Dosimetric study of volumetric modulated arc therapy fields for total marrow irradiation

PurposeTo investigate the effect on target coverage and organs at risk sparing by using 10 versus 6 MV for VMAT total marrow irradiation of obese patients.Methods and MaterialsTwenty‐six total marrow irradiation, TMI, treatment plans delivered between December 2014 and June 2017 were reviewed and 10 were chosen for replanning based on patient characteristics and plan metrics. Beam geometry and isocenter placement were conserved, energy was changed from 6 to 10 MV and plans were reoptimized. Resulting dose distributions were compared to original plans to evaluate any potential advantage of choosing one energy over the other.ResultsTarget coverage and total monitor units were consistent between the 6 and 10 MV plans when averaged over all ten patients. Improvement in the conformity index (−11.0%, P = 0.009) when using 10 MV was statistically significant compared to the 6 MV plans. Volumes of normal tissue receiving 50%, 75%, and 90% Rx all decreased for the 10 MV plans compared to the original 6 MV plans. The mean dose to individual OARs decreased significantly for all investigated structures except for the lenses, oral cavity, and genitalia. The largest decreases in Dmean were found for the rectum (22.4%, P = 0.004) and bladder (18.1%, P = 0.005). The three highest priorities for sparing during plan optimization (lungs, liver, and heart), showed decreases of 7.6%, 16.1%, and 13.0%.ConclusionsUse of a higher energy 10 MV beam provided similar dose to target while achieving increased OAR and normal tissue sparing for the patients reviewed in this study.

Section: Introductionmentioning

confidence: 99%

Energy‐dependent OAR sparing and dose conformity for total marrow irradiation of obese patients

Cherpak

Monajemi

Chytyk-Praznik

et al. 2018

“…Each isocentre receives two 360 degree VMAT arcs. As per previous planning studies, offset arcs with a 4 cm overlap and 90° collimator produced the best dose distribution 11, 13, 14. These are then optimized in stages on a 5 mm dose grid.…”

Section: Methodsmentioning

confidence: 77%

“…Helical tomotherapy (HT) based methods have been used for TMI/TMLI2, 3, 4, 5 as well as TBI 5, 6, 7. Using conventional linacs, intensity modulated radiotherapy (IMRT) TMI delivery proved feasible,8, 9 however, the predominant linac approach utilizes volumetric modulated arc therapy (VMAT) using Varian RapidArc (Varian Medical Systems, Palo Alto, CA, USA) 10, 11, 12, 13, 14, 15, 16, 17…”

Section: Introductionmentioning

confidence: 99%

Verification of junction dose between VMAT arcs of total body irradiation using a Sun Nuclear ArcCHECK phantom

Morrison

Symons

Woodings

et al. 2017

A volumetric modulated arc therapy (VMAT) approach to total body irradiation (TBI) has recently been introduced at our institution. The planning target volume (PTV) is divided into separate sub‐volumes, each being treated with 2 arcs with their own isocentre. Pre‐treatment quality assurance of beams is performed on a Sun Nuclear ArcCHECK diode array. Measurement of junction regions between VMAT arcs with separate isocentres has previously been performed with point dose ionization chamber measurements, or with films. Translations of the ArcCHECK with respect to a known distance between the adjacent isocentres of two arcs, which are repeated with the ArcCHECK in an inverted position, allows the recording of a junction dose map. A 3%/3 mm global gamma analysis (10% threshold) pass rate for arc junctions were comparable to their component arcs. Dose maps of junction regions between adjacent arcs with different isocentres can be readily measured on a Sun Nuclear ArcCHECK diode array.

“…It has also been established in the literature that in order to achieve improved dose sparing for lungs, it is more important to reduce the lower doses to larger lung volume than to reduce the higher doses to lesser volume 11 , 19 . This has been achieved using AMT‐TBI which successfully manipulates lung doses to recommended tolerance levels.…”

Section: Discussionmentioning

confidence: 99%

“…Constant and variable bed velocity TBI, aperture modulated TBI, and radiological depth‐based TBI are a few examples of dynamic TBI techniques 1 , 4 , 5 , 8 , 9 . Some other techniques suggest the use of sweeping arc fields similar to volumetric‐modulated arc therapy (VMAT) techniques 10 , 11 …”

Section: Introductionmentioning

confidence: 99%

Translating bed total body irradiation lung shielding and dose optimization using asymmetric MLC apertures

Salhi

Brown

Ahmed

et al. 2016

A revised translating bed total body irradiation (TBI) technique is developed for shielding organs at risk (lungs) to tolerance dose limits, and optimizing dose distribution in three dimensions (3D) using an asymmetrically‐adjusted, dynamic multileaf collimator. We present a dosimetric comparison of this technique with a previously developed symmetric MLC‐based TBI technique. An anthropomorphic RANDO phantom is CT scanned with 3 mm slice thickness. Radiological depths (RD) are calculated on individual CT slices along the divergent ray lines. Asymmetric MLC apertures are defined every 9 mm over the phantom length in the craniocaudal direction. Individual asymmetric MLC leaf positions are optimized based on RD values of all slices for uniform dose distributions. Dose calculations are performed in the Eclipse treatment planning system over these optimized MLC apertures. Dose uniformity along midline of the RANDO phantom is within the confidence limit (CL) of 2.1% (with a confidence probability p=0.065). The issue of over‐ and underdose at the interfaces that is observed when symmetric MLC apertures are used is reduced from more than ±4% to less than ±1.5% with asymmetric MLC apertures. Lungs are shielded by 20%, 30%, and 40% of the prescribed dose by adjusting the MLC apertures. Dose‐volume histogram analysis confirms that the revised technique provides effective lung shielding, as well as a homogeneous dose coverage to the whole body. The asymmetric technique also reduces hot and cold spots at lung‐tissue interfaces compared to previous symmetric MLC‐based TBI technique. MLC‐based shielding of OARs eliminates the need to fabricate and setup cumbersome patient‐specific physical blocks.PACS number(s): 87.55.‐x, 87.55.de, 87.55.D‐