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Abstract
The purpose of this study was to evaluate a methodology to reduce scatter and leakage radiations to patients’ surface and shallow depths during conventional and advanced external beam radiotherapy. Superflab boluses of different thicknesses were placed on top of a stack of solid water phantoms, and the bolus effect on surface and shallow depth doses for both open and intensity‐modulated radiotherapy (IMRT) beams was evaluated using thermoluminescent dosimeters and ion chamber measurements. Contralateral breast dose reduction caused by the bolus was evaluated by delivering clinical postmastectomy radiotherapy (PMRT) plans to an anthropomorphic phantom. For the solid water phantom measurements, surface dose reduction caused by the Superflab bolus was achieved only in out‐of‐field area and on the incident side of the beam, and the dose reduction increased with bolus thickness. The dose reduction caused by the bolus was more significant at closer distances from the beam. Most of the dose reductions occurred in the first 2‐cm depth and stopped at 4‐cm depth. For clinical PMRT treatment plans, surface dose reductions using a 1‐cm Superflab bolus were up to 31% and 62% for volumetric‐modulated arc therapy and 4‐field IMRT, respectively, but there was no dose reduction for Tomotherapy. A Superflab bolus can be used to reduce surface and shallow depth doses during external beam radiotherapy when it is placed out of the beam and on the incident side of the beam. Although we only validated this dose reduction strategy for PMRT treatments, it is applicable to any external beam radiotherapy and can potentially reduce patients’ risk of developing radiation‐induced side effects.
Highlights
The number of cancer survivors has been increasing
Doses increased at the other points: dose increment at point 1 was because the bolus moved the surface dose closer to the maximum dose point; dose increments at point 2 and point 4 were due to the backscattering photons from the bolus and the backscatter increased with bolus thickness
We evaluated surface and shallow depth dose reductions under various conditions by placing the Superflab boluses of various thicknesses on a solid water phantom
Summary
The number of cancer survivors has been increasing. It is estimated that cancer survivors will account for about 5.4% of the US population in 2024, and approximately half of all cancer patients receive radiotherapy as a part of their treatments (www.cancer.gov). While the goal of radiotherapy is to deliver a highly conformal dose to the tumor area only, normal tissues outside the target receive radiation doses including medium to high dose adjacent to the target, scatter and leakage doses from the treatment machine, and scatter dose within the patient. These normal tissue doses can cause a spectrum of acute and chronic radiogenic side effects for the patients.[1,2,3,4,5,6,7,8,9,10,11,12,13,14] Epidemiologic studies indicate the majority of second cancers occurred in the low- or intermediate-dose areas,[15,16] and current data support linear-no-threshold dose-risk model indicating a finite risk of developing second cancer even for the lowest radiation dose.[17,18] The advanced radiotherapy techniques like intensity-modulated radiotherapy (IMRT) will increase the low-dose volume because of beam modulations and can increase the risk of developing second cancers.[19,20]
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