| Autor: |
Julie A. Raffi, John A. Micka, Cliff G. Hammer, Jana E. Musgrove, John W. Winston, Terresa J. Ricci-Ott, Larry A. DeWerd, S Davis, Keith A. Kunugi |
| Rok vydání: |
2010 |
| Předmět: |
|
| Zdroj: |
Medical Physics. 37:2693-2702 |
| ISSN: |
0094-2405 |
| Popis: |
Purpose: Intracavitary accelerated partial breast irradiation (APBI) has become a popular treatment for early stage breast cancer in recent years due to its shortened course of treatment and simplified treatment planning compared to traditional external beam breast conservation therapy. However, the exit dose to the skin is a major concern and can be a limiting factor for these treatments. Most treatment planning systems (TPSs) currently used for high dose-rate (HDR) I 192 r brachytherapy overestimate the exit skindose because they assume a homogeneous water medium and do not account for finite patient dimensions. The purpose of this work was to quantify the TPS overestimation of the exit skindose for a group of patients and several phantom configurations. Methods: The TPS calculated skindose for 59 HDR I 192 r APBI patients was compared to the skindose measured with LiF:Mg,Ti thermoluminescent dosimeters(TLDs). Additionally, the TPS calculated dose was compared to the TLD measured dose and the Monte Carlo(MC) calculated dose for eight phantom configurations. Four of the phantom configurations simulated treatment conditions with no scattering material beyond the point of measurement and the other four configurations simulated the homogeneous scattering conditions assumed by the TPS. Since the calibrationTLDs for this work were irradiated with C 137 s and the experimental irradiations were performed with I 192 r , experiments were performed to determine the intrinsic energy dependence of the TLDs. Correction factors that relate the dose at the point of measurement (center of TLD) to the dose at the point of interest (basal skin layer) were also determined and applied for each irradiation geometry. Results: The TLD intrinsic energy dependence for I 192 r relative to C 137 s was 1.041 ± 1.78 % . The TPS overestimated the exit skindose by an average of 16% for the group of 59 patients studied, and by 9%–15% for the four phantom setups simulating treatment conditions. For the four phantom setups simulating the conditions assumed by the TPS, the TPS calculated dose agreed well with the TLD and MC results (within 3% and 1%, respectively). The inverse square geometry correction factor ranged from 1.023 to 1.042, and an additional correction factor of 0.978 was applied to account for the lack of charged particle equilibrium in the TLD and basal skin layer. Conclusions: TPS calculations that assume a homogeneous water medium overestimate the exit skindose for intracavitary APBI treatments. It is important to determine the actual skindose received during intracavitary APBI to determine the skindose-response relationship and establish dose limits for optimal skin sparing. This study has demonstrated that TLDs can measure the skindose with an expanded uncertainty ( k = 2 ) of 5.6% when the proper corrections are applied. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
Plný text