Abstract
A thermobrachytherapy surface applicator (TBSA) was developed for simultaneous heat and brachytherapy treatment of chest wall (CW) recurrence of breast cancer. The ability to comfortably secure the applicator over the upper torso relative to the CW target throughout treatment is assessed on volunteers. Male and postmastectomy female volunteers were enrolled to evaluate applicator secure fit to CW. Female subjects with intact breast were also enrolled to assess the ability to treat challenging cases. Magnetic resonance (MR) images of volunteers wearing a TBSA over the upper torso were acquired once every 15 minutes for 90 minutes. Applicator displacement over this time period required for treatment preplanning and delivery was assessed using MR visible markers. Applicator comfort and tolerability were assessed using a questionnaire. Probability estimates of applicator displacements were used to investigate dosimetric impact for the worst‐case variation in radiation source‐to‐skin distance for 5 and 10 mm deep targets spread 17×13 cm on a torso phantom. Average and median displacements along lateral and radial directions were less than 1.2 mm over 90 minutes for all volunteers. Maximum lateral and radial displacements were measured to be less than 1 and 1.5 mm, respectively, for all CW volunteers and less than 2 mm for intact breast volunteers, excluding outliers. No complaint of pain or discomfort was reported. Phantom treatment planning for the maximum displacement of 2 mm indicated <10% increase in skin dose with <5% loss of homogeneity index (HI) for ‐2 mm uniform HDR source displacement. For +2 mm uniform displacement, skin dose decreased and HI increased by 20%. The volunteer study demonstrated that such large and uniform displacements should be rare for CW subjects, and the measured variation is expected to be low for multifraction conformal brachytherapy treatment.PACS numbers: 41.20.Jb, 41.75.‐i, 44.
Highlights
224 Arunachalam et al.: Preclinical study of thermobrachytherapy surface applicator (TBSA) demonstrated that tumor thermal enhancement ratio (TER) can be increased from 1.5 for sequential treatments to as high as 5.0 when hyperthermia is combined simultaneously with radiation.[6]
Superficial hyperthermia is delivered using the conformal microwave array (CMA) through a thin layer of body-conforming water bolus.[15,16,17,18,19] A pilot study of using CMA applicator for patients with CW recurrence provided excellent controlled heating and good patient tolerance.[24]. A parallel array of high dose rate (HDR) brachytherapy catheters on the back side of the water bolus is used to deliver conformal radiation dose to the chest wall disease through the microwave array made of thin copper sheet and coupling water layer.[20]. Phantom studies of TBSA reported nearly uniform surface cooling capability of the water bolus and very good applicator conformity to a contoured torso phantom.[20,21,22] Excellent agreement was obtained between skin dose calculated with the HDR treatment planning system and measured with dosimeters on a tissue equivalent CT phantom.[23]
The purpose of this study is to assess the ability to maintain the relative distance between the HDR brachytherapy catheters and CW separated by a body conforming water bolus to deliver the prescribed radiation dose, and to evaluate applicator comfort during a typical thermobrachy therapy treatment
Summary
224 Arunachalam et al.: Preclinical study of TBSA demonstrated that tumor TER can be increased from 1.5 for sequential treatments to as high as 5.0 when hyperthermia is combined simultaneously with radiation.[6]. Superficial hyperthermia is delivered using the CMA through a thin layer of body-conforming water bolus.[15,16,17,18,19] A pilot study of using CMA applicator for patients with CW recurrence provided excellent controlled heating and good patient tolerance.[24] A parallel array of HDR brachytherapy catheters on the back side of the water bolus is used to deliver conformal radiation dose to the chest wall disease through the microwave array made of thin copper sheet and coupling water layer.[20] Phantom studies of TBSA reported nearly uniform surface cooling capability of the water bolus and very good applicator conformity to a contoured torso phantom.[20,21,22] Excellent agreement was obtained between skin dose calculated with the HDR treatment planning system and measured with dosimeters on a tissue equivalent CT phantom.[23]. The specific objectives of the volunteer study are: 1) assess ease of placement and time required to treatment preparations; 2) determine patient comfort limitations; 3) quantify lateral movement of TBSA relative to the predefined target; 4) quantify variation in the HDR brachytherapy catheter (source) to skin surface distance; and 5) determine dosimetric impact of the variations determined in step 4
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