The optimization of superficial planning target volumes (PTVs) with helical tomotherapy

Abstract

When the planning target volume (PTV), extends close to or beyond the skin, inverse‐planned intensity‐modulated radiotherapy can boost the fluence from tangential angles to superficial parts of the PTV due to the buildup effect. This can result in significant regions of high dose upon a small movement in the patient's position. We analyzed different methods of reducing this effect in the TomoTherapy planning system, including using pretend bolus, clipping the PTV back from the skin surface, and combinations of both. No alternative technique was seen to be unconditionally superior to a 5 mm planning bolus. A clip distance of 3 mm gave acceptable results, but consideration should be given to the reduction in minimum dose or increase in maximum dose seen in clip distances just 1 mm less or more, respectively, when treating head and neck cases in TomoTherapy.PACS numbers: 87.55.de, 87.55.dh

A mathematical deconvolution formulation for superficial dose distribution measurement by Cerenkov light dosimetry

“…However, the true significance of the proposed method is in the relationship between measured Cerenkov photons and the incident beam fluence as represented by Eq. (5). The beam fluence is often measured for IMRT QA by an instrument with a 2D detector array.…”

“…In these cases, knowledge of the superficial dose delivered during treatment would improve the therapeutic outcome of the radiation therapy . Superficial dose is measured within the build‐up region and depends on both beam and patient parameters including beam energy, beam angle, field size, patient positioning, tissue surface structure, and tissue composition . These factors, in addition to any error of superficial dose calculated by the treatment planning system, may lead to over‐ or underdosing of the skin through the course of EBRT …”

Effect of Changing Phantom Thickness on Helical Radiotherapy Plan: Dosimetric Analysis

“…Reductions in body thickness can cause an overdosage in normal tissue around the target [23,31]. Similar studies have shown that reducing the amount of bolus used leads to an increased maximum dose [32,33]. The HT treatment machine hasn't got any auto-segmentation tools that routinely help in finding the shapes of ROI's.…”

“The optimization of superficial planning target volumes (PTVs) with helical tomotherapy”. [JACMP, 15 (6), 2014]

“…Typographical error/misrepresentation of results in the original “Chart 4”, showing the data for the “Pretend Bolus” (PB) which is actually showing the same data as Chart 5.…”