Multi-Institutional Phase I Feasibility Trial of Vertebral Body Sparing CSI for Pediatric Brain Tumors

PURPOSE/OBJECTIVE(S)

Craniospinal irradiation (CSI) is an essential part of curative treatment for several pediatric brain tumors. Proton CSI allows for sparing of the organs anterior to the vertebral bodies (VBs), but this technique still includes the entire VB in the target for growing children. providing no advantage in marrow sparing or adverse effects on growth. Advances in proton therapy including Proton Beam Scanning (PBS) allow for delivery of proton CSI with substantial vertebral body sparing (VBS). We sought to determine the feasibility of VBS CSI using PBS based on the effects on tumor control and growth, and the occurrence of grade III/IV hematologic toxicity.

MATERIALS/METHODS

Clinical and treatment characteristics were recorded for 20 pediatric patients with medulloblastoma (n = 14) or germ cell tumor (GCT) (n = 6) who received proton VBS CSI without concurrent chemotherapy or with concurrent single-agent vincristine in a multi-institutional clinical trial. The following standard variables were extracted for each patient: age, histology, radiation dose, chemotherapy regimen, and growth hormone replacement status. Complete blood counts (CBC) with differential and data on height/weight were recorded at baseline pre-RT, weekly during RT, and after completion of cancer treatment. Hematologic toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4 (CTCAE v4).

RESULTS

Median age of 13 male and 7 female patients receiving proton VBS CSI was 10 years (range: 5.1 - 15.1). All GCT patients (n = 6, 30%) received pre-RT chemo. Median CSI dose was 23.4 Gy (range: 21.0 - 37.8), and total dose to tumor bed was 54 Gy in 18 patients (90%) while 2 patients with pure germinoma received a total dose of 36 and 37.5 Gy, respectively. 11 patients (55%) did not receive concurrent vincristine. At a median follow up of 26.4 months (range: 12.5 - 56.3) from the start of RT, no patients relapsed. 17 patients (85%) developed grade ≥3 hematologic toxicity including grade 3 lymphopenia (n = 16), leukopenia (n = 9), neutropenia (n = 8), anemia (n = 1), and grade 4 neutropenia (n = 1). The patient who developed grade 4 neutropenia had low white blood counts prior to RT. 14 patients (70%) received post-RT chemo. No patients required platelet transfusion during RT. Those findings are similar to historical controls. 4 patients started growth hormone replacement therapy after RT. No patients developed spine deformities after the completion of treatment.

CONCLUSION

Proton VBS CSI is a feasible and well tolerated treatment for children with brain tumors. Longer follow up is needed to assess for late effects on tumor control. It is too early to assess for height in this cohort but for the patients that had longer follow up, normal height was achieved.

Increased Complication Rates with Proton Therapy in Breast Cancer Patients with Immediate, Implant-Based Reconstruction: Single-Institution Comparative Effectiveness Analysis

PURPOSE/OBJECTIVE(S)

To compare the impact of protons vs. photons on breast reconstruction complications, for patients (pts) receiving postmastectomy radiation (PMRT) with either single-stage direct-to-implant (DTI) or two-staged expander/implant (TE/I).

MATERIALS/METHODS

We reviewed the charts of 578 pts who underwent immediate reconstruction followed by radiation at our institution between 2010 and 2020. Pts with implant-based reconstruction using either TE/I or DTI and PMRT delivery in the presence of the prosthesis were included. Pts enrolled in active ongoing clinical trials were excluded from the analysis. The photon group received 3D conformal or IMRT/VMAT treatment with a median dose of 50-50.4 Gy in 25 to 28 fractions. For proton pts, treatment was delivered mainly with pencil beam scanning technique (PBS); few pts received passively scattered proton spread-out Bragg peak (SOBP). The complications were defined as infection/skin necrosis (I/N) requiring operative debridement, capsular contracture (CC) necessitating capsulotomy, and overall implant failure (ORF) as the removal of the permanent implant irrespective of replacement outcomes (i.e., with and without salvage reconstruction). We fit inverse-probability weighted cumulative incidence curves to adjust for confounding and non-random loss to follow-up. Various sensitivity analyses were conducted.

RESULTS

Four hundred ninety-five pts were available for the final analysis with an overall median follow-up of 55 months. 66 (13%) received protons, of which14 were treated with SOBP protons. 137 (28%) and 256 (56%) received photons with and without chest wall boost (CWB), respectively. The 5-year inverse probability-weighted risk of CC post-PMRT was 31% for protons vs. 10% for photons (RR:3.09, 95% CI: 1.77, 5.40). The 5 years ORF risk was 35.6% in protons compared to 22.7% in photons pts (RR: 1.57; 95% CI 1.0, 2.48). Hazard ratios from the adjusted Cox models were 3.79 (p<0.001) for CC and 2.05 (p<0.01) for ORF. No difference in I/N was noted between protons and photons pts. Sensitivity analysis showed that protons significantly increased CC risk vs photons both with CWB (HR:3.56, P<0.001) and without CWB (HR:3.9, p<0.001). Similar outcomes were observed with ORF, where protons increased the rate of ORF compared to photons, irrespective of CWB (HR 1.8, p = 0.038 with CWB; HR 2.4, p = 0.004 without CWB). No differences between PBS and SOBP proton techniques were noted.

CONCLUSION

Compared to photons, proton therapy increases the risk of capsular contracture requiring surgical intervention and hence overall reconstruction failure. This data should inform discussions about the risks and benefits of protons in patients with reconstruction, while awaiting mature data from ongoing clinical trials (RADCOMP) utilizing protons for breast cancer.

Proton vs. Photons for Breast Cancer Patients with Immediate, Implant-Based Reconstruction Receiving Postmastectomy Radiotherapy: A Multicenter Pooled Analysis

PURPOSE/OBJECTIVE(S)

Proton therapy improves postmastectomy radiotherapy (PMRT) normal tissue sparing compared with photon techniques. However, little is understood about its effect on reconstruction outcomes. The primary objective was to evaluate complication rates in breast cancer patients treated with proton (PRO) versus photon (PHO) PMRT following immediate, implant-based breast reconstruction.

MATERIALS/METHODS

Consecutive patients with breast cancer who underwent mastectomy and immediate reconstruction with a tissue expander (TE) or permanent implant (PI) and PRO or PHO PMRT between 2011 and 2022 were included from two institutions. Complication rate was defined as the sum of reconstruction failure (explantation without replacement), unplanned prosthesis exchange, and other unplanned revisional surgery. Each complication type was analyzed as an independent endpoint.

RESULTS

Among 733 patients, median follow-up was 4.4 years; 36.5% (267) were treated with PRO and 63.5% (466) with PHO. There was no difference in age, BMI, or comorbidities between the two groups. PRO was more likely to have had, two-stage reconstruction and pre-pectoral implant placement (p<.01). Median dose was 50-50.4 Gy in 25-28 fractions, with only 50 receiving hypofractionation. Bolus was used in all PHO patients. Regional nodes were more likely to be included in PRO (99.6% v. 83.7% PHO, p<.01). Although there was no difference in the use of chest wall boost between groups, the axillary nodes were more frequently boosted in PRO (25.1% vs 2.8% PHO, p<.01). The overall rate of complications at 4 years was 26.7% (95% CI = 23.3-30.5). The 4-year rate of reconstruction failure, unplanned exchange, and other surgery was 8.2% (95% CI = 6.3-10.7), 17.4% (95% CI = 14.6-20.8), and 12.5% (95% CI = 10.1-15.5), respectively. On MVA, PRO did not confer an increased risk of reconstruction complications compared to PHO. Significant risk factors for reconstruction failure included TE-to-autologous approach [HR versus direct-to-implant reference: 4.05 (95% CI = 1.60-10.22)], TE-to-permanent implant approach [HR = 2.06 (95% CI = 1.12-3.79)], chest wall boost [HR = 2.20 (95% CI = 1.21-4.02)], and any lymph node boost [HR = 2.33 (95% CI = 1.10-4.97)]. Compared to direct-to-implant, two-stage reconstruction was also associated with a higher rate of unplanned exchange [HR for TE/PI = 1.49 (95% CI = 1.01-2.20)] and revisional surgery [HR for TE-to-autologous = 3.95 (95% CI = 1.64-9.52)]. Prepectoral implant placement was correlated with reduced risk of revisional surgery, relative to subpectoral placement [HR = 0.42 (95% CI = 0.22-0.81)].

CONCLUSION

This represents the largest combined series to date comparing PRO and PHO PMRT. Despite a higher rate of two-stage reconstruction, nodal irradiation, and nodal boost in PRO, there was no significant difference in the risk of complications between protons and photons. Differences in PRO delivery techniques between institutions and dosimetric details such as skin dose will be presented in person.

Comparison between Pre-Pectoral and Post-Pectoral Implant Reconstruction and Different Radiation Modalities on Breast Reconstruction Complications

PURPOSE/OBJECTIVE(S)

Single Stage direct to implant (DTI) is a rising reconstruction approach. It has been speculated that prepectoral implant placement reduces reconstruction complications as well as using newer postmastectomy radiation (PMRT) modalities as protons. Largest series in this topic included 350 DTI patients with less than 30 patients receiving PMRT.

MATERIALS/METHODS

We reviewed the charts of 2,187 patients (pts) who underwent mastectomy and reconstruction at our institution between 2000 and 2020. Pts only receiving DTI with and without PMRT were included. PMRT was delivered either with 3D conformal photon +/- chest wall electron boost (CWB) or proton therapy mainly with pencil beam scanning. All pts received conventional fractionation (50-50.4 Gy in 25-28 fractions). Patients on active protons clinical trials were excluded. Primary endpoints were reconstruction complications defined as infection/necrosis (I/N) requiring debridement; capsular contracture (CC) requiring capsulotomy and overall reconstruction failure (ORF: removal of permanent implant for any complication with and without salvage reconstruction). Subgroup analysis for pts receiving PMRT was done to explore impact of proton and photons on complications. Logistic and cox regression were used.

RESULTS

Eight hundred nine pts received DTI, with an overall median follow-up of 6.2 years. Among the entire cohort, 78/809 (9.7%) had prepectoral implants while the rest had subpectoral implants with and without alloderm support. Of the entire cohort 391/809 (48.5%) received PMRT, among those 43/391 (11%) received protons. The 5 years cumulative incidence of CC was 8.5% and 6.6% among prepectoral vs subpectoral implants (HR = 1.2, p = 0.7). The 5 years cumulative incidence of ORF was 32.2% and 28.2% among prepectoral vs subpectoral implants (HR 1.1, p = 0.6). For pts receiving PMRT, the 5 years cumulative incidence of CC were 26.0% and 8.6% among protons vs photons (HR 3.7, p < 0.0005). The 5 years cumulative incidence of ORF were 38.2% and 30.1% among protons vs photons (HR 1.4, p = 0.2). Multivariable logistic regression analysis accounting for BMI, smoking history, diabetes, and PMRT showed no significant difference between prepectoral implants versus subpectoral coverage for CC (OR = 0.7, p = 0.5), and for ORF (OR = 0.9, p = 0.8). Subgroup multivariable analysis for those receiving PMRT only showed protons compared to photons significantly increased the risk of CC (OR = 5.3, p < 0.0001) and ORF (OR = 2.1, p = 0.03). No significant difference in I/N was noted between photons and protons or between prepectoral and subpectoral pts.

CONCLUSION

For breast cancer patients receiving single stage direct to implant reconstruction with and without PMRT, prepectoral implant placement did not reduce the risk of complications. Proton therapy compared to photons significantly increased the risk of capsular contracture requiring capsulotomies and significantly increased overall reconstruction failures with implants removal.