Abstract
The purpose of this study was to introduce a three‐field monoisocentric inverse treatment planning method without half‐beam blocks for breast cancer radiation treatments. Three‐field monoisocentric breast treatment planning with half‐beam blocks limits the tangential field length to 20 cm. A dual‐isocenter approach accommodates patients with larger breasts, but prolongs treatment time and may introduce dose uncertainty at the matching plane due to daily setup variations. We developed a novel monoisocentric, three‐field treatment planning method without half‐beam blocking. The new beam‐matching method utilizes the full field size with a single isocenter. Furthermore, an open/IMRT hybrid inverse optimization method was employed to improve dose uniformity and coverage. Geometric beam matching was achieved by rotating the couch, collimator, and gantry together. Formulae for three‐field geometric matching were derived and implemented in Pinnacle scripts. This monoisocentric technique can be used for patients with larger breast size. The new method has no constraints on the length of tangential fields. Compared with the dual‐isocenter method, it can significantly reduce patient setup time and uncertainties.PACS number: 87.55.D‐
Highlights
The role of adjuvant radiation following lumpectomy or mastectomy in select patients is well documented.[1]
Half-beam blocking is the most common approach in order to match the supraclavicular field and tangential breast fields.[5,6,7,8] In this approach, the supraclavicular and tangential breast fields are matched at the midplane of the radiation field
This monoisocentric beam-matching method with half-beam block does not require a second setup during treatment delivery, which can reduce treatment time and dose uncertainties in the matching plane.[5] the maximum tangential field length is limited to half of the full field size, or 20 cm for most linac machines with this method, which is inadequate for some patients
Summary
The role of adjuvant radiation following lumpectomy or mastectomy in select patients is well documented.[1]. In order to match with the supraclavicular field, the tangential fields need to have a couch angle and collimator angle to ensure that the superior border of the tangential breast fields matches the inferior border of the supraclavicular field. This dual-isocenter, three-field arrangement removes the limitation on the length of the breast fields. Does this procedure prolong the treatment time, it causes uncertainties in the field matching.[3,9] The dose gradient on the field edge is very high, and a 1–2 mm mismatch may cause significant dose variation in the matching plane
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