A 60-year-old gentleman with no comorbidities was evaluated for light headedness and breathlessness in October 2016. His electrocardiogram (ECG) showed complete heart block confirmed by Holter. He underwent a permanent MRI dual-chamber rate-modulated pacemaker implantation in left infraclavicular area on October 2016. He was not pacemaker dependent.
In December 2017, he presented with intermittent fever for three weeks. Clinical examination revealed hepatosplenomegaly. CT showed multiple intra-abdominal
necrotic lymph nodes, hepatosplenomegaly with multiple hypodense lesions in the liver and spleen. He underwent USG guided splenic lesion biopsy and histopathology was consistent with Classical Hodgkin’s lymphoma, mixed cellularity subtype; Immunohistochemistry was positive for CD15, CD30.
PET CT revealed multiple metabolically active nodes in the right supraclavicular fossa, mediastinum, upper abdomen, with lesions in liver and spleen. The maximum standard uptake value (SUV) noted in the mediastinum was 10.02 and the largest nodal size was 1.6cm. The disease was staged as Classical Hodgkin’s Lymphoma stage IV. He received chemotherapy with 6 cycles of EBVD regimen (Etoposide, Bleomycin, Vinblastine, and Dacarbazine). Doxorubicin was not given so as to avoid anthracycline induced cardiotoxicity. Reassessment PET CT at the end of chemotherapy had shown disease response and he was advised RT to the mediastinum.
Radiation Therapy
An in-house workflow algorithm (Fig:1) was developed for patients with pacemaker requiring radiotherapy.
Pretreatment Discussion
When a patient with a pacemaker requires RT, the possibility of malfunctioning of pacemaker during radiation that would necessitate replacement of the same should be considered. In conjunction with the cardiologist, a consensus was reached to proceed with radiation therapy without relocating the pacemaker as there was a low likelihood of interaction between the CIED and radiation therapy.
Radiation Therapy Planning and Simulation
It would be ideal to do the post chemotherapy disease evaluation imaging as a planning CT/PETCT to avoid excess radiation to the pacemaker. The patient was immobilized with a vacloc cushion with arms abducted above the head in supine position. Simulation CT was taken in Siemens Somatom CT Simulator machine with slice thickness 5mm and pitch of 1. As per AAPM TG 203, CT imaging involving helical scan with pitch >1 is preferred to prevent long periods of direct irradiation of the device.
Contouring
The target volume and organs at risk were delineated as per the International Lymphoma Radiation Oncology Group (ILROG) guidelines. The pulse generator and the leads were also contoured (Fig:2).
Treatment Planning
AAPM TG 203 recommends avoiding protons and instead to use photon energies ≤10MV in order to reduce neutron induced upsets in memory or logic circuits of the pacemaker. Anteroposterior fields were avoided to minimize the cardiac dose and considering the close proximity of the pacemaker to the PTV. AAPM TG 34 recommends a dose of <2Gy to the pacemaker whereas AAPM TG 203 recommends to restrict the dose to <5Gy for CIEDs in low -medium risk categories [1,3]. This patient belonged to the low-risk category as per the risk stratification by AAPM TG 203 [1] as the patient was not pacemaker dependent and the expected dose to the pacemaker was < 2 Gy.
The planning was done with 6 MV photons and the prescribed dose was 30 Gy in 15 fractions using rapid arc technique. It is advisable to limit the number of fractions so as to reduce the radiation exposure to the pacemaker. A full arc with appropriate blocks to prevent entry and exit of beams through the pacemaker were used. AAPM TG 203 has recommended in vivo measurement of the dose if the device is from 3 to 10 cm from the field edge. The pacemaker was at 7.14, 5.99 and 1.30 cm from the isodose 50%(15Gy), 25%(7.5Gy) and 5%(1.5Gy) lines respectively (Fig:2). The dose to the pacemaker was found to be 1.28 Gy (treatment planning system calculated) and 1.15 Gy (in-vivo dosimetry with optically stimulated luminescent dosimeter).
Treatment Execution
The position and function of the pacemaker was confirmed by the cardiac electrophysiologist. CIED monitoring was done twice weekly during RT to rule out malfunctioning and treatment delivery was in the midday.
For the patient position and the tumour location verification, Cone Beam Computed Tomography (CBCT) was done for the first three days followed by once a week up to a total of 5 CBCTs. It was ensured that the pacemaker was not included in the range of the CBCT to help reduce the dose to the pacemaker. RT was delivered in Aug-Sept 2018, two years after the implantation of the pacemaker.
Post-treatment Follow Up
Cardiac Evaluation
The patient had undergone regular clinical evaluation and pacemaker interrogation under the guidance of the cardiac electrophysiologist. The Pacemaker interrogation was done once a year and no abnormality has been detected in the last two and half years (Table-1). The last interrogation done in March 2021 showed normal pacemaker functioning
Table: 1. The Pacemaker interrogation was done at 1, 1.5 and 2 years after radiation therapy. The pacemaker was found to have normal function. There were no signs of radiation induced damage.
Parameter
|
One year after Implantation
(Aug 2017)
|
One year after radiation Therapy
(Aug 2019)
|
One and half years after radiation therapy
(March 2020)
|
Two and a half years after radiation therapy
(March 2021)
|
Sensing (millivolt)
|
Ventricular
|
14.5
|
16.3
|
V: 13.7
|
V: 14.1
|
Atrial
|
4.2
|
3.9
|
3.7
|
3.4
|
[email protected]
|
Ventricular
|
0.7
|
V: 0.4
|
V:0.5
|
V:0.5
|
Atrial
|
0.6
|
0.4
|
0.5
|
0.4
|
Impedance (ohms)
|
Ventricular
|
621
|
V:624
|
V: 585
|
V: 585
|
Atrial
|
721
|
624
|
585
|
585
|
Longevity (years)
|
13 years
|
9 years 6 months
|
9 years 1month
|
8 years
6 months
|
Impression
|
Normal
Function
|
Normal Function
|
Normal
Function
|
Normal function
|
Oncological Evaluation
PET CT done 3 months and one year after completion of RT showed interval reduction in the size of the node and SUV. He was clinicoradiologically disease free at the last follow up in Sep 2021