SU-E-T-258: Assessment of Radiation Induced Second Cancer Risks in Proton Therapy and IMRT for Organs inside the Main Radiation Field

PURPOSE

Radiation therapy can potentially cause a second malignancy. There is clinical evidence that those occur typically within the beam path in the medium/high dose region. The purpose of this study was to assess the risk for developing a radiation induced tumor within the treated volume and to compare this risk for proton therapy and IMRT.

METHODS

Fully contoured age and gender specific whole body phantoms (4-year and 14-year old) were uploaded into a treatment planning system and typical tumor volumes were contoured based on patients treated for optic glioma and vertebral body Ewing's sarcoma. Lifetime attributable risks (LARs) for developing a second malignancy were calculated using a risk model incorporating factors for cell kill, mutations, repopulation, and inhomogeneous organ doses.

RESULTS

For standard fractionation schemes, the LAR for developing a second malignancy from radiation therapy alone were found to be up to 2.7% for a 4-year old optic glioma patient treated with IMRT considering a soft tissue carcinoma risk model only. Sarcoma risks were found to be below 1% in all cases. For the 14-year old, risks were found to be about a factor of 2 lower. For the Ewing's sarcoma cases the risks based on the sarcoma model were typically higher than the carcinoma risks, i.e. up to 1.3% LAR for soft tissue sarcoma. Generally, the risk from proton therapy turned out to be lower by a factor of 2 to 10. However, comparison of a 3-field and 4-field proton plan shows that the distribution of the dose, i.e., the particular treatment plan, plays a role as well.

CONCLUSIONS

In general, proton therapy can significantly reduce the risk for developing an in-field second malignancy. Risk analysis based on our formalism could be applied within treatment planning programs to guide treatment plans for pediatric patients. Federal Share of program income earned by Massachusetts General Hospital on NIH/NCI C06 CA059267.

Phase II cisplatin, irinotecan, cetuximab and concurrent radiation therapy followed by surgery for locally advanced esophageal cancer

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Background: Weekly irinotecan, cisplatin, and concurrent radiation therapy is a well-tolerated, active regimen in locally advanced esophageal cancer. (Ilson. JCO 2003) Cetuximab, an EGFR inhibitor, is a potent radiation sensitizer in head and neck cancer. (Bonner. Proc ASCO 2004) Methods: In this phase II trial, patients (pts) with T2–4N0–1M0–1A esophageal adenocarcinoma (A) or squamous cell carcinoma (S) receive 5040 cGy/28 fractions of radiation therapy (RT) and concurrent weekly cisplatin 30mg/m2 plus irinotecan 65 mg/m2 on weeks 1, 2, 4, and 5, followed by surgery 4–8 weeks after completion of RT. Additionally, pts receive weekly infusions of cetuximab 250 mg during RT, up to one week before surgery, and for 6 months following surgery. Results: Seventeen pts have been entered: male: female = 14:3, median age 54, ECOG PS 0:1 = 6:11, A:S = 17:0, stage IIA:IIB:III:IVA = 6:1:8:2, tumor location-esophagus-mid:lower:gastroesophageal junction = 1:4:12, >10% weight loss-yes:no = 8:9. Of 17 pts entered, 15 pts have proceeded to surgery, 1 pt died from Aspergillus infection resulting in respiratory failure and sepsis, and 1 pt is pending surgery. Of the 15 pts who underwent surgery, 2 (13%) had a complete pathologic response; pathologic stage for other pts: 0 = 1, I = 3, IIA = 3, IIB = 1, III = 4, IV = 1. Grade III/IV toxicity (17 pts) was: diarrhea 9 pts, neutropenia 9 pts, febrile neutropenia 5 pts, anorexia 5 pts, vomiting 4 pts, fatigue 3 pts, mucositis 1 pt. Chemotherapy dose attenuation was required for diarrhea in 5 pts, for neutropenia in 4 pts, and for folliculitis in 1 pt. One patient was removed from study during week 6 for prolonged diarrhea/ dehydration. Due to the 2-step design of the trial, accrual is on hold pending a 3rd required pathologic CR in the first 17 patients. Conclusions: Compared to other trials of irinotecan, cisplatin, radiation therapy, and surgery in similar groups of esophageal cancer patients, early results for this combination with cetuximab suggest a lower complete response rate and higher overall toxicity. Additional data will be available at ASCO. Supported by Bristol-Myers Squibb.

No significant financial relationships to disclose.