Purpose: The cancer incidence rate in pregnant women is increasing, due to both the new trend for delaying pregnancy into late reproductive ages and early detection of common cancers associated with pregnancy. When radiation treatment is chosen, the safety concern for the mother and fetus must be fully addressed. However, previous studies of fetal dose, such as those reported by AAPM TG‐36, had been limited to homogenous water phantoms and surface measurements that are not quantitative. This paper presents our effort to develop medical accelerators and ICRP standard reference pregnant patient models for Monte Carlo calculations of nontarget doses during radiation treatments. Method and Materials: The Monte Carlo program MCNPX was used to develop a complete model of a Varian Clinac 2100C. Peripheral dose profiles in a water phantom were investigated for the following square fields defined by the jaws: 5 cm × 5 cm, 10 cm × 10 cm, and 20 cm × 20 cm. Anatomically‐realistic pregnant patient and fetal models at different stages of gestation representing ICRP reference female patients were developed using latest anatomical modeling technologies. Results: The peripheral dose characteristics as a function of distance from the field edge for 5 cm × 5 cm, 10 cm × 10 cm, and 20 cm × 20 cm field sizes at several depths are consistent with previous studies. The change in peripheral dose as a function of depth is small for each field size. The peripheral dose increases as field size increases. Conclusion: Calculations of organ doses to a pregnant patient and fetus have been demonstrated. Such data will help better assess the risks to the mother and fetus from radiation treatment procedures. The tools we have developed can be adopted for routine use to optimize the treatment planning for pregnant patients.
The study goal was to clarify the therapeutic effect and the absorbed dose of radionuclide phosphorus-32 for skin hemangiomas and the consequent risk of side effects in these patients. Phosphorus-32 is an β emitter and is used for skin hemangioma treatment. In comparison with the few Gy per minute of the linear accelerators, the dose rate of phosphorus-32 for hemangiomas is much <1 Gy/hour; so, the latter is called low-dose-rate radiation. To achieve the therapeutic dose, continuous hours or days of radiation is necessary. For strawberry hemangiomas, the phosphorus-32 applicator was tightly placed on the lesion site for several hours until reaching therapeutic dose. The absorbed dose was estimated by radiochromic films. The absorbed dose of phosphorus-32 irradiation declined exponentially with a depth from 0 to 2.5 mm. Of the 316 patients with strawberry hemangiomas, the lesion disappeared completely within 3 months after one-time treatment in 259 cases (82%). For cavernous hemangiomas, 370KBq phosphorus-32 colloid was injected into the hemangioma each square centimeter, and the absorbed radiation was estimated by theoretical calculation. Forty-two of the 58 patients with cavernous hemangiomas (72%) had lesions that completely disappeared within 3 months after receiving one to six treatments. Thus, the phosphorus-32 for strawberry hemangiomas and the chromium phosphate-32 colloid for cavernous hemangiomas were clearly efficacious.
Purpose: To develop a 2nd dose validation software for helical TomoTherapy, study the sensitivity of the commission data variation on the final dosimetry impact, and inter‐fraction setup uncertainty effect for patient quality assurance. Method and Materials: A 2nd dose validation software for helical TomoTherapy, called MU‐Tomo, has been developed to independently validates point dose upon archived patient documents, initial coordinates and planned dose of point of calculation, and common dosimetric functions. MU‐Tomo has been validated with a hundred cancer cases (30 prostate, 26 head&neck, 18 lung, 17 pelvis, and 9 brain patients). Sensitivity studies were performed by oscillating fluctuation regions of off‐axis profiles, shifting, and rotating profiles. Daily setup shifts were quantified into systematic and random shifts to evaluate dosimetric variations, separately. Results: For dose validation, 98% of dose differences are within ±5% with mean 0.20%±2.06%. Sensitivity studies show linear response by oscillating OARy, 15 times larger dose variation by shifting OARy than OARx, and less than 1.5% difference by rotating OARx in ±6° and more than 5% in ±1° by rotating OARy. Systematic variations are up to −10.02%±3.00%. Mean random variations are up to −5.65%±1.90%. ANOVA analyses show significant differences among patient random dosimetric variations and systematic dosimetric variations between head&neck‐brain group and body group. Variations are not significantly correlated with treatment fraction number with the Pearson correlation analysis. The overall random dosimetric impacts to each patient are ‐ 0.0053%±1.11%. Conclusion: MU‐Tomo, has been developed for TomoTherapy dose validation. Sensitivity studies on fifty patients have been evaluated that OARy profiles are more sensitive than OARx in dose calculation. Dosimetric consequences due to inter‐fractional setup shifts on a hundred helical tomotherapy patients were assessed. Conflict of Interest: This project was supported in part by Oncology Data Systems, Inc., Oklahoma City, OK, USA.
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