Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_6_3169 - Evaluation of Irregular Surface Compensator Technique Using FFF for Dibh Left-Side Breast Radiation

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Evaluation of Irregular Surface Compensator Technique Using FFF for Dibh Left-Side Breast Radiation
J. L. Peng1, M. Ashenafi1, D. G. McDonald1, C. Mart2, N. C. Koch1, J. L. Harper1, W. Godwin1, and K. N. Vanek1; 1Medical University of South Carolina, Charleston, SC, 2Medical University Of South Carolina, Charleston, SC

Purpose/Objective(s): With the increasing use of deep inspiration breath hold (DIBH) techniques for left-sided breast cancer to reduce the heart toxicity, treatment efficiency could be the significant factor to impact the treatment accuracy of DIBH technique. The aim of this study was to determine the optimal technique for DIBH left-breast irradiation, with a focus on irregular surface compensator (ISC) and flatten-filter free (FFF) delivery.

Materials/Methods: Ten DIBH left breast cases were randomly selected. Each case was contoured following guidelines included in the RTOG1304 protocol, and planned using both field-in-field(FIF) and ISC techniques with FFF delivery. ISC is a tool in our treatment planning system which enables improved dose homogeneity for irregular shapes. The fluence distribution required to produce a planar dose perpendicular to the central axis at a specified depth and then delivered using a dynamic MLC field. The fluence value of the superficial region is also applied in order to ease MLC movement in the flash region. A prescription dose of 42.56Gy delivered in 16 fractions was used for all cases. Plans were compared and evaluated by several dose metrics as well as the treatment time. Differences were assessed for statistical significance(p<0.05) by use of Student's t-test.

Results: For targets, both plans exhibited similar coverage(V95%).ISC significantly improved the dose homogeneity index, and the maximum dose. Additionally, ISC provided slightly lower mean heart dose than FIF(2.7Gy v.s.3.1Gy,p=0.05).ISC also reduced V20Gy of the ipsilateral lung(18% v.s.22%).Finally, because of the dynamic MLC delivery, the ISC reduced the delivery time by 55% and the breath hold time by 40% per field as compared to FIF. Additionally, with FFF delivery in ISC plans, the delivery time is additional 30%-40% faster than the flattened beam.

Conclusion: ISC technique not only guarantees skin flash, but also offers improved plan efficiency, better normal tissue sparing, and shorter treatment time compared to FIF. With the shorter delivery time and FFF delivery with high dose rate, patient motion associated with breath hold is also reduced. The ISC technique with FFF delivery is a suitable replacement for FIF in DIBH left-side breast treatment.

Author Disclosure: J.L. Peng: None. M. Ashenafi: None. D.G. McDonald: None. C. Mart: None. K.N. Vanek: None.

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