Late mortality in Hodgkin's disease: can we reduce it?

Comparison of passive-beam proton therapy, helical tomotherapy and 3D conformal radiation therapy in Hodgkin's lymphoma female patients receiving involved-field or involved site radiation therapy

PURPOSE

Second cancers and cardiovascular toxicities are long term radiation toxicity in locally advanced Hodgkin's lymphomas. In this study, we evaluate the potential reduction of dose to normal tissue with helical tomotherapy and proton therapy for Hodgkin's lymphoma involved-field or involved-site irradiation compared to standard 3D conformal radiation therapy.

PATIENTS AND METHODS

Fourteen female patients with supradiaphragmatic Hodgkin's lymphoma were treated at our institution with 3D conformal radiation therapy or helical tomotherapy to a dose of 30Gy in 15 fractions. A planning comparison was achieved including proton therapy with anterior/posterior passive scattered beams weighted 20Gy/10Gy.

RESULTS

Mean doses to breasts, lung tissue and heart with proton therapy were significantly lower compared to helical tomotherapy and to 3D conformal radiation therapy. Helical tomotherapy assured the best protection of lungs from doses above 15Gy with the V20Gy equal to 16.4%, compared to 19.7% for proton therapy (P=0.01) or 22.4% with 3D conformal radiation therapy (P<0.01). Volumes of lung receiving doses below 15Gy were significantly larger for helical tomotherapy than for proton therapy or 3D conformal radiation therapy, with respective lung doses V10Gy=37.2%, 24.6% and 27.4%. Also, in the domain of low doses, the volumes of breast that received more than 10Gy or more than 4Gy with helical tomotherapy were double the corresponding volumes for proton therapy, with V4Gy representing more than a third of one breast volume with helical tomotherapy.

CONCLUSIONS

Helical tomotherapy achieved a better protection to the lungs for doses above 15Gy than passive proton therapy or 3D conformal radiation therapy. However, dose distributions could generally be improved by using protons even with our current passive-beam technology, especially allowing less low dose spreading and better breast tissue sparing, which is an important factor to consider when treating Hodgkin's lymphomas in female patients. Prospective clinical study is needed to evaluate the tolerance and confirm these findings.

Can we reduce the incidence of second primary malignancies occurring after radiotherapy? A critical review

Second primary malignancies (SPMs) occurring after oncological treatment have become a major concern during the past decade. Their incidence has long been underestimated because most patients had a short life expectancy after treatment or their follow-up was shorter than 15 years. With major improvement of long-term survival, longer follow-up, cancer registries and end-result programs, it was found that the cumulative incidence of SPM could be as high as 20% of patients treated by radiotherapy. This cumulative proportion varies with several factors, which ought to be studied more accurately. The delay between irradiation and solid tumor emergence is seldom shorter than 10 years and can be as long as half a century. Thus, inclusion in a cohort of patients with a short follow-up leads to an underestimation of the proportion of SPM caused by treatment, unless actuarial cumulative incidence is computed. The incidence varies with the tissue and organs, the age of the patient at treatment, hereditary factors, but also, and probably mainly, with dose distribution, size of the irradiated volume, dose, and dose-rate. An effort toward a reduction in their incidence is mandatory. Preliminary data suggest that SPMs are mainly observed in tissues having absorbed doses above 2 Gy (fractionated irradiation) and that their incidence increases with the dose. However, in children thyroid and breast cancers are observed following doses as low as 100 mGy, and in adults lung cancers have been reported for doses of 500 mGy, possibly due to interaction with tobacco. The dose distribution and the dose per fraction have a major impact. However, the preliminary data regarding these factors need confirmation. Dose-rates appear to be another important factor. Some data suggest that certain patients, who could be identified, have a high susceptibility to radiocancer induction. Efforts should be made to base SPM reduction on solid data and not on speculation or models built on debatable hypotheses regarding the dose-carcinogenic effect relationship. In parallel, radiation therapy philosophy must evolve, and the aim of treatment should be to deliver the minimal effective radiation therapy rather than the maximal tolerable dose.