Abstract
PurposeBolus electron conformal therapy (BECT) is a clinically useful, well‐documented, and available technology. The addition of intensity modulation (IM) to BECT reduces volumes of high dose and dose spread in the planning target volume (PTV). This paper demonstrates new techniques for a process that should be suitable for planning and delivering IM‐BECT using passive radiotherapy intensity modulation for electrons (PRIME) devices.MethodsThe IM‐BECT planning and delivery process is an addition to the BECT process that includes intensity modulator design, fabrication, and quality assurance. The intensity modulator (PRIME device) is a hexagonal matrix of small island blocks (tungsten pins of varying diameter) placed inside the patient beam‐defining collimator (cutout). Its design process determines a desirable intensity‐modulated electron beam during the planning process, then determines the island block configuration to deliver that intensity distribution (segmentation). The intensity modulator is fabricated and quality assurance performed at the factory (.decimal, LLC, Sanford, FL). Clinical quality assurance consists of measuring a fluence distribution in a plane perpendicular to the beam in a water or water‐equivalent phantom. This IM‐BECT process is described and demonstrated for two sites, postmastectomy chest wall and temple. Dose plans, intensity distributions, fabricated intensity modulators, and quality assurance results are presented.ResultsIM‐BECT plans showed improved D90‐10 over BECT plans, 6.4% versus 7.3% and 8.4% versus 11.0% for the postmastectomy chest wall and temple, respectively. Their intensity modulators utilized 61 (single diameter) and 246 (five diameters) tungsten pins, respectively. Dose comparisons for clinical quality assurance showed that for doses greater than 10%, measured agreed with calculated dose within 3% or 0.3 cm distance‐to‐agreement (DTA) for 99.9% and 100% of points, respectively.ConclusionThese results demonstrated the feasibility of translating IM‐BECT to the clinic using the techniques presented for treatment planning, intensity modulator design and fabrication, and quality assurance processes.
Highlights
These results demonstrated the feasibility of translating intensity modulation (IM)-Bolus electron conformal therapy (BECT) to the clinic using the techniques presented for treatment planning, intensity modulator design and fabrication, and quality assurance processes
BECT offers the potential for lower whole body dose, reducing secondary cancer risks, and equal or lower dose to nearby critical structures, reducing normal tissue complications, as compared to that of intensity modulated x-ray therapy (IMXT)
Electrons have been an important modality for [1] the treatment of skin, lip, head, and neck tumors, [2] boost doses to superficial lymph nodes, and [3] postmastectomy chest wall irradiation.2–5 Since the onset of 3D treatment planning, BECT has been shown useful for posterior chest wall6–8; postmastectomy chest wall7,9–11; ear, parotid, and buccal mucosa7,12; nose13; and extremities
Summary
These results demonstrated the feasibility of translating IM-BECT to the clinic using the techniques presented for treatment planning, intensity modulator design and fabrication, and quality assurance processes. In BECT, a variable thickness bolus abutting the patient surface is used to modulate laterally the therapeutic range, for example, R90, so that the 90% dose surface conforms to (circumscribes) the patient planning target volume (PTV). The typical BECT treatment and delivery process consists of patient immobilization, CT scanning, PTV and normal tissue delineation, beam design, bolus design, dose calculation, bolus fabrication, and quality assurance.. The process, detailed and demonstrated for two patient sites, includes adding techniques for design, fabrication, and quality assurance of the intensity modulator to the current BECT process.
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