated while the gantry was held stationary at a tangent angle. Target dose coverage was normalized to the 3D-CRT plan. Comparative endpoints were dose to normal breast tissue, lungs, and heart and monitor units prescribed. RESULTS Compared with 3D-CRT, C-ARC, IMRT, and VMAT all significantly reduced the ipsilateral breast V50% by the same amount (mean, 7.8%). Only C-ARC and IMRT plans significantly reduced the contralateral breast maximum dose, the ipsilateral lung V5Gy, and the heart V5%. C-ARC used on average 40%, 30%, and 10% fewer monitor units compared with 3D-CRT, IMRT, and VMAT, respectively. CONCLUSIONS C-ARC provides improved dosimetry and treatment efficiency, which should reduce the risks of toxicity and secondary malignancy. Its tangent geometry avoids irradiation of critical structures that is unavoidable using the en face geometry of VMAT.

Predictors of Long-Term Toxicity Using Three-Dimensional Conformal External Beam Radiotherapy to Deliver Accelerated Partial Breast Irradiation

PURPOSE We analyzed variables associated with long-term toxicity using three-dimensional conformal external beam radiation therapy (3D-CRT) to deliver accelerated partial breast irradiation. METHODS AND MATERIALS One hundred patients treated with 3D-CRT accelerated partial breast irradiation were evaluated using Common Terminology Criteria for Adverse Events version 4.0 scale. Cosmesis was scored using Harvard criteria. Multiple dosimetric and volumetric parameters were analyzed for their association with worst and last (W/L) toxicity outcomes. RESULTS Sixty-two patients had a minimum of 36 months of toxicity follow-up (median follow-up, 4.8 years). The W/L incidence of poor-fair cosmesis, any telangiectasia, and grade ≥2 induration, volume reduction, and pain were 16.4%/11.5%, 24.2%/14.5%, 16.1%/9.7%, 17.7%/12.9%, and 11.3%/3.2%, respectively. Only the incidence of any telangiectasia was found to be predicted by any dosimetric parameter, with the absolute breast volume receiving 5% to 50% of the prescription dose (192.5 cGy-1925 cGy) being significant. No associations with maximum dose, volumes of lumpectomy cavity, breast, modified planning target volume, and PTV, dose homogeneity index, number of fields, and photon energy used were identified with any of the aforementioned toxicities. Non-upper outer quadrant location was associated with grade ≥2 volume reduction (p = 0.02 W/p = 0.04 L). A small cavity-to-skin distance was associated with a grade ≥2 induration (p = 0.03 W/p = 0.01 L), a borderline significant association with grade ≥2 volume reduction (p = 0.06 W/p = 0.06 L) and poor-fair cosmesis (p = 0.08 W/p = 0.09 L), with threshold distances ranging from 5 to 8 mm. CONCLUSIONS No dose--volume relationships associated with long-term toxicity were identified in this large patient cohort with extended follow-up. Cosmetic results were good-to-excellent in 88% of patients at 5 years.

Effect of Lumpectomy Cavity Volume Change on the Clinical Target Volume for Accelerated Partial Breast Irradiation: A Deformable Registration Study

PURPOSE Previous studies have shown that lumpectomy cavity volumes can change significantly in the weeks following surgery. The effect of this volume change on the surrounding tissue that constitutes the clinical target volume (CTV) for accelerated partial breast irradiation and boost treatment after whole breast irradiation has not been previously studied. In the present study, we used deformable registration to estimate the effect of lumpectomy cavity volume changes on the CTV for accelerated partial breast irradiation and discuss the implications for target construction. METHODS AND MATERIALS The data from 13 accelerated partial breast irradiation patients were retrospectively analyzed. Deformable registration was used to propagate contours from the initial planning computed tomography scan to a later computed tomography scan acquired at the start of treatment. The changes in cavity volume and CTV, distance between cavity and CTV contours (i.e., CTV margin), and CTV localization error after cavity registration were determined. RESULTS The mean ± standard deviation change in cavity volume and CTV between the two computed tomography scans was -35% ± 23% and -14% ± 12%, respectively. An increase in the cavity-to-CTV margin of 2 ± 2 mm was required to encompass the CTV, and this increase correlated with the cavity volume change. Because changes in the cavity and CTV were not identical, a localization error of 2-3 mm in the CTV center of mass occurred when the cavity was used as the reference for image guidance. CONCLUSION Deformable registration suggested that CTV margins do not remain constant as the cavity volume changes. This finding has implications for planning target volume and CTV construction.

Differences in Effective Target Volume Between Various Techniques of Accelerated Partial Breast Irradiation

PURPOSE Different cavity expansions are used to define the clinical target volume (CTV) for accelerated partial breast irradiation (APBI) delivered via balloon brachytherapy (1 cm) vs. three-dimensional conformal radiotherapy (3D-CRT) (1.5 cm). Previous studies have argued that the CTVs generated by these different margins are effectively equivalent. In this study, we use deformable registration to assess the effective CTV treated by balloon brachytherapy on clinically representative 3D-CRT planning images. METHODS AND MATERIALS Ten patients previously treated with the MammoSite were studied. Each patient had two computed tomography (CT) scans, one acquired before and one after balloon implantation. In-house deformable registration software was used to deform the MammoSite CTV onto the balloonless CT set. The deformed CTV was validated using anatomical landmarks common to both CT scans. RESULTS The effective CTV treated by the MammoSite was on average 7% ± 10% larger and 38% ± 4% smaller than 3D-CRT CTVs created using uniform expansions of 1 and 1.5 cm, respectively. The average effective CTV margin was 1.0 cm, the same as the actual MammoSite CTV margin. However, the effective CTV margin was nonuniform and could range from 5 to 15 mm in any given direction. Effective margins <1 cm were attributable to poor cavity-balloon conformance. Balloon size relative to the cavity did not significantly correlate with the effective margin. CONCLUSION In this study, the 1.0-cm MammoSite CTV margin treated an effective volume that was significantly smaller than the 3D-CRT CTV based on a 1.5-cm margin.