Hadrontherapy for intra- or para-cardiac tumors: evaluation of cardiac radiation dose distribution and acute cardiac effects

Background

There is growing interest in the possibility of using X-rays and hadrons (protons and carbon ions) for antiarrhythmic purposes both at the ventricular and the atrial level, but knowledge about the effects on cardiac tissue outside the target is still limited. Hadron therapy has the dosimetric advantage over photons of a greater ability to concentrate high doses on the target while minimizing the off-target dose. Oncological studies have shown a linear relationship between the mean total heart dose (Dm-heart) of X-rays and the long-term risk of heart damage, particularly when the Dm-heart is>5 Gray (Gy).

Objectives

We designed a prospective study aimed at investigating the effect of heavy particles on cardiac structure and function and on cardiac rhythm in patients undergoing hadrontherapy for intra or para-cardiac tumors.

Methods

Patients candidates to hadrontherapy with a mean predicted cardiac dose grather than zero underwent close cardiological monitoring including blood pressure detection, 12-lead ECG, 12-lead Holter ECG (including time-domain indices of heart rate variability in all cases and Brugada leads in selected cases), cardiac US and cardiac (troponin and natriuretic peptides) and inflammatory biomarkers. These assessments were obtained at baseline, during (ECG and biomarkers only) and at the end of the hadrontherapy cycle, and then every 3–6 months as appropriate. Physicists and radiotherapists collaborated to implement a robust optimization of the treatment plan aimed at minimizing cardiac dose. We present the results of the monitoring up to the end of the hadrontherapy.

Results

17 consecutive patients (56±18 years, range 20–77 years, 59% male) have been enrolled to date, including 3 cases (18%) of intra-cardiac tumors (2 primary and 1 metastatic), who have undergone to 16±6 sessions of radiotherapy each, in 71% of cases with respiratory gating during delivery. Most patients (76%) were treated with carbon ions, the remaining with protons (mean total dose on the neoplastic target 51.8±10.7 Gy, from 2 to 4.2 Gy per fraction). Sixty-one percent of patients had ≥1 cardiovascular risk factor, 6% had a known heart disease (valvular cardiomyopathy despite aortic valve replacement with biological prosthesis and post-surgical pericarditis). The mean dose on the whole heart was 3.58±2.05 Gy, the maximum dose was 33.78±23.99 Gy, with a very variable dose distribution on cardiac substructures depending on the tumor site (table). At the end of the scheduled radiotherapy sessions (24±9 days), no significant changes were observed in cardiac function, cardiac rhythm, ventricular repolarization, biomarkers and autonomic indices.

Conclusions

Hadrontherapy with protons and carbon ions aimed at the treatment of para-cardiac or intra-cardiac tumors allowed to maintain a low heart Dm and showed no signs of acute cardiac toxicity. The collection of potential cardiac effects in the medium and long term is ongoing.

Funding Acknowledgement

Type of funding sources: None.

Dosimetric effect of variable rectum and sigmoid colon filling during carbon ion radiotherapy to sacral chordoma

PURPOSE

Carbon ion radiotherapy (CIRT) is sensitive to anatomical density variations. We examined the dosimetric effect of variable intestinal filling condition during CIRT to ten sacral chordoma patients.

METHODS

For each patient, eight virtual computed tomography scans (vCTs) were generated by varying the density distribution within the rectum and the sigmoid in the planning computed tomography (pCT) with a density override approach mimicking a heterogeneous combination of gas and feces. Totally full and empty intestinal preparations were modelled. In addition, five different intestinal filling conditions were modelled by a mixed density pattern derived from two combined and weighted Gaussian distributions simulating gas and feces respectively. Finally, a patient-specific mixing proportion was estimated by evaluating the daily amount of gas detected in the cone beam computed tomography (CBCT). Dose distribution was recalculated on each vCT and dose volume histograms (DVHs) were examined.

RESULTS

No target coverage degradation was observed at different vCTs. Rectum and sigma dose degradation ranged respectively between: [-6.7; 21.6]GyE and [-0.7; 15.4]GyE for D_50%; [-377.4; 1197.9] and [-95.2; 1027.5] for AUC; [-1.2; 10.7]GyE and [-2.6; 21.5]GyE for D_1%.

CONCLUSIONS

Variation of intestinal density can greatly influence the penetration depth of charged particle and might compromise dose distribution. In particular cases, with large clinical target volume in very close proximity to rectum and sigmoid colon, it is appropriate to evaluate the amount of gas present in the daily CBCT images even if it is totally included in the reference planning structures.

Inter-fractional monitoring of [Formula: see text]C ions treatments: results from a clinical trial at the CNAO facility

The high dose conformity and healthy tissue sparing achievable in Particle Therapy when using C ions calls for safety factors in treatment planning, to prevent the tumor under-dosage related to the possible occurrence of inter-fractional morphological changes during a treatment. This limitation could be overcome by a range monitor, still missing in clinical routine, capable of providing on-line feedback. The Dose Profiler (DP) is a detector developed within the INnovative Solution for In-beam Dosimetry in hadronthErapy (INSIDE) collaboration for the monitoring of carbon ion treatments at the CNAO facility (Centro Nazionale di Adroterapia Oncologica) exploiting the detection of charged secondary fragments that escape from the patient. The DP capability to detect inter-fractional changes is demonstrated by comparing the obtained fragment emission maps in different fractions of the treatments enrolled in the first ever clinical trial of such a monitoring system, performed at CNAO. The case of a CNAO patient that underwent a significant morphological change is presented in detail, focusing on the implications that can be drawn for the achievable inter-fractional monitoring DP sensitivity in real clinical conditions. The results have been cross-checked against a simulation study.

Determination of ion recombination and polarity effect correction factors for a plane-parallel ionization Bragg peak chamber under proton and carbon ion pencil beams

Within the dosimetric characterization of particle beams, laterally-integrated depth-dose-distributions (IDDs) are measured and provided to the treatment planning system (TPS) for beam modeling or used as a benchmark for Monte Carlo (MC) simulations. The purpose of this work is the evaluation, in terms of ion recombination and polarity effect, of the dosimetric correction to be applied to proton and carbon ion curves as a function of linear energy transfer (LET). LET was calculated with a MC code for selected IDDs. Several regions of Bragg peak (BP) curve were investigated. The charge was measured with the plane-parallel BP-ionization chamber mounted in the Peakfinder as a field detector, by delivering a fixed number of particles at the maximum flux. The dose rate dependence was evaluated for different flux levels. The chamber was connected to an electrometer and exposed to un-scanned pencil beams. For each measurement the chamber was supplied with {±400, +200, +100} V. Recombination and polarity correction factors were then calculated as a function of depth and LET in water. Three energies representative of the clinical range were investigated for both particle types. The corrected IDDs (IDD ^k s) were then compared against MC. Recombination correction factors were LET and energy dependent, ranging from 1.000 to 1.040 (±0.5%) for carbon ions, while nearly negligible for protons. Moreover, no corrections need to be applied due to polarity effect being  <0.5% along the whole IDDs for both particle types. IDD ^k s showed a better agreement than uncorrected curves when compared to MC, with a reduction of the mean absolute variation from 1.2% to 0.9%. The aforementioned correction factors were estimated and applied along the IDDs, showing an improved agreement against MC. Results confirmed that corrections are not negligible for carbon ions, particularly around the BP region.

In vivo radiobiological assessment of the new clinical carbon ion beams at CNAO

In this article, the in vivo study performed to evaluate the uniformity of biological doses within an hypothetical target volume and calculate the values of relative biological effectiveness (RBE) at different depths in the spread-out Bragg peak (SOBP) of the new CNAO (National Centre for Oncological Hadrontherapy) carbon beams is presented, in the framework of a typical radiobiological beam calibration procedure. The RBE values (relative to (60)Co γ rays) of the CNAO active scanning carbon ion beams were determined using jejunal crypt regeneration in mice as biological system at the entrance, centre and distal end of a 6-cm SOBP. The RBE values calculated from the iso-effective doses to reduce crypt survival per circumference to 10, ranged from 1.52 at the middle of the SOBP to 1.75 at the distal position and are in agreement with those previously reported from other carbon ion facilities. In conclusion, this first set of in vivo experiments shows that the CNAO carbon beam is radiobiologically comparable with the NIRS (National Institute of Radiological Sciences, Chiba, Japan) and GSI (Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany) ones.

Effectiveness of stereotactic body radiotherapy in the treatment of inoperable early-stage lung cancer

BACKGROUND

Non-small cell lung cancer (NSCLC) is the leading cause of cancer death worldwide. Stereotactic body irradiation offers a non-invasive treatment modality for patients with early stage NSCLC who are not amenable to surgery or other invasive approaches because of their poor medical condition.

PATIENTS AND METHODS

Forty-three inoperable patients with NSCLC were treated with SBRT at our institution. A mean total dose of 30.5 Gy in 1-4 fractions was applied. The median follow-up duration was 14 months (range 6-36 months).

RESULTS

The actuarial survival at two years was 53%: two patients died from cancer progression whereas a further 8 patients died from comorbidities. Acute toxicity was practically absent, with 7 (16.3%) patients suffering from grade 1 symptoms and two from (4.6%) grade II effects. At the time of this report, only 1 patient had grade II and 6 patients (13.9%) grade I chronic symptoms.

CONCLUSION

Our results compare favourably with recently published studies and confirm that stereotactic radiotherapy has the potential to produce high local control rates with a low risk of lung toxicity in patients not amenable to curative resection. The low grade of side-effects is encouraging for shortening the treatment using a greater dose per fraction.