Optimum radiation source for radiation therapy of skin cancer.

Habib Safigholi,Ali S Meigooni,William Y Song

doi:10.1120/jacmp.v16i5.5407

Abstract

Several different applicators have been designed for treatment of skin cancers, such as scalp, hand, and legs using Ir‐192 HDR brachytherapy sources (IR‐HDRS), miniature electronic brachytherapy sources (eBT), and external electron beam radiation therapy (EEBRT). Although, all of these methodologies may deliver the desired radiation dose to the skin, but the dose to the underlying bone may become the limiting factor for selection of the optimum treatment technique. In this project, dose to the underlying bone has been evaluated as a function of the radiation type, thickness of the bone, and thickness of the soft tissue on top of bone, assuming the same radiation dose delivery to the skin. These evaluations are performed using Monte Carlo (MC) simulation technique with MCNP5 code. The results of these investigations indicate that, for delivery of the same skin dose with a 50 keV eBT, 4 MeV or 6 MeV EEBRT techniques, the average doses received by the underlying bones are 5.31, 2, or 1.75 times the dose received from IR‐HDRS technique, respectively. These investigations indicate that, for the treatment of skin cancer condition with bone immediately beneath skin, the eBT technique may not be the most suitable technique, as it may lead to excessive bone dose relative to IR‐HDRS and 6 MeV or 4 MeV electron beams.PACS number: 87.53.Jw, 87.55.K‐

Highlights

220 Safigholi et al.: Skin cancer radiation therapybrachytherapy.[2,3,6,7] Several groups have shown different percentages of tumor control results for nonmelanoma skin cancer treatment using superficial X-rays with 93%–100%,(4) orthovoltage X-rays with 87%,(8) electron beams with 72%–88%,(4) isotope-based HDR brachytherapy with 92%–98%,(6) and 100% for electronic brachytherapy sources (eBT) up to 2013.(6)The physical differences between these types of skin radiation are shown by comparison of their percentage depth doses and dose profiles
For external electron beam therapy, a protocol with about 40 Gy to 60 Gy total dose is delivered at the rate of 2 Gy to 3 Gy per fractions within four to six weeks.[4,6] for brachytherapy, skin treatment by IR-HDRs and eBT, the patient receives 6 to 8 fractions for a total dose ranging from 30 Gy to 40 Gy in two weeks.[3,7,9,10,11] Normally, all of these treatments are performed assuming homogenous tissue condition and ignoring the underlying bone
These results indicate that the normalized dose values to the skin layer for 70 keV photons in homogenous and heterogeneous conditions are nearly the same

Summary

Introduction

220 Safigholi et al.: Skin cancer radiation therapybrachytherapy.[2,3,6,7] Several groups have shown different percentages of tumor control results for nonmelanoma skin cancer treatment using superficial X-rays with 93%–100%,(4) orthovoltage X-rays with 87%,(8) electron beams with 72%–88%,(4) isotope-based HDR brachytherapy with 92%–98%,(6) and 100% for eBT up to 2013.(6)The physical differences between these types of skin radiation are shown by comparison of their percentage depth doses and dose profiles. The percentage depth-dose curves of electron beams, with a field size of greater than the practical range of the electrons, have sharp falloffs beyond the depth of the maximum dose This property is beneficial in electron beam therapy for sparing the tissues beyond the range of the electron beams. For external electron beam therapy, a protocol with about 40 Gy to 60 Gy total dose is delivered at the rate of 2 Gy to 3 Gy per fractions within four to six weeks.[4,6] for brachytherapy, skin treatment by IR-HDRs and eBT, the patient receives 6 to 8 fractions for a total dose ranging from 30 Gy to 40 Gy in two weeks.[3,7,9,10,11] Normally, all of these treatments are performed assuming homogenous tissue condition and ignoring the underlying bone

Objectives

Methods

Results

Conclusion